Tomcat源码分析(三) -- Catalina做了什么

Catalina的初始化

Catalina的load方法

public void load() {
    //如果已经被 loaded 了直接返回
    if (loaded) {
        return;
    }
    //设置loaded为true，表示已经被加载了
    loaded = true;

    long t1 = System.nanoTime();
    //这里初始化temp目录
    initDirs();

    // Before digester - it may be needed
    initNaming();

    // Create and execute our Digester
    //创建 Digester 对象，这个 Digester 是用来解析xml配置文件的
    Digester digester = createStartDigester();

    //解析xml配置文件
    InputSource inputSource = null;
    InputStream inputStream = null;
    File file = null;
    try {
        try {
            //获取serve.xml文件
            file = configFile();
            inputStream = new FileInputStream(file);
            inputSource = new InputSource(file.toURI().toURL().toString());
        } catch (Exception e) {
            if (log.isDebugEnabled()) {
                log.debug(sm.getString("catalina.configFail", file), e);
            }
        }
        if (inputStream == null) {
            try {
                inputStream = getClass().getClassLoader()
                    .getResourceAsStream(getConfigFile());
                inputSource = new InputSource
                    (getClass().getClassLoader()
                     .getResource(getConfigFile()).toString());
            } catch (Exception e) {
                if (log.isDebugEnabled()) {
                    log.debug(sm.getString("catalina.configFail",
                                           getConfigFile()), e);
                }
            }
        }

        // This should be included in catalina.jar
        // Alternative: don't bother with xml, just create it manually.
        if (inputStream == null) {
            try {
                inputStream = getClass().getClassLoader()
                    .getResourceAsStream("server-embed.xml");
                inputSource = new InputSource
                    (getClass().getClassLoader()
                     .getResource("server-embed.xml").toString());
            } catch (Exception e) {
                if (log.isDebugEnabled()) {
                    log.debug(sm.getString("catalina.configFail",
                                           "server-embed.xml"), e);
                }
            }
        }


        if (inputStream == null || inputSource == null) {
            if  (file == null) {
                log.warn(sm.getString("catalina.configFail",
                                      getConfigFile() + "] or [server-embed.xml]"));
            } else {
                log.warn(sm.getString("catalina.configFail",
                                      file.getAbsolutePath()));
                if (file.exists() && !file.canRead()) {
                    log.warn("Permissions incorrect, read permission is not allowed on the file.");
                }
            }
            return;
        }

        try {
            inputSource.setByteStream(inputStream);
            digester.push(this);
            //这里会为当前的 Catalina 设置一个 StandardServer 对象，是通过反射设置的
            //猜测这里的 inputSource 会解析成一个 StandardServer 对象
            digester.parse(inputSource);
        } catch (SAXParseException spe) {
            log.warn("Catalina.start using " + getConfigFile() + ": " +
                     spe.getMessage());
            return;
        } catch (Exception e) {
            log.warn("Catalina.start using " + getConfigFile() + ": " , e);
            return;
        }
    } finally {
        if (inputStream != null) {
            try {
                inputStream.close();
            } catch (IOException e) {
                // Ignore
            }
        }
    }

    //为 StandardServer 对象设置属性
    getServer().setCatalina(this);
    getServer().setCatalinaHome(Bootstrap.getCatalinaHomeFile());
    getServer().setCatalinaBase(Bootstrap.getCatalinaBaseFile());

    // Stream redirection
    initStreams();

    // Start the new server
    try {
        //调用 Server 的 init 方法
        //这里会先进入 org.apache.catalina.util.LifecycleBase 的init方法，模板方法
        getServer().init();
    } catch (LifecycleException e) {
        if (Boolean.getBoolean("org.apache.catalina.startup.EXIT_ON_INIT_FAILURE")) {
            throw new java.lang.Error(e);
        } else {
            log.error("Catalina.start", e);
        }
    }

    long t2 = System.nanoTime();
    if(log.isInfoEnabled()) {
        log.info("Initialization processed in " + ((t2 - t1) / 1000000) + " ms");
    }
}

Catalina的start方法

public void start() {
    //如果未被初始化，先调用初始化方法
    if (getServer() == null) {
        load();
    }

    if (getServer() == null) {
        log.fatal("Cannot start server. Server instance is not configured.");
        return;
    }

    long t1 = System.nanoTime();

    // Start the new server
    try {
        //调用 StandardServer 的start方法
        getServer().start();
    } catch (LifecycleException e) {
        log.fatal(sm.getString("catalina.serverStartFail"), e);
        try {
            getServer().destroy();
        } catch (LifecycleException e1) {
            log.debug("destroy() failed for failed Server ", e1);
        }
        return;
    }

    long t2 = System.nanoTime();
    if(log.isInfoEnabled()) {
        log.info("Server startup in " + ((t2 - t1) / 1000000) + " ms");
    }

    // Register shutdown hook
    if (useShutdownHook) {
        if (shutdownHook == null) {
            shutdownHook = new CatalinaShutdownHook();
        }
        //添加一个钩子回调
        //CatalinaShutdownHook 的功能主要是调用 Catalina.this.stop() 方法
        Runtime.getRuntime().addShutdownHook(shutdownHook);

        // If JULI is being used, disable JULI's shutdown hook since
        // shutdown hooks run in parallel and log messages may be lost
        // if JULI's hook completes before the CatalinaShutdownHook()
        LogManager logManager = LogManager.getLogManager();
        if (logManager instanceof ClassLoaderLogManager) {
            ((ClassLoaderLogManager) logManager).setUseShutdownHook(
                false);
        }
    }

    if (await) {
        //阻塞在这，调用的 server 的await方法
        await();
        stop();
    }
}

Catalina的stop方法

public void stop() {
    try {
        // Remove the ShutdownHook first so that server.stop()
        // doesn't get invoked twice
        if (useShutdownHook) {
            //移除钩子回调
            Runtime.getRuntime().removeShutdownHook(shutdownHook);

            // If JULI is being used, re-enable JULI's shutdown to ensure
            // log messages are not lost
            LogManager logManager = LogManager.getLogManager();
            if (logManager instanceof ClassLoaderLogManager) {
                ((ClassLoaderLogManager) logManager).setUseShutdownHook(
                    true);
            }
        }
    } catch (Throwable t) {
        ExceptionUtils.handleThrowable(t);
        // This will fail on JDK 1.2. Ignoring, as Tomcat can run
        // fine without the shutdown hook.
    }

    // Shut down the server
    try {
        //获取 Server 对象
        Server s = getServer();
        LifecycleState state = s.getState();
        if (LifecycleState.STOPPING_PREP.compareTo(state) <= 0
            && LifecycleState.DESTROYED.compareTo(state) >= 0) {
            // Nothing to do. stop() was already called
        } else {
            //调用Server的stop方法
            s.stop();
            //销毁server对象
            s.destroy();
        }
    } catch (LifecycleException e) {
        log.error("Catalina.stop", e);
    }

}

小结

• Catalina 主要工作是操作 Server 对象，注意 这里的 Server 对象是一个接口。实现类是 StandardServer
• Catalina 在 load 方法中通过 Digester 解析xml文件生成 StandardServer
• Catalina 的 load 方法调用了 StandardServer 对象的 init 方法
• Catalina 的 start 方法调用了 StandardServer 对象 的 start 方法
• Catalina 的 stop 方法调用了 StandardServer 对象的 stop 方法和 destroy 方法