I upgraded this morning, figuring that the changes related to the .gsp views and their pre-compiling would reduce the cold start issues I’m having with Google AppEngine.

However the 1.2-M2 release of Grails, doesn’t fly on Google AppEngine right now. As far as I can see on the mailing list others have had this issue as well.

The problem I’m experiencing is that the LogManager cannot instantiate.

Context initialization failed
org.springframework.beans.factory.access.BootstrapException: Error executing bootstraps; nested exception is org.codehaus.groovy.runtime.InvokerInvocationException: java.lang.NoClassDefFoundError: java.util.logging.LogManager is a restricted class. Please see the Google App Engine developer's guide for more details.
	at org.codehaus.groovy.grails.web.context.GrailsContextLoader.createWebApplicationContext(GrailsContextLoader.java:74)
	at org.springframework.web.context.ContextLoader.initWebApplicationContext(ContextLoader.java:197)
	at org.springframework.web.context.ContextLoaderListener.contextInitialized(ContextLoaderListener.java:47)
	at org.mortbay.jetty.handler.ContextHandler.startContext(ContextHandler.java:530)

And

Context initialization failed
org.springframework.beans.factory.access.BootstrapException: Error executing bootstraps; nested exception is org.codehaus.groovy.runtime.InvokerInvocationException: java.lang.NoClassDefFoundError: Could not initialize class com.google.apphosting.runtime.security.shared.stub.java.util.logging.LogManager

Update: Chad has created a JIRA for this issue located here:http://jira.codehaus.org/browse/GRAILSPLUGINS-1546

Also here is a link to the discussion on the Grails thread:

http://www.nabble.com/java.util.logging.LogManager-is-a-restricted-class.-Please-see-the–Google-App-Engine-developer%27s-guide-for-more-details.-td25453128.html

I’ve been having this issue for a while. Putting it off, but now I had to get my hands dirty. The findBy… methods weren’t returning any objects even though there were data fitting the specified values.

So tonight I finally took the time to take a look at it. My theory was that I could figure out what was wrong by reading the code in JpaPluginSupport.groovy, located in the GORM-JPA plugin.

Now I didn’t find out why its not working. It even looks like its not supported, but I can’t say for sure. What I did however, was find a workaround.

Instead of doing

User.findByEmail(newSaga.email)

I do

User.findWhere(email: newSaga.email)

Using the findWhere method I get results. This is the workaround I’ll go for for now.

Sending emails with Google AppEngine is quite straight forward once you get a hang of things. I ran into some issues, for example I never got the high level api’s to work. The code executed but the emails were never received. Instead I went for Google AppEngines own “low level” api, it worked much better.

What I did is that I set up a really simple MailService, similar to that which is installed with the Mail plug in. However, I do not handle templates instead I just send strings with the mail message.

package mail

import com.google.appengine.api.mail.MailService
import com.google.appengine.api.mail.MailService.Message
import com.google.appengine.api.mail.MailServiceFactory
import javax.mail.MessagingException
import javax.mail.internet.AddressException

class MailService {

 boolean transactional = true

 def sendMail(subject, msgBody, too) {

 try {
 def service = MailServiceFactory.getMailService();

 def msg = new com.google.appengine.api.mail.MailService.Message();
 msg.setSender("xxx");
 msg.setTo(too);
 msg.setSubject(subject);
 msg.setHtmlBody(msgBody);
 service.send(msg);

 } catch (AddressException e) {
 // ...
 } catch (MessagingException e) {
 // ...
 }

 }
}

As you can see it is quite straight forward. I’d like to mention though that in the above code you see a red xxx. This is where you put your sender address. It needs to either be the email to an admin (registered developer) of the app, or it has to be a user logged in using Google’s own login.

With the low-level api it throws an exception like the one below:

Uncaught exception from servlet
org.codehaus.groovy.runtime.InvokerInvocationException: java.lang.IllegalArgumentException: Unauthorized Sender: Unauthorized sender

Good luck!

I ran into an issue last night where Google AppEngine wouldn’t persist my entities. If I create an entity using the parameters provided by Grails; then the Save operations would fail with the following error

Uncaught exception from servlet
org.codehaus.groovy.runtime.InvokerInvocationException: groovy.lang.MissingMethodException: No signature of method: java.lang.StringBuilder.leftShift() is applicable for argument types: (org.codehaus.groovy.runtime.GStringImpl) values: [(login.email  = ?1 )]
	at com.studentsonly.grails.plugins.uiperformance.CacheFilter.doFilter(CacheFilter.java:71)
	at com.google.apphosting.runtime.jetty.SaveSessionFilter.doFilter(SaveSessionFilter.java:35)
	at com.google.apphosting.utils.servlet.TransactionCleanupFilter.doFilter(TransactionCleanupFilter.java:43)
	at com.google.apphosting.runtime.jetty.AppVersionHandlerMap.handle(AppVersionHandlerMap.java:237)
	at com.google.apphosting.runtime.jetty.RpcRequestParser.parseAvailable(RpcRequestParser.java:76)
	at com.google.apphosting.runtime.jetty.JettyServletEngineAdapter.serviceRequest(JettyServletEngineAdapter.java:139)
	at com.google.apphosting.runtime.JavaRuntime.handleRequest(JavaRuntime.java:235)
	at com.google.apphosting.base.RuntimePb$EvaluationRuntime$6.handleBlockingRequest(RuntimePb.java:4823)
	at com.google.apphosting.base.RuntimePb$EvaluationRuntime$6.handleBlockingRequest(RuntimePb.java:4821)
	at com.google.net.rpc.impl.BlockingApplicationHandler.handleRequest(BlockingApplicationHandler.java:24)
	at com.google.net.rpc.impl.RpcUtil.runRpcInApplication(RpcUtil.java:359)
	at com.google.net.rpc.impl.Server$2.run(Server.java:820)
	...

The issue is described here. I tried their solution and it works fine for me.

I ran into another problem with Google AppEngine. I finally got it to save my entities, only to find it crashing as I wanted to send them back again rendered as JSON.

I had a piece of code looking like this:

def services = {
 params.max = Math.min(params.max ? params.max.toInteger() : 10, 100)
 render Offering.list(params) as JSON;
 }

The code is simple enough, it loads all the Service offerings using GORM and then renders them as JSON using the built in converter. This resulted in the following error:

Uncaught exception from servlet
org.codehaus.groovy.runtime.InvokerInvocationException: org.codehaus.groovy.grails.web.converters.exceptions.ConverterException: Error converting Bean with class org.codehaus.groovy.reflection.ClassLoaderForClassArtifacts
...
Caused by: org.codehaus.groovy.grails.web.converters.exceptions.ConverterException: Error converting Bean with class org.codehaus.groovy.reflection.ClassLoaderForClassArtifacts
	at grails.converters.JSON.value(JSON.java:199)
	at grails.converters.JSON.convertAnother(JSON.java:156)
...
	at com.google.apphosting.runtime.security.shared.intercept.java.lang.reflect.Method_$3.run(Method_.java:149)
	at java.security.AccessController.doPrivileged(Native Method)
	at com.google.apphosting.runtime.security.shared.intercept.java.lang.reflect.Method_.privilegedInvoke(Method_.java:147)
	at com.google.apphosting.runtime.security.shared.intercept.java.lang.reflect.Method_.invoke(Method_.java:120)
	... 26 more
Caused by: java.lang.reflect.InvocationTargetException
	at com.google.apphosting.runtime.security.shared.intercept.java.lang.reflect.Method_$3.run(Method_.java:149)
	at java.security.AccessController.doPrivileged(Native Method)
	at com.google.apphosting.runtime.security.shared.intercept.java.lang.reflect.Method_.privilegedInvoke(Method_.java:147)
	at com.google.apphosting.runtime.security.shared.intercept.java.lang.reflect.Method_.invoke(Method_.java:120)
...
Caused by: java.security.AccessControlException: access denied (java.lang.RuntimePermission getClassLoader)
	at java.security.AccessControlContext.checkPermission(Unknown Source)
	at java.security.AccessController.checkPermission(Unknown Source)
	at java.lang.SecurityManager.checkPermission(Unknown Source)
	at java.lang.ClassLoader.getParent(Unknown Source)
	... 59 more

The problem is that the GORM loads the class with some meta data attached to it. I’m not allowed to reflect over this meta data, so the normal converter fails with the above error. I took the privilege to shorten the stack trace somewhat.

The work around is simple and elegant. I use the groovy collection method called select. With this I can construct a list with maps with the fields I want in my JSON and render them using the normal converter.

def services = {
 params.max = Math.min(params.max ? params.max.toInteger() : 10, 100)
 def list =  Offering.list(params);
 render list.collect { offering->[id:offering.id, name:offering.name]} as JSON
 }

The above code works fine on Google AppEngine.

I hope this helps someone else.

Moving from Mor.ph AppSpace to Google AppEngine isn’t as easy as I hoped.

Installing AppEngine plug in

Initially moving the Application by installing the app-engine plug in is straight forward. Except that the command-line written in the plug in page for executing the initial setup is wrong. Ive corrected it now.

Windows users need to run the update command with the following command-line:

%APPENGINE_HOME%/bin/appcfg.cmd update ./target/war

Also unless the app-engine code executes correctly it will not clean up the staging directory. This causes problems if your using plug ins such as the ui-performance plug in. That is written to execute on a “clean” staging directory. If you it’s not cleaned up the plug in will try to compress the gziped version the files as well.

GORM

The problem however is that the GORM functions are not available, since the AppEngine is using a different data storage not supported by Hibernate.

There is a solution to this, install the GORM-JPA plug in. This gives you most GORM functions, but using Google AppEngines data storage.

Issues

From here I’ve run into several issues along the way. The framework for deploying to Google AppEngine crashes when running on Windows machines; if you have allot of libraries and classes in your project. Google AppEngine fails to save my entities, JSON conversion is acting up as it tries to serialize class meta data for some reason, which is were I’m currently stuck.

Light at the end of the Tunnel

Now I’d also like to mention that these issues are being ironed out. There are people looking at most of them, it’s just that Grails on Google AppEngine is relatively young so to speak. Even Java on Google AppEngine is quite new, if not Google AppEngine in it self.

Also I’d also like to mention the dashboard on Google AppEngine. It’s great!

The Dashboard on Google AppEngine gives the overview logs I got from Mor.ph, but they are presented better. They also give me some summaries on where most errors occur (which URLs crash) and which URLs are consuming the most CPU. This helps me to optimize specific URLs.

Since my application uses a REST service consumed through AJAX I can optimize parts of the application on the back end, and monitor the usage of parts of the web service.

I ran into a problem with Grails on Google AppEngine. When I was saving my entities it tried to save the wrong type of entity. I ran out of ideas on this one and brought it up on the Grails User mailinglist.

I started to work on some reproduction code and then I went to Denmark for some vacation. When I get back however, Keith Thomas had run into the same issue and figured out that it had something to do with the constraints on the domain classes.

Sure enough removing the constraints fixed the issue with saving. Ill try to see if the problem is specific to some kinds of constraints, since I still have my reproduction project to test it in.