How do you run a recursive file search in Java on Linux Ubuntu?

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Hi. I'm trying to run a recursive file search in Java to return a list of all .mp3 files on the system. Now, my background is in .NET, and I'm fairly new to both Linux and Java. My goal is to create a small crossplatform app that is capable of doing this search for me. On the account I need the application to be launched from a website, I figured my best bet was Java. Anyway, I based the code I have now off an article I read online. This is my current code:

Java

startSearch();

List<String> fs = new ArrayList<String>();
public void startSearch()
{

    File[] roots = File.listRoots();

    for(int i = 0; i < roots.length; i++)
    {
        File[] files = new File(roots[i].toString()).listFiles();
        getFiles(files);
    }

    JOptionPane.showMessageDialog(null, fs.get(0)); //This is just to test the function...

}

public void getFiles(File[] files)
{

    for(File file : files) ***
    {
        if(file.isDirectory())
        {
            getFiles(file.listFiles());
        }
        else
        {
            fs.add(file.toString());
        }
    }
}

However, whenever I run it I get the following error on the line above, marked with the ***:

java.lang.NullPointerException
	at Form1.getFiles(Form1.java:132)
	at Form1.getFiles(Form1.java:136)
	at Form1.startSearch(Form1.java:122)
	at Form1.initialize(Form1.java:111)
	at Form1.<init>(Form1.java:56)
	at Form1$1.run(Form1.java:42)
	at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:226)
	at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:673)
	at java.awt.EventQueue.access$300(EventQueue.java:96)
	at java.awt.EventQueue$2.run(EventQueue.java:634)
	at java.awt.EventQueue$2.run(EventQueue.java:632)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:105)
	at java.awt.EventQueue.dispatchEvent(EventQueue.java:643)
	at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:275)
	at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:200)
	at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:190)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:185)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:177)
	at java.awt.EventDispatchThread.run(EventDispatchThread.java:138)

Any ideas what's wrong? I think it might have something to do with the fact the only drive name returned is '/' and it doesn't know where to look or something. I'm so used to drive based (C:/) filesystems. Any help would be appreciated. Thanks in advance!

Posted 10-May-13 0:56am

RadXPictures

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E.F. Nijboer 10-May-13 7:17am

Maybe try this console example first. Just to check out what happens. It should result in / on linux.
http://www.tutorialspoint.com/java/io/file_listroots.htm

Richard MacCutchan 10-May-13 7:25am

Two minutes with your debugger should show you what the content of each variable is, against what it should be.

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Richard MacCutchan · Answer 1 · 2013-05-10T01:37:00

Solution 1

Java

for(int i = 0; i < roots.length; i++)
{
	File[] files = new File(roots[i].toString()).listFiles();
	if (files != null)
		getFiles(files);
}

Posted 10-May-13 1:37am

Richard MacCutchan

Comments

RadXPictures 10-May-13 10:40am

I appreciate the help Richard.. unfortunately, adding the != null conditional doesn't seem to correct the problem. When you referred to "two minutes with the debugger".. where in Eclipse may I find that? The only debugger I've been using is the console..

Richard MacCutchan 10-May-13 12:11pm

1. Adding that if clause did it for me, although I don't have a Linux system to test on.
2. eclipse has a built in debugger; it's on the Run menu item.

Jayarajantk · Answer 2 · 2013-05-13T01:58:00

Either

Java

for(int i = 0; i < roots.length; i++) {
 File[] files = new File(roots[i].toString()).listFiles();
 if (files != null) {
  getFiles(files);
 }
}

or

Java

public void getFiles(File[] files) {
 if(files != null) {
  for(File file : files) {
   if(file.isDirectory()) {
    getFiles(file.listFiles());
   }
   else {
    fs.add(file.toString());
   }
  }
 }
}

How do you run a recursive file search in Java on Linux Ubuntu?

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