this getClass getClassLoader getResource and NullPointerException

Question

I have created a minimal maven project with a single child module in eclipse helios   In the src test resources folder I have put a single file  install xml   In the folder src test java I have created a single package with a single class that does      Test   public void doit   throws Exception       URL url   this getClass   getClassLoader   getResource  install xml        System out println url getPath            but when I run the code as a junit 4 unit test I just get a NullPointerException  This has worked fine a million of times before  Any ideas   I have followed this guide   http   www fuyun org 2009 11 how-to-read-input-files-in-maven-junit   but still get the same error

User · Answer

I had the same issue working on a project with Maven. Here how I fixed it: I just put the sources (images, musics and other stuffs) in the resources directory:

src/main/resources

I created the same structure for the packages in the resources directory too. For example:

If my class is on

com.package1.main

In the resources directory I put one package with the same name

com.package1.main

So I use

getClass().getResource("resource.png");

User · Answer

It should be getResource   install xml     The resource names are relative to where the getClass   class resides  e g  if your test is org example foo MyTest class then getResource  install xml   will look in org example foo install xml   If your install xml is in src test resources  it s in the root of the classpath  hence you need to prepend the resource name with     Also  if it works only sometimes  then it might be because Eclipse has cleaned the output directory  e g  target test-classes  and the resource is simply missing from the runtime classpath  Verify that using the Navigator view of Eclipse instead of the Package explorer  If the files is missing  run the mvn package goal

User · Answer

I think I did encounter the same issue as yours  I created a simple mvn project and used  mvn eclipse eclipse  to setup a eclipse project    For example  my source file  Router java  locates in  java main org jhoh mvc   And Router java wants to read file  routes  which locates in  java main org jhoh mvc resources   I run  Router java  in eclipse  and eclipse s console got NullPointerExeption  I set pom xml with this setting to make all   class java bytecode files locate in build directory    lt build gt       lt defaultGoal gt package lt  defaultGoal gt       lt directory gt   basedir  build lt  directory gt   lt build gt    I went to directory  build classes org jhoh mvc resources   and there is no  routes   Eclipse DID NOT copy  routes  to  build classes org jhoh mvc resources   I think you can copy your  install xml  to your   class bytecode directory  NOT in your source code directory

User · Answer

When you use  this getClass   getResource  myFile ext     getResource will try to find the resource relative to the package  If you use   this getClass   getResource   myFile ext     getResource will treat it as an absolute path and simply call the classloader like you would have if you d done   this getClass   getClassLoader   getResource  myFile ext     The reason you can t use a leading   in the ClassLoader path is because all ClassLoader paths are absolute and so   is not a valid first character in the path

User · Answer

I had the same issue with the following conditions    The resource files are in the same package as the java source files  in the java source folder  src test java   I build the project with maven on the command line and the build failed on the tests with the NullPointerException  The command line build did not copy the resource files to the test-classes folder  which explained the build failure  When going to eclipse after the command line build and rerun the tests in eclipse I also got the NullPointerException in eclipse  When I cleaned the project  deleted the content of the target folder  and rebuild the project in Eclipse the test did run correctly  This explains why it runs when you start with a clean project    I fixed this by placing the resource files in the resources folder in test  src test resources using the same package structure as the source class   BTW I used getClass   getResource

User · Answer

One other thing to look at that solved it for me     In an Eclipse   Maven project  I had Java classes in src test java in which I was using the this getClass   getResource  someFile ext    pattern to look for resources in src test resources where the resource file was in the same package location in the resources source folder as the test class was in the the test source folder  It still failed to locate them    Right click on the src test resources source folder  Build Path  then  configure inclusion   exclusion filters   I added a new inclusion filter of      ext to make sure my files weren t getting scrubbed  my tests now can find their resource files

User · Answer

tul     When you use  getClass   getResource fileName  it considers the location of the fileName is the same location of the of the calling class  When you use  getClass   getClassLoader   getResource fileName  it considers the location of the fileName is the root - in other words bin folder    Source     package Sound  public class ResourceTest       public static void main String   args            String fileName    Kalimba mp3           System out println fileName           System out println new ResourceTest   getClass   getResource fileName            System out println new ResourceTest   getClass   getClassLoader   getResource fileName              Output     Kalimba mp3 file  C  Users User Workspaces MyEclipse 208 5 JMplayer bin Sound Kalimba mp3 file  C  Users User Workspaces MyEclipse 208 5 JMplayer bin Kalimba mp3

User · Answer

When eclipse runs the test case it will look for the file in target classes not src test resources  When the resource is saved eclipse should copy it from src test resources to target classes if it has changed but if for some reason this has not happened then you will get this error  Check that the file exists in target classes to see if this is the problem

[eclipse] this.getClass().getClassLoader().getResource("...") and NullPointerException

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