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1. tomcat类加载思维导向图
2. java 类加载思维导向图
3. tomcat类加载顺序
当应用需要到某个类时，则会按照下面的顺序进行类加载：
1 使用bootstrap引导类加载器加载，加载jvm所需的基础类
2 使用system系统类加载器加载，加载tomcat启动类等相关
3 使用应用类加载器在WEB-INF/classes中加载，加载部署的项目
4 使用应用类加载器在WEB-INF/lib中加载，加载部署的项目依赖的jar
5 使用common类加载器在CATALINA_HOME/lib中加载, 加载tomcat依赖的一些通用jar，例如servlet.jart
4. tomcat所有的加载器
5. 源码分析
tomcat启动类 Bootstrap
涉及类加载器
ClassLoader commonLoader = null;
ClassLoader catalinaLoader = null;
ClassLoader sharedLoader = null;
类加载器初始化
从main方法开始
public static void main(String args[]) {
synchronized (daemonLock) {
if (daemon == null) {
// Don't set daemon until init() has completed
Bootstrap bootstrap = new Bootstrap();
try {
// 初始化
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();
// 启动
} else if (command.equals("start")) {
daemon.setAwait(true);
daemon.load(args);
daemon.start();
if (null == daemon.getServer()) {
System.exit(1);
}
} 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);
}
}
start启动之后，调用start()方法
/**
* Start the Catalina daemon.
* @throws Exception Fatal start error
*/
public void start() throws Exception {
if (catalinaDaemon == null) {
init();
}
Method method = catalinaDaemon.getClass().getMethod("start", (Class [])null);
method.invoke(catalinaDaemon, (Object [])null);
}
调用Init()方法
/**
* Initialize daemon.
* @throws Exception Fatal initialization error
*/
public void init() throws Exception {
initClassLoaders();
// 打破双亲委托加载机制
Thread.currentThread().setContextClassLoader(catalinaLoader);
SecurityClassLoad.securityClassLoad(catalinaLoader);
// Load our startup class and call its process() method
if (log.isDebugEnabled())
log.debug("Loading startup class");
// 初始化Catalina
Class<?> startupClass = catalinaLoader.loadClass("org.apache.catalina.startup.Catalina");
Object startupInstance = startupClass.getConstructor().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;
}
private void initClassLoaders() {
try {
// 先初始化CommonLoader
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();
}
// CommonLoader为parent类加载器
catalinaLoader = createClassLoader("server", commonLoader);
// CommonLoader为parent类加载器
sharedLoader = createClassLoader("shared", commonLoader);
} catch (Throwable t) {
handleThrowable(t);
log.error("Class loader creation threw exception", t);
System.exit(1);
}
}
此处给出类加载器的关系
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