What is the difference between Class getResource and ClassLoader getResource

Question

I wonder what the difference is between Class getResource   and ClassLoader getResource     edit  I especially want to know if any caching is involved on file directory level  As in  are directory listings cached in the Class version    AFAIK the following should essentially do the same  but they are not   getClass   getResource    getClass   getClassLoader   getResource     I discovered this when fiddling with some report generation code that creates a new file in WEB-INF classes  from an existing file in that directory  When using the method from Class  I could find files that were there at deployment using getClass   getResource    but when trying to fetch the newly created file  I recieved a null object  Browsing the directory clearly shows that the new file is there  The filenames were prepended with a forward slash as in   myFile txt    The ClassLoader version of getResource   on the other hand did find the generated file  From this experience it seems that there is some kind of caching of the directory listing going on  Am I right  and if so  where is this documented   From the API docs on Class getResource       Finds a resource   with a given name  The rules for   searching resources associated with a   given class are implemented by the   defining class loader of the class    This method delegates to this object s   class loader  If this object was   loaded by the bootstrap class loader    the method delegates to   ClassLoader getSystemResource java lang String     To me  this reads  Class getResource is really calling its own classloader s getResource     Which would be the same as doing getClass   getClassLoader   getResource    But it is obviously not  Could someone please provide me with some illumination into this matter

User · Answer

Class getResource can take a  relative  resource name  which is treated relative to the class s package  Alternatively you can specify an  absolute  resource name by using a leading slash  Classloader resource paths are always deemed to be absolute   So the following are basically equivalent   foo bar Baz class getResource  xyz txt    foo bar Baz class getClassLoader   getResource  foo bar xyz txt      And so are these  but they re different from the above    foo bar Baz class getResource   data xyz txt    foo bar Baz class getClassLoader   getResource  data xyz txt

User · Answer

Had to look it up in the specs    Class getResource String resource  ClassLoader getResource String resource    Class s getResource   - documentation states the difference      This method delegates the call to its class loader  after making these changes to the resource name  if the resource name starts with      it is unchanged  otherwise  the package name is prepended to the resource name after converting     to      If this object was loaded by the bootstrap loader  the call is delegated to ClassLoader getSystemResource

User · Answer

To answer the question whether there is any caching going on   I investigated this point further by running a stand-alone Java application that continuously loaded a file from disk using the getResourceAsStream ClassLoader method  I was able to edit the file  and the changes were reflected immediately  i e   the file was reloaded from disk without caching   However   I m working on a project with several maven modules and web projects that have dependencies on each other  I m using IntelliJ as my IDE to compile and run the web projects   I noticed that the above seemed to no longer hold true  the reason being that the file that I was being loaded is now baked into a jar and deployed to the depending web project  I only noticed this after trying to change the file in my target folder  to no avail  This made it seem as though there was caching going on

User · Answer

The first call searches relative to the  class file while the latter searches relative to the classpath root   To debug issues like that  I print the URL   System out println  getClass   getResource getClass   getSimpleName       class

User · Answer

Class getResources would retrieve the resource by the classloader which load the object  While ClassLoader getResource would retrieve the resource using the classloader specified

User · Answer

Another more efficient way to do is just use  Value  Value  quot classpath sss json quot   private Resource resource    and after that you can just get the file this way File file   resource getFile

User · Answer

All these answers around here  as well as the answers in this question  suggest that loading absolute URLs  like   foo bar properties  treated the same by class getResourceAsStream String  and class getClassLoader   getResourceAsStream String   This is NOT the case  at least not in my Tomcat configuration version  currently 7 0 40    MyClass class getResourceAsStream   foo bar properties       works    MyClass class getClassLoader   getResourceAsStream   foo bar properties       does NOT work    Sorry  I have absolutely no satisfying explanation  but I guess that tomcat does dirty tricks and his black magic with the classloaders and cause the difference  I always used class getResourceAsStream String  in the past and haven t had any problems   PS  I also posted this over here

User · Answer

I tried reading from input1 txt which was inside one of my packages together with the class which was trying to read it   The following works   String fileName   FileTransferClient class getResource  input1 txt   getPath     System out println fileName    BufferedReader bufferedTextIn   new BufferedReader new FileReader fileName      The most important part was to call getPath   if you want the correct path name in String format  DO NOT USE toString   because it will add some extra formatting text which will TOTALLY MESS UP the fileName  you can try it and see the print out    Spent 2 hours debugging this

[java] What is the difference between Class.getResource() and ClassLoader.getResource()?

Examples related to java

Examples related to classloader

Examples related to getresource