熟悉Tomcat的工程师们，肯定都知道Tomcat是如何启动与停止的。对于startup.sh、startup.bat、shutdown.sh、shutdown.bat等脚本或者批处理命令，大家一定知道改如何使用它，但是它们究竟是如何实现的，尤其是shutdown.sh脚本（或者shutdown.bat）究竟是如何和Tomcat进程通信的呢？本文将通过对Tomcat7.0的源码阅读，深入剖析这一过程。
由于在生产环境中，Tomcat一般部署在linux系统下，所以本文将以startup.sh和shutdown.sh等shell脚本为准，对Tomcat的启动与停止进行分析。
我们启动Tomcat的命令如下：
sh startup.sh
所以，将从shell脚本startup.sh开始分析Tomcat的启动过程。startup.sh的脚本代码见代码清单1。
代码清单1
os400=falsecase "`uname`" inOS400*) os400=true;;esac# resolve links - $0 may be a softlinkPRG="$0"while [ -h "$PRG" ] ; do ls=`ls -ld "$PRG"` link=`expr "$ls" : '.*-> /(.*/)$'` if expr "$link" : '/.*' > /dev/null; then PRG="$link" else PRG=`dirname "$PRG"`/"$link" fidonePRGDIR=`dirname "$PRG"`EXECUTABLE=catalina.sh# Check that target executable existsif $os400; then # -x will Only work on the os400 if the files are: # 1. owned by the user # 2. owned by the PRIMARY group of the user # this will not work if the user belongs in secondary groups evalelse if [ ! -x "$PRGDIR"/"$EXECUTABLE" ]; then echo "Cannot find $PRGDIR/$EXECUTABLE" echo "The file is absent or does not have execute permission" echo "This file is needed to run this program" exit 1 fifiexec "$PRGDIR"/"$EXECUTABLE" start "$@"
代码清单1中有两个主要的变量，分别是：
根据最后一行代码：exec "$PRGDIR"/"$EXECUTABLE" start "$@"，我们知道执行了shell脚本catalina.sh，并且传递参数start。catalina.sh中接收到start参数后的执行的脚本分支见代码清单2。
代码清单2
elif [ "$1" = "start" ] ; then# 此处省略参数校验的脚本 shift touch "$CATALINA_OUT" if [ "$1" = "-security" ] ; then if [ $have_tty -eq 1 ]; then echo "Using Security Manager" fi shift eval "/"$_RUNjava/"" "/"$LOGGING_CONFIG/"" $LOGGING_MANAGER $JAVA_OPTS $CATALINA_OPTS / -Djava.endorsed.dirs="/"$JAVA_ENDORSED_DIRS/"" -classpath "/"$CLASSPATH/"" / -Djava.security.manager / -Djava.security.policy=="/"$CATALINA_BASE/conf/catalina.policy/"" / -Dcatalina.base="/"$CATALINA_BASE/"" / -Dcatalina.home="/"$CATALINA_HOME/"" / -Djava.io.tmpdir="/"$CATALINA_TMPDIR/"" / org.apache.catalina.startup.Bootstrap "$@" start / >> "$CATALINA_OUT" 2>&1 "&" else eval "/"$_RUNJAVA/"" "/"$LOGGING_CONFIG/"" $LOGGING_MANAGER $JAVA_OPTS $CATALINA_OPTS / -Djava.endorsed.dirs="/"$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 "&" fi if [ ! -z "$CATALINA_PID" ]; then echo $! > "$CATALINA_PID" fi echo "Tomcat started."
从代码清单2可以看出，最终使用java命令执行了org.apache.catalina.startup.Bootstrap类中的main方法，参数也是start。Bootstrap的main方法的实现见代码清单3。
代码清单3
/** * Main method, used for testing only. * * @param args Command line arguments to be processed */ 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) { t.printStackTrace(); return; } daemon = bootstrap; } 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 { log.warn("Bootstrap: command /"" + command + "/" does not exist."); } } catch (Throwable t) { t.printStackTrace(); } }
从代码清单3可以看出，当传递参数start的时候，command等于start，此时main方法的执行步骤如下：
步骤一 初始化Bootstrap
Bootstrap的init方法（见代码清单4）的执行步骤如下:
代码清单4
/** * Initialize daemon. */ public void init() throws Exception { // Set Catalina path setCatalinaHome(); setCatalinaBase(); initClassLoaders(); Thread.currentThread().setContextClassLoader(catalinaLoader); SecurityClassLoad.securityClassLoad(catalinaLoader); // Load our startup class and call its process() method if (log.isDebugEnabled()) log.debug("Loading startup class"); Class<?> startupClass = catalinaLoader.loadClass ("org.apache.catalina.startup.Catalina"); Object startupInstance = startupClass.newInstance(); // Set the shared extensions class loader 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; }
步骤二 加载、解析server.xml配置文件
当传递参数start的时候，会调用Bootstrap的load方法（见代码清单5），其作用是用反射调用catalinaDaemon（类型是Catalina）的load方法加载和解析server.xml配置文件，具体细节已在《TOMCAT源码分析——SERVER.XML文件的加载与解析》一文中详细介绍，有兴趣的朋友可以选择阅读。
代码清单5
/** * Load daemon. */ private void load(String[] arguments) throws Exception { // Call the load() method String methodName = "load"; Object param[]; Class<?> paramTypes[]; if (arguments==null || arguments.length==0) { paramTypes = null; param = null; } else { paramTypes = new Class[1]; paramTypes[0] = arguments.getClass(); param = new Object[1]; param[0] = arguments; } Method method = catalinaDaemon.getClass().getMethod(methodName, paramTypes); if (log.isDebugEnabled()) log.debug("Calling startup class " + method); method.invoke(catalinaDaemon, param); }
步骤三 启动Tomcat
当传递参数start的时候，调用Bootstrap的load方法之后会接着调用start方法（见代码清单6）启动Tomcat，此方法实际是用反射调用了catalinaDaemon（类型是Catalina）的start方法。
代码清单6
/** * Start the Catalina daemon. */ public void start() throws Exception { if( catalinaDaemon==null ) init(); Method method = catalinaDaemon.getClass().getMethod("start", (Class [] )null); method.invoke(catalinaDaemon, (Object [])null); }
Catalina的start方法（见代码清单7）的执行步骤如下：
代码清单7
/** * Start a new server instance. */ 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(); // Start the new server try { getServer().start(); } catch (LifecycleException e) { log.error("Catalina.start: ", e); } long t2 = System.nanoTime(); if(log.isInfoEnabled()) log.info("Server startup in " + ((t2 - t1) / 1000000) + " ms"); try { // Register 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); } } } catch (Throwable t) { // This will fail on JDK 1.2. Ignoring, as Tomcat can run // fine without the shutdown hook. } if (await) { await(); stop(); } }
Catalina的await方法（见代码清单8）实际只是代理执行了Server容器的await方法。
代码清单8
/** * Await and shutdown. */ public void await() { getServer().await(); }
以Server的默认实现StandardServer为例，其await方法（见代码清单9）的执行步骤如下：
代码清单9
public void await() { // Negative values - don't wait on port - tomcat is embedded or we just don't like ports gja if( port == -2 ) { // undocumented yet - for embedding apps that are around, alive. return; } if( port==-1 ) { while( true ) { try { Thread.sleep( 10000 ); } catch( InterruptedException ex ) { } if( stopAwait ) return; } } // Set up a server socket to wait on ServerSocket serverSocket = null; try { serverSocket = new ServerSocket(port, 1, InetAddress.getByName(address)); } catch (IOException e) { log.error("StandardServer.await: create[" + address + ":" + port + "]: ", e); System.exit(1); } // Loop waiting for a connection and a valid command while (true) { // Wait for the next connection Socket socket = null; InputStream stream = null; try { socket = serverSocket.accept(); socket.setSoTimeout(10 * 1000); // Ten seconds stream = socket.getInputStream(); } catch (accessControlException ace) { log.warn("StandardServer.accept security exception: " + ace.getMessage(), ace); continue; } catch (IOException e) { log.error("StandardServer.await: accept: ", e); System.exit(1); } // Read a set of characters from the socket StringBuilder command = new StringBuilder(); 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; } if (ch < 32) // Control character or EOF terminates loop break; command.append((char) ch); expected--; } // Close the socket now that we are done with it try { socket.close(); } catch (IOException e) { // Ignore } // Match against our command string boolean match = command.toString().equals(shutdown); if (match) { log.info(sm.getString("standardServer.shutdownViaPort")); break; } else log.warn("StandardServer.await: Invalid command '" + command.toString() + "' received"); } // Close the server socket and return try { serverSocket.close(); } catch (IOException e) { // Ignore } }
至此，Tomcat启动完毕。很多人可能会问，执行sh shutdown.sh脚本时，是如何与Tomcat进程通信的呢？如果要与Tomcat的ServerSocket通信，socket客户端如何知道服务端的连接地址与端口呢？下面会慢慢说明。
我们停止Tomcat的命令如下：
sh shutdown.sh
所以，将从shell脚本shutdown.sh开始分析Tomcat的停止过程。shutdown.sh的脚本代码见代码清单10。
代码清单10
os400=falsecase "`uname`" inOS400*) os400=true;;esac# resolve links - $0 may be a softlinkPRG="$0"while [ -h "$PRG" ] ; do ls=`ls -ld "$PRG"` link=`expr "$ls" : '.*-> /(.*/)$'` if expr "$link" : '/.*' > /dev/null; then PRG="$link" else PRG=`dirname "$PRG"`/"$link" fidonePRGDIR=`dirname "$PRG"`EXECUTABLE=catalina.sh# Check that target executable existsif $os400; then # -x will Only work on the os400 if the files are: # 1. owned by the user # 2. owned by the PRIMARY group of the user # this will not work if the user belongs in secondary groups evalelse if [ ! -x "$PRGDIR"/"$EXECUTABLE" ]; then echo "Cannot find $PRGDIR/$EXECUTABLE" echo "The file is absent or does not have execute permission" echo "This file is needed to run this program" exit 1 fifiexec "$PRGDIR"/"$EXECUTABLE" stop "$@"
代码清单10和代码清单1非常相似，其中也有两个主要的变量，分别是：
根据最后一行代码：exec "$PRGDIR"/"$EXECUTABLE" stop "$@"，我们知道执行了shell脚本catalina.sh，并且传递参数stop。catalina.sh中接收到stop参数后的执行的脚本分支见代码清单11。
代码清单11
elif [ "$1" = "stop" ] ; then #省略参数校验脚本 eval "/"$_RUNJAVA/"" $LOGGING_MANAGER $JAVA_OPTS / -Djava.endorsed.dirs="/"$JAVA_ENDORSED_DIRS/"" -classpath "/"$CLASSPATH/"" / -Dcatalina.base="/"$CATALINA_BASE/"" / -Dcatalina.home="/"$CATALINA_HOME/"" / -Djava.io.tmpdir="/"$CATALINA_TMPDIR/"" / org.apache.catalina.startup.Bootstrap "$@" stop
从代码清单11可以看出，最终使用java命令执行了org.apache.catalina.startup.Bootstrap类中的main方法，参数是stop。从代码清单3可以看出，当传递参数stop的时候，command等于stop，此时main方法的执行步骤如下：
步骤一 初始化Bootstrap
已经在启动过程分析中介绍， 不再赘述。
步骤二 停止服务
通过调用Bootstrap的stopServer方法（见代码清单12）停止Tomcat，其实质是用反射调用catalinaDaemon（类型是Catalina）的stopServer方法。
代码清单12
/** * Stop the standalone server. */ public void stopServer(String[] arguments) throws Exception { Object param[]; Class<?> paramTypes[]; if (arguments==null || arguments.length==0) { paramTypes = null; param = null; } else { paramTypes = new Class[1]; paramTypes[0] = arguments.getClass(); param = new Object[1]; param[0] = arguments; } Method method = catalinaDaemon.getClass().getMethod("stopServer", paramTypes); method.invoke(catalinaDaemon, param); }
Catalina的stopServer方法（见代码清单13）的执行步骤如下：
代码清单13
public void stopServer() { stopServer(null); } public void stopServer(String[] arguments) { if (arguments != null) { arguments(arguments); } if( getServer() == null ) { // Create and execute our Digester Digester digester = createStopDigester(); digester.setClassLoader(Thread.currentThread().getContextClassLoader()); File file = configFile(); try { InputSource is = new InputSource("file://" + file.getAbsolutePath()); FileInputStream fis = new FileInputStream(file); is.setByteStream(fis); digester.push(this); digester.parse(is); fis.close(); } catch (Exception e) { log.error("Catalina.stop: ", e); System.exit(1); } } // Stop the existing server try { if (getServer().getPort()>0) { Socket socket = new Socket(getServer().getAddress(), getServer().getPort()); OutputStream stream = socket.getOutputStream(); String shutdown = getServer().getShutdown(); for (int i = 0; i < shutdown.length(); i++) stream.write(shutdown.charAt(i)); stream.flush(); stream.close(); socket.close(); } else { log.error(sm.getString("catalina.stopServer")); System.exit(1); } } catch (IOException e) { log.error("Catalina.stop: ", e); System.exit(1); } }
最后，我们看看Catalina的stop方法（见代码清单14）的实现，其执行步骤如下：
代码清单14
/** * Stop an existing server instance. */ public void stop() { try { // Remove the ShutdownHook first so that server.stop() // doesn't get invoked twice if (useShutdownHook) { Runtime.getRuntime().removeShutdownHook(shutdownHook); // If JULI is being used, re-enable JULI's shutdown to ensure // log messages are not lost jiaan LogManager logManager = LogManager.getLogManager(); if (logManager instanceof ClassLoaderLogManager) { ((ClassLoaderLogManager) logManager).setUseShutdownHook( true); } } } catch (Throwable t) { // This will fail on JDK 1.2. Ignoring, as Tomcat can run // fine without the shutdown hook. } // Shut down the server try { getServer().stop(); } catch (LifecycleException e) { log.error("Catalina.stop", e); } }
通过对Tomcat源码的分析我们了解到Tomcat的启动和停止都离不开org.apache.catalina.startup.Bootstrap。当停止Tomcat时，已经启动的Tomcat作为socket服务端，停止脚本启动的Bootstrap进程作为socket客户端向服务端发送shutdown命令，两个进程通过共享server.xml里Server标签的端口以及地址信息打通了socket的通信。
如需转载，请标明本文作者及出处——作者：jiaan.gja，本文原创首发：博客园，原文链接：http://www.VEVb.com/jiaan-geng/p/4872550.html
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