【Tomcat】容器 之 Host

tomcat4.0版本。

Host容器的职责是根据url的context来匹配特定的context容器处理请求。host在url中就是域名。

host的构造方法会加入basic的valve：

/**
     * Create a new StandardHost component with the default basic Valve.
     */
    public StandardHost() {

        super();
        pipeline.setBasic(new StandardHostValve());

    }

在start方法加入了一个errorReport的valve：

/**
     * Start this host.
     *
     * @exception LifecycleException if this component detects a fatal error
     *  that prevents it from being started
     */
    public synchronized void start() throws LifecycleException {

        // Set error report valve
        if ((errorReportValveClass != null)
            && (!errorReportValveClass.equals(""))) {
            try {
                Valve valve = (Valve) Class.forName(errorReportValveClass)
                    .newInstance();
                addValve(valve);
            } catch (Throwable t) {
                log(sm.getString
                    ("standardHost.invalidErrorReportValveClass", 
                     errorReportValveClass));
            }
        }

        // Set dispatcher valve
        addValve(new ErrorDispatcherValve());

        super.start();

    }

最终匹配context的方法在stardardhostvalve中的invoke方法：

public void invoke(Request request, Response response,
                       ValveContext valveContext)
        throws IOException, ServletException {

        // Validate the request and response object types
        if (!(request.getRequest() instanceof HttpServletRequest) ||
            !(response.getResponse() instanceof HttpServletResponse)) {
            return;     // NOTE - Not much else we can do generically
        }

        // Select the Context to be used for this Request
        StandardHost host = (StandardHost) getContainer();
        Context context = (Context) host.map(request, true);
        if (context == null) {
            ((HttpServletResponse) response.getResponse()).sendError
                (HttpServletResponse.SC_INTERNAL_SERVER_ERROR,
                 sm.getString("standardHost.noContext"));
            return;
        }

        // Bind the context CL to the current thread
        Thread.currentThread().setContextClassLoader
            (context.getLoader().getClassLoader());

        // Update the session last access time for our session (if any)
        HttpServletRequest hreq = (HttpServletRequest) request.getRequest();
        String sessionId = hreq.getRequestedSessionId();
        if (sessionId != null) {
            Manager manager = context.getManager();
            if (manager != null) {
                Session session = manager.findSession(sessionId);
                if ((session != null) && session.isValid())
                    session.access();
            }
        }

        // Ask this Context to process this request
        context.invoke(request, response);

        Thread.currentThread().setContextClassLoader
            (StandardHostValve.class.getClassLoader());

    }

其中会调用host的map方法匹配一个context，调用context的invoke方法处理请求：

/**
     * Return the Context that would be used to process the specified
     * host-relative request URI, if any; otherwise return <code>null</code>.
     *
     * @param uri Request URI to be mapped
     */
    public Context map(String uri) {

        if (debug > 0)
            log("Mapping request URI '" + uri + "'");
        if (uri == null)
            return (null);

        // Match on the longest possible context path prefix
        if (debug > 1)
            log("  Trying the longest context path prefix");
        Context context = null;
        String mapuri = uri;
        while (true) {
            context = (Context) findChild(mapuri);
            if (context != null)
                break;
            int slash = mapuri.lastIndexOf('/');
            if (slash < 0)
                break;
            mapuri = mapuri.substring(0, slash);
        }

        // If no Context matches, select the default Context
        if (context == null) {
            if (debug > 1)
                log("  Trying the default context");
            context = (Context) findChild("");
        }

        // Complain if no Context has been selected
        if (context == null) {
            log(sm.getString("standardHost.mappingError", uri));
            return (null);
        }

        // Return the mapped Context (if any)
        if (debug > 0)
            log(" Mapped to context '" + context.getPath() + "'");
        return (context);

    }