Java 6 on OS X is 64 bit only so I believe hosted mode isn't going to work with Java 6 on OS X until the browser 
plugin solution that supports 64 bit JVMs is released. This is unfortunate as there is not a non-64 bit Java 6 
solution available for OS X, in contrast to other platforms, so there is no workaround available.

Bob, can you investigate and see if this is a real issue?  jgw suggests it's most 
likely valid.  If so, we should issue a good error message in BootStrapPlatform (kind 
like we're going to do for Safari 2 installations).

Possible duplicate; marking for RC2 so we can at least issue a helpful error.

Will investigate.

Issue confirmed.  The OS X Java6 needs 64-bit libraries.

http://groups.google.com/group/Google-Web-Toolkit-Contributors/t/3148e9abc44d5aa4

hi Bob,
is this issue (jvm6) based on jvm64bit some issues (swt implementation) or lack of 64-bit browser (all public 
safari browsers are compiled 32-bit)?
If i remember well there are related topics on java-dev apple lists

regards,
Peter

Both, actually.  We need to run SWT and Safari within the JVM process.  The
Java5-only restriction on OSX will be lifted with the out-of-process hosted mode
since we can eliminate SWT for Swing.

Improved error response in r3048.

this has been marked "FixedNotReleased" because there is now a better error response. Is there any hope of an 
actual fix at some point? This bug means that Apple developers cannot use Java 6 for GWT apps, which is a fairly 
major restriction.

This only affects running hosted-mode with the Apple-supplied Java 1.6 runtime, other
platforms are not affected.  Developers who need to write server-based components
that rely on OS X Java 1.6 can use -noserver while running the hosted-mode shell with
1.5.

This issue will be completely moot upon delivery of out-of-process hosted mode.

1_5_RC2 has been released.

Is this issue fixed now? Can you please confirm?

No, this has absolutely not been fixed in any of the 1.5.x releases... why has it been marked Fixed?

If the user attempts to run the shell on OS X Java 6, they get the message "You must use a Java 1.5 runtime to 
use GWT Hosted Mode on Mac OS X."

At the very least, this should be marked NotGoingToFix or track it as a dupe on a feature request for out-of-
process hosted mode which is claimed to side-step this issue.

Would it be possible to keep this issue open until OOP hosted mode is delivered?  Some of us have starred this 
issue in hopes of being notified when the issue is actually fixed.

I agree.  This is a pretty unfortunate problem.  Java 6 on osx works fine.  Please
enable hosted mode to run with it.  I hate having to use bootcamp.  Using --noserver
and setting up my scripts to hot deploy are just a pain in the as.

This is not 'fixed'; not by my definition of the term. If I were the dev manager in
charge of this feature, I'd re-open the issue, for resolution by out-of-process
hosted mode.

I think this issue should be kept open as it is a major restriction not being able to
use Java 1.6, but for those osx developers you can switch java versions via the
/Applications/Utilities/Java/Java Preferences.app back to 1.5 for when you are
developing and needing hosted mode, I can't think of that many differences between
the versions that you will miss and then switch back once you no longer require
hosted mode.

I got my demo application run with java 1.5.0 on Mac OS 10.4 Tiger. Good lucks, guys.

Let me second the opinions of those above that marking this fixed as there is an unacceptable workaround to 
revert back to 1.5 is pure bug-triage ballocks. Even though switching between JVM versions is easy enough 
with the Java preferences app, it doesn't help a lot if you have JDK 1.6 dependencies in your project.

thats exactly my problem! i tried everything
this blog does help: http://grack.com/blog/2009/04/19/the-final-word-on-google-eclipse-plugin-osx-
crashes/comment-page-1/#comment-35

so i can compile now but i can't run it...

With Eclipse being released on Mac supporting JRE6 and 64 bit java would it be possible to fix this, or are there 
any other issues? 

Are you guys working on this, or should I try and hack it?

Hi I am using a project that has dependencies with java 1.6 and i receive this error.
You must use a Java 1.5 runtime to use GWT Hosted Mode on Mac OS X.

Also, I tried the GWT plugin with Galileo and it doesnt work either.

i cant run my apps or example apps in eclipse with any configuration...
its just too buggy... but i love gwt and dont want to go back to windows and ubuntu is not an option since i have 
a mac :S

coding on a vm
mac developers really need get 2.0! i just can't wait guys!

just updated my eclipse to get last appengine 1.2.2 and gwt 1.7.
No Eclipse plugin update that would resolve the problem ?
hosted mode on mac with a 1.5 jre is really cumbersome... 

I have been able to compile and Run Java 1.6 with gwt on macosx using netbeans 2.7 and the latest 
gwt4nb Plugin 

Running snow leopard - no way I can run Java 1.5.  Does this mean no GWT love?  Is 
nobody at Google doing GWT on Snow Leopard yet? :)

Using Snow Leopard and GWT does not run.  Get this error:
You must use a Java 1.5 runtime to use GWT Hosted Mode on Mac OS X.

Even tried Java 1.6 32-bit version.

Just upgraded to Snow Leopard, Eclipse 3.5 Java EE, and fresh install of the Google
Plugin GWT 1.7 and App Engine SDK 1.2.2. 

It seems as if I won't be making too much progress on this machine for a bit:

"You must use a Java 1.5 runtime to use GWT Hosted Mode on Mac OS X."

I appreciate the work that goes into this project. I just hope that I can get back to
work soon.

may i know when will this be fixed?

Sorry, any update on this? I'm understand because why the status is fixed.

Ok this is a problem. Eclipse Galileo didn't run on Tiger, so I went through the
trouble of upgrading to Snow Leopard hoping to do GWT dev on 1.6. Now it wants 1.5
back? You know most student developers in universities run macs these days. Get it to
work Google! I'll be doing my dev on Echo3 for now.

This isn't really Google's problem to fix.
The issue stems from Eclipse's SWT hasn't yet been ported to Cocoa, and requires a 32-bit java.

Here's a way to downgrade to java 1.5:
http://wiki.oneswarm.org/index.php/OS_X_10.6_Snow_Leopard

Isn't the 64-bit SWT Cocoa port available since December last year? See
https://bugs.eclipse.org/bugs/show_bug.cgi?id=239301

+1 for the instructions here  (comment 33)

http://wiki.oneswarm.org/index.php/OS_X_10.6_Snow_Leopard

GWT happy again.

thx for thw workaround

I noticed that it should be possible for Google to release a quick 
patch of GWT 1.6.x that should allow users to run the legacy hosted 
mode under a Java 1.6 VM now. 

GWT's hosted mode, on the Mac, does an explicit check to ensure that 
Java 1.5 is being used.  This check only existed because under 
Leopard, Java 1.5 is the only 32-bit JVM that was available.  (I 
believe 1.6 was 64-bit only). 

I installed Snow Leopard today, and it appears that while it only has 
Java 1.6, it appears to have both a 64-bit mode and a 32-bit mode. 
(Open "/Applications/Utilities/Java Preferences.app", and under the 
"General" tab you can see both of these modes.) 

So I think it should be possible to simply remove the explicit check 
that GWT does for Java 1.5.   Has anybody attempted this?

For those still on Mac OS Leopard (Not snow leopard yet), here is what I did.  I have
both 1.6 and 1.5 installed on the mac.  I got it working by going to Project
Properties -> Run/Debug Settings -> Selected the Project -> "Edit..." -> JRE  Then
changed to Alternate JRE and selected 1.5.  Perhaps everyone knows this already but
it took me a little while to discover.  

Just tried changing the GRE using the procedure in Comment 38 and it doesn't work
(with an out-of-the-box Snow Leopard distribution).

It's inexcusable that this problem is marked 'fixed'.  All I did was install Snow
Leopard, and now GWT effectively doesn't work. At minimum, there should be some sort
of FAQ describing, in detail, how to work around this problem.

Allen, I agree.  I stuck my neck out and filed a new one.   Here's the link, in case anybody wants to follow:

http://code.google.com/p/google-web-toolkit/issues/detail?id=3998

Here's a workaround, which I've also posted to the newer thread. Note that this
workaround does not fix the real problem, which is that hosted mode does not work
with a 64-bit 1.6 JVM. However, it will get you working again:

If you look in the directory that holds the JVM versions
(/System/Library/Frameworks/JavaVM.framework/Versions/), you'll see that 1.5 and
1.5.0 are just symlinks to the 1.6 jvm. This means that changing the defaults in
Eclipse will have no effect, since all that you'll be doing is pointing to a symlink
that just points back to the original directory. What you need is a *real* 32-bit 1.5
JVM, which doesn't ship with Snow Leopard.

I did some rooting around and found the following instructions for downgrading your
JVM to a *real* 32-bit 1.5.0 JVM. This process doesn't remove the 64-bit 1.6 JVM from
the system, so it's still there if you need it.  It does, however, make a real 32-bit
1.5 JVM be the default JVM, and that will make GWT happy:

http://wiki.oneswarm.org/index.php/OS_X_10.6_Snow_Leopard

As an aside, these instructions require you to have a wget installed. I'm not sure if
there's one in Snow Leopard (there didn't used to be), but you can get one from
http://kevinhenrikson.com/2006/06/18/macos-x-1046-wget/ or you can download the
latest version and compile it by following these instructions:
http://www.asitis.org/installing-wget-for-mac-os-x

I just had success following the procedure on the oneswarm.org wiki too.   Enough to get me by.

You can force the Java 1.6 version on Snow Leopard to run in 32-bit mode by adding the vm flag "-d32".
If you do this, SWT works fine, which was the problem to begin with, that Java 6 in Leopard was 64-bit only.

I havn't tried starting GWT hosted mode with this, but technically this should work. That is unless there's an 
explicit check whether the user is running Mac and using java 6.

-d32 doesn't appear to work. Given that the error is 'You must use a Java 1.5 runtime
to use GWT Hosted Mode on Mac OS X.' I suspect Hans speculation that there is an
explicit check is accurate.

Hi,
I have followed the instructions in
http://wiki.oneswarm.org/index.php/OS_X_10.6_Snow_Leopard
but with no effort.
Instead of the "You must use a Java 1.5 runtime to use GWT Hosted Mode on Mac OS X." warning I get an 
Exception:
 java.lang.UnsupportedClassVersionError: Bad version number in .class file
	at java.lang.ClassLoader.findBootstrapClass(Native Method)
	at java.lang.ClassLoader.findBootstrapClass0(ClassLoader.java:946)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:308)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:280)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:251)
	at sun.security.jca.ProviderConfig$3.run(ProviderConfig.java:234)
	at java.security.AccessController.doPrivileged(Native Method)
	at sun.security.jca.ProviderConfig.doLoadProvider(ProviderConfig.java:225)
	at sun.security.jca.ProviderConfig.getProvider(ProviderConfig.java:205)
	at sun.security.jca.ProviderList.loadAll(ProviderList.java:254)
	at sun.security.jca.ProviderList.removeInvalid(ProviderList.java:271)
	at sun.security.jca.Providers.getFullProviderList(Providers.java:185)
	at java.security.Security.getProviders(Security.java:422)
	at java.security.Security.getProviders(Security.java:569)
	at java.security.Security.getProviders(Security.java:515)
	at org.apache.derby.client.am.EncryptionManager.<init>(Unknown Source)
...
The class to be loaded seems to be "com.apple.crypto.provider.Apple".

Regards
Andreas

Andreas, the message that you have given:  

     "java.lang.UnsupportedClassVersionError: Bad version number in .class file"  

...indicates that there are .class files hanging around from a prior build using Java 1.6.   Try to clean your whole 
project and build it again.

Hi Pohl,
thanks for the answer. I have found the error. It was due to a misconfiguration in Eclipse. I have mixed the 1.6 
and 1.5 jars when I added the Java 1.5 Library.
Now it works.
Regards
Andreas

I've tried out the approach mentioned by pohl.longsine in an earlier message. By modifying the 
BootStrapPlatform class to bypass the check for Java 5 it's possible to use java -d32 (to choose 32 bit mode) to 
run hosted mode on Snow Leopard with no problems. I have more details in my blog post 
http://development.lombardi.com/?p=1012 but it was really very simple. I would hope we'd see a quick release 
of GWT 1.7.1 to fix this but till then this works well.

Thanks Alex.  Copying the BootStrapPlatform class in our project and bypassing the
1.5 check worked for us.  Thanks again..

Thanks Alex!! Just worked fine! 

Hopefully this fix is included soon in the standard distribution.

10.6.2 seems to have broken this fix. Was working great for me until I updated to latest Snow Leopard last 
night; now I'm getting:

Process:         java [2065]
Path:            /System/Library/Frameworks/JavaVM.framework/Versions/1.6.0/Home/bin/java
Identifier:      java
Version:         ??? (???)
Code Type:       X86 (Native)
Parent Process:  java [2050]

PlugIn Path:       /Users/jimt/.m2/repository/com/google/gwt/gwt-dev/1.6.4/libgwt-ll.jnilib
PlugIn Identifier: libgwt-ll.jnilib
PlugIn Version:    ??? (???)

Date/Time:       2009-11-13 10:19:32.235 -0800
OS Version:      Mac OS X 10.6.2 (10C540)
Report Version:  6

Exception Type:  EXC_BAD_ACCESS (SIGBUS)
Exception Codes: KERN_PROTECTION_FAILURE at 0x0000000000000010
Crashed Thread:  0  Dispatch queue: com.apple.main-thread

Application Specific Information:

Java information:
 Exception type: Bus Error (0xa) at pc=0x98cd877b

 Java VM: Java HotSpot(TM) Client VM (14.1-b02-90 mixed mode macosx-x86)

Current thread (0x01824000):  JavaThread "Thread-0" daemon [_thread_in_native, id=-1604791040, 
stack(0xbf800000,0xc0000000)]
Stack: [0xbf800000,0xc0000000]
Java frames: (J=compiled Java code, j=interpreted, Vv=VM code)
J  com.google.gwt.dev.shell.mac.LowLevelSaf.gcUnprotect(II)V
J  com.google.gwt.dev.shell.mac.JsValueSaf.setJsVal(I)V
j  com.google.gwt.dev.shell.mac.JsValueSaf.setUndefined()V+7
J  
com.google.gwt.dev.shell.JsValueGlue.set(Lcom/google/gwt/dev/shell/JsValue;Lcom/google/gwt/dev/shell/C
ompilingClassLoader;Ljava/lang/Class;Ljava/lang/Object;)V
...

jimtomlinson:  The Safari 4.0.4 update breaks GWT hosted mode on the Mac; it's not limited to Snow Leopard.  
See http://code.google.com/p/google-web-toolkit/issues/detail?id=4220.

Sweet; I replaced the gcUnprotected(int, int) with an empty method as mentioned at
http://populationjim.com/2009/11/13/downgrade-safari-from-404-to-get-gwt-working
et voila! Figured I'd already hacked gwt to get 1.6.4 running on my mac (can't get our project to move to new gwt 
yet), so why the heck not?

Thanks; you saved my keester!