Tomcat 源码解析（二）--Bootstrap.jar

[www1350]

之前我们看到其实启动脚本就是使用Bootstrap 的main启动的

解析Bootstrap

Bootstrap 的main

public static void main(String args[]) {

        if (daemon == null) {
            // Don't set daemon until init() has completed
            Bootstrap bootstrap = new Bootstrap();
            try {
                bootstrap.init();
            } catch (Throwable t) {
                handleThrowable(t);
                t.printStackTrace();
                return;
            }
            daemon = bootstrap;
        } else {
            // When running as a service the call to stop will be on a new
            // thread so make sure the correct class loader is used to prevent
            // a range of class not found exceptions.
            Thread.currentThread().setContextClassLoader(daemon.catalinaLoader);
        }

        try {
            String command = "start";
            if (args.length > 0) {
                command = args[args.length - 1];
            }

            if (command.equals("startd")) {
                args[args.length - 1] = "start";
                daemon.load(args);
                daemon.start();
            } else if (command.equals("stopd")) {
                args[args.length - 1] = "stop";
                daemon.stop();
            } else if (command.equals("start")) {
                daemon.setAwait(true);
//调用load ,最后调用Catalina#load
                daemon.load(args);
//调用start
                daemon.start();
            } else if (command.equals("stop")) {
                daemon.stopServer(args);
            } else if (command.equals("configtest")) {
                daemon.load(args);
                if (null==daemon.getServer()) {
                    System.exit(1);
                }
                System.exit(0);
            } else {
                log.warn("Bootstrap: command \"" + command + "\" does not exist.");
            }
        } catch (Throwable t) {
            // Unwrap the Exception for clearer error reporting
            if (t instanceof InvocationTargetException &&
                    t.getCause() != null) {
                t = t.getCause();
            }
            handleThrowable(t);
            t.printStackTrace();
            System.exit(1);
        }

    }

init

public void init() throws Exception {

        initClassLoaders();

//设置目前线程的类装载器catalinaLoader
        Thread.currentThread().setContextClassLoader(catalinaLoader);

        SecurityClassLoad.securityClassLoad(catalinaLoader);

        // 加载类Catalina并实例化最后赋值给catalinaDaemon
        if (log.isDebugEnabled())
            log.debug("Loading startup class");
        Class<?> startupClass =
            catalinaLoader.loadClass
            ("org.apache.catalina.startup.Catalina");
        Object startupInstance = startupClass.newInstance();

        // 以 sharedLoader 作为入参通过反射调用该对象的 setParentClassLoader 方法。
 //也就是sharedLoader作为父ClassLoader
        if (log.isDebugEnabled())
            log.debug("Setting startup class properties");
        String methodName = "setParentClassLoader";
        Class<?> paramTypes[] = new Class[1];
        paramTypes[0] = Class.forName("java.lang.ClassLoader");
        Object paramValues[] = new Object[1];
        paramValues[0] = sharedLoader;
        Method method =
            startupInstance.getClass().getMethod(methodName, paramTypes);
        method.invoke(startupInstance, paramValues);

        catalinaDaemon = startupInstance;

    }

    private void initClassLoaders() {
        try {
//catalina.properties 的common.loader（"${catalina.base}/lib","${catalina.base}/lib/*.jar","${catalina.home}/lib","${catalina.home}/lib/*.jar"）  
//创建commonLoader类加载器
            commonLoader = createClassLoader("common", null);
            if( commonLoader == null ) {
                // no config file, default to this loader - we might be in a 'single' env.
                commonLoader=this.getClass().getClassLoader();
            }
//server.loader （搜索路径空）
//创建catalinaLoader类加载器 
            catalinaLoader = createClassLoader("server", commonLoader);
//shared.loader （搜索路径空）
//创建sharedLoader类加载器
            sharedLoader = createClassLoader("shared", commonLoader);
        } catch (Throwable t) {
            handleThrowable(t);
            log.error("Class loader creation threw exception", t);
            System.exit(1);
        }
    }

start

    public void start()
        throws Exception {
        if( catalinaDaemon==null ) init();

//通过反射调用执行Catalina #start
        Method method = catalinaDaemon.getClass().getMethod("start", (Class [] )null);
        method.invoke(catalinaDaemon, (Object [])null);

    }

解析Catalina

public void load() {

        long t1 = System.nanoTime();

        initDirs();

        // Before digester - it may be needed

        initNaming();

        // 创建Digester
        Digester digester = createStartDigester();

        InputSource inputSource = null;
        InputStream inputStream = null;
        File file = null;
        try {
//读取CatalinaBase/conf/server.xml
            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 {
//读conf/server.xml
                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);
            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 {
            try {
                inputStream.close();
            } catch (IOException e) {
                // Ignore
            }
        }
//Server 设置Catalina为本实例,设置CatalinaHome、CatalinaBase 初始化
        getServer().setCatalina(this);
        getServer().setCatalinaHome(Bootstrap.getCatalinaHomeFile());
        getServer().setCatalinaBase(Bootstrap.getCatalinaBaseFile());

        // Stream redirection
        initStreams();

        // Start the new server
        try {
            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");
        }

    }

其中Digester是很重要的东西，重点在

//创建Digester
Digester digester = createStartDigester();  
//读取conf/server.xml，放入流
inputSource.setByteStream(inputStream);  
//吧当前对象压入
digester.push(this);  
//解析xml
digester.parse(inputSource);  
getServer().setCatalina(this);  
//调用 Server 接口对象的 init 方法。其实就是StandardServer的init(内部initInternal)
getServer().init();  

这样经过对 xml 文件的解析将会产生 org.apache.catalina.core.StandardServer、org.apache.catalina.core.StandardService、org.apache.catalina.connector.Connector、org.apache.catalina.core.StandardEngine、org.apache.catalina.core.StandardHost、org.apache.catalina.core.StandardContext 等等

Catalina的start

public void start() {

        if (getServer() == null) {
            load();
        }

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

        long t1 = System.nanoTime();

        // 调用Server的start
        try {
            getServer().start();
        } catch (LifecycleException e) {
            log.fatal(sm.getString("catalina.serverStartFail"), e);
            try {
//destroy
                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");
        }

        // 注册 shutdown hook
        if (useShutdownHook) {
            if (shutdownHook == null) {
                shutdownHook = new CatalinaShutdownHook();
            }
            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) {
            await();
            stop();
        }
    }