在Java中查找资源时，两个类在相同的代码上提供不同的输出

Question

i have two classes as

public class CsvReaderExample { 
    public static void main(String[] args) {
        try {               
    String file=CsvReaderExample.class.getResource("/saralbitta/common/db/DateNepali.csv").getFile();

Next class is

 public class LoanIssueView extends ViewPart {
    public LoanIssueView() {    
            }
            @Override
   public void createPartControl(Composite parent) {
   String file=LoanIssueView.class.getResource("/saralbitta/common/db/DateNepali.csv").getFile();

When i print file in both the classes i am so surprised that in one class i get the outPut as below in first case

 /E:/myskbbl/saralbitta/bin/saralbitta/common/db/DateNepali.csv 

similarly in second case i get outPut as

/saralbitta/common/db/DateNepali.csv

Why the two classes with same code give different output. i am getting fileNotFoundException in second case as i need the output like in first case. How can i obtain the like the output like first case in the second one?

Answer 1

Are the classes CsvReaderExample and LoanIssueView contained in different bundles/plugins? Each bundle has its own classpath and cannot see the classes of other bundles, unless you allow it. Interbundle dependencies are declared in the Manifest.

Edit: Ok then it's clear. In the first case OSGi is not started, so it's a normal Java application. In the second case OSGi is started and each bundle gets its own classloader. I would try to request the Resource from the bundle. Use the getResource() method there http://www.osgi.org/javadoc/r4v43/core/org/osgi/framework/Bundle.html#getResource%28java.lang.String%29 . You can acquire a bundle reference from the BundleContext . You get the BundleContext from the BundleActivator start() method http://www.osgi.org/javadoc/r4v43/core/org/osgi/framework/BundleActivator.html#start%28org.osgi.framework.BundleContext%29 . Note that the URL you acquire, is not a File URL. Use FileLocator to convert the URL to a File URL http://help.eclipse.org/indigo/index.jsp?topic=%2Forg.eclipse.platform.doc.isv%2Freference%2Fapi%2Forg%2Feclipse%2Fcore%2Fruntime%2FFileLocator.html .

Answer 2

Where are these programs executed from? When the resource is looked up, there is an algorithm by which the absolute name is determined. It also depends on the class loader. Probably that is why you see different results.

Answer 3

It should be related to the difference in classpath setting. Check the classpath setting for both apps.

Answer 4

Check the documentation for both getResource and findResource

In first case, getResource() is returning you the file string. But in second case, somehow the getResource() is not able to find the path and tries to invoke findResource() method, as stated in it's documentation:

getResource :

This method will first search the parent class loader for the resource; if the parent is null the path of the class loader built-in to the virtual machine is searched. That failing, this method will invoke findResource(String) to find the resource.

Probably this might be reason here for different return strings, as different methods might be getting called depending on the flow.