Reading a resource file from within jar

Question

I would like to read a resource from within my jar like so  File file  file   new File getClass   getResource  quot  file txt quot   toURI     BufferedReader reader   new BufferedReader new FileReader file       Read the file  and it works fine when running it in Eclipse  but if I export it to a jar  and then run it  there is an IllegalArgumentException  Exception in thread  quot Thread-2 quot  java lang IllegalArgumentException  URI is not hierarchical  and I really don t know why but with some testing I found if I change file   new File getClass   getResource  quot  file txt quot   toURI      to file   new File getClass   getResource  quot  folder file txt quot   toURI      then it works the opposite  it works in jar but not eclipse   I m using Eclipse and the folder with my file is in a class folder

User · Accepted Answer

Rather than trying to address the resource as a File just ask the ClassLoader to return an InputStream for the resource instead via getResourceAsStream:

InputStream in = getClass().getResourceAsStream("/file.txt"); 
BufferedReader reader = new BufferedReader(new InputStreamReader(in));

As long as the file.txt resource is available on the classpath then this approach will work the same way regardless of whether the file.txt resource is in a classes/ directory or inside a jar.

The URI is not hierarchical occurs because the URI for a resource within a jar file is going to look something like this: file:/example.jar!/file.txt. You cannot read the entries within a jar (a zip file) like it was a plain old File.

This is explained well by the answers to:

User · Answer

Below code works with Spring boot kotlin    val authReader   InputStreamReader javaClass getResourceAsStream   file1 json

User · Answer

To access a file in a jar you have two options    Place the file in directory structure matching your package name  after extracting  jar file  it should be in the same directory as  class file   then access it using getClass   getResourceAsStream  file txt   Place the file at the root  after extracting  jar file  it should be in the root   then access it using Thread currentThread   getContextClassLoader   getResourceAsStream  file txt     The first option may not work when jar is used as a plugin

User · Answer

You can use class loader which will read from classpath as ROOT path  without     in the beginning   InputStream in   getClass   getClassLoader   getResourceAsStream  file txt     BufferedReader reader   new BufferedReader new InputStreamReader in

User · Answer

Up until now  December 2017   this is the only solution I found which works both inside and outside the IDE   Use PathMatchingResourcePatternResolver  Note  it works also in spring-boot  In this example I m reading some files located in src main resources my folder    try          Get all the files under this inner resource folder  my folder     String scannedPackage    my folder         PathMatchingResourcePatternResolver scanner   new PathMatchingResourcePatternResolver        Resource   resources   scanner getResources scannedPackage        if  resources    null    resources length    0          log warn  Warning  could not find any resources in this scanned package      scannedPackage       else           for  Resource resource   resources                log info resource getFilename                    Read the file content  I used BufferedReader  but there are other solutions for that               BufferedReader bufferedReader   new BufferedReader new InputStreamReader resource getInputStream                  String line   null              while   line   bufferedReader readLine       null                                                                                                  bufferedReader close                      catch  Exception e        throw new Exception  Failed to read the resources folder      e getMessage    e

User · Answer

If you are using spring  then you can use the the following method to read file from src main resources   import java io BufferedReader  import java io IOException  import java io InputStream  import java io InputStreamReader  import org springframework core io ClassPathResource     public String readFileToString String path  throws IOException        StringBuilder resultBuilder   new StringBuilder          ClassPathResource resource   new ClassPathResource path        try           InputStream inputStream   resource getInputStream            BufferedReader bufferedReader   new BufferedReader new InputStreamReader inputStream             String line         while   line   bufferedReader readLine       null            resultBuilder append line                       return resultBuilder toString

User · Answer

For some reason classLoader getResource   always returned null when I deployed the web application to WildFly 14  getting classLoader from getClass   getClassLoader   or Thread currentThread   getContextClassLoader   returns null   getClass   getClassLoader   API doc says    Returns the class loader for the class  Some implementations may use null to represent the bootstrap class loader  This method will return null in such implementations if this class was loaded by the bootstrap class loader    may be if you are using WildFly and yours web application try this  request getServletContext   getResource   returned the resource url  Here request is an object of ServletRequest

User · Answer

I have found a fix  BufferedReader br   new BufferedReader new InputStreamReader Main class getResourceAsStream path       Replace  Main  with the java class you coded it in  replace  path  with the path within the jar file   for example  if you put State1 txt in the package com issac state  then type the path as   com issac state State1  if you run Linux or Mac  If you run Windows then type the path as   com issac state State1   Don t add the  txt extension to the file unless the File not found exception occurs

User · Answer

The problem is that certain third party libraries require file pathnames rather than input streams  Most of the answers don t address this issue   In this case  one workaround is to copy the resource contents into a temporary file  The following example uses jUnit s TemporaryFolder       private List lt String gt  decomposePath String path           List lt String gt  reversed   Lists newArrayList            File currFile   new File path           while currFile    null               reversed add currFile getName                 currFile   currFile getParentFile                      return Lists reverse reversed              private String writeResourceToFile String resourceName  throws IOException           ClassLoader loader   getClass   getClassLoader            InputStream configStream   loader getResourceAsStream resourceName           List lt String gt  pathComponents   decomposePath resourceName           folder newFolder pathComponents subList 0  pathComponents size   - 1  toArray new String 0             File tmpFile   folder newFile resourceName           Files copy configStream  tmpFile toPath    REPLACE EXISTING           return tmpFile getAbsolutePath

User · Answer

If you wanna read as a file  I believe there still is a similar solution       ClassLoader classLoader   getClass   getClassLoader        File file   new File classLoader getResource  file test xml   getFile

User · Answer

Make sure that you  work with the correct separator  I replaced all   in a relative path with a File separator  This worked fine in the IDE  however did not work in the build JAR

User · Answer

This code works both in Eclipse and in Exported Runnable JAR private String writeResourceToFile String resourceName  throws IOException       File outFile   new File certPath   File separator   resourceName        if  outFile isFile            return outFile getAbsolutePath             InputStream resourceStream   null              Java  In caso di JAR dentro il JAR applicativo      URLClassLoader urlClassLoader    URLClassLoader Cypher class getClassLoader        URL url   urlClassLoader findResource resourceName       if  url    null            URLConnection conn   url openConnection            if  conn    null                resourceStream   conn getInputStream                             if  resourceStream    null            Files copy resourceStream  outFile toPath    StandardCopyOption REPLACE EXISTING           return outFile getAbsolutePath          else           System out println  quot Embedded Resource  quot    resourceName    quot  not found  quot                   return  quot  quot

User · Answer

I had this problem before and I made fallback way for loading  Basically first way work within  jar file and second way works within eclipse or other IDE   public class MyClass        public static InputStream accessFile             String resource    my-file-located-in-resources txt               this is the path within the jar file         InputStream input   MyClass class getResourceAsStream   resources     resource           if  input    null                   this is how we load file within editor  eg eclipse              input   MyClass class getClassLoader   getResourceAsStream resource                      return input

User · Answer

In my case I finally made it with import java lang Thread  import java io BufferedReader  import java io InputStreamReader   final BufferedReader in   new BufferedReader new InputStreamReader        Thread currentThread   getContextClassLoader   getResourceAsStream  quot file txt quot          no initial slash in file txt

[java] Reading a resource file from within jar

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