How to read a file from jar in Java

Question

I want to read an XML file that is located inside one of the jars included in my class path  How can I read any file which is included in the jar

User · Answer

Check first your class loader   ClassLoader classLoader   Thread currentThread   getContextClassLoader     if  classLoader    null        classLoader   Class class getClassLoader       classLoader getResourceAsStream  xmlFileNameInJarFile xml        xml file location at xxx jar      folder      folder    xmlFileNameInJarFile xml

User · Answer

Just for completeness  there has recently been a question on the Jython mailinglist where one of the answers referred to this thread   The question was how to call a Python script that is contained in a  jar file from within Jython  the suggested answer is as follows  with  InputStream  as explained in one of the answers above   PythonInterpreter execfile InputStream

User · Answer

Ah  this is one of my favorite subjects  There are essentially two ways you can load a resource through the classpath      Class getResourceAsStream resource    and  ClassLoader getResourceAsStream resource     there are other ways which involve getting a URL for the resource in a similar fashion  then opening a connection to it  but these are the two direct ways    The first method actually delegates to the second  after mangling the resource name  There are essentially two kinds of resource names  absolute  e g    path to resource resource   and relative  e g   resource     Absolute paths start with         Here s an example which should illustrate   Consider a class com example A   Consider two resources  one located at  com example nested  the other at  top  in the classpath   The following program shows nine possible ways to access the two resources    package com example   public class A        public static void main String args                  Class getResourceAsStream         Object resource   A class getResourceAsStream  nested            System out println  1  A class nested     resource            resource   A class getResourceAsStream   com example nested            System out println  2  A class  com example nested     resource            resource   A class getResourceAsStream  top            System out println  3  A class top     resource            resource   A class getResourceAsStream   top            System out println  4  A class  top     resource               ClassLoader getResourceAsStream         ClassLoader cl   A class getClassLoader            resource   cl getResourceAsStream  nested                    System out println  5  cl nested     resource            resource   cl getResourceAsStream   com example nested            System out println  6  cl  com example nested     resource           resource   cl getResourceAsStream  com example nested            System out println  7  cl com example nested     resource            resource   cl getResourceAsStream  top            System out println  8  cl top     resource            resource   cl getResourceAsStream   top            System out println  9  cl  top     resource              The output from the program is    1  A class nested java io BufferedInputStream 19821f 2  A class  com example nested java io BufferedInputStream addbf1 3  A class top null 4  A class  top java io BufferedInputStream 42e816 5  cl nested null 6  cl  com example nested null 7  cl com example nested java io BufferedInputStream 9304b1 8  cl top java io BufferedInputStream 190d11 9  cl  top null   Mostly things do what you d expect   Case-3 fails because class relative resolving is with respect to the Class  so  top  means   com example top   but   top  means what it says   Case-5 fails because classloader relative resolving is with respect to the classloader  But  unexpectedly Case-6 also fails  one might expect   com example nested  to resolve properly   To access a nested resource through the classloader you need to use Case-7  i e  the nested path is relative to the root of the classloader   Likewise Case-9 fails  but Case-8 passes   Remember  for java lang Class  getResourceAsStream   does delegate to the classloader         public InputStream getResourceAsStream String name            name   resolveName name           ClassLoader cl   getClassLoader0            if  cl  null                   A system class              return ClassLoader getSystemResourceAsStream name                     return cl getResourceAsStream name           so it is the behavior of resolveName   that is important     Finally  since it is the behavior of the classloader that loaded the class that essentially controls getResourceAsStream    and the classloader is often a custom loader  then the resource-loading rules may be even more complex   e g  for Web-Applications   load from WEB-INF classes or WEB-INF lib in the context of the web application  but not from other web-applications which are isolated   Also  well-behaved classloaders delegate to parents  so that duplicateed resources in the classpath may not be accessible using this mechanism

User · Answer

If you want to read that file from inside your application use   InputStream input   getClass   getResourceAsStream   classpath to my file      The path starts with      but that is not the path in your file-system  but in your classpath  So if your file is at the classpath  org xml  and is called myxml xml your path looks like   org xml myxml xml    The InputStream reads the content of your file  You can wrap it into an Reader  if you want   I hope that helps

User · Answer

A JAR is basically a ZIP file so treat it as such   Below contains an example on how to extract one file from a WAR file  also treat it as a ZIP file  and outputs the string contents   For binary you ll need to modify the extraction process  but there are plenty of examples out there for that     public static void main String args          String relativeFilePath    style someCSSFile css       String zipFilePath     someDirectory someWarFile war       String contents   readZipFile zipFilePath relativeFilePath       System out println contents      public static String readZipFile String zipFilePath  String relativeFilePath        try           ZipFile zipFile   new ZipFile zipFilePath           Enumeration lt   extends ZipEntry gt  e   zipFile entries             while  e hasMoreElements                  ZipEntry entry    ZipEntry  e nextElement                   if the entry is not directory and matches relative file then extract it             if   entry isDirectory    amp  amp  entry getName   equals relativeFilePath                     BufferedInputStream bis   new BufferedInputStream                          zipFile getInputStream entry                       Read the file                        With Apache Commons I O                  String fileContentsStr   IOUtils toString bis   UTF-8                            With Guava                   String fileContentsStr   new String ByteStreams toByteArray bis  Charsets UTF 8                      close the input stream                  bis close                    return fileContentsStr                else                   continue                                catch  IOException e            logger error  IOError      e           e printStackTrace              return null      In this example I m using Apache Commons I O and if you are using Maven here is the dependency    lt dependency gt       lt groupId gt commons-io lt  groupId gt       lt artifactId gt commons-io lt  artifactId gt       lt version gt 2 4 lt  version gt   lt  dependency gt

[java] How to read a file from jar in Java?

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