Difference between revisions of "Jetty/Feature/ContextProvider"

Revision as of 16:23, 28 April 2011

Introduction

Jetty provides capability to deploy an arbitrary context or web application with Jetty-specific configuration. This capability is implemented via the ContextProvider mechanism which is now an extension of the core deployment infrastructure.

Feature

The ContextProvider may be used to (hot)deploy an arbitrary Context or Web Application with Jetty specific configuration. To statically deploy only standard web applications at startup, use the WebApp Deployer.

Overview

Typically a ContextDeployer is defined in a jetty.xml file, within the stock jetty distribution this file is named jetty-contexts.xml:

 
 <Configure id="Server" class="org.eclipse.jetty.server.Server">
        <Ref id="DeploymentManager">
          <Call name="addAppProvider">
            <Arg>
              <New class="org.eclipse.jetty.deploy.providers.ContextProvider">
                <Set name="monitoredDir"><Property name="jetty.home" default="." />/contexts</Set>
                <Set name="scanInterval">1</Set>
              </New>
            </Arg>
          </Call>
        </Ref>
</Configure>

The ContextProvider will scan the monitoredDir directory at intervals of scanInterval seconds for xml descriptors that define contexts. Any contexts found are deployed to the passed contexts reference to a HandlerContainer (this is normally an instance of ContextHandlerCollection). The deployment descriptors are in jetty xml format and define and configure individual contexts. A minimal example is:

 <?xml version="1.0"  encoding="ISO-8859-1"?>
 <!DOCTYPE Configure PUBLIC "-//Mort Bay Consulting//DTD Configure//EN" "http://jetty.mortbay.org/configure.dtd">
 <Configure class="org.eclipse.jetty.webapp.WebAppContext">
   <Set name="contextPath">/test</Set>
   <Set name="war"><SystemProperty name="jetty.home" default<nowiki>=</nowiki>"."/>/webapps/test</Set>
 </Configure>

This example creates an instance of WebAppContext and sets the contextPath to be "/test" and the resourceBase to be "$jetty.home/webapps/test". Because the context used is a standard web application context, when started it will inspect the resourceBase for a WEB-INF/web.xml for further configuration.

The ContextProvider is added to the server as a LifeCycle. This simply means that the deployer will be started and stopped with the server. Ie when server.start() is called, then start will also be called on the deployer.

Property value substitution

The ContextProvider can automatically do property substitution on the context files that it deploys. You define a ConfigurationManager that manages the properties and pass this into the ContextDeployer. There is currently one implementation of the ConfigurationManager, and that is the org.mortbay.jetty.deployer.FileConfigurationManager that reads a properties file and makes available the property values to the ContextDeployer. Here's how you would configure the ContextDeployer:

 <Configure id="Server" class="org.eclipse.jetty.server.Server">
        <Ref id="DeploymentManager">
          <Call name="addAppProvider">
            <Arg>
              <New class="org.eclipse.jetty.deploy.providers.ContextProvider">
                <Set name="monitoredDir"><Property name="jetty.home" default="." />/contexts</Set>
                <Set name="scanInterval">1</Set>
                <Set name="configurationManager">
                  <New class="org.mortbay.jetty.deployer.FileConfigurationManager">
                     <Set name="file"><SystemProperty name="jetty.home" default="."/>/foo.properties</Set>
                  </New>
                </Set>
              </New>
            </Arg>
          </Call>
        </Ref>
</Configure>

Here's an example of the contents of the foo.properties file:

 
 foo = /funkyapp

Here's how you would use this in a context xml file:

 <?xml version="1.0"  encoding="ISO-8859-1"?>
 <!DOCTYPE Configure PUBLIC "-//Mort Bay Consulting//DTD Configure//EN" "http://jetty.mortbay.org/configure.dtd">
 <Configure class="org.mortbay.jetty.webapp.WebAppContext">
   <Set name="contextPath"><Property name="foo"/></Set>
   <Set name="war"><SystemProperty name="jetty.home" default="."/>/webapps/test</Set>
 </Configure>

Contexts

Because the class of the context is defined in the Configure clause, any type of ContextHandler may be deployed with this mechanism, included base ContextHandler, ServletContextHandler, WebAppContext or any class derived from them.

Hot deploy

If the scan interval is non-zero, the configuration directory is scanned at that interval (in seconds) for changes to the deployment descriptors. If a descriptor is added to the directory, the new context will be deployed. If a descriptor is touched/updated then it's context will be stopped, reconfigured and redeployed. If a descriptor is removed, then it's context will be stopped and removed from the server.

If the scan interval is zero, then the directory is only scanned at startup.

Other things to configure

This mechanism allows the most of the API available on ContextHandler or its derived classes to be called to configure the web application. Useful things to configure include:

• setAttribute
• setClassLoader
• setContextPath
• setVirtualHosts
• addServlet
• setConfigurations
• setExtraClassPath
• setDefaultsDescriptor
• setDescriptor
• setOverrideDescriptor
• setSystemClasses
• setServerClasses