Question

I have written a Java GUI using SWT. I package the application using an ANT script (fragment below).

<jar destfile="./build/jars/swtgui.jar" filesetmanifest="mergewithoutmain">
  <manifest>
    <attribute name="Main-Class" value="org.swtgui.MainGui" />
    <attribute name="Class-Path" value="." />
  </manifest>
  <fileset dir="./build/classes" includes="**/*.class" />
  <zipfileset excludes="META-INF/*.SF" src="lib/org.eclipse.swt.win32.win32.x86_3.5.2.v3557f.jar" />
</jar>

This produces a single jar which on Windows I can just double click to run my GUI. The downside is that I have had to explicitly package the windows SWT package into my jar.

I would like to be able to run my application on other platforms (primarily Linux and OS X). The simplest way to do it would be to create platform specific jars which packaged the appropriate SWT files into separate JARs.

Is there a better way to do this? Is it possible to create a single JAR which would run on multiple platforms?

Answer 1

I have a working implementation which is now referenced from the SWT FAQ.

This approach is now available to use as an ANT task: SWTJar

[EDIT] SWTJar has now been updated to use Alexey Romanov’s solution as described above.

build.xml

First I build a jar containing all of my application classes.

<!-- UI (Stage 1) -->   
<jarjar jarfile="./build/tmp/intrace-ui-wrapper.jar">
  <fileset dir="./build/classes" includes="**/shared/*.class" />
  <fileset dir="./build/classes" includes="**/client/gui/**/*.class" />
  <zipfileset excludes="META-INF/*.MF" src="lib/miglayout-3.7.3.1-swt.jar"/>
</jarjar>

Next, I build a jar to contain all of the following:

• JARs
  • The jar which I just built
  • All the SWT jars
• Classes
  • The “Jar-In-Jar” classloader classes
  • A special loader class – see below

Here is the fragment from build.xml.

<!-- UI (Stage 2) -->
<jarjar jarfile="./build/jars/intrace-ui.jar">
  <manifest>
    <attribute name="Main-Class" value="org.intrace.client.loader.TraceClientLoader" />
    <attribute name="Class-Path" value="." />
  </manifest>
  <fileset dir="./build/classes" includes="**/client/loader/*.class" />
  <fileset dir="./build/tmp" includes="intrace-ui-wrapper.jar" />
  <fileset dir="./lib" includes="swt-*.jar" />
  <zipfileset excludes="META-INF/*.MF" src="lib/jar-in-jar-loader.jar"/>
</jarjar>

TraceClientLoader.java

This loader class uses the jar-in-jar-loader to create a ClassLoader which loads classes from two jars.

• The correct SWT jar
• The application wrapper jar

Once we have this classloader we can launch the actual application main method using reflection.

public class TraceClientLoader
{
  public static void main(String[] args) throws Throwable
  {    
    ClassLoader cl = getSWTClassloader();
    Thread.currentThread().setContextClassLoader(cl);    
    try
    {
      try
      {
        System.err.println("Launching InTrace UI ...");
        Class<?> c = Class.forName("org.intrace.client.gui.TraceClient", true, cl);
        Method main = c.getMethod("main", new Class[]{args.getClass()});
        main.invoke((Object)null, new Object[]{args});
      }
      catch (InvocationTargetException ex)
      {
        if (ex.getCause() instanceof UnsatisfiedLinkError)
        {
          System.err.println("Launch failed: (UnsatisfiedLinkError)");
          String arch = getArch();
          if ("32".equals(arch))
          {
            System.err.println("Try adding '-d64' to your command line arguments");
          }
          else if ("64".equals(arch))
          {
            System.err.println("Try adding '-d32' to your command line arguments");
          }
        }
        else
        {
          throw ex;
        }
      }
    }
    catch (ClassNotFoundException ex)
    {
      System.err.println("Launch failed: Failed to find main class - org.intrace.client.gui.TraceClient");
    }
    catch (NoSuchMethodException ex)
    {
      System.err.println("Launch failed: Failed to find main method");
    }
    catch (InvocationTargetException ex)
    {
      Throwable th = ex.getCause();
      if ((th.getMessage() != null) &&
          th.getMessage().toLowerCase().contains("invalid thread access"))
      {
        System.err.println("Launch failed: (SWTException: Invalid thread access)");
        System.err.println("Try adding '-XstartOnFirstThread' to your command line arguments");
      }
      else
      {
        throw th;
      }
    }
  }

  private static ClassLoader getSWTClassloader()
  {
    ClassLoader parent = TraceClientLoader.class.getClassLoader();    
    URL.setURLStreamHandlerFactory(new RsrcURLStreamHandlerFactory(parent));
    String swtFileName = getSwtJarName();      
    try
    {
      URL intraceFileUrl = new URL("rsrc:intrace-ui-wrapper.jar");
      URL swtFileUrl = new URL("rsrc:" + swtFileName);
      System.err.println("Using SWT Jar: " + swtFileName);
      ClassLoader cl = new URLClassLoader(new URL[] {intraceFileUrl, swtFileUrl}, parent);

      try
      {
        // Check we can now load the SWT class
        Class.forName("org.eclipse.swt.widgets.Layout", true, cl);
      }
      catch (ClassNotFoundException exx)
      {
        System.err.println("Launch failed: Failed to load SWT class from jar: " + swtFileName);
        throw new RuntimeException(exx);
      }

      return cl;
    }
    catch (MalformedURLException exx)
    {
      throw new RuntimeException(exx);
    }                   
  }

  private static String getSwtJarName()
  {
    // Detect OS
    String osName = System.getProperty("os.name").toLowerCase();    
    String swtFileNameOsPart = osName.contains("win") ? "win" : osName
        .contains("mac") ? "osx" : osName.contains("linux")
        || osName.contains("nix") ? "linux" : "";
    if ("".equals(swtFileNameOsPart))
    {
      throw new RuntimeException("Launch failed: Unknown OS name: " + osName);
    }

    // Detect 32bit vs 64 bit
    String swtFileNameArchPart = getArch();

    String swtFileName = "swt-" + swtFileNameOsPart + swtFileNameArchPart
        + "-3.6.2.jar";
    return swtFileName;
  }

  private static String getArch()
  {
    // Detect 32bit vs 64 bit
    String jvmArch = System.getProperty("os.arch").toLowerCase();
    String arch = (jvmArch.contains("64") ? "64" : "32");
    return arch;
  }
}

[EDIT] As stated above, for those looking for the “jar-in-jar classloader”: It’s included in Eclipse’s JDT (the Java IDE built on Eclipse). Open org.eclipse.jdt.ui_*version_number*.jar with an archiver and you will find a file jar-in-jar-loader.zip inside. I renamed this to jar-in-jar-loader.jar.

intrace-ui.jar – this is the jar which I built using the process described above. You should be able to run this single jar on any of win32/64, linux32/64 and osx32/64.

[EDIT] This answer is now referenced from the SWT FAQ.