Chapter 9. Web Applications - JBoss Application Server 4.0.1 release2 Guide 英文版指南文档

The AbstractWebContainer is an abstract class that implements the org.jboss.web.AbstractWebContainerMBean interface used by the JBoss J2EE deployer to delegate the task of installing war files needing to be deployed. We'll look at some of the key methods of the AbstractWebContainer below.

public boolean accepts(DeploymentInfo sdi)
{
    String warFile = sdi.url.getFile();
    return warFile.endsWith("war") || warFile.endsWith("war/");
}

The accepts method is implemented by JBoss deployers to indicate which type of deployments they accept. The AbstractWebContainer handles the deployments of WARs as JARs or unpacked directories.

public synchronized void start(DeploymentInfo di) throws DeploymentException
{
    Thread thread = Thread.currentThread();
    ClassLoader appClassLoader = thread.getContextClassLoader();

    try {
        // Create a classloader for the war to ensure a unique ENC
        URL[] empty = {};
        URLClassLoader warLoader = URLClassLoader.newInstance(empty, di.ucl);
        thread.setContextClassLoader(warLoader);
        WebDescriptorParser webAppParser = new DescriptorParser(di);

        String webContext = di.webContext;
        if (webContext != null) {
            if (webContext.length() > 0 && webContext.charAt(0) !=
                '/') {
                webContext = "/" + webContext;
            }
        }

        // Get the war URL
        URL warURL = di.localUrl != null ? di.localUrl : di.url;
        if (log.isDebugEnabled()) {
            log.debug("webContext: " + webContext);
            log.debug("warURL: " + warURL);
            log.debug("webAppParser: " + webAppParser);
        }

        // Parse the web.xml and jboss-web.xml descriptors
        WebMetaData metaData = (WebMetaData) di.metaData;
        parseMetaData(webContext, warURL, di.shortName, metaData);

        WebApplication warInfo = new WebApplication(metaData);
        warInfo.setDeploymentInfo(di);
        performDeploy(warInfo, warURL.toString(), webAppParser);
        deploymentMap.put(warURL.toString(), warInfo);

        // Generate an event for the startup
        super.start(di);
    } catch(DeploymentException e) {
        throw e;
    } catch(Exception e) {
        throw new DeploymentException("Error during deploy", e);
    } finally {
        thread.setContextClassLoader(appClassLoader);
    }
}

This section corresponds to the start method. This method is a template pattern method implementation. The argument to the deploy method is the WAR deployment info object. This contains the URL to the WAR, the UnifiedClassLoader for the WAR, the parent archive such as an EAR, and the J2EE application.xml context-root if the WAR is part of an EAR.

The first step of the start method is to save the current thread context class loader and then create another URLClassCloader (warLoader) using the WAR UnifiedClassLoader as its parent. This warLoader is used to ensure a unique JNDI ENC (enterprise naming context) for the WAR will be created. Chapter 3, Naming on JBoss mentioned that the java:comp context's uniqueness was determined by the class loader that created the java:comp context. The warLoader ClassLoader is set as the current thread context class loader before the performDeploy call is made. Next, the web.xml and jboss-web.xml descriptors are parsed by calling parseMetaData. Next, the web container-specific subclass is asked to perform the actual deployment of the WAR through the performDeploy call. The WebApplication object for this deployment is stored in the deployed application map using the warUrl as the key. The final step is to restore the thread context class loader to the one that existed at the start of the method.

protected abstract void performDeploy(WebApplication webApp, String warUrl,
                                      WebDescriptorParser webAppParser) 
    throws Exception;

This is the signature for the abstract performDeploy method. This method is called by the start method and must be overridden by subclasses to perform the web container specific deployment steps. A WebApplication is provided as an argument, and this contains the metadata from the web.xml descriptor, and the jboss-web.xml descriptor. The metadata contains the context-root value for the web module from the J2EE application.xml descriptor, or if this is a stand-alone deployment, the jboss-web.xml descriptor. The metadata also contains any jboss-web.xml descriptor virtual-host value. On return from performDeploy, the WebApplication must be populated with the class loader of the servlet context for the deployment. The warUrl argument is the string for the URL of the Web application WAR to deploy. The webAppParser argument is a callback handle the subclass must use to invoke the parseWebAppDescriptors method to set up the Web application JNDI environment. This callback provides a hook for the subclass to establish the web application JNDI environment before any servlets are created that are to be loaded on startup of the WAR. A subclass' performDeploy method implementation needs to be arranged so that it can call the parseWebAppDescriptors before starting any servlets that need to access JNDI for JBoss resources like EJBs, resource factories, and so on. One important setup detail that needs to be handled by a subclass implementation is to use the current thread context class loader as the parent class loader for any Web container-specific class loader created. Failure to do this results in problems for web applications that attempt to access EJBs or JBoss resources through the JNDI ENC.

public synchronized void stop(DeploymentInfo di)
    throws DeploymentException
{
    URL warURL = di.localUrl != null ? di.localUrl : di.url;
    String warUrl = warURL.toString();
    try {
        performUndeploy(warUrl);
        // Remove the web application ENC...
        deploymentMap.remove(warUrl);
        // Generate an event for the stop
        super.stop(di);
    } catch(DeploymentException e) {
        throw e;
    } catch(Exception e) {
        throw new DeploymentException("Error during deploy", e);
    }
}

This is the stop method. It calls the subclass performUndeploy method to perform the container-specific undeployment steps. After undeploying the application, the warUrl is unregistered from the deployment map. The warUrl argument is the string URL of the WAR as originally passed to the performDeploy method.

protected abstract void performUndeploy(String warUrl) throws Exception;

This is the signature of the abstract performUndeploy method, which is called from the stop method. A call to performUndeploy asks the subclass to perform the Web container-specific undeployment steps.

public void setConfig(Element config)
{
}

The setConfig method is a stub method that subclasses can override if they want to support an arbitrary extended configuration beyond that which is possible through MBean attributes. The config argument is the parent DOM element for an arbitrary hierarchy given by the child element of the Config attribute in the mbean element specification of the jboss-service.xml descriptor of the web container service. You'll see an example use of this method and config value when you look at the MBean that supports embedding Tomcat into JBoss.

protected void parseWebAppDescriptors(DeploymentInfo di, 
                                      ClassLoader loader,
                                      WebMetaData metaData)
    throws Exception
{
    log.debug("AbstractWebContainer.parseWebAppDescriptors, Begin");
    InitialContext iniCtx = new InitialContext();
    Context envCtx = null;
    Thread currentThread = Thread.currentThread();
    ClassLoader currentLoader = currentThread.getContextClassLoader();
    try {
        // Create a java:comp/env environment unique for the web application
        log.debug("Creating ENC using ClassLoader: "+loader);
        ClassLoader parent = loader.getParent();
        while (parent != null ) {
            log.debug(".."+parent);
            parent = parent.getParent();
        }
        currentThread.setContextClassLoader(loader);
        metaData.setENCLoader(loader);
        envCtx = (Context) iniCtx.lookup("java:comp");
        // Add a link to the global transaction manager
        envCtx.bind("UserTransaction", new LinkRef("UserTransaction"));
        log.debug("Linked java:comp/UserTransaction to JNDI name: UserTransaction");
        envCtx = envCtx.createSubcontext("env");
    } finally {
        currentThread.setContextClassLoader(currentLoader);
    }
                
    Iterator envEntries = metaData.getEnvironmentEntries();
    log.debug("addEnvEntries");
    addEnvEntries(envEntries, envCtx);
                
    Iterator resourceEnvRefs = metaData.getResourceEnvReferences();
    log.debug("linkResourceEnvRefs");
    linkResourceEnvRefs(resourceEnvRefs, envCtx);

    Iterator resourceRefs = metaData.getResourceReferences();
    log.debug("linkResourceRefs");
    linkResourceRefs(resourceRefs, envCtx);
              
    Iterator ejbRefs = metaData.getEjbReferences();
    log.debug("linkEjbRefs");
    linkEjbRefs(ejbRefs, envCtx, di);
                
    Iterator ejbLocalRefs = metaData.getEjbLocalReferences();
    log.debug("linkEjbLocalRefs");                
    linkEjbLocalRefs(ejbLocalRefs, envCtx, di);
               
    String securityDomain = metaData.getSecurityDomain();
    log.debug("linkSecurityDomain");
    linkSecurityDomain(securityDomain, envCtx);
                
    log.debug("AbstractWebContainer.parseWebAppDescriptors, End");
 }

The parseWebAppDescriptors method is invoked from within the subclass performDeploy method when it invokes the webAppParser.parseWebAppDescriptors callback to setup the web application ENC (java:comp/env) env-entry, resource-env-ref, resource-ref, local-ejb-ref and ejb-ref values declared in the web.xml descriptor. The creation of the env-entry values does not require a jboss-web.xml descriptor. The creation of the resource-env-ref, resource-ref, and ejb-ref elements does require a jboss-web.xml descriptor for the JNDI name of the deployed resources/EJBs. Because the ENC context is private to the web application, the web application class loader is used to identify the ENC. The loader argument is the class loader for the web application, and may not be null. The metaData argument is the WebMetaData argument passed to the subclass performDeploy method. The implementation of the parseWebAppDescriptors uses the metadata information from the WAR deployment descriptors and then creates the JNDI ENC bindings.

protected void addEnvEntries(Iterator envEntries, Context envCtx)
    throws ClassNotFoundException, NamingException
{
}

The addEnvEntries method creates the java:comp/env web application env-entry bindings that were specified in the web.xml descriptor.

protected void linkResourceEnvRefs(Iterator resourceEnvRefs, Context envCtx)
    throws NamingException
{
}

The linkResourceEnvRefs method maps the java:comp/env/xxx web application JNDI ENC resource-env-ref web.xml descriptor elements onto the deployed JNDI names using the mappings specified in the jboss-web.xml descriptor.

protected void linkResourceRefs(Iterator resourceRefs, Context envCtx)
    throws NamingException
{
}

The linkResourceRefs method maps the java:comp/env/xxx web application JNDI ENC resource-ref web.xml descriptor elements onto the deployed JNDI names using the mappings specified in the jboss-web.xml descriptor.

protected void linkEjbRefs(Iterator ejbRefs, Context envCtx, DeploymentInfo di)
    throws NamingException
{
}

The linkEjbRefs method maps the java:comp/env/ejb web application JNDI ENC ejb-ref web.xml descriptor elements onto the deployed JNDI names using the mappings specified in the jboss-web.xml descriptor.

protected void linkEjbLocalRefs(Iterator ejbRefs, Context envCtx,
                                DeploymentInfo di)
    throws NamingException
{
}

The linkEjbLocalRefs method maps the java:comp/env/ejb Web application JNDI ENC ejb-local-ref web.xml descriptor elements onto the deployed JNDI names using the ejb-link mappings specified in the web.xml descriptor.

protected void linkSecurityDomain(String securityDomain, Context envCtx)
    throws NamingException
{
}

The linkSecurityDomain method creates a java:comp/env/security context that contains a securityMgr binding pointing to the AuthenticationManager implementation and a realmMapping binding pointing to the RealmMapping implementation that is associated with the security domain for the web application. Also creates is a subject binding that provides dynamic access to the authenticated Subject associated with the request thread. If the jboss-web.xml descriptor contained a security-domain element, the bindings are javax.naming.LinkRefs to the JNDI name specified by the security-domain element, or subcontexts of this name. If there was no security-domain element, the bindings are to org.jboss.security.plugins.NullSecurityManager instance that simply allows all authentication and authorization checks.

public String[] getCompileClasspath(ClassLoader loader)
{
}

The getCompileClasspath method is a utility method available for web containers to generate a classpath that walks up the class loader chain starting at the given loader and queries each class loader for the URLs it serves to build a complete classpath of URL strings. This is needed by some JSP compiler implementations (Jasper for one) that expect to be given a complete classpath for compilation.

To integrate a web container into JBoss you need to create a subclass of AbstractWebContainer and implement the required performDeploy(WebApplication, String, WebDescriptorParser) and performUndeploy(String) methods as described in the preceding section. The following additional integration points should be considered as well.

// Get the username and password from the request context...
HttpServletRequest request = ...;
String username = getUsername(request);
String password = getPassword(request);

// Get the JBoss security manager from the ENC context
InitialContext iniCtx = new InitialContext();
AuthenticationManager securityMgr = (AuthenticationManager)
    iniCtx.lookup("java:comp/env/security/securityMgr");

SimplePrincipal principal = new SimplePrincipal(username);
if (securityMgr.isValid(principal, password)) {
    // Indicate the user is allowed access to the web content...
    // Propagate the user info to JBoss for any calls into made by the servlet
    SecurityAssociation.setPrincipal(principal);
    SecurityAssociation.setCredential(password.toCharArray());
} else {
    // Deny access...
}

// Get the username & required roles from the request context...
HttpServletRequest request = ...;
String username = getUsername(request);
String[] roles = getContentRoles(request);

// Get the JBoss security manager from the ENC context
InitialContext iniCtx = new InitialContext();
RealmMapping securityMgr = (RealmMapping)
    iniCtx.lookup("java:comp/env/security/realmMapping");

SimplePrincipal principal = new SimplePrincipal(username);
Set requiredRoles = new HashSet(java.util.Arrays.asList(roles));

if (securityMgr.doesUserHaveRole(principal, requiredRoles)) {
    // Indicate user has the required roles for the web content...
} else {
    // Deny access...
}