Switching between 64 bit and 32 bit JVMs in Windows

I run Vista 64 bit on my laptop to get at the ludicrous 6Gb of memory that I seem to need to do my work these days. However I find that because of native library dependencies there are often times when I need to switch between 32 and 64 bit JVMs.

To do so I hacked together this simple batch file which allows you to simply switch JAVA_HOME:

xjava.bat:

@echo off
@rem Allow swiching between 64 and 32 bit versions of jvm. 

SET OLD_JAVA_HOME=%JAVA_HOME%

@rem Process switch 
set XJAVA_SWITCH=%1
shift
if "%XJAVA_SWITCH%" == "" goto DISPLAY_CURRENT
if "%XJAVA_SWITCH%" == "-64" goto SET_64 
if "%XJAVA_SWITCH%" == "-32" goto SET_32
goto DISPLAY_JAVA_HOME_AND_CHECK_FOR_CMD_TO_EXEC

:SET_32
if "%JAVA_32_HOME%" == "" goto ERROR_32 
set JAVA_HOME=%JAVA_32_HOME%
goto DISPLAY_JAVA_HOME_AND_CHECK_FOR_CMD_TO_EXEC

:ERROR_32
echo Error: JAVA_32_HOME not set.
goto DONE

:SET_64
if "%JAVA_64_HOME%" == "" goto ERROR_64 
set JAVA_HOME=%JAVA_64_HOME%
goto DISPLAY_JAVA_HOME_AND_CHECK_FOR_CMD_TO_EXEC

:ERROR_64
echo Error: JAVA_64_HOME not set.
goto DONE

:DISPLAY_CURRENT
@ECHO JAVA_HOME=%JAVA_HOME%
goto DONE

:DISPLAY_JAVA_HOME_AND_CHECK_FOR_CMD_TO_EXEC
@rem Display JAVA_HOME
@ECHO JAVA_HOME=%JAVA_HOME%
if "%JAVA_HOME%" == "%JAVA_32_HOME" echo "Using 32 bit JVM"
if "%JAVA_HOME%" == "%JAVA_64_HOME" echo "Using 64 bit JVM"

@rem Check for java command to execute, otherwise we just set JAVA_HOME 
if "%1" == "" goto DONE
set _ARGS=%*
set _ARGS=%_ARGS:-32=%
set _ARGS=%_ARGS:-64=%
"%JAVA_HOME%/bin/java" %_ARGS% 
set JAVA_HOME=%OLD_JAVA_HOME%
goto DONE

:DONE

Save as xjava.bat somwhere on your path. You then need to define the environment variables: JAVA_32_HOME and JAVA_64_HOME.

You then use this as follows:

1. Print the current JAVA_HOME: xjava
2. Switch to 32 bit VM: xjava -32
3. Switch to 64 bit VM: xjava -64
4. Run java with JAVA_HOME set to the appropriate vm: xjava [-32|-64] MyClass

Running GWTTestSuite in JUnit 4.4 without the ClassCastException

Running unit tests using the Google Web Toolkit that extends GWTTestCase can be very slow and time consuming, since the JUnitShell has to be restarted for each test. You can speed up testing a lot by instead using GWTTestSuite to group these tests into a single suite than only needs to start the JUnitShell once. The developer's guide gives the following example:

public class MapsTestSuite extends GWTTestSuite {
    public static Test suite() {
        TestSuite suite = new TestSuite("Test for a Maps Application");
        suite.addTestSuite(MapTest.class);
        suite.addTestSuite(EventTest.class);
        suite.addTestSuite(CopyTest.class);
        return suite;
    }
}

However, running this using the junit.testui.TestRunner in JUnit4.4 (for example if you are running from the command line using the Maven GWT plugin) gives the following helpful error:

Error: java.lang.ClassCastException

Instead you want to do the following:

public class MapsTestSuite extends TestCase {
    public static Test suite() {
        GWTTestSuite suite = new GWTTestSuite("Test for a Maps Application");
        suite.addTestSuite(MapTest.class);
        suite.addTestSuite(EventTest.class);
        suite.addTestSuite(CopyTest.class);
        return suite;
    }
}

i.e. Extend TestCase rather than GWTTestSuite to overcome this problem.