Tomcat源码分析--启动

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2021-03-26 08:37

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首先找到catalina.sh中的启动脚本:

eval $_NOHUP "\"$_RUNJAVA\"" "\"$CATALINA_LOGGING_CONFIG\"" $LOGGING_MANAGER "$JAVA_OPTS" "$CATALINA_OPTS" \
      -D$ENDORSED_PROP="\"$JAVA_ENDORSED_DIRS\"" \
      -classpath "\"$CLASSPATH\"" \
      -Dcatalina.base="\"$CATALINA_BASE\"" \
      -Dcatalina.home="\"$CATALINA_HOME\"" \
      -Djava.io.tmpdir="\"$CATALINA_TMPDIR\"" \
      org.apache.catalina.startup.Bootstrap "$@" start \
      >> "$CATALINA_OUT" 2>&1 "&"

启动类为org.apache.catalina.startup.Bootstrap,在Bootstrap类中找到main方法:

    public static void main(String args[]) {
        if (daemon == null) {
            // Don't set daemon until init() has completed
            Bootstrap bootstrap = new Bootstrap();
            try {
                //初始化Bootstrap
                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);
                daemon.load(args);
                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);
        }
 
    }


初始化Bootstrap

在main方法中会首先初始化Bootstrap,然后解析command,根据不同的command执行不同的逻辑处理,通过catalina.sh启动Tomcat传人的参数是"start",不过看代码中command默认也是start。我们首先看Bootstrap的初始化方法bootstrap.init():

public void init() throws Exception {
        //初始化类加载器
        initClassLoaders();
        //设置TCCL
        Thread.currentThread().setContextClassLoader(catalinaLoader);
 
        SecurityClassLoad.securityClassLoad(catalinaLoader);
        
        //加载并创建启动类:Catalina
        Class<?> startupClass =
            catalinaLoader.loadClass
            ("org.apache.catalina.startup.Catalina");
        Object startupInstance = startupClass.newInstance();
        //通过反射设置parentClassLoader属性
        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);
        //赋值启动类到catalinaDaemon属性
        catalinaDaemon = startupInstance;
    }


初始化动作主要是初始化类加载器,然后加载并实例化启动类(Catalina)。这里初始化的类加载器是common、shared、catalina三个类加载器,没有初始化WebApp的类加载器:

private void initClassLoaders() {
        try {
            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();
            }
            catalinaLoader = createClassLoader("server", commonLoader);
            sharedLoader = createClassLoader("shared", commonLoader);
        } catch (Throwable t) {
            handleThrowable(t);
            log.error("Class loader creation threw exception", t);
            System.exit(1);
        }
    }


6.x以后的版本合并了share、common等目录,可以根据参数server.loader、share.loader等决定是否启动老的结构,以创建sharedClassLoader为例:

private ClassLoader createClassLoader(String name, ClassLoader parent)
        throws Exception {
        //创建shareClassLoader时,name参数是share
        String value = CatalinaProperties.getProperty(name + ".loader");
        if ((value == null) || (value.equals("")))
            //如果没有配置share.loader,那么使用直接返回父类加载器
            return parent;
        ......
        //创建shareClassLoader的逻辑
}


再回到bootstrap.init()的逻辑,创建好类加载器之后,catalinaDemon已经被赋值为一个Catalina对象。


解析command参数

Bootstrap初始化工作完成后,进入command==start的处理逻辑:

if (command.equals("start")) {
    daemon.setAwait(true);
    daemon.load(args);
    daemon.start();
}


一共就三行代码,首先是setAwait(true),看看Bootstrap.setAwait方法:

public void setAwait(boolean await)
        throws Exception {
 
        Class<?> paramTypes[] = new Class[1];
        paramTypes[0] = Boolean.TYPE;
        Object paramValues[] = new Object[1];
        paramValues[0] = Boolean.valueOf(await);
        Method method =
            catalinaDaemon.getClass().getMethod("setAwait", paramTypes);
        method.invoke(catalinaDaemon, paramValues);
 
    }

通过反射调用了catalinaDaemon的setAwait方法,前面提到了,catalinaDaemon在Bootstrap初始化的时候生成,我们这里直接看它的setAwait方法:

protected boolean await = false;
public void setAwait(boolean b) {
    await = b;
}

方法很简单,就是设置await属性,这里将其设置为了true。然后再回到Bootstrap处理start指令的流程中:

daemon.setAwait(true);//将Catalina的await属性设置为true
daemon.load(args);//加载初始化Tomcat的核心组件
daemon.start();//解析文件,启动组件

启动组件

daemon.load方法主要加载Tomcat的核心组件,这个部分后面再分析,我们直接看daemon.start()方法是如何启动组件的:

public void start()
        throws Exception {
        if( catalinaDaemon==null ) init();
 
        Method method = catalinaDaemon.getClass().getMethod("start", (Class [] )null);
        method.invoke(catalinaDaemon, (Object [])null);
 
    }

还是通过反射调用Catalina的start方法(部分代码):

    protected boolean useShutdownHook = true;
    public void start() {
        if (getServer() == null) {
            //生成server实例
            load();
        }
        if (getServer() == null) {
            log.fatal("Cannot start server. Server instance is not configured.");
            return;
        }
        // 启动server
        getServer().start();
        //注册一个shutdownhOOK
        if (useShutdownHook) {
            if (shutdownHook == null) {
                shutdownHook = new CatalinaShutdownHook();
            }
            Runtime.getRuntime().addShutdownHook(shutdownHook);
            LogManager logManager = LogManager.getLogManager();
            if (logManager instanceof ClassLoaderLogManager) {
                ((ClassLoaderLogManager) logManager).setUseShutdownHook(
                        false);
            }
        }
        if (await) {
            //await
            await();
            stop();
        }
    }

load()方法会解析server.xml节点,对应初始化很多对象,包括server、engine、host、connector等等。最主要的就是顶层Server节点,对应的StandardServer对象:

digester.addObjectCreate("Server","org.apache.catalina.core.StandardServer","className");

这部分流程后面再分析。启动server后,首先注册了一个shutdownHook(关于shutdownHook可以参考JAVA之ShutdownHook源码分析),主要应对不是通过socket正常退出的情况。前面通过反射设置了await属性为true,所以进入await()方法:

public void await() {
        getServer().await();
    }

阻塞主线程

Catalina的await方法又调用了getServer的await方法,server在前面的load阶段已经创建,指定的是org.apache.catalina.core.StandardServer,进入它的await方法:

public void await() {
        if( port == -2 ) {
            //内嵌的tomcat,直接返回
            return;
        }
        if( port==-1 ) {
         //如果==-1,根据stopAwait参数间隔10秒死检查循环
            try {
                awaitThread = Thread.currentThread();
                while(!stopAwait) {
                    try {
                        Thread.sleep( 10000 );
                    } catch( InterruptedException ex ) {
                        // continue and check the flag
                    }
                }
            } finally {
                awaitThread = null;
            }
            return;
        }
 
        //根据port创建一个ServerSocket,如果port小于0,会抛出异常
        try {
            awaitSocket = new ServerSocket(port, 1,
                    InetAddress.getByName(address));
        } catch (IOException e) {
            log.error("StandardServer.await: create[" + address
                               + ":" + port
                               + "]: ", e);
            return;
        }
 
        try {
            awaitThread = Thread.currentThread();
 
            // Loop waiting for a connection and a valid command
            while (!stopAwait) {
             //根据标识死循环
                ServerSocket serverSocket = awaitSocket;
                if (serverSocket == null) {
                    break;
                }
 
                // Wait for the next connection
                Socket socket = null;
                StringBuilder command = new StringBuilder();
                try {
                    InputStream stream;
                    long acceptStartTime = System.currentTimeMillis();
                    try {
                     //调用accept方法阻塞,等待连接
                        socket = serverSocket.accept();
                        socket.setSoTimeout(10 * 1000);  // Ten seconds
                        stream = socket.getInputStream();
                    } catch (SocketTimeoutException ste) {
                        // This should never happen but bug 56684 suggests that
                        // it does.
                        log.warn(sm.getString("standardServer.accept.timeout",
                                Long.valueOf(System.currentTimeMillis() - acceptStartTime)), ste);
                        continue;
                    } catch (AccessControlException ace) {
                        log.warn("StandardServer.accept security exception: "
                                + ace.getMessage(), ace);
                        continue;
                    } catch (IOException e) {
                        if (stopAwait) {
                            // Wait was aborted with socket.close()
                            break;
                        }
                        log.error("StandardServer.await: accept: ", e);
                        break;
                    }
 
                    // 从socket中读取数据,shutdown是一个字符串可以在server.xml中配置,默认为SHUTDOWN
                    int expected = 1024; // Cut off to avoid DoS attack
                    while (expected < shutdown.length()) {
                        if (random == null)
                            random = new Random();
                        expected += (random.nextInt() % 1024);
                    }
                    while (expected > 0) {
                        int ch = -1;
                        try {
                            ch = stream.read();
                        } catch (IOException e) {
                            log.warn("StandardServer.await: read: ", e);
                            ch = -1;
                        }
                        // Control character or EOF (-1) terminates loop
                        if (ch < 32 || ch == 127) {
                            break;
                        }
                        command.append((char) ch);
                        expected--;
                    }
                } finally {
                    // Close the socket now that we are done with it
                    try {
                        if (socket != null) {
                            socket.close();
                        }
                    } catch (IOException e) {
                        // Ignore
                    }
                }
 
                boolean match = command.toString().equals(shutdown);
                if (match) {
                 //如果读取的数据是shutdown对应的字符串就跳出死循环
                    log.info(sm.getString("standardServer.shutdownViaPort"));
                    break;
                } else
                    log.warn("StandardServer.await: Invalid command '"
                            + command.toString() + "' received");
            }
        } finally {
            ServerSocket serverSocket = awaitSocket;
            awaitThread = null;
            awaitSocket = null;
 
            // Close the server socket and return
            if (serverSocket != null) {
                try {
                 //断开socket连接
                    serverSocket.close();
                } catch (IOException e) {
                    // Ignore
                }
            }
        }
    }


代码逻辑很长,其实主要就干几件事:


如果port==-2,表示是内嵌的tomcat,直接返回

如果port==-1,根据标识死循环阻塞

否则根据port创建一个ServerSocket,并且循环阻塞等待socket连接,直到接收到shutdown指令

shutdown指令和对应的port可以在server.xml中自行配置:

<Server port="8005" shutdown="SHUTDOWN">
......
</Server>

就通过这样的方式阻塞主线程,直到shutdown。await方法返回后,调用Catalina.stop()方法停止服务器。大体流程如下:




————————————————

版权声明:本文为CSDN博主「黄智霖-blog」的原创文章,遵循CC 4.0 BY-SA版权协议,转载请附上原文出处链接及本声明。

原文链接:

https://blog.csdn.net/huangzhilin2015/article/details/115048022




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