How do I create a Java string from the contents of a file

Question

I ve been using the idiom below for some time now  And it seems to be the most wide-spread  at least on the sites I ve visited   Is there a better different way to read a file into a string in Java   private String readFile String file  throws IOException       BufferedReader reader   new BufferedReader new FileReader  file        String         line   null      StringBuilder  stringBuilder   new StringBuilder        String         ls   System getProperty  line separator         try           while  line   reader readLine       null                stringBuilder append line               stringBuilder append ls                      return stringBuilder toString          finally           reader close

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With Java 7  this is my preferred option to read a UTF-8 file   String content   new String Files readAllBytes Paths get filename     UTF-8      Since Java 7  the JDK has the new java nio file API  which provides many shortcuts  so 3rd party libraries are not always required for simple file operations

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That code will normalize line breaks  which may or may not be what you really want to do   Here s an alternative which doesn t do that  and which is  IMO  simpler to understand than the NIO code  although it still uses java nio charset Charset    public static String readFile String file  String csName              throws IOException       Charset cs   Charset forName csName       return readFile file  cs      public static String readFile String file  Charset cs              throws IOException          No real need to close the BufferedReader InputStreamReader        as they re only wrapping the stream     FileInputStream stream   new FileInputStream file       try           Reader reader   new BufferedReader new InputStreamReader stream  cs            StringBuilder builder   new StringBuilder            char   buffer   new char 8192           int read          while   read   reader read buffer  0  buffer length    gt  0                builder append buffer  0  read                     return builder toString          finally              Potential issue here  if this throws an IOException             it will mask any others  Normally I d use a utility            method which would log exceptions and swallow them         stream close

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Also if your file happens to be inside a jar  you can also use this   public String fromFileInJar String path        try   Scanner scanner                new Scanner getClass   getResourceAsStream path              return scanner useDelimiter    A   next              The path should start with    for instance if your jar is  my jar com some thing a txt   Then you want to invoke it like this   String myTxt   fromFileInJar   com com thing a txt

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That code will normalize line breaks  which may or may not be what you really want to do   Here s an alternative which doesn t do that  and which is  IMO  simpler to understand than the NIO code  although it still uses java nio charset Charset    public static String readFile String file  String csName              throws IOException       Charset cs   Charset forName csName       return readFile file  cs      public static String readFile String file  Charset cs              throws IOException          No real need to close the BufferedReader InputStreamReader        as they re only wrapping the stream     FileInputStream stream   new FileInputStream file       try           Reader reader   new BufferedReader new InputStreamReader stream  cs            StringBuilder builder   new StringBuilder            char   buffer   new char 8192           int read          while   read   reader read buffer  0  buffer length    gt  0                builder append buffer  0  read                     return builder toString          finally              Potential issue here  if this throws an IOException             it will mask any others  Normally I d use a utility            method which would log exceptions and swallow them         stream close

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If you need a string processing  parallel processing  Java 8 has the great Stream API   String result   Files lines Paths get  file txt                         parallel      for parallel processing                       map String  trim     to change line                         filter line - gt  line length    gt  2     to filter some lines by a predicate                                              collect Collectors joining        to join lines   More examples are available in JDK samples sample lambda BulkDataOperations that can be downloaded from Oracle Java SE 8 download page   Another one liner example  String out   String join   n   Files readAllLines Paths get  file txt

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Be aware when using fileInputStream available   the returned integer does not have to represent the actual file size  but rather the guessed amount of bytes the system should be able to read from the stream without blocking IO  A safe and simple way could look like this  public String readStringFromInputStream FileInputStream fileInputStream        StringBuffer stringBuffer   new StringBuffer        try           byte   buffer          while  fileInputStream available    gt  0                buffer   new byte fileInputStream available                 fileInputStream read buffer               stringBuffer append new String buffer   ISO-8859-1                     catch  FileNotFoundException e          catch  IOException e          return stringBuffer toString        It should be considered that this approach is not suitable for multi-byte character encodings like UTF-8

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Also if your file happens to be inside a jar  you can also use this   public String fromFileInJar String path        try   Scanner scanner                new Scanner getClass   getResourceAsStream path              return scanner useDelimiter    A   next              The path should start with    for instance if your jar is  my jar com some thing a txt   Then you want to invoke it like this   String myTxt   fromFileInJar   com com thing a txt

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If you re looking for an alternative that doesn t involve a third-party library  e g  Commons I O   you can use the Scanner class   private String readFile String pathname  throws IOException        File file   new File pathname       StringBuilder fileContents   new StringBuilder  int file length                  try  Scanner scanner   new Scanner file             while scanner hasNextLine                  fileContents append scanner nextLine     System lineSeparator                       return fileContents toString

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After Ctrl F ing after Scanner  I think that the Scanner solution should be listed too  In the easiest to read fashion it goes like this   public String fileToString File file  Charset charset      Scanner fileReader   new Scanner file  charset     fileReader useDelimiter    Z        Z means EOF    String out   fileReader next      fileReader close      return out      If you use Java 7 or newer  and you really should  consider using try-with-resources to make the code easier to read  No more dot-close stuff littering everything  But that s mostly a stylistic choice methinks   I m posting this mostly for completionism  since if you need to do this a lot  there should be things in java nio file Files that should do the job better   My suggestion would be to use Files readAllBytes Path  to grab all the bytes  and feed it to new String byte   Charset  to get a String out of it that you can trust  Charsets will be mean to you during your lifetime  so beware of this stuff now   Others have given code and stuff  and I don t want to steal their glory

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I cannot comment other entries yet  so I ll just leave it here   One of best answers here  https   stackoverflow com a 326448 1521167    private String readFile String pathname  throws IOException    File file   new File pathname   StringBuilder fileContents   new StringBuilder  int file length     Scanner scanner   new Scanner file   String lineSeparator   System getProperty  line separator     try       while scanner hasNextLine                      fileContents append scanner nextLine     lineSeparator             return fileContents toString      finally       scanner close          still has one flaw  It always puts new line char in the end of string  which may cause some weirds bugs  My suggestion is to change it to       private String readFile String pathname  throws IOException       File file   new File pathname       StringBuilder fileContents   new StringBuilder  int  file length         Scanner scanner   new Scanner new BufferedReader new FileReader file         String lineSeparator   System getProperty  line separator         try           if  scanner hasNextLine                  fileContents append scanner nextLine                       while  scanner hasNextLine                  fileContents append lineSeparator   scanner nextLine                       return fileContents toString          finally           scanner close

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in java 8   there are a new Class      java util stream Stream   A stream represents a sequence of elements and supports different kind of operations to perform computations upon those elements  to Read more about it    Oracle Documentation  Here an Example    import java nio charset StandardCharsets  import java nio file Files  import java nio file Paths  import java util stream Stream   public Class ReadFile    public  static String readFile String filePath     StringBuilder  stringBuilder   new StringBuilder        String ls   System getProperty  line separator            try                try  Stream lt String gt  lines   Files lines Paths get filePath   StandardCharsets UTF 8                     for  String line    Iterable lt String gt   lines  iterator                            stringBuilder append line                         stringBuilder append ls                                                catch  Exception e                e printStackTrace                     return stringBuilder toString

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That code will normalize line breaks  which may or may not be what you really want to do   Here s an alternative which doesn t do that  and which is  IMO  simpler to understand than the NIO code  although it still uses java nio charset Charset    public static String readFile String file  String csName              throws IOException       Charset cs   Charset forName csName       return readFile file  cs      public static String readFile String file  Charset cs              throws IOException          No real need to close the BufferedReader InputStreamReader        as they re only wrapping the stream     FileInputStream stream   new FileInputStream file       try           Reader reader   new BufferedReader new InputStreamReader stream  cs            StringBuilder builder   new StringBuilder            char   buffer   new char 8192           int read          while   read   reader read buffer  0  buffer length    gt  0                builder append buffer  0  read                     return builder toString          finally              Potential issue here  if this throws an IOException             it will mask any others  Normally I d use a utility            method which would log exceptions and swallow them         stream close

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There is a variation on the same theme that uses a for loop  instead of a while loop  to limit the scope of the line variable   Whether it s  better  is a matter of personal taste   for String line   reader readLine    line    null  line   reader readLine          stringBuilder append line       stringBuilder append ls

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Guava has a method similar to the one from Commons IOUtils that Willi aus Rohr mentioned   import com google common base Charsets  import com google common io Files           String text   Files toString new File path   Charsets UTF 8     EDIT by PiggyPiglet Files toString is deprecated  and due for removal Octobor 2019  Instead use Files asCharSource new File path   StandardCharsets UTF 8  read     EDIT by Oscar Reyes  This is the  simplified  underlying code on the cited library   InputStream in   new FileInputStream file   byte   b    new byte file length     int len   b length  int total   0   while  total  lt  len      int result   in read b  total  len - total     if  result    -1        break        total    result     return new String  b   Charsets UTF 8      Edit  by Jonik   The above doesn t match the source code of recent Guava versions  For the current source  see the classes Files  CharStreams  ByteSource and CharSource in com google common io package

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Be aware when using fileInputStream available   the returned integer does not have to represent the actual file size  but rather the guessed amount of bytes the system should be able to read from the stream without blocking IO  A safe and simple way could look like this  public String readStringFromInputStream FileInputStream fileInputStream        StringBuffer stringBuffer   new StringBuffer        try           byte   buffer          while  fileInputStream available    gt  0                buffer   new byte fileInputStream available                 fileInputStream read buffer               stringBuffer append new String buffer   ISO-8859-1                     catch  FileNotFoundException e          catch  IOException e          return stringBuffer toString        It should be considered that this approach is not suitable for multi-byte character encodings like UTF-8

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import java nio charset StandardCharsets  import java nio file Files  import java nio file Paths   String content   new String Files readAllBytes Paths get  readMe txt     StandardCharsets UTF 8     since java 7 you can do it this way

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You can try Scanner and File class  a few lines solution   try     String content   new Scanner new File  file txt    useDelimiter    Z   next      System out println content     catch FileNotFoundException e      System out println  not found

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Read all text from a file Java 11 added the readString   method to read small files as a String  preserving line terminators  String content   Files readString path  StandardCharsets US ASCII    For versions between Java 7 and 11  here s a compact  robust idiom  wrapped up in a utility method  static String readFile String path  Charset encoding    throws IOException     byte   encoded   Files readAllBytes Paths get path      return new String encoded  encoding      Read lines of text from a file Java 7 added a convenience method to read a file as lines of text  represented as a List lt String gt   This approach is  quot lossy quot  because the line separators are stripped from the end of each line  List lt String gt  lines   Files readAllLines Paths get path   encoding    Java 8 added the Files lines   method to produce a Stream lt String gt   Again  this method is lossy because line separators are stripped  If an IOException is encountered while reading the file  it is wrapped in an UncheckedIOException  since Stream doesn t accept lambdas that throw checked exceptions  try  Stream lt String gt  lines   Files lines path  encoding       lines forEach System out  println      This Stream does need a close   call  this is poorly documented on the API  and I suspect many people don t even notice Stream has a close   method  Be sure to use an ARM-block as shown  If you are working with a source other than a file  you can use the lines   method in BufferedReader instead  Memory utilization The first method  that preserves line breaks  can temporarily require memory several times the size of the file  because for a short time the raw file contents  a byte array   and the decoded characters  each of which is 16 bits even if encoded as 8 bits in the file  reside in memory at once  It is safest to apply to files that you know to be small relative to the available memory  The second method  reading lines  is usually more memory efficient  because the input byte buffer for decoding doesn t need to contain the entire file  However  it s still not suitable for files that are very large relative to available memory  For reading large files  you need a different design for your program  one that reads a chunk of text from a stream  processes it  and then moves on to the next  reusing the same fixed-sized memory block  Here   quot large quot  depends on the computer specs  Nowadays  this threshold might be many gigabytes of RAM  The third method  using a Stream lt String gt  is one way to do this  if your input  quot records quot  happen to be individual lines   Using the readLine   method of BufferedReader is the procedural equivalent to this approach   Character encoding One thing that is missing from the sample in the original post is the character encoding  There are some special cases where the platform default is what you want  but they are rare  and you should be able justify your choice  The StandardCharsets class defines some constants for the encodings required of all Java runtimes  String content   readFile  quot test txt quot   StandardCharsets UTF 8    The platform default is available from the Charset class itself  String content   readFile  quot test txt quot   Charset defaultCharset       Note  This answer largely replaces my Java 6 version  The utility of Java 7 safely simplifies the code  and the old answer  which used a mapped byte buffer  prevented the file that was read from being deleted until the mapped buffer was garbage collected  You can view the old version via the  quot edited quot  link on this answer

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If you re willing to use an external library  check out Apache Commons IO  200KB JAR   It contains an org apache commons io FileUtils readFileToString   method that allows you to read an entire File into a String with one line of code   Example   import java io    import java nio charset    import org apache commons io     public String readFile   throws IOException       File file   new File  data txt        return FileUtils readFileToString file  StandardCharsets UTF 8

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This one uses the method RandomAccessFile readFully  it seems to be available from JDK 1 0    public static String readFileContent String filename  Charset charset  throws IOException       RandomAccessFile raf   null      try           raf   new RandomAccessFile filename   r            byte   buffer   new byte  int raf length             raf readFully buffer           return new String buffer  charset         finally           closeStream raf              private static void closeStream Closeable c        if  c    null            try               c close              catch  IOException ex                   do nothing

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Using JDK 8 or above   no external libraries used  You can create a new String object from the file content  Using classes from java nio file package    public String readStringFromFile String filePath  throws IOException       String fileContent   new String Files readAllBytes Paths get filePath         return fileContent

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If you re looking for an alternative that doesn t involve a third-party library  e g  Commons I O   you can use the Scanner class   private String readFile String pathname  throws IOException        File file   new File pathname       StringBuilder fileContents   new StringBuilder  int file length                  try  Scanner scanner   new Scanner file             while scanner hasNextLine                  fileContents append scanner nextLine     System lineSeparator                       return fileContents toString

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If you re looking for an alternative that doesn t involve a third-party library  e g  Commons I O   you can use the Scanner class   private String readFile String pathname  throws IOException        File file   new File pathname       StringBuilder fileContents   new StringBuilder  int file length                  try  Scanner scanner   new Scanner file             while scanner hasNextLine                  fileContents append scanner nextLine     System lineSeparator                       return fileContents toString

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Gathered all the possible ways to read the File as String from Disk or Network    Guava  Google using classes Resources  Files  static Charset charset   com google common base Charsets UTF 8  public static String guava ServerFile  URL url   throws IOException       return Resources toString  url  charset      public static String guava DiskFile  File file   throws IOException       return Files toString  file  charset              APACHE - COMMONS IO using classes IOUtils  FileUtils  static Charset encoding   org apache commons io Charsets UTF 8  public static String commons IOUtils  URL url   throws IOException       java io InputStream in   url openStream        try           return IOUtils toString  in  encoding          finally           IOUtils closeQuietly in           public static String commons FileUtils  File file   throws IOException       return FileUtils readFileToString  file  encoding          List lt String gt  lines   FileUtils readLines  fileName  encoding        return lines stream   collect  Collectors joining   n                  Java 8 BufferReader using Stream API  public static String streamURL Buffer  URL url   throws IOException       java io InputStream source   url openStream        BufferedReader reader   new BufferedReader  new InputStreamReader  source            List lt String gt  lines   reader lines   collect  Collectors toList          return reader lines   collect  Collectors joining  System lineSeparator          public static String streamFile Buffer  File file   throws IOException       BufferedReader reader   new BufferedReader  new FileReader  file          return reader lines   collect Collectors joining System lineSeparator                Scanner Class with regex  A  which matches the beginning of input   static String charsetName   java nio charset StandardCharsets UTF 8 toString    public static String streamURL Scanner  URL url   throws IOException       java io InputStream source   url openStream        Scanner scanner   new Scanner source  charsetName  useDelimiter    A        return scanner hasNext     scanner next           public static String streamFile Scanner  File file   throws IOException       Scanner scanner   new Scanner file  charsetName  useDelimiter    A        return scanner hasNext     scanner next                   Java 7  java nio file Files readAllBytes   public static String getDiskFile Java7  File file   throws IOException       byte   readAllBytes   java nio file Files readAllBytes Paths get  file getAbsolutePath           return new String  readAllBytes              BufferedReader using InputStreamReader   public static String getDiskFile Lines  File file   throws IOException       StringBuffer text   new StringBuffer        FileInputStream fileStream   new FileInputStream  file        BufferedReader br   new BufferedReader  new InputStreamReader  fileStream          for   String line   line   br readLine       null            text append  line   System lineSeparator          return text toString             Example with main method to access the above methods   public static void main String   args  throws IOException       String fileName    E  parametarisation csv       File file   new File  fileName         String fileStream   commons FileUtils  file                   guava DiskFile  file                   streamFile Buffer  file                   getDiskFile Java7  file                   getDiskFile Lines  file        System out println    File Over Disk    n   fileStream          try           String src    https   code jquery com jquery-3 2 1 js           URL url   new URL  src             String urlStream   commons IOUtils  url                       guava ServerFile  url                       streamURL Scanner  url                       streamURL Buffer  url            System out println    File Over Network    n   urlStream          catch  MalformedURLException e            e printStackTrace                 see   Ways to convert an InputStream to a String

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Using JDK 8 or above   no external libraries used  You can create a new String object from the file content  Using classes from java nio file package    public String readStringFromFile String filePath  throws IOException       String fileContent   new String Files readAllBytes Paths get filePath         return fileContent

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Gathered all the possible ways to read the File as String from Disk or Network    Guava  Google using classes Resources  Files  static Charset charset   com google common base Charsets UTF 8  public static String guava ServerFile  URL url   throws IOException       return Resources toString  url  charset      public static String guava DiskFile  File file   throws IOException       return Files toString  file  charset              APACHE - COMMONS IO using classes IOUtils  FileUtils  static Charset encoding   org apache commons io Charsets UTF 8  public static String commons IOUtils  URL url   throws IOException       java io InputStream in   url openStream        try           return IOUtils toString  in  encoding          finally           IOUtils closeQuietly in           public static String commons FileUtils  File file   throws IOException       return FileUtils readFileToString  file  encoding          List lt String gt  lines   FileUtils readLines  fileName  encoding        return lines stream   collect  Collectors joining   n                  Java 8 BufferReader using Stream API  public static String streamURL Buffer  URL url   throws IOException       java io InputStream source   url openStream        BufferedReader reader   new BufferedReader  new InputStreamReader  source            List lt String gt  lines   reader lines   collect  Collectors toList          return reader lines   collect  Collectors joining  System lineSeparator          public static String streamFile Buffer  File file   throws IOException       BufferedReader reader   new BufferedReader  new FileReader  file          return reader lines   collect Collectors joining System lineSeparator                Scanner Class with regex  A  which matches the beginning of input   static String charsetName   java nio charset StandardCharsets UTF 8 toString    public static String streamURL Scanner  URL url   throws IOException       java io InputStream source   url openStream        Scanner scanner   new Scanner source  charsetName  useDelimiter    A        return scanner hasNext     scanner next           public static String streamFile Scanner  File file   throws IOException       Scanner scanner   new Scanner file  charsetName  useDelimiter    A        return scanner hasNext     scanner next                   Java 7  java nio file Files readAllBytes   public static String getDiskFile Java7  File file   throws IOException       byte   readAllBytes   java nio file Files readAllBytes Paths get  file getAbsolutePath           return new String  readAllBytes              BufferedReader using InputStreamReader   public static String getDiskFile Lines  File file   throws IOException       StringBuffer text   new StringBuffer        FileInputStream fileStream   new FileInputStream  file        BufferedReader br   new BufferedReader  new InputStreamReader  fileStream          for   String line   line   br readLine       null            text append  line   System lineSeparator          return text toString             Example with main method to access the above methods   public static void main String   args  throws IOException       String fileName    E  parametarisation csv       File file   new File  fileName         String fileStream   commons FileUtils  file                   guava DiskFile  file                   streamFile Buffer  file                   getDiskFile Java7  file                   getDiskFile Lines  file        System out println    File Over Disk    n   fileStream          try           String src    https   code jquery com jquery-3 2 1 js           URL url   new URL  src             String urlStream   commons IOUtils  url                       guava ServerFile  url                       streamURL Scanner  url                       streamURL Buffer  url            System out println    File Over Network    n   urlStream          catch  MalformedURLException e            e printStackTrace                 see   Ways to convert an InputStream to a String

User · Answer

You can try Scanner and File class  a few lines solution   try     String content   new Scanner new File  file txt    useDelimiter    Z   next      System out println content     catch FileNotFoundException e      System out println  not found

User · Answer

If it s a text file why not use apache commons-io     It has the following method  public static String readFileToString File file  throws IOException   If you want the lines as a list use  public static List lt String gt  readLines File file  throws IOException

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That code will normalize line breaks  which may or may not be what you really want to do   Here s an alternative which doesn t do that  and which is  IMO  simpler to understand than the NIO code  although it still uses java nio charset Charset    public static String readFile String file  String csName              throws IOException       Charset cs   Charset forName csName       return readFile file  cs      public static String readFile String file  Charset cs              throws IOException          No real need to close the BufferedReader InputStreamReader        as they re only wrapping the stream     FileInputStream stream   new FileInputStream file       try           Reader reader   new BufferedReader new InputStreamReader stream  cs            StringBuilder builder   new StringBuilder            char   buffer   new char 8192           int read          while   read   reader read buffer  0  buffer length    gt  0                builder append buffer  0  read                     return builder toString          finally              Potential issue here  if this throws an IOException             it will mask any others  Normally I d use a utility            method which would log exceptions and swallow them         stream close

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I cannot comment other entries yet  so I ll just leave it here   One of best answers here  https   stackoverflow com a 326448 1521167    private String readFile String pathname  throws IOException    File file   new File pathname   StringBuilder fileContents   new StringBuilder  int file length     Scanner scanner   new Scanner file   String lineSeparator   System getProperty  line separator     try       while scanner hasNextLine                      fileContents append scanner nextLine     lineSeparator             return fileContents toString      finally       scanner close          still has one flaw  It always puts new line char in the end of string  which may cause some weirds bugs  My suggestion is to change it to       private String readFile String pathname  throws IOException       File file   new File pathname       StringBuilder fileContents   new StringBuilder  int  file length         Scanner scanner   new Scanner new BufferedReader new FileReader file         String lineSeparator   System getProperty  line separator         try           if  scanner hasNextLine                  fileContents append scanner nextLine                       while  scanner hasNextLine                  fileContents append lineSeparator   scanner nextLine                       return fileContents toString          finally           scanner close

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in java 8   there are a new Class      java util stream Stream   A stream represents a sequence of elements and supports different kind of operations to perform computations upon those elements  to Read more about it    Oracle Documentation  Here an Example    import java nio charset StandardCharsets  import java nio file Files  import java nio file Paths  import java util stream Stream   public Class ReadFile    public  static String readFile String filePath     StringBuilder  stringBuilder   new StringBuilder        String ls   System getProperty  line separator            try                try  Stream lt String gt  lines   Files lines Paths get filePath   StandardCharsets UTF 8                     for  String line    Iterable lt String gt   lines  iterator                            stringBuilder append line                         stringBuilder append ls                                                catch  Exception e                e printStackTrace                     return stringBuilder toString

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If you do not have access to the Files class  you can use a native solution   static String readFile File file  String charset          throws IOException       FileInputStream fileInputStream   new FileInputStream file       byte   buffer   new byte fileInputStream available         int length   fileInputStream read buffer       fileInputStream close        return new String buffer  0  length  charset

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Since JDK 11   String file       Path path   Paths get file   String content   Files readString path      Or readString path  someCharset   if you need a Charset different from UTF-8

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There is a variation on the same theme that uses a for loop  instead of a while loop  to limit the scope of the line variable   Whether it s  better  is a matter of personal taste   for String line   reader readLine    line    null  line   reader readLine          stringBuilder append line       stringBuilder append ls

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User java nio Files to read all lines of file   public String readFile   throws IOException           File fileToRead   new File  file path            List lt String gt  fileLines   Files readAllLines fileToRead toPath             return StringUtils join fileLines  StringUtils EMPTY

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If you re willing to use an external library  check out Apache Commons IO  200KB JAR   It contains an org apache commons io FileUtils readFileToString   method that allows you to read an entire File into a String with one line of code   Example   import java io    import java nio charset    import org apache commons io     public String readFile   throws IOException       File file   new File  data txt        return FileUtils readFileToString file  StandardCharsets UTF 8

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If you do not have access to the Files class  you can use a native solution   static String readFile File file  String charset          throws IOException       FileInputStream fileInputStream   new FileInputStream file       byte   buffer   new byte fileInputStream available         int length   fileInputStream read buffer       fileInputStream close        return new String buffer  0  length  charset

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Use code   File file   new File  input txt    BufferedInputStream bin   new BufferedInputStream new FileInputStream                  file    byte   buffer   new byte  int  file length     bin read buffer   String fileStr   new String buffer     fileStr contains output in String

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User java nio Files to read all lines of file   public String readFile   throws IOException           File fileToRead   new File  file path            List lt String gt  fileLines   Files readAllLines fileToRead toPath             return StringUtils join fileLines  StringUtils EMPTY

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There is a variation on the same theme that uses a for loop  instead of a while loop  to limit the scope of the line variable   Whether it s  better  is a matter of personal taste   for String line   reader readLine    line    null  line   reader readLine          stringBuilder append line       stringBuilder append ls

User · Answer

A very lean solution based on Scanner   Scanner scanner   new Scanner  new File  poem txt      String text   scanner useDelimiter    A   next    scanner close       Put this call in a finally block   Or  if you want to set the charset   Scanner scanner   new Scanner  new File  poem txt     UTF-8     String text   scanner useDelimiter    A   next    scanner close       Put this call in a finally block   Or  with a try-with-resources block  which will call scanner close   for you   try  Scanner scanner   new Scanner  new File  poem txt     UTF-8           String text   scanner useDelimiter    A   next        Remember that the Scanner constructor can throw an IOException  And don t forget to import java io and java util   Source  Pat Niemeyer s blog

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If it s a text file why not use apache commons-io     It has the following method  public static String readFileToString File file  throws IOException   If you want the lines as a list use  public static List lt String gt  readLines File file  throws IOException

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public static String slurp  final File file  throws IOException       StringBuilder result   new StringBuilder         BufferedReader reader   new BufferedReader new FileReader file         try           char   buf   new char 1024            int r   0           while   r   reader read buf      -1                result append buf  0  r                       finally           reader close               return result toString

User · Answer

A flexible solution using IOUtils from Apache commons-io in combination with StringWriter   Reader input   new FileReader    StringWriter output   new StringWriter    try     IOUtils copy input  output     finally     input close      String fileContents   output toString      It works with any reader or input stream  not just with files   for example when reading from a URL

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If you need a string processing  parallel processing  Java 8 has the great Stream API   String result   Files lines Paths get  file txt                         parallel      for parallel processing                       map String  trim     to change line                         filter line - gt  line length    gt  2     to filter some lines by a predicate                                              collect Collectors joining        to join lines   More examples are available in JDK samples sample lambda BulkDataOperations that can be downloaded from Oracle Java SE 8 download page   Another one liner example  String out   String join   n   Files readAllLines Paths get  file txt

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With Java 7  this is my preferred option to read a UTF-8 file   String content   new String Files readAllBytes Paths get filename     UTF-8      Since Java 7  the JDK has the new java nio file API  which provides many shortcuts  so 3rd party libraries are not always required for simple file operations

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This one uses the method RandomAccessFile readFully  it seems to be available from JDK 1 0    public static String readFileContent String filename  Charset charset  throws IOException       RandomAccessFile raf   null      try           raf   new RandomAccessFile filename   r            byte   buffer   new byte  int raf length             raf readFully buffer           return new String buffer  charset         finally           closeStream raf              private static void closeStream Closeable c        if  c    null            try               c close              catch  IOException ex                   do nothing

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If you re willing to use an external library  check out Apache Commons IO  200KB JAR   It contains an org apache commons io FileUtils readFileToString   method that allows you to read an entire File into a String with one line of code   Example   import java io    import java nio charset    import org apache commons io     public String readFile   throws IOException       File file   new File  data txt        return FileUtils readFileToString file  StandardCharsets UTF 8

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Guava has a method similar to the one from Commons IOUtils that Willi aus Rohr mentioned   import com google common base Charsets  import com google common io Files           String text   Files toString new File path   Charsets UTF 8     EDIT by PiggyPiglet Files toString is deprecated  and due for removal Octobor 2019  Instead use Files asCharSource new File path   StandardCharsets UTF 8  read     EDIT by Oscar Reyes  This is the  simplified  underlying code on the cited library   InputStream in   new FileInputStream file   byte   b    new byte file length     int len   b length  int total   0   while  total  lt  len      int result   in read b  total  len - total     if  result    -1        break        total    result     return new String  b   Charsets UTF 8      Edit  by Jonik   The above doesn t match the source code of recent Guava versions  For the current source  see the classes Files  CharStreams  ByteSource and CharSource in com google common io package

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Use code   File file   new File  input txt    BufferedInputStream bin   new BufferedInputStream new FileInputStream                  file    byte   buffer   new byte  int  file length     bin read buffer   String fileStr   new String buffer     fileStr contains output in String

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Using this library  it is one line   String data   IO from new File  data txt    toString

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Using this library  it is one line   String data   IO from new File  data txt    toString

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A flexible solution using IOUtils from Apache commons-io in combination with StringWriter   Reader input   new FileReader    StringWriter output   new StringWriter    try     IOUtils copy input  output     finally     input close      String fileContents   output toString      It works with any reader or input stream  not just with files   for example when reading from a URL

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Since JDK 11   String file       Path path   Paths get file   String content   Files readString path      Or readString path  someCharset   if you need a Charset different from UTF-8

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If you re willing to use an external library  check out Apache Commons IO  200KB JAR   It contains an org apache commons io FileUtils readFileToString   method that allows you to read an entire File into a String with one line of code   Example   import java io    import java nio charset    import org apache commons io     public String readFile   throws IOException       File file   new File  data txt        return FileUtils readFileToString file  StandardCharsets UTF 8

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To read a File as binary and convert at the end  public static String readFileAsString String filePath  throws IOException       DataInputStream dis   new DataInputStream new FileInputStream filePath        try           long len   new File filePath  length            if  len  gt  Integer MAX VALUE  throw new IOException  File   filePath   too large  was   len   bytes             byte   bytes   new byte  int  len           dis readFully bytes           return new String bytes   UTF-8          finally           dis close

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Read all text from a file Java 11 added the readString   method to read small files as a String  preserving line terminators  String content   Files readString path  StandardCharsets US ASCII    For versions between Java 7 and 11  here s a compact  robust idiom  wrapped up in a utility method  static String readFile String path  Charset encoding    throws IOException     byte   encoded   Files readAllBytes Paths get path      return new String encoded  encoding      Read lines of text from a file Java 7 added a convenience method to read a file as lines of text  represented as a List lt String gt   This approach is  quot lossy quot  because the line separators are stripped from the end of each line  List lt String gt  lines   Files readAllLines Paths get path   encoding    Java 8 added the Files lines   method to produce a Stream lt String gt   Again  this method is lossy because line separators are stripped  If an IOException is encountered while reading the file  it is wrapped in an UncheckedIOException  since Stream doesn t accept lambdas that throw checked exceptions  try  Stream lt String gt  lines   Files lines path  encoding       lines forEach System out  println      This Stream does need a close   call  this is poorly documented on the API  and I suspect many people don t even notice Stream has a close   method  Be sure to use an ARM-block as shown  If you are working with a source other than a file  you can use the lines   method in BufferedReader instead  Memory utilization The first method  that preserves line breaks  can temporarily require memory several times the size of the file  because for a short time the raw file contents  a byte array   and the decoded characters  each of which is 16 bits even if encoded as 8 bits in the file  reside in memory at once  It is safest to apply to files that you know to be small relative to the available memory  The second method  reading lines  is usually more memory efficient  because the input byte buffer for decoding doesn t need to contain the entire file  However  it s still not suitable for files that are very large relative to available memory  For reading large files  you need a different design for your program  one that reads a chunk of text from a stream  processes it  and then moves on to the next  reusing the same fixed-sized memory block  Here   quot large quot  depends on the computer specs  Nowadays  this threshold might be many gigabytes of RAM  The third method  using a Stream lt String gt  is one way to do this  if your input  quot records quot  happen to be individual lines   Using the readLine   method of BufferedReader is the procedural equivalent to this approach   Character encoding One thing that is missing from the sample in the original post is the character encoding  There are some special cases where the platform default is what you want  but they are rare  and you should be able justify your choice  The StandardCharsets class defines some constants for the encodings required of all Java runtimes  String content   readFile  quot test txt quot   StandardCharsets UTF 8    The platform default is available from the Charset class itself  String content   readFile  quot test txt quot   Charset defaultCharset       Note  This answer largely replaces my Java 6 version  The utility of Java 7 safely simplifies the code  and the old answer  which used a mapped byte buffer  prevented the file that was read from being deleted until the mapped buffer was garbage collected  You can view the old version via the  quot edited quot  link on this answer

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Based on  erickson s answer  you can use   public String readAll String fileName  throws IOException       List lt String gt  lines   Files readAllLines new File fileName  toPath         return String join   n   lines toArray new String lines size

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In one line  Java 8   assuming you have a Reader   String sMessage   String join   n   reader lines   collect Collectors toList

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Java attempts to be extremely general and flexible in all it does  As a result  something which is relatively simple in a scripting language  your code would be replaced with  open file  read    in python  is a lot more complicated  There doesn t seem to be any shorter way of doing it  except using an external library  like Willi aus Rohr mentioned   Your options    Use an external library  Copy this code into all your projects  Create your own mini-library which contains functions you use often    Your best bet is probably the 2nd one  as it has the least dependencies

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import java nio file Files                 String readFile String filename                File f   new File filename               try                   byte   bytes   Files readAllBytes f toPath                     return new String bytes  UTF-8                  catch  FileNotFoundException e                    e printStackTrace                  catch  IOException e                    e printStackTrace                              return

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To read a File as binary and convert at the end  public static String readFileAsString String filePath  throws IOException       DataInputStream dis   new DataInputStream new FileInputStream filePath        try           long len   new File filePath  length            if  len  gt  Integer MAX VALUE  throw new IOException  File   filePath   too large  was   len   bytes             byte   bytes   new byte  int  len           dis readFully bytes           return new String bytes   UTF-8          finally           dis close

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Java attempts to be extremely general and flexible in all it does  As a result  something which is relatively simple in a scripting language  your code would be replaced with  open file  read    in python  is a lot more complicated  There doesn t seem to be any shorter way of doing it  except using an external library  like Willi aus Rohr mentioned   Your options    Use an external library  Copy this code into all your projects  Create your own mini-library which contains functions you use often    Your best bet is probably the 2nd one  as it has the least dependencies

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After Ctrl F ing after Scanner  I think that the Scanner solution should be listed too  In the easiest to read fashion it goes like this   public String fileToString File file  Charset charset      Scanner fileReader   new Scanner file  charset     fileReader useDelimiter    Z        Z means EOF    String out   fileReader next      fileReader close      return out      If you use Java 7 or newer  and you really should  consider using try-with-resources to make the code easier to read  No more dot-close stuff littering everything  But that s mostly a stylistic choice methinks   I m posting this mostly for completionism  since if you need to do this a lot  there should be things in java nio file Files that should do the job better   My suggestion would be to use Files readAllBytes Path  to grab all the bytes  and feed it to new String byte   Charset  to get a String out of it that you can trust  Charsets will be mean to you during your lifetime  so beware of this stuff now   Others have given code and stuff  and I don t want to steal their glory

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Read all text from a file Java 11 added the readString   method to read small files as a String  preserving line terminators  String content   Files readString path  StandardCharsets US ASCII    For versions between Java 7 and 11  here s a compact  robust idiom  wrapped up in a utility method  static String readFile String path  Charset encoding    throws IOException     byte   encoded   Files readAllBytes Paths get path      return new String encoded  encoding      Read lines of text from a file Java 7 added a convenience method to read a file as lines of text  represented as a List lt String gt   This approach is  quot lossy quot  because the line separators are stripped from the end of each line  List lt String gt  lines   Files readAllLines Paths get path   encoding    Java 8 added the Files lines   method to produce a Stream lt String gt   Again  this method is lossy because line separators are stripped  If an IOException is encountered while reading the file  it is wrapped in an UncheckedIOException  since Stream doesn t accept lambdas that throw checked exceptions  try  Stream lt String gt  lines   Files lines path  encoding       lines forEach System out  println      This Stream does need a close   call  this is poorly documented on the API  and I suspect many people don t even notice Stream has a close   method  Be sure to use an ARM-block as shown  If you are working with a source other than a file  you can use the lines   method in BufferedReader instead  Memory utilization The first method  that preserves line breaks  can temporarily require memory several times the size of the file  because for a short time the raw file contents  a byte array   and the decoded characters  each of which is 16 bits even if encoded as 8 bits in the file  reside in memory at once  It is safest to apply to files that you know to be small relative to the available memory  The second method  reading lines  is usually more memory efficient  because the input byte buffer for decoding doesn t need to contain the entire file  However  it s still not suitable for files that are very large relative to available memory  For reading large files  you need a different design for your program  one that reads a chunk of text from a stream  processes it  and then moves on to the next  reusing the same fixed-sized memory block  Here   quot large quot  depends on the computer specs  Nowadays  this threshold might be many gigabytes of RAM  The third method  using a Stream lt String gt  is one way to do this  if your input  quot records quot  happen to be individual lines   Using the readLine   method of BufferedReader is the procedural equivalent to this approach   Character encoding One thing that is missing from the sample in the original post is the character encoding  There are some special cases where the platform default is what you want  but they are rare  and you should be able justify your choice  The StandardCharsets class defines some constants for the encodings required of all Java runtimes  String content   readFile  quot test txt quot   StandardCharsets UTF 8    The platform default is available from the Charset class itself  String content   readFile  quot test txt quot   Charset defaultCharset       Note  This answer largely replaces my Java 6 version  The utility of Java 7 safely simplifies the code  and the old answer  which used a mapped byte buffer  prevented the file that was read from being deleted until the mapped buffer was garbage collected  You can view the old version via the  quot edited quot  link on this answer

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Read all text from a file Java 11 added the readString   method to read small files as a String  preserving line terminators  String content   Files readString path  StandardCharsets US ASCII    For versions between Java 7 and 11  here s a compact  robust idiom  wrapped up in a utility method  static String readFile String path  Charset encoding    throws IOException     byte   encoded   Files readAllBytes Paths get path      return new String encoded  encoding      Read lines of text from a file Java 7 added a convenience method to read a file as lines of text  represented as a List lt String gt   This approach is  quot lossy quot  because the line separators are stripped from the end of each line  List lt String gt  lines   Files readAllLines Paths get path   encoding    Java 8 added the Files lines   method to produce a Stream lt String gt   Again  this method is lossy because line separators are stripped  If an IOException is encountered while reading the file  it is wrapped in an UncheckedIOException  since Stream doesn t accept lambdas that throw checked exceptions  try  Stream lt String gt  lines   Files lines path  encoding       lines forEach System out  println      This Stream does need a close   call  this is poorly documented on the API  and I suspect many people don t even notice Stream has a close   method  Be sure to use an ARM-block as shown  If you are working with a source other than a file  you can use the lines   method in BufferedReader instead  Memory utilization The first method  that preserves line breaks  can temporarily require memory several times the size of the file  because for a short time the raw file contents  a byte array   and the decoded characters  each of which is 16 bits even if encoded as 8 bits in the file  reside in memory at once  It is safest to apply to files that you know to be small relative to the available memory  The second method  reading lines  is usually more memory efficient  because the input byte buffer for decoding doesn t need to contain the entire file  However  it s still not suitable for files that are very large relative to available memory  For reading large files  you need a different design for your program  one that reads a chunk of text from a stream  processes it  and then moves on to the next  reusing the same fixed-sized memory block  Here   quot large quot  depends on the computer specs  Nowadays  this threshold might be many gigabytes of RAM  The third method  using a Stream lt String gt  is one way to do this  if your input  quot records quot  happen to be individual lines   Using the readLine   method of BufferedReader is the procedural equivalent to this approach   Character encoding One thing that is missing from the sample in the original post is the character encoding  There are some special cases where the platform default is what you want  but they are rare  and you should be able justify your choice  The StandardCharsets class defines some constants for the encodings required of all Java runtimes  String content   readFile  quot test txt quot   StandardCharsets UTF 8    The platform default is available from the Charset class itself  String content   readFile  quot test txt quot   Charset defaultCharset       Note  This answer largely replaces my Java 6 version  The utility of Java 7 safely simplifies the code  and the old answer  which used a mapped byte buffer  prevented the file that was read from being deleted until the mapped buffer was garbage collected  You can view the old version via the  quot edited quot  link on this answer

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import java nio file Files                 String readFile String filename                File f   new File filename               try                   byte   bytes   Files readAllBytes f toPath                     return new String bytes  UTF-8                  catch  FileNotFoundException e                    e printStackTrace                  catch  IOException e                    e printStackTrace                              return

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public static String slurp  final File file  throws IOException       StringBuilder result   new StringBuilder         BufferedReader reader   new BufferedReader new FileReader file         try           char   buf   new char 1024            int r   0           while   r   reader read buf      -1                result append buf  0  r                       finally           reader close               return result toString

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There is a variation on the same theme that uses a for loop  instead of a while loop  to limit the scope of the line variable   Whether it s  better  is a matter of personal taste   for String line   reader readLine    line    null  line   reader readLine          stringBuilder append line       stringBuilder append ls

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A very lean solution based on Scanner   Scanner scanner   new Scanner  new File  poem txt      String text   scanner useDelimiter    A   next    scanner close       Put this call in a finally block   Or  if you want to set the charset   Scanner scanner   new Scanner  new File  poem txt     UTF-8     String text   scanner useDelimiter    A   next    scanner close       Put this call in a finally block   Or  with a try-with-resources block  which will call scanner close   for you   try  Scanner scanner   new Scanner  new File  poem txt     UTF-8           String text   scanner useDelimiter    A   next        Remember that the Scanner constructor can throw an IOException  And don t forget to import java io and java util   Source  Pat Niemeyer s blog

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If you re looking for an alternative that doesn t involve a third-party library  e g  Commons I O   you can use the Scanner class   private String readFile String pathname  throws IOException        File file   new File pathname       StringBuilder fileContents   new StringBuilder  int file length                  try  Scanner scanner   new Scanner file             while scanner hasNextLine                  fileContents append scanner nextLine     System lineSeparator                       return fileContents toString

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Java attempts to be extremely general and flexible in all it does  As a result  something which is relatively simple in a scripting language  your code would be replaced with  open file  read    in python  is a lot more complicated  There doesn t seem to be any shorter way of doing it  except using an external library  like Willi aus Rohr mentioned   Your options    Use an external library  Copy this code into all your projects  Create your own mini-library which contains functions you use often    Your best bet is probably the 2nd one  as it has the least dependencies

User · Answer

Java attempts to be extremely general and flexible in all it does  As a result  something which is relatively simple in a scripting language  your code would be replaced with  open file  read    in python  is a lot more complicated  There doesn t seem to be any shorter way of doing it  except using an external library  like Willi aus Rohr mentioned   Your options    Use an external library  Copy this code into all your projects  Create your own mini-library which contains functions you use often    Your best bet is probably the 2nd one  as it has the least dependencies

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import java nio charset StandardCharsets  import java nio file Files  import java nio file Paths   String content   new String Files readAllBytes Paths get  readMe txt     StandardCharsets UTF 8     since java 7 you can do it this way

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Based on  erickson s answer  you can use   public String readAll String fileName  throws IOException       List lt String gt  lines   Files readAllLines new File fileName  toPath         return String join   n   lines toArray new String lines size

User · Answer

In one line  Java 8   assuming you have a Reader   String sMessage   String join   n   reader lines   collect Collectors toList

[java] How do I create a Java string from the contents of a file?

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