Tomcat源码---启动.初始化(加载类包)分析三

24cun_cn

　　一,启动
　　Tomcat是从org.apache.catalina.startup.Bootstrap#main()开始启动.代码如下:

  public static void main(String args[]) {
if (daemon == null) {
daemon = new Bootstrap();
try {
daemon.init();
} catch (Throwable t) {
t.printStackTrace();
return;
}
}
try {
String command = "start";
if (args.length > 0) {
command = args[args.length - 1];
}
if (command.equals("startd")) {
args[0] = "start";
daemon.load(args);
daemon.start();
} else if (command.equals("stopd")) {
args[0] = "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();
}
}
　　从以上可以很清楚的看懂tomcat是通过参数的不同进行相应的命令调用.
　　启动之前要进行相应的init()初始化,进行相应的环境设置以及包的加,以下我们查看下init的方法.
　　二,初始化(Bootstrap#init())

public void init()throws Exception
{
// Set Catalina path
setCatalinaHome();
setCatalinaBase();
//将tomcat/lib下的jar包进行加载
initClassLoaders();
//将classload设置进线程,以便我们使用时进行调用
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();
// 将sharedLoader设置进Catalina类中
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;
}

　　从以上的初始化我们对他一一进行分析
　　1,

setCatalinaHome();
setCatalinaBase();
　　根据源代码主要设置了以下路径:
　　System.setProperty("catalina.home", System.getProperty("user.dir"));
　　2,

    //将tomcat/lib下的jar包进行加载
initClassLoaders();
　　tomcat中的加载方式是:
　　a) Set up classloaders 
　　commonLoader (common)-> System Loader
　　sharedLoader (shared)-> commonLoader -> System Loader
　　catalinaLoader(server) -> commonLoader -> System Loader

    private void initClassLoaders() {
try {
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();
}
catalinaLoader = createClassLoader("server", commonLoader);
sharedLoader = createClassLoader("shared", commonLoader);
} catch (Throwable t) {
log.error("Class loader creation threw exception", t);
System.exit(1);
}
}
 　　createClassLoader的加载方式:
　　//这个类的主要作用是从  catalina.properties读取信息进行加载

private ClassLoader createClassLoader(String name, ClassLoader parent)
throws Exception {
// 获取与ClassLoader相关的属性值，可能为 common.loader,server.loader, shared.loader  
// 定义在org/apache/catalina/startup/catalina.properties  
String value = CatalinaProperties.getProperty(name + ".loader");
if ((value == null) || (value.equals("")))
return parent;
ArrayList repositoryLocations = new ArrayList();
ArrayList repositoryTypes = new ArrayList();
int i;
StringTokenizer tokenizer = new StringTokenizer(value, ",");
while (tokenizer.hasMoreElements()) {
String repository = tokenizer.nextToken();
// Local repository
boolean replace = false;
String before = repository;
while ((i=repository.indexOf(CATALINA_HOME_TOKEN))>=0) {
replace=true;
if (i>0) {
repository = repository.substring(0,i) + getCatalinaHome()
+ repository.substring(i+CATALINA_HOME_TOKEN.length());
} else {
repository = getCatalinaHome()
+ repository.substring(CATALINA_HOME_TOKEN.length());
}
}
while ((i=repository.indexOf(CATALINA_BASE_TOKEN))>=0) {
replace=true;
if (i>0) {
repository = repository.substring(0,i) + getCatalinaBase()
+ repository.substring(i+CATALINA_BASE_TOKEN.length());
} else {
repository = getCatalinaBase()
+ repository.substring(CATALINA_BASE_TOKEN.length());
}
}
if (replace && log.isDebugEnabled())
log.debug("Expanded " + before + " to " + replace);
// Check for a JAR URL repository
try {
URL url=new URL(repository);
repositoryLocations.add(repository);
repositoryTypes.add(ClassLoaderFactory.IS_URL);
continue;
} catch (MalformedURLException e) {
// Ignore
}
if (repository.endsWith("*.jar")) {
repository = repository.substring
(0, repository.length() - "*.jar".length());
repositoryLocations.add(repository);
repositoryTypes.add(ClassLoaderFactory.IS_GLOB);
} else if (repository.endsWith(".jar")) {
repositoryLocations.add(repository);
repositoryTypes.add(ClassLoaderFactory.IS_JAR);
} else {
repositoryLocations.add(repository);
repositoryTypes.add(ClassLoaderFactory.IS_DIR);
}
}
String[] locations = (String[]) repositoryLocations.toArray(new String[0]);
Integer[] types = (Integer[]) repositoryTypes.toArray(new Integer[0]);
ClassLoader classLoader = ClassLoaderFactory.createClassLoader
(locations, types, parent);
// Retrieving MBean server
MBeanServer mBeanServer = null;
if (MBeanServerFactory.findMBeanServer(null).size() > 0) {
mBeanServer =
(MBeanServer) MBeanServerFactory.findMBeanServer(null).get(0);
} else {
mBeanServer = MBeanServerFactory.createMBeanServer();
}
///用jmx对该classloader进行管理
// Register the server classloader
ObjectName objectName =
new ObjectName("Catalina:type=ServerClassLoader,name=" + name);
mBeanServer.registerMBean(classLoader, objectName);
return classLoader;
}
 　　根据以上的设置tomcat主要对类加载作了以下方式:
　　b) Load startup class (reflection)
　　org.apache.catalina.startup.Catalina
　　setParentClassloader -> sharedLoader
　　Thread.contextClassloader -> catalinaLoader
　　---------------------------------------------------------------------------------------------------------------------------
　　以下对java中的类加载进行归纳:
　　可参考文章:http://blog.chenlb.com/2009/06/java-classloader-architecture.html
　　以上用线程设置classloader的目的是:
　　java默认的线程上下文类加载器是 系统类加载器(AppClassLoader)。
　　使用Thread.currentThread().setContextClassLoader(classloader)时，线程上下文
Classloader就变成了指定的Classloader了。此时，在本线程或子线程的任意一处地方，调用Thread.currentThread().
getContextClassLoader()，都可以得到前面设置的Classloader。
　　如果要扩展classloader对类包进行加载也可扩展URLCloassLoader类