java.lang.NoClassDefFoundError (Java, Eclipse, Fuse-JNA, Ubuntu)

Question

via eclipse, I am trying to run builtin example of file system (HelloFS.java) of fuse-jna, but it gives me java.lang.NoClassDefFoundError .

My source project is in /home/syed/workspace/HelloFS

fuse-jna class files are in home/syed/Downloads/fuse-jna-master/build/classes/main/net/fusejna

In eclipse, I added class folder via buildpath and also jre path in envirnment file. I attached snapshot below.

Please help me run this example in eclipse.

error:

Exception in thread "main" java.lang.NoClassDefFoundError: com/sun/jna/Structure
    at net.fusejna.FuseFilesystem.mount(FuseFilesystem.java:545)
    at net.fusejna.FuseFilesystem.mount(FuseFilesystem.java:550)
    at HelloFS.main(HelloFS.java:22)
Caused by: java.lang.ClassNotFoundException: com.sun.jna.Structure
    at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
    ... 3 more

here is code of builtin example file system (with not red underline, which i think means that eclipse build path is entered correctly, ):

import java.io.File;
import java.nio.ByteBuffer;

import net.fusejna.DirectoryFiller;
import net.fusejna.ErrorCodes;
import net.fusejna.FuseException;
import net.fusejna.StructFuseFileInfo.FileInfoWrapper;
import net.fusejna.StructStat.StatWrapper;
import net.fusejna.types.TypeMode.NodeType;
import net.fusejna.util.FuseFilesystemAdapterFull;

public class HelloFS extends FuseFilesystemAdapterFull
{
    public static void main(String args[]) throws FuseException
    {
        /*if (args.length != 1) {
            System.err.println("Usage: HelloFS <mountpoint>");
            System.exit(1);
        }*/
        new HelloFS().log(true).mount("./testfs1");
    }

    private final String filename = "/hello.txt";
    private final String contents = "Hello World!\n";

    @Override
    public int getattr(final String path, final StatWrapper stat)
    {
        if (path.equals(File.separator)) { // Root directory
            stat.setMode(NodeType.DIRECTORY);
            return 0;
        }
        if (path.equals(filename)) { // hello.txt
            stat.setMode(NodeType.FILE).size(contents.length());
            return 0;
        }
        return -ErrorCodes.ENOENT();
    }

    @Override
    public int read(final String path, final ByteBuffer buffer, final long size, final long offset, final FileInfoWrapper info)
    {
        // Compute substring that we are being asked to read
        final String s = contents.substring((int) offset,
                (int) Math.max(offset, Math.min(contents.length() - offset, offset + size)));
        buffer.put(s.getBytes());
        return s.getBytes().length;
    }

    @Override
    public int readdir(final String path, final DirectoryFiller filler)
    {
        filler.add(filename);
        return 0;
    }
}

This is envirnment file contents:

    PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games"
    JAVA_HOME="/usr/lib/jvm/java-6-openjdk-i386"

This is fuse-jna classes path

I added /main folder

========================================================

@Viktor K. Thanks for the help,

the above mentioned error is fixed by downloading and adding com.sun.jna » jna to referece library

but now it shows me new error as

Dec 28, 2013 1:18:25 PM HelloFS getName
INFO: Method succeeded. Result: null
Dec 28, 2013 1:18:25 PM HelloFS getOptions
INFO: Method succeeded. Result: null
Exception in thread "main" java.lang.NoSuchMethodError: com.sun.jna.Platform.getOSType()I
at net.fusejna.Platform.init(Platform.java:39)
at net.fusejna.Platform.fuse(Platform.java:26)
at net.fusejna.FuseJna.init(FuseJna.java:113)
at net.fusejna.FuseJna.mount(FuseJna.java:172)
at net.fusejna.FuseFilesystem.mount(FuseFilesystem.java:545)
at net.fusejna.FuseFilesystem.mount(FuseFilesystem.java:550)
at HelloFS.main(HelloFS.java:22)

=======================================================

Hmmm

The one that I downloaded was not campatable I think,

in temp folder of fuse-jna

/home/syed/Downloads/fuse-jna-master/build/tmp/expandedArchives/jna-3.5.2.jar_r4n26u14up0smlb84ivcvfnke/

there was jna3.5.2 classes, I imported that to libraray, now its working fine.

My problem solved. Thanks a lot.

Answer 1

The problem is not in Fuse-JNA library. Fuse-JNA library is obviously dependent on jna library (can be found in public maven repository http://mvnrepository.com/artifact/com.sun.jna/jna). You need to add this library as dependency in your project. You can see that in your project's referenced libraries there is no com.sun.jna package available.

In general - if you want to use package A (in your case Fuse-JNA) and the package A depends on package B (in your case JNA) you have to add JNA package yourself as dependency to your project. In general it is very hard to find out what are all required dependencies of the packages that you want to use - therefore many projects are using maven (or any alternative like gradle). Check this if you want to learn more : Why maven? What are the benefits?. I strongly suggest to use a tool for dependency resolution (like maven) over manual dependency resolution.

Another approach is to download a fuse jar with all dependencies - if you believe that it is the only library you'll need. However, adding jar with dependencies can lead to a big disaster if you add later other dependencies. This could lead to dependencies conflict, which is hard to find problem.