标签：tomcat源码
Catalina的作用是初始化各个组件，并开始启动各个组件。3，初始化命名空间(tomcat会使用JNDI技术，比如在server.xml中配置了数据库连接池的话，就使用了JNDI)。最后还包装了System.out和System.err。
这里面的重点就是Digester解析server.xml的过程，先来看看start方法：
public void start() {
//这里剔除了一些判断，日志，服务器钩子函数，等代码
......
if (getServer() == null) {
load();
}
......
getServer().start();
if (await) {
await();
stop();
}
} public void load() {
//这个方法的篇幅过长，我踢掉一些对流程不重要的代码
Digester digester = createStartDigester();
InputSource inputSource = null;
InputStream inputStream = null;
File file = null;
try {
//获取sever.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);
}
}
//将sever.xml对应的流传给digester，由digester解析它。
inputSource.setByteStream(inputStream);
//这个方法很重要，它将自己也就是Catalina这个对象放到了digester对象里的一个栈里面，后面解析xml实例化server后
//会从栈里拿出Catalina对象调用它的setServer方法来设置Catalina.server属性。server里的service属性也是通过这种形式
//设置的。
digester.push(this);
digester.parse(inputSource);
//server实例化后,将设置server.catalina属性，这里Catalina和Server是双向关联的。
getServer().setCatalina(this);
// 包装了System.out和System.err
initStreams();
getServer().init();
}
/**
* Create and configure the Digester we will be using for startup.
*/
protected Digester createStartDigester() {
Digester digester = new Digester();
digester.addObjectCreate("Server",
"org.apache.catalina.core.StandardServer",
"className");
digester.addSetProperties("Server");
digester.addSetNext("Server",
"setServer",
"org.apache.catalina.Server");
digester.addObjectCreate("Server/GlobalNamingResources",
"org.apache.catalina.deploy.NamingResources");
digester.addSetProperties("Server/GlobalNamingResources");
digester.addSetNext("Server/GlobalNamingResources",
"setGlobalNamingResources",
"org.apache.catalina.deploy.NamingResources");
digester.addObjectCreate("Server/Listener",
null, // MUST be specified in the element
"className");
digester.addSetProperties("Server/Listener");
digester.addSetNext("Server/Listener",
"addLifecycleListener",
"org.apache.catalina.LifecycleListener");
digester.addObjectCreate("Server/Service",
"org.apache.catalina.core.StandardService",
"className");
digester.addSetProperties("Server/Service");
digester.addSetNext("Server/Service",
"addService",
"org.apache.catalina.Service");
digester.addObjectCreate("Server/Service/Listener",
null, // MUST be specified in the element
"className");
digester.addSetProperties("Server/Service/Listener");
digester.addSetNext("Server/Service/Listener",
"addLifecycleListener",
"org.apache.catalina.LifecycleListener");
//Executor
digester.addObjectCreate("Server/Service/Executor",
"org.apache.catalina.core.StandardThreadExecutor",
"className");
digester.addSetProperties("Server/Service/Executor");
digester.addSetNext("Server/Service/Executor",
"addExecutor",
"org.apache.catalina.Executor");
digester.addRule("Server/Service/Connector",
new ConnectorCreateRule());
digester.addRule("Server/Service/Connector",
new SetAllPropertiesRule(new String[]{"executor"}));
digester.addSetNext("Server/Service/Connector",
"addConnector",
"org.apache.catalina.connector.Connector");
digester.addObjectCreate("Server/Service/Connector/Listener",
null, // MUST be specified in the element
"className");
digester.addSetProperties("Server/Service/Connector/Listener");
digester.addSetNext("Server/Service/Connector/Listener",
"addLifecycleListener",
"org.apache.catalina.LifecycleListener");
// Add RuleSets for nested elements
digester.addRuleSet(new NamingRuleSet("Server/GlobalNamingResources/"));
digester.addRuleSet(new EngineRuleSet("Server/Service/"));
digester.addRuleSet(new HostRuleSet("Server/Service/Engine/"));
digester.addRuleSet(new ContextRuleSet("Server/Service/Engine/Host/"));
addClusterRuleSet(digester, "Server/Service/Engine/Host/Cluster/");
digester.addRuleSet(new NamingRuleSet("Server/Service/Engine/Host/Context/"));
// When the 'engine' is found, set the parentClassLoader.
digester.addRule("Server/Service/Engine",
new SetParentClassLoaderRule(parentClassLoader));
addClusterRuleSet(digester, "Server/Service/Engine/Cluster/");
return (digester);
}digester实例化Server时是实例化了它的子类StanderServer。
进入addObjectCreate方法：
public void addObjectCreate(String pattern, String className,
String attributeName) {
addRule(pattern,
new ObjectCreateRule(className, attributeName));
}
每调用一个add*方法都为pattern映射了一个Rule的子类，addSetProperties，addSetNext都为pattern映射了一个Rule的子类。
这个映射关系被存放在RulesBase.cache中：
public class RulesBase implements Rules {
protected HashMap<String,List<Rule>> cache =
new HashMap<String,List<Rule>>();
}public abstract class Rule {
public Digester getDigester() {
return (this.digester);
}
public void begin(String namespace, String name, Attributes attributes)
throws Exception {
begin(attributes);
}
public void end(String namespace, String name)
throws Exception {
end();
}
} digester.addObjectCreate("Server",
"org.apache.catalina.core.StandardServer",
"className");
digester.addSetProperties("Server");
digester.addSetNext("Server",
"setServer",
"org.apache.catalina.Server"); public void begin(String namespace, String name, Attributes attributes)
throws Exception {
Class<?> clazz = digester.getClassLoader().loadClass(realClassName);
Object instance = clazz.newInstance();
digester.push(instance);
} @Override
public void end(String namespace, String name) throws Exception {
Object child = digester.peek(0);
Object parent = digester.peek(1);
if (digester.log.isDebugEnabled()) {
if (parent == null) {
digester.log.debug("[SetNextRule]{" + digester.match +
"} Call [NULL PARENT]." +
methodName + "(" + child + ")");
} else {
digester.log.debug("[SetNextRule]{" + digester.match +
"} Call " + parent.getClass().getName() + "." +
methodName + "(" + child + ")");
}
}
IntrospectionUtils.callMethod1(parent, methodName,
child, paramType, digester.getClassLoader());
}在调用这个方法前，degister的成员变量stack已经push和pop好几个对象了，每次标签开始解析时创建对象push到stack里面，标签结束后从stack里pop出来。因为<Server>标签是顶层标签，所以server对象最先被创建并push到stack里面（Catalina一直在栈底），最后被pop出来，所以结束标签</server>解析时和开始一样，stack依然还是两个元素，server在栈顶，Catalina在栈底。 Object child = digester.peek(0);Object
parent = digester.peek(1);分别取出了栈顶和栈底的元素。server.xml的解析不是很好叙述，它的关系有点复杂。要记住一点server.xml的每一级标签对应一个tomcat组件,被外层标签包裹的标签是外层标签的一个属性比如serveice是server的一个属性。xml在被解析时会根据当前的事件（开始，或结束）来调用对应节点的解析规则，创建对象，并通过栈来完成对象之间的关联关系。标签：tomcat源码
原文地址：http://blog.csdn.net/ilovezhangxian/article/details/40827195
