Read String line by line

Question

Given a string that isn t too long  what is the best way to read it line by line   I know you can do   BufferedReader reader   new BufferedReader new StringReader  lt string gt     reader readLine      Another way would be to take the substring on the eol   final String eol   System getProperty  line separator    output   output substring output indexOf eol   1      Any other maybe simpler ways of doing it   I have no problems with the above approaches  just interested to know if any of you know something that may look simpler and more efficient

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Or use new try with resources clause combined with Scanner      try  Scanner scanner   new Scanner value             while  scanner hasNextLine                  String line   scanner nextLine                   process the line

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Using Apache Commons IOUtils you can do this nicely via  List lt String gt  lines   IOUtils readLines new StringReader string      It s not doing anything clever  but it s nice and compact  It ll handle streams as well  and you can get a LineIterator too if you prefer

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You can use the stream api and a StringReader wrapped in a BufferedReader which got a lines   stream output in java 8   import java util stream    import java io    class test       public static void main String    a            String s    this is a  nmultiline rstring r nusing different newline styles            new BufferedReader new StringReader s   lines   forEach               line  - gt  System out println  one line of the string      line                       Gives  one line of the string  this is a one line of the string  multiline one line of the string  string one line of the string  using different newline styles   Just like in BufferedReader s readLine  the newline character s  themselves are not included  All kinds of newline separators are supported  in the same string even

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The easiest and most universal approach would be to just use the regex Linebreak matcher  R which matches Any Unicode linebreak sequence   Pattern NEWLINE   Pattern compile    R   String lines     NEWLINE split input     see https   docs oracle com en java javase 11 docs api java base java util regex Pattern html

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You can try the following regular expression    r  n   Code   String input     nab n n     n ncd nef n n n n n   String   lines   input split    r   n   -1   int n   1  for String line   lines        System out printf   tLine  02d    s   n   n    line       Output   Line 01    Line 02  ab  Line 03    Line 04        Line 05    Line 06  cd  Line 07  ef  Line 08    Line 09    Line 10    Line 11    Line 12

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Since I was especially interested in the efficiency angle  I created a little test class  below   Outcome for 5 000 000 lines   Comparing line breaking performance of different solutions Testing 5000000 lines Split  all   14665 ms Split  CR only   3752 ms Scanner  10005 Reader  2060   As usual  exact times may vary  but the ratio holds true however often I ve run it   Conclusion  the  simpler  and  more efficient  requirements of the OP can t be satisfied simultaneously  the split solution  in either incarnation  is simpler  but the Reader implementation beats the others hands down   import java io BufferedReader  import java io IOException  import java io StringReader  import java util ArrayList  import java util List  import java util Scanner          Test class for splitting a string into lines at linebreaks     public class LineBreakTest           Main method  pass in desired line count as first parameter  default   10000          public static void main String   args            int lineCount   args length    0   10000   Integer parseInt args 0            System out println  Comparing line breaking performance of different solutions            System out printf  Testing  d lines n   lineCount           String text   createText lineCount           testSplitAllPlatforms text           testSplitWindowsOnly text           testScanner text           testReader text              private static void testSplitAllPlatforms String text            long start   System currentTimeMillis            text split   n r  r            System out printf  Split  regexp    d n   System currentTimeMillis   - start              private static void testSplitWindowsOnly String text            long start   System currentTimeMillis            text split   n            System out printf  Split  CR only    d n   System currentTimeMillis   - start              private static void testScanner String text            long start   System currentTimeMillis            List lt String gt  result   new ArrayList lt  gt             try  Scanner scanner   new Scanner text                 while  scanner hasNextLine                      result add scanner nextLine                                     System out printf  Scanner   d n   System currentTimeMillis   - start              private static void testReader String text            long start   System currentTimeMillis            List lt String gt  result   new ArrayList lt  gt             try  BufferedReader reader   new BufferedReader new StringReader text                  String line   reader readLine                while  line    null                    result add line                   line   reader readLine                            catch  IOException exc                   quit                   System out printf  Reader   d n   System currentTimeMillis   - start              private static String createText int lineCount            StringBuilder result   new StringBuilder            StringBuilder lineBuilder   new StringBuilder            for  int i   0  i  lt  20  i                  lineBuilder append  word                       String line   lineBuilder toString            for  int i   0  i  lt  lineCount  i                  result append line               result append   n                      return result toString

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You can also use the split method of String   String   lines   myString split System getProperty  line separator       This gives you all lines in a handy array    I don t know about the performance of split  It uses regular expressions

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You can also use   String   lines   someString split   n      If that doesn t work try replacing  n with  r n

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There is also Scanner   You can use it just like the BufferedReader   Scanner scanner   new Scanner myString   while  scanner hasNextLine        String line   scanner nextLine         process the line   scanner close      I think that this is a bit cleaner approach that both of the suggested ones

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Solution using Java 8 features such as Stream API and Method references  new BufferedReader new StringReader myString            lines   forEach System out  println     or  public void someMethod String myLongString         new BufferedReader new StringReader myLongString                lines   forEach this  parseString      private void parseString String data          do something

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Since Java 11  there is a new method String lines          Returns a stream of lines extracted from this string     separated by line terminators             public Stream lt String gt  lines             Usage    line1 nline2 nlines3       lines        forEach System out  println

[java] Read String line by line

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