Webapp ClassLoading

Usually, Web applications that are deployed in production environments depend on external, third-party libraries for different functionality. WSO2 Web application management feature provides capability to load classes from different locations to your applications.

Through the WSO2 Application Server's runtime environment, you can control class loading per server/application. The default runtimes are sufficient for most users, but you can also define your own runtimes. There are three default run-times available so far as follows:

• Tomcat  Environment : This is the minimal runtime, which is identical to a pure Tomcat runtime. It only has Tomcat, Servelet, JSP, EL, JSTL available in the server-level classpath. If you want additional JARs, you should package them with the Web application or place in Tomcat environment's extension directory.
• Carbon  Environment : This consists of both the Tomcat environment and the WSO2 Carbon runtime. It does not provide CXF or Spring dependencies. If you want additional Jars, you should package them with the Web application or place in WSO2 Carbon environment's extension directory.
• CXF Environment : This consists of the Tomcat environment, CXF and Spring. It does not provide the Carbon runtime. If you want additional Jars, you should package them with the Web application or place in CXF environment's lib directory.

Next, let's take a look at how to place your external dependencies in a running Carbon server in order to configure class loading per application or server.

Configuring Class Loading

To configure class loading, you should add the class-loading configuration in a file by the name webapp-classloading.xml, and place it in the META-INF directory of a Web application. All the artifacts related to a Web application is saved in <PRODUCT_HOME>/repository/deployment/server/<Web_Application_Type>/<Web_Application_Name>. For example, <PRODUCT_HOME>/repository/deployment/server/jaxwebapps/SampleApp.

webapp-classloading.xml file takes following format.

<Classloading xmlns="http://wso2.org/projects/as/classloading"> 
   <Environments>{Runtime Environment Names} </Environments> 
</Classloading> 

Shown below is the webapp-classloading.xml file configuration to specify CXF as the runtime environment:

<Classloading xmlns="http://wso2.org/projects/as/classloading">
   <Environments>CXF</Environments>
</Classloading>

You might want to access some Carbon features in a CXF application. To achieve this, specify a comma-separated list of environments in webapp-classloading.xml. The following example specifies both CXF and Carbon as the runtime environments:

<Classloading xmlns="http://wso2.org/projects/as/classloading">
   <Environments>CXF,Carbon</Environments>
</Classloading>

Runtime Environment Extensions

You can share dependencies with a number of applications without packaging them with each and every one of them.To do this, place the common dependencies in the following directories depending on your environment.

• In Tomcat Environment - <PRODUCT_HOME>/lib/runtimes/ext
• In Carbon Environment - <PRODUCT_HOME>/repository/components/lib
• In CXF or any Custom Environment – Use the environment's lib directory. For example, <PRODUCT_HOME>/lib/runtimes/cxf

Adding Custom Runtime Environments

To define custom runtime environments, add a new element as <ExclusiveEnvironments> in <PRODUCT_HOME>/repository/conf/tomcat/webapp-classloading-environments.xml file.  

The following steps explain how to define a custom runtime environment for Spring.

1. Modify the webapp-classloading-environments.xml file with following entries.

<ExclusiveEnvironments> 
   <ExclusiveEnvironment> 
      <Name>Spring</Name> 
      <Classpath>${carbon.home}/lib/runtimes/spring/*.jar;${carbon.home}/lib/runtimes/spring/</Classpath> 
   </ExclusiveEnvironment> 
</ExclusiveEnvironments>

2. Next, create and copy related Spring dependencies to <PRODUCT_HOME>/lib/runtimes/spring directory.

3. Add the following entries to the webapp-classloading.xml file of each Web application to use them in the Spring runtime environment defined above.

<Classloading xmlns="http://wso2.org/projects/as/classloading">
   <Environments>CXF,Carbon</Environments>
</Classloading>

Upgrading Existing Runtime Environments

The CXF runtime environment comes by default with core CXF 2.7.5 and core Spring 3.0.7 dependencies. If you want to upgrade to a different CXF version, there are two recommendations:

• • Upgrade the CXF runtime environment : You can replace the existing CXF/Spring dependent JARs in the <PRODUCT_HOME>/lib/runtimes/cxf directory, with new CXF/Spring JARs.

  • Instead of upgrading server-level CXF dependencies, you can package all the required JARs in the Web-INF/lib directory of the Web application and deploy that in the Tomcat runtime environment.

If you want to add optional CXF/Spring JARs, copy them to <PRODUCT_HOME>/lib/runtimes/cxf directory after ensuring that they are compatible with the existing JARs.