Java Frameworks and Integrations in Google App Engine and Managed VM's

Java Frameworks, Integrations supported in Google App Engine and Managed VM

As per definition from Google docs, Google App Engine is a Platform as a Service (PaaS) offering that lets you build and run applications on Google’s infrastructure. App Engine applications are easy to build, easy to maintain, and easy to scale as your traffic and data storage needs change. With App Engine, there are no servers for you to maintain. You simply upload your application and it’s ready to go.

When your App Engine application is running in the cloud, Google provides a scalable number of instances of your app's modules. Each instance runs in its own hosting environment. From the beginning, the App Engine hosting environment has been a sandbox, containing your code, a webserver, and a language runtime. Aside from your application code, the other components in the App Engine hosting environment are immutable and managed by Google. The language runtime is modified in order to enforce the sandbox constraints, disabling some of the usual language APIs (such as access to the file system).

App Engine now offers a second hosting option: Managed VMs. The managed VM hosting environment lets you run App Engine applications on configurable Compute Engine Virtual Machines (VMs). The VM hosting environment offers more flexibility and provides more CPU and memory options.

You can choose the hosting environment (sandboxed or managed VM) separately for each module in your application. This means an application can contain a mix of modules that use different hosting environments. For instance, you might use the sandbox environment for your client-facing frontend, and use a module running in a managed VM for backend processing. Note that every instance of any specific module will run in the same type of environment.

This article will give the list of java supporting frameworks and integrations that are executed or not executed in google app engine and Managed VM.

Apache wicket in Google App Engine

When Wicket is started in development mode, exceptions are raised because Wicket spawns threads to check resource files such as HTML files for modifications. Need to disable resource modification checking by setting the resource poll frequency in WicketApplication's init() method to null.

We cannot use the SecondLevelCacheSessionStore in the app engine, which is the default. At least not with a DiskPageStore, because this serializes the pages to the disk. But writing to the disk is not allowed in the app engine. You can use the simple HttpSessionStore implementation instead (this increases HTTP session size), by overridingnewSessionStore() in our WicketApplication:

Struts2 in google app engine

Struts 2 need a listener to run in GAE environment and listener is configured in web.xml

This listener class is a class which implements ServletContextListener,HttpSessionListener, HttpSessionAttributeListener.

Call OgnlRuntime.setSecurityManager(null); in the contextIntialized method

TextBlok  class source code is available in

https://groups.google.com/forum/#!topic/google-appengine-java/3YTkT2BEmMQ

Sometimes the below exception occurs while executing Struts2 app

java.security.AccessControlException: access denied ("java.io.FilePermission" "jar:file:\..\war\WEB-INF\lib\struts2-core-2.3.15.3.jar" "read")

This exception only occurs when trying to run a Struts 2 application on Google App Engine for Windows.

In order to solve this problem when running under Google App Engine for Windows the working solution is to implement a custom plugin / extension point that implements the following interfaces com.opensymphony.xwork2.FileManager and com.opensymphony.xwork2.FileManagerFactory.

This issue will not occur in google cloud app engine as it is not windows environment

Running Java Server Faces in google app engine

JSF 2 is using “javax.naming.InitialContext” that’s not supported in GAE.

To solve this, you need to get a copy of the JSF’s source code, clone the WebConfiguration.java, comment methods that are using “javax.naming.InitialContext” class, put it in “src/com/sun/faces/comfig/WebConfiguration.java“. Now, your newly created WebConfiguration.java class will overload the original WebConfiguration.java.

You need to put this el-ri-1.0.jar, otherwise, you will hit error message – Unable to instantiate ExpressionFactory ‘com.sun.el.ExpressionFactoryImpl’.

Apache CXF not supporting in google app engine

Error - java.lang.NoClassDefFoundError: javax.management.ObjectName is a restricted class. Please see the Google  App Engine developer's guide for more details.

Alternative way of using light weight webservice in google app engine is Guice injection and Sitebricks framework released by Google.

Spring Framework

Spring - RMI not supported in google app engine since RMI is not supported by Google App Engine

Spring-Httpinvoker is supported in Google App Engine

Spring-Hessian is supported in Google App engine

Spring MVC with Restful Webservices is supported in Google App Engine

Spring WebFlow is supported in Google App engine

Spring – Security ACL (Domain object security) not working in App engine. Spring security ACL needs to be customized integrating with Google App engine Datastore

Hibernate

Hibernate is working in Google App Engine with database as cloud SQL.

Hibernate with Ehcache is not working as Ehcache used disk I/O internally. Ehcache needs to be customized integrating with Google App Engine Datastore

BPM tools in google app engine

Activiti workflow is not working in google app engine

JBPM  is working in Google app engine

I tried to implement Activiti workflow in google app engine. Google app engine has some restrictions like access permissions, file writing operations. Due to these restrictions, Activiti workflow is not getting executed in google app engine properly. I am using Activiti 5.11 version.

By customizing ExceptionManager, ExpressionFactoryImpl, file writing issue has been solved. But after invoking Activiti workflow app, getting below issue

Getting the below error

Error creating bean with name 'processEngine': FactoryBean threw exception on object creation; nested exception is java.security.AccessControlException: access denied ("java.lang.RuntimePermission" "modifyThreadGroup")

Enterprise Service Bus in Google App Engine

Apache Camel

All components of Apache Camel are not supported by Google App engine. Below tables lists components that are supported by corresponding services in Google App Engine.

Search API

Lucene Search is working in Google App Engine

Reporting Library

Dynamic reporting library which has designer defined by java code is not working in Google App Engine since this uses internally java.awt.Color package which is not supported by Google App Engine

Itext library is working in Google App engine.

Rule Engine

Drools and MVEL libraries are working in google app engine

Here is the list of summary of frameworks and integrations that are supported and not supported in Google App Engine and Managed VM