Tomcat源码学习（二）--Tomcat_7.0.70 启动分析
一、运行Tomcat_7.0.70源码
项目build成功后，刷新整个项目，会发现多出一个output目录：java
为了让应用跑起来，能够检查一下output\build\conf下是否已经有配置文件，这些文件实际是从项目根路径conf目录下拷贝过来的。shell
找到BootStarp.java文件，Debug前加入默认的catalina home路径做为启动参数。apache
路径设置为output下build的绝对路径。好比我本身的机器设置的值是-Dcatalina.home="W:\workspace\tc7.0.70\output\build"bootstrap
这样就能够愉快的在文件中加入断点Debug源码分析了。运行以后的效果图： OK，源码到此运行成功，完美~tomcat
二、启动分析
上面运行源码用的BootStarp.java这个类中的main方法（后面再对这个main方法作分析），实际上咱们在用Tomcat的时候,大部分都是使用脚本文件startup.sh、startup.bat、shutdown.sh、shutdown.bat等脚本或者批处理命令来启动Tomcat的.你们必定知道改如何使用它，可是它们到底是如何实现的，下面就一点一点的分析。app
因为在生产环境中，Tomcat通常部署在Linux系统下，因此将以startup.sh和shutdown.sh等shell脚本为准，对Tomcat的启动与中止进行分析。dom
Linux下启动Tomcat的命令：socket
sh startup.sh
下面将从shell脚本startup.sh开始分析Tomcat的启动过程。ide
startup.sh脚本代码清单：oop
# Better OS/400 detection: see Bugzilla 31132 os400=false case "`uname`" in OS400*) os400=true;; esac # resolve links - $0 may be a softlink PRG="$0" while [ -h "$PRG" ] ; do ls=`ls -ld "$PRG"` link=`expr "$ls" : '.*-> \(.*\)$'` if expr "$link" : '/.*' > /dev/null; then PRG="$link" else PRG=`dirname "$PRG"`/"$link" fi done PRGDIR=`dirname "$PRG"` EXECUTABLE=catalina.sh # Check that target executable exists if $os400; then # -x will Only work on the os400 if the files are: # 1. owned by the user # 2. owned by the PRIMARY group of the user # this will not work if the user belongs in secondary groups eval else if [ ! -x "$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 fi fi exec "$PRGDIR"/"$EXECUTABLE" start "$@"
从代码清单能够看出有两个主要的变量，分别是：
1. PRGDIR：当前shell脚本所在的路径； 2. EXECUTABLE：脚本catalina.sh。
exec "$PRGDIR"/"$EXECUTABLE" start "$@" 咱们知道执行了shell脚本catalina.sh，而且传递参数start。
catalina.sh 脚本代码（部分）清单：
shift touch "$CATALINA_OUT" if [ "$1" = "-security" ] ; then if [ $have_tty -eq 1 ]; then echo "Using Security Manager" fi shift eval $_NOHUP "\"$_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 $_NOHUP "\"$_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."
从上面能够看出，脚本最终使用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方法的实现以下：
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")) {
//传递参数为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);
}
}
当传递参数start的时候，command等于start，此时main方法的执行步骤以下：
-
初始化Bootstrap
public void init() throws Exception{ // Set Catalina path setCatalinaHome(); //1.设置Catalina路径，默认为Tomcat的根目录 setCatalinaBase(); initClassLoaders();//2.初始化Tomcat的类加载器 Thread.currentThread().setContextClassLoader(catalinaLoader);//3.并设置线程上下文类加载器 SecurityClassLoad.securityClassLoad(catalinaLoader); // Load our startup class and call its process() method if (log.isDebugEnabled()) log.debug("Loading startup class"); //4.用反射实例化org.apache.catalina.startup.Catalina对象，而且使用反射调用其setParentClassLoader方法，给Catalina对象设置Tomcat类加载体系的顶级加载器（Java自带的三种类加载器除外） 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; } -
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：
/** * 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);//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。 if (log.isDebugEnabled()) log.debug("Calling startup class " + method); method.invoke(catalinaDaemon, param); }
备注：如何加载和解析server.xml配置文件，后面会博客会陆续给出。
-
启动Tomcat
当传递参数start的时候，调用Bootstrap的load方法以后会接着调用start方法：
/** * Start the Catalina daemon. */ public void start() throws Exception { if( catalinaDaemon==null ) init(); Method method = catalinaDaemon.getClass().getMethod("start", (Class [] )null);//启动Tomcat，此方法实际是用反射调用了catalinaDaemon（类型是Catalina）的start方法 method.invoke(catalinaDaemon, (Object [])null); }
Catalina的start方法以下：
/**
* Start a new server instance.
*/
public void start() {
//1.验证Server容器是否已经实例化
if (getServer() == null) {
load(); //若是没有实例化Server容器，还会再次调用Catalina的load方法加载和解析server.xml，这也说明Tomcat只容许Server容器经过配置在server.xml的方式生成，用户也能够本身实现Server接口建立自定义的Server容器以取代默认的StandardServer。
}
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(); //2.启动Server容器
} 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();//3.设置关闭钩子
}
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();//4.最后调用Catalina的await方法循环等待接收Tomcat的shutdown命令
stop();//5.若是Tomcat运行正常且没有收到shutdown命令，是不会向下执行此方法的，当接收到shutdown命令，Catalina的await方法会退出循环等待，而后顺序执行stop方法中止Tomcat
}
}
Catalina的await方法实际只是代理执行了Server容器的await方法。
/**
* Await and shutdown.
*/
public void await() {
getServer().await();
}
以Server的默认实现StandardServer为例，其await方法以下：
@Override
public void await() {
// Negative values - don't wait on port - tomcat is embedded or we just don't like ports
if( port == -2 ) {
// undocumented yet - for embedding apps that are around, alive.
return;
}
if( port==-1 ) {
try {
awaitThread = Thread.currentThread();
while(!stopAwait) {
try {
Thread.sleep( 10000 );
} catch( InterruptedException ex ) {
// continue and check the flag
}
}
} finally {
awaitThread = null;
}
return;
}
// Set up a server socket to wait on
try {
awaitSocket = new ServerSocket(port, 1,
InetAddress.getByName(address));//建立socket链接的服务端对象ServerSocket
} 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) {
ServerSocket serverSocket = awaitSocket;
if (serverSocket == null) {
break;
}
// Wait for the next connection
Socket socket = null;
StringBuilder command = new StringBuilder();//建立一个对象循环接收socket中的字符
try {
InputStream stream;
long acceptStartTime = System.currentTimeMillis();
try {
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;
}
// Read a set of characters from the socket
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--;
}
} finally {
// Close the socket now that we are done with it
try {
if (socket != null) {
socket.close();
}
} catch (IOException e) {
// Ignore
}
}
// Match against our command string
boolean match = command.toString().equals(shutdown);
if (match) { //若是接收到的命令与SHUTDOWN匹配（因为使用了equals，因此shutdown命令必须是大写的），那么退出循环等待
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 {
serverSocket.close();
} catch (IOException e) {
// Ignore
}
}
}
}
至此，Tomcat启动完毕。
备注：如何启动server，这里不作过多解释，后面会有专门的博客介绍《容器启动过程分析》。
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