tomcat 源码分析之初始化

顺德公农庄

　　tomcat 初始化可以从启动类Bootstrap入手它的main方法

  public static void main(String args[]) {
if (daemon == null) {
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);
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);
}
}
从上面的方法我们可以看出先进行tomcat的初始化然后根据命令启动tomcat
public void init()
throws Exception
{
setCatalinaHome();
setCatalinaBase();
//初始化类加载器
initClassLoaders();
设置当前类加载器为catalinaLoader      
Thread.currentThread().setContextClassLoader(catalinaLoader);
SecurityClassLoad.securityClassLoad(catalinaLoader);

if (log.isDebugEnabled())
log.debug("Loading startup class");
//获取Catalina类实例
Class<?> startupClass =
catalinaLoader.loadClass
("org.apache.catalina.startup.Catalina");
Object startupInstance = startupClass.newInstance();
//
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);
//通过反射设置Catalina 的父加载器为shareLoader
method.invoke(startupInstance, paramValues);
catalinaDaemon = startupInstance;
}
//我们看下上面几个类加载器的初始化
private void initClassLoaders() {
try {
//这个加载器会加载tomcat 下面的lib
//common.loader=${catalina.base}/lib,${catalina.base}/lib/*.jar,${catalina.home}/lib,${catalina.home}/lib/*.jar
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();
}
//父加载器为 commonLoader         
catalinaLoader = createClassLoader("server", commonLoader);
sharedLoader = createClassLoader("shared", commonLoader);
} catch (Throwable t) {
handleThrowable(t);
log.error("Class loader creation threw exception", t);
System.exit(1);
}
}

     接下来会根据参数调catalina的start（）方法


public void start() {
if (getServer() == null) {
//创建Server
load();
}
if (getServer() == null) {
log.fatal("Cannot start server. Server instance is not configured.");
return;
}
long t1 = System.nanoTime();
try {
getServer().start();
} 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");
}
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();
stop();
}
}
 上面主要做的功能室 初始化Server，然后启动Server，再注册CatalinaShutdownHook，在jvm关闭前执行一些操作我们来看下load（）方法

public void load() {
long t1 = System.nanoTime();
initDirs();
// Before digester - it may be needed
initNaming();
// Digester类是解析Server.xml准备的类，根据规则解析
Digester digester = createStartDigester();
InputSource inputSource = null;
InputStream inputStream = null;
File file = null;
try {
//获取tomcat conf文件下的Server.xml配置文件
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 {
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);
开始解析server.xml
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
}
}
getServer().setCatalina(this);
// Stream redirection
initStreams();
try {
初始化Server
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");
}
}