Tomcat源碼學習（二）--Tomcat_7.0.70 啓動分析
一、運行Tomcat_7.0.70源碼
項目build成功後，刷新整個項目，會發現多出一個output目錄：java
爲了讓應用跑起來，能夠檢查一下output\build\conf下是否已經有配置文件，這些文件實際是從項目根路徑conf目錄下拷貝過來的。shell
找到BootStarp.java文件，Debug前加入默認的catalina home路徑做爲啓動參數。apache
路徑設置爲output下build的絕對路徑。好比我本身的機器設置的值是-Dcatalina.home="W:\workspace\tc7.0.70\output\build"bootstrap
這樣就能夠愉快的在文件中加入斷點Debug源碼分析了。運行以後的效果圖： OK，源碼到此運行成功，完美~tomcat
二、啓動分析
上面運行源碼用的BootStarp.java這個類中的main方法（後面再對這個main方法作分析），實際上咱們在用Tomcat的時候,大部分都是使用腳本文件startup.sh、startup.bat、shutdown.sh、shutdown.bat等腳本或者批處理命令來啓動Tomcat的.你們必定知道改如何使用它，可是它們到底是如何實現的，下面就一點一點的分析。app
因爲在生產環境中，Tomcat通常部署在Linux系統下，因此將以startup.sh和shutdown.sh等shell腳本爲準，對Tomcat的啓動與中止進行分析。dom
Linux下啓動Tomcat的命令：socket
sh startup.sh
下面將從shell腳本startup.sh開始分析Tomcat的啓動過程。ide
startup.sh腳本代碼清單：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 "$@"
從代碼清單能夠看出有兩個主要的變量，分別是：
1. PRGDIR：當前shell腳本所在的路徑； 2. EXECUTABLE：腳本catalina.sh。
exec "$PRGDIR"/"$EXECUTABLE" start "$@" 咱們知道執行了shell腳本catalina.sh，而且傳遞參數start。
catalina.sh 腳本代碼（部分）清單：
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."
從上面能夠看出，腳本最終使用java命令執行了org.apache.catalina.startup.Bootstrap類中的main方法，參數也是start。Bootstrap的main方法的實現以下：
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")) {
//傳遞參數爲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);
}
}
當傳遞參數start的時候，command等於start，此時main方法的執行步驟以下：
-
初始化Bootstrap
public void init() throws Exception{ // Set Catalina path setCatalinaHome(); //1.設置Catalina路徑，默認爲Tomcat的根目錄 setCatalinaBase(); initClassLoaders();//2.初始化Tomcat的類加載器 Thread.currentThread().setContextClassLoader(catalinaLoader);//3.並設置線程上下文類加載器 SecurityClassLoad.securityClassLoad(catalinaLoader); // Load our startup class and call its process() method if (log.isDebugEnabled()) log.debug("Loading startup class"); //4.用反射實例化org.apache.catalina.startup.Catalina對象，而且使用反射調用其setParentClassLoader方法，給Catalina對象設置Tomcat類加載體系的頂級加載器（Java自帶的三種類加載器除外） 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; } -
加載、解析server.xml配置文件
當傳遞參數start的時候，會調用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);//用反射調用catalinaDaemon（類型是Catalina）的load方法加載和解析server.xml配置文件。 if (log.isDebugEnabled()) log.debug("Calling startup class " + method); method.invoke(catalinaDaemon, param); }
備註：如何加載和解析server.xml配置文件，後面會博客會陸續給出。
-
啓動Tomcat
當傳遞參數start的時候，調用Bootstrap的load方法以後會接着調用start方法：
/** * Start the Catalina daemon. */ public void start() throws Exception { if( catalinaDaemon==null ) init(); Method method = catalinaDaemon.getClass().getMethod("start", (Class [] )null);//啓動Tomcat，此方法實際是用反射調用了catalinaDaemon（類型是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.驗證Server容器是否已經實例化
if (getServer() == null) {
load(); //若是沒有實例化Server容器，還會再次調用Catalina的load方法加載和解析server.xml，這也說明Tomcat只容許Server容器經過配置在server.xml的方式生成，用戶也能夠本身實現Server接口建立自定義的Server容器以取代默認的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.啓動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.設置關閉鉤子
}
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.最後調用Catalina的await方法循環等待接收Tomcat的shutdown命令
stop();//5.若是Tomcat運行正常且沒有收到shutdown命令，是不會向下執行此方法的，當接收到shutdown命令，Catalina的await方法會退出循環等待，而後順序執行stop方法中止Tomcat
}
}
Catalina的await方法實際只是代理執行了Server容器的await方法。
/**
* Await and shutdown.
*/
public void await() {
getServer().await();
}
以Server的默認實現StandardServer爲例，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鏈接的服務端對象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();//建立一個對象循環接收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) { //若是接收到的命令與SHUTDOWN匹配（因爲使用了equals，因此shutdown命令必須是大寫的），那麼退出循環等待
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啓動完畢。
備註：如何啓動server，這裏不作過多解釋，後面會有專門的博客介紹《容器啓動過程分析》。
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