How to list the files inside a JAR file

Question

I have this code which reads all the files from a directory       File textFolder   new File  text directory         File    texFiles   textFolder listFiles  new FileFilter                public boolean accept  File file                    return file getName   endsWith   txt                           It works great  It fills the array with all the files that end with   txt  from directory  text directory    How can I read the contents of a directory in a similar fashion within a JAR file    So what I really want to do is  to list  all the images inside my JAR file  so I can load them with    ImageIO read this getClass   getResource  CompanyLogo png        That one works because the  CompanyLogo  is  hardcoded  but the number of images inside the JAR file could be from 10 to 200 variable length     EDIT  So I guess my main problem would be  How to know the name of the JAR file where my main class lives   Granted I could read it using java util Zip   My Structure is like this   They are like   my jar  Main class my jar  Aux class my jar  Other class my jar  images image01 png my jar  images image02a png my jar  images imwge034 png my jar  images imagAe01q png my jar  META-INF manifest    Right now I m able to load for instance  images image01 png  using        ImageIO read this getClass   getResource  images image01 png      But only because I know the file name  for the rest I have to load them dynamically

User · Answer

A jar file is just a zip file with a structured manifest. You can open the jar file with the usual java zip tools and scan the file contents that way, inflate streams, etc. Then use that in a getResourceAsStream call, and it should be all hunky dory.

EDIT / after clarification

It took me a minute to remember all the bits and pieces and I'm sure there are cleaner ways to do it, but I wanted to see that I wasn't crazy. In my project image.jpg is a file in some part of the main jar file. I get the class loader of the main class (SomeClass is the entry point) and use it to discover the image.jpg resource. Then some stream magic to get it into this ImageInputStream thing and everything is fine.

InputStream inputStream = SomeClass.class.getClassLoader().getResourceAsStream("image.jpg");
JPEGImageReaderSpi imageReaderSpi = new JPEGImageReaderSpi();
ImageReader ir = imageReaderSpi.createReaderInstance();
ImageInputStream iis = new MemoryCacheImageInputStream(inputStream);
ir.setInput(iis);
....
ir.read(0); //will hand us a buffered image

User · Answer

There are two very useful utilities both called JarScan    www inetfeedback com jarscan jarscan dev java net   See also this question  JarScan  scan all JAR files in all subfolders for specific class

User · Answer

Given an actual JAR file  you can list the contents using JarFile entries    You will need to know the location of the JAR file though - you can t just ask the classloader to list everything it could get at   You should be able to work out the location of the JAR file based on the URL returned from ThisClassName class getResource  ThisClassName class    but it may be a tiny bit fiddly

User · Answer

Code that works for both IDE s and  jar files   import java io    import java net    import java nio file    import java util    import java util stream     public class ResourceWalker       public static void main String   args  throws URISyntaxException  IOException           URI uri   ResourceWalker class getResource   resources   toURI            Path myPath          if  uri getScheme   equals  jar                  FileSystem fileSystem   FileSystems newFileSystem uri  Collections  lt String  Object gt emptyMap                 myPath   fileSystem getPath   resources              else               myPath   Paths get uri                     Stream lt Path gt  walk   Files walk myPath  1           for  Iterator lt Path gt  it   walk iterator    it hasNext                  System out println it next

User · Answer

I ve ported acheron55 s answer to Java 7 and closed the FileSystem object   This code works in IDE s  in jar files and in a jar inside a war on Tomcat 7  but note that it does not work in a jar inside a war on JBoss 7  it gives FileSystemNotFoundException  Provider  vfs  not installed  see also this post    Furthermore  like the original code  it is not thread safe  as suggested by errr   For these reasons I have abandoned this solution  however  if you can accept these issues  here is my ready-made code   import java io IOException  import java net    import java nio file    import java nio file attribute BasicFileAttributes  import java util Collections   public class ResourceWalker        public static void main String   args  throws URISyntaxException  IOException           URI uri   ResourceWalker class getResource   resources   toURI            System out println  Starting from      uri           try  FileSystem fileSystem    uri getScheme   equals  jar     FileSystems newFileSystem uri  Collections  lt String  Object gt emptyMap      null                 Path myPath   Paths get uri               Files walkFileTree myPath  new SimpleFileVisitor lt Path gt                        Override                 public FileVisitResult visitFile Path file  BasicFileAttributes attrs  throws IOException                       System out println file                       return FileVisitResult CONTINUE

User · Answer

So I guess my main problem would be  how to know the name of the jar where my main class lives       Assuming that your project is packed in a Jar  not necessarily true    you can use ClassLoader getResource   or findResource   with the class name  followed by  class  to get the jar that contains a given class   You ll have to parse the jar name from the URL that gets returned  not that tough   which I will leave as an exercise for the reader  -   Be sure to test for the case where the class is not part of a jar

User · Answer

I would like to expand on acheron55 s answer  since it is a very non-safe solution  for several reasons    It doesn t close the FileSystem object  It doesn t check if the FileSystem object already exists  It isn t thread-safe    This is somewhat a safer solution   private static ConcurrentMap lt String  Object gt  locks   new ConcurrentHashMap lt  gt      public void walk String path  throws Exception        URI uri   getClass   getResource path  toURI        if   jar  equals uri getScheme              safeWalkJar path  uri         else           Files walk Paths get path             private void safeWalkJar String path  URI uri  throws Exception        synchronized  getLock uri                    this ll close the FileSystem object at the end         try  FileSystem fs   getFileSystem uri                 Files walk fs getPath path                       private Object getLock URI uri         String fileName   parseFileName uri         locks computeIfAbsent fileName  s - gt  new Object         return locks get fileName      private String parseFileName URI uri         String schemeSpecificPart   uri getSchemeSpecificPart        return schemeSpecificPart substring 0  schemeSpecificPart indexOf           private FileSystem getFileSystem URI uri  throws IOException        try           return FileSystems getFileSystem uri         catch  FileSystemNotFoundException e            return FileSystems newFileSystem uri  Collections  lt String  String gt emptyMap                  There s no real need to synchronize over the file name  one could simply synchronize on the same object every time  or make the method synchronized   it s purely an optimization   I would say that this is still a problematic solution  since there might be other parts in the code that use the FileSystem interface over the same files  and it could interfere with them  even in a single threaded application   Also  it doesn t check for nulls  for instance  on getClass   getResource     This particular Java NIO interface is kind of horrible  since it introduces a global singleton non thread-safe resource  and its documentation is extremely vague  a lot of unknowns due to provider specific implementations   Results may vary for other FileSystem providers  not JAR   Maybe there s a good reason for it being that way  I don t know  I haven t researched the implementations

User · Answer

Just a different way of listing reading files from a jar URL and it does it recursively for nested jars  https   gist github com trung 2cd90faab7f75b3bcbaa  URL urlResource   Thead currentThread   getContextClassLoader   getResource  foo    JarReader read urlResource  new InputStreamCallback          Override     public void onFile String name  InputStream is  throws IOException              got file name and content stream

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Here s a method I wrote for a  run all JUnits under a package   You should be able to adapt it to your needs   private static void findClassesInJar List lt String gt  classFiles  String path  throws IOException       final String   parts   path split    Q jar    E        if  parts length    2            String jarFilename   parts 0      jar           String relativePath   parts 1  replace File separatorChar                JarFile jarFile   new JarFile jarFilename           final Enumeration lt JarEntry gt  entries   jarFile entries            while  entries hasMoreElements                  final JarEntry entry   entries nextElement                final String entryName   entry getName                if  entryName startsWith relativePath                     classFiles add entryName replace      File separatorChar                                      Edit  Ah  in that case  you might want this snippet as well  same use case       private static File findClassesDir Class lt   gt  clazz        try           String path   clazz getProtectionDomain   getCodeSource   getLocation   getFile            final String codeSourcePath   URLDecoder decode path   UTF-8            final String thisClassPath   new File codeSourcePath  clazz getPackage   getName   repalce      File separatorChar          catch  UnsupportedEncodingException e            throw new AssertionError  impossible   e

User · Answer

erickson s answer  worked perfectly    Here s the working code   CodeSource src   MyClass class getProtectionDomain   getCodeSource    List lt String gt  list   new ArrayList lt String gt      if  src    null         URL jar   src getLocation        ZipInputStream zip   new ZipInputStream  jar openStream         ZipEntry ze   null       while    ze   zip getNextEntry        null             String entryName   ze getName            if  entryName startsWith  images    amp  amp   entryName endsWith   png                   list add  entryName                          webimages   list toArray  new String  list size          And I have just modify my load method from this   File   webimages        BufferedImage image   ImageIO read this getClass   getResource webimages nextIndex  getName         To this   String     webimages        BufferedImage image   ImageIO read this getClass   getResource webimages nextIndex

User · Answer

CodeSource src   MyClass class getProtectionDomain   getCodeSource    if  src    null      URL jar   src getLocation      ZipInputStream zip   new ZipInputStream jar openStream       while true        ZipEntry e   zip getNextEntry        if  e    null        break      String name   e getName        if  name startsWith  path to your dir                Do something with this entry                            else        Fail           Note that in Java 7  you can create a FileSystem from the JAR  zip  file  and then use NIO s directory walking and filtering mechanisms to search through it  This would make it easier to write code that handles JARs and  exploded  directories

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Here is an example of using Reflections library to recursively scan classpath by regex name pattern augmented with a couple of Guava perks to to fetch resources contents   Reflections reflections   new Reflections  com example package   new ResourcesScanner     Set lt String gt  paths   reflections getResources Pattern compile       template       Map lt String  String gt  templates   new LinkedHashMap lt  gt     for  String path   paths        log info  Found     path       String templateName   Files getNameWithoutExtension path       URL resource   getClass   getClassLoader   getResource path       String text   Resources toString resource  StandardCharsets UTF 8       templates put templateName  text       This works with both jars and exploded classes

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The most robust mechanism for listing all resources in the classpath is currently to use this pattern with ClassGraph  because it handles the widest possible array of classpath specification mechanisms  including the new JPMS module system   I am the author of ClassGraph       How to know the name of the JAR file where my main class lives    URI mainClasspathElementURI  try  ScanResult scanResult   new ClassGraph   whitelistPackages  x y z            enableClassInfo   scan          mainClasspathElementURI               scanResult getClassInfo  x y z MainClass   getClasspathElementURI           How can I read the contents of a directory in a similar fashion within a JAR file     List lt String gt  classpathElementResourcePaths  try  ScanResult scanResult   new ClassGraph   overrideClasspath mainClasspathElementURI           scan          classpathElementResourcePaths   scanResult getAllResources   getPaths        There are lots of other ways to deal with resources too

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public static ArrayList lt String gt  listItems String path  throws Exception      InputStream in   ClassLoader getSystemClassLoader   getResourceAsStream path       byte   b   new byte in available         in read b       String data   new String b       String   s   data split   n        List lt String gt  a   Arrays asList s       ArrayList lt String gt  m   new ArrayList lt  gt  a       return m

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Some time ago I made a function that gets classess from inside JAR   public static Class   getClasses String packageName   throws ClassNotFoundException      ArrayList lt Class gt  classes   new ArrayList lt Class gt           packageName   packageName replaceAll                   File f   new File jarName       if f exists             try              JarInputStream jarFile   new JarInputStream                      new FileInputStream  jarName                JarEntry jarEntry               while true                    jarEntry jarFile getNextJarEntry                     if jarEntry    null                       break                                    if  jarEntry getName    startsWith  packageName    amp  amp                           jarEntry getName    endsWith    class                            classes add Class forName jarEntry getName                                replaceAll                                          substring 0  jarEntry getName   length   - 6                                                       catch  Exception e               e printStackTrace                       Class   classesA   new Class classes size             classes toArray classesA           return classesA       else         return null

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One more for the road that s a bit more flexible for matching specific filenames because it uses wildcard globbing  In a functional style this could resemble  import java io IOException  import java net URISyntaxException  import java nio file FileSystem  import java nio file Files  import java nio file Path  import java nio file Paths  import java util function Consumer   import static java nio file FileSystems getDefault  import static java nio file FileSystems newFileSystem  import static java util Collections emptyMap          Responsible for finding file resources      public class ResourceWalker              Globbing pattern to match font names          public static final String GLOB FONTS    quot     ttf otf  quot                param directory The root directory to scan for files matching the glob        param c         The consumer function to call for each matching path                       found        throws URISyntaxException Could not convert the resource to a URI        throws IOException        Could not walk the tree          public static void walk      final String directory  final String glob  final Consumer lt Path gt  c       throws URISyntaxException  IOException       final var resource   ResourceWalker class getResource  directory        final var matcher   getDefault   getPathMatcher   quot glob  quot    glob         if  resource    null           final var uri   resource toURI          final Path path        FileSystem fs   null         if   quot jar quot  equals  uri getScheme                 fs   newFileSystem  uri  emptyMap              path   fs getPath  directory                  else           path   Paths get  uri                   try  final var walk   Files walk  path  10               for  final var it   walk iterator    it hasNext                  final Path p   it next              if  matcher matches  p                   c accept  p                                  finally           if  fs    null     fs close                           Consider parameterizing the file extensions  left an exercise for the reader  Be careful with Files walk  According to the documentation   This method must be used within a try-with-resources statement or similar control structure to ensure that the stream s open directories are closed promptly after the stream s operations have completed   Likewise  newFileSystem must be closed  but not before the walker has had a chance to visit the file system paths

[java] How to list the files inside a JAR file?

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