tomcat源码分析系列之启动---暗度陈仓

xuanhao

　　
前面我们分析了tomcat是如何启动的，但我们好像并没有看到我们期待发生的诸如在什么地方启动了服务，什么地方启动了监听，好像只是做了些加载资源、设置环境变量等鸡毛蒜皮的事，这到底是怎么回事？我们回顾一下前面提到的一个函数：解析server.xml的函数




protected Digester createStartDigester() {
long t1=System.currentTimeMillis();
// Initialize the digester
Digester digester = new Digester();
digester.setValidating(false);
digester.setRulesValidation(true);
HashMap<Class<?>, List<String>> fakeAttributes =
new HashMap<Class<?>, List<String>>();
ArrayList<String> attrs = new ArrayList<String>();
attrs.add("className");
fakeAttributes.put(Object.class, attrs);
digester.setFakeAttributes(fakeAttributes);
digester.setClassLoader(StandardServer.class.getClassLoader());
// Configure the actions we will be using
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/"));
digester.addRuleSet(new ClusterRuleSet("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));
digester.addRuleSet(new ClusterRuleSet("Server/Service/Engine/Cluster/"));
long t2=System.currentTimeMillis();
if (log.isDebugEnabled())
log.debug("Digester for server.xml created " + ( t2-t1 ));
return (digester);
}
　　在前面我们并没有详细去看这个函数，只是知道它解析了server.xml文件，现在我们深入这个方法看一下。这个方法里反复调用了下面三个方法：

addObjectCreate，addSetProperties，addSetNext
　　我们看一下这三个方法到底做了些什么。

/**
* Add an "object create" rule for the specified parameters.
*添加一个“创建对象”的规则
* @param pattern Element matching pattern 匹配模式
* @param className Default Java class name to be created 默认要实例的java类
* @param attributeName Attribute name that optionally overrides
*  the default Java class name to be created
* @see ObjectCreateRule
*/
public void addObjectCreate(String pattern, String className,
String attributeName) {
addRule(pattern,
new ObjectCreateRule(className, attributeName));
}
　　这个方法就是定义了一个创建对象的规则：匹配的规则（遇到server.xml里什么样的表达式），默认要实例化的类名，默认的一个属性名（xml配置属性）。就是说如果server.xml里遇到跟规则相匹配的项，如果没有设定指定attributeName属性的值，则使用这里设置的默认的类。

/**
* Add a "set properties" rule for the specified parameters.
*
* @param pattern Element matching pattern
* @see SetPropertiesRule
*/
public void addSetProperties(String pattern) {
addRule(pattern,
new SetPropertiesRule());
}
　　定义了一个调用setter方法的规则：把这个值设置给谁

/**
* Add a "set next" rule for the specified parameters.
*
* @param pattern Element matching pattern
* @param methodName Method name to call on the parent element
* @param paramType Java class name of the expected parameter type
*  (if you wish to use a primitive type, specify the corresponding
*  Java wrapper class instead, such as <code>java.lang.Boolean</code>
*  for a <code>boolean</code> parameter)
* @see SetNextRule
*/
public void addSetNext(String pattern, String methodName,
String paramType) {
addRule(pattern,
new SetNextRule(methodName, paramType));
}
　　这个方法很关键，第一个参数依旧是匹配的规则，第二个参数是要调用父元素的方法名，第三个参数是方法需要的参数类型。看到这个我们或许明白了点。我们再回头看下前面提到的方法：

digester.addObjectCreate("Server",
"org.apache.catalina.core.StandardServer",
"className");
digester.addSetProperties("Server");
digester.addSetNext("Server",
"setServer",
"org.apache.catalina.Server");
　　上面这几句话就是说，遇到Server，如果没有设置className属性，就实例化org.apache.catalina.core.StandardServer的一个对象（如果设置了className,就使用设置的Class），把这个对象赋值给Catalina的server属性（调用server的setter方法）。

digester.addObjectCreate("Server/GlobalNamingResources",
"org.apache.catalina.deploy.NamingResources");
digester.addSetProperties("Server/GlobalNamingResources");
digester.addSetNext("Server/GlobalNamingResources",
"setGlobalNamingResources",
"org.apache.catalina.deploy.NamingResources");
　　匹配到server的下级节点： GlobalNamingResources，就创建一个org.apache.catalina.deploy.NamingResources的实例，调用server的setGlobalNamingResources方法。其他的类似，再次不一一赘述。但有一个方法我们不能漏掉：StandardServer下的addService方法（StandardService下的addExecutor方法、StandardServic下的addConnector方法与它类似）：

/**
* Add a new Service to the set of defined Services.
*
* @param service The Service to be added
*/
@Override
public void addService(Service service) {
service.setServer(this);
synchronized (services) {
Service results[] = new Service[services.length + 1];
System.arraycopy(services, 0, results, 0, services.length);
results[services.length] = service;
services = results;
if (getState().isAvailable()) {
try {
service.start();
} catch (LifecycleException e) {
// Ignore
}
}
// Report this property change to interested listeners
support.firePropertyChange("service", null, service);
}
}

　　这个方法除了调用setter外，还做了一件重要的事情： service.start();这个start方法属于Lifecycle接口，在LifecycleBase里实现，

@Override
public final synchronized void init() throws LifecycleException {
if (!state.equals(LifecycleState.NEW)) {
invalidTransition(Lifecycle.BEFORE_INIT_EVENT);
}
setStateInternal(LifecycleState.INITIALIZING, null, false);
try {
initInternal();
} catch (LifecycleException e) {
setStateInternal(LifecycleState.FAILED, null, false);
throw e;
}
setStateInternal(LifecycleState.INITIALIZED, null, false);
}

protected abstract void initInternal() throws LifecycleException;
/**
* {@inheritDoc}
*/
@Override
public final synchronized void start() throws LifecycleException {
if (LifecycleState.STARTING_PREP.equals(state) ||
LifecycleState.STARTING.equals(state) ||
LifecycleState.STARTED.equals(state)) {
if (log.isDebugEnabled()) {
Exception e = new LifecycleException();
log.debug(sm.getString("lifecycleBase.alreadyStarted",
toString()), e);
} else if (log.isInfoEnabled()) {
log.info(sm.getString("lifecycleBase.alreadyStarted",
toString()));
}
return;
}
if (state.equals(LifecycleState.NEW)) {
init();
} else if (!state.equals(LifecycleState.INITIALIZED) &&
!state.equals(LifecycleState.STOPPED)) {
invalidTransition(Lifecycle.BEFORE_START_EVENT);
}
setStateInternal(LifecycleState.STARTING_PREP, null, false);
try {
startInternal();
} catch (LifecycleException e) {
setStateInternal(LifecycleState.FAILED, null, false);
throw e;
}
if (state.equals(LifecycleState.FAILED) ||
state.equals(LifecycleState.MUST_STOP)) {
stop();
} else {
// Shouldn't be necessary but acts as a check that sub-classes are
// doing what they are supposed to.
if (!state.equals(LifecycleState.STARTING)) {
invalidTransition(Lifecycle.AFTER_START_EVENT);
}
setStateInternal(LifecycleState.STARTED, null, false);
}
}

/**
* Sub-classes must ensure that the state is changed to
* {@link LifecycleState#STARTING} during the execution of this method.
* Changing state will trigger the {@link Lifecycle#START_EVENT} event.
*
* If a component fails to start it may either throw a
* {@link LifecycleException} which will cause it's parent to fail to start
* or it can place itself in the error state in which case {@link #stop()}
* will be called on the failed component but the parent component will
* continue to start normally.
*
* @throws LifecycleException
*/
protected abstract void startInternal() throws LifecycleException;


　　
LifecycleBase的start方法是一个典型的Template Method 模式。在分析这个之前，我先看一下类关系图：

　　LifecycleBase最后又调用个实现类里的initInternal和startInternal方法，所以我们只需要看具体类里的这两个方法就可以了。
　　StandardService里的initInternal

/**
* Invoke a pre-startup initialization. This is used to allow connectors
* to bind to restricted ports under Unix operating environments.
*/
@Override
protected void initInternal() throws LifecycleException {
super.initInternal();
if (container != null) {
container.init();
}
// Initialize any Executors
for (Executor executor : findExecutors()) {
if (executor instanceof LifecycleMBeanBase) {
((LifecycleMBeanBase) executor).setDomain(getDomain());
}
executor.init();
}
// Initialize our defined Connectors
synchronized (connectors) {
for (Connector connector : connectors) {
try {
connector.init();
} catch (Exception e) {
String message = sm.getString(
"standardService.connector.initFailed", connector);
log.error(message, e);
if (Boolean.getBoolean("org.apache.catalina.startup.EXIT_ON_INIT_FAILURE"))
throw new LifecycleException(message);
}
}
}
}

　　startInternal

/**
* Start nested components ({@link Executor}s, {@link Connector}s and
* {@link Container}s) and implement the requirements of
* {@link org.apache.catalina.util.LifecycleBase#startInternal()}.
*
* @exception LifecycleException if this component detects a fatal error
*  that prevents this component from being used
*/
@Override
protected void startInternal() throws LifecycleException {
if(log.isInfoEnabled())
log.info(sm.getString("standardService.start.name", this.name));
setState(LifecycleState.STARTING);
// Start our defined Container first
if (container != null) {
synchronized (container) {
container.start();
}
}
synchronized (executors) {
for (Executor executor: executors) {
executor.start();
}
}
// Start our defined Connectors second
synchronized (connectors) {
for (Connector connector: connectors) {
try {
// If it has already failed, don't try and start it
if (connector.getState() != LifecycleState.FAILED) {
connector.start();
}
} catch (Exception e) {
log.error(sm.getString(
"standardService.connector.startFailed",
connector), e);
}
}
}
}
　　init和start的顺序都是这样的：Catalina->Server->Service.Service里启动了Container、Executor、Connector
　　ContainerBase的startInternal方法：

/**
* Start this component and implement the requirements
* of {@link org.apache.catalina.util.LifecycleBase#startInternal()}.
*
* @exception LifecycleException if this component detects a fatal error
*  that prevents this component from being used
*/
@Override
protected synchronized void startInternal() throws LifecycleException {
// Start our subordinate components, if any
if ((loader != null) && (loader instanceof Lifecycle))
((Lifecycle) loader).start();
logger = null;
getLogger();
if ((logger != null) && (logger instanceof Lifecycle))
((Lifecycle) logger).start();
if ((manager != null) && (manager instanceof Lifecycle))
((Lifecycle) manager).start();
if ((cluster != null) && (cluster instanceof Lifecycle))
((Lifecycle) cluster).start();
if ((realm != null) && (realm instanceof Lifecycle))
((Lifecycle) realm).start();
if ((resources != null) && (resources instanceof Lifecycle))
((Lifecycle) resources).start();
// Start our child containers, if any
Container children[] = findChildren();
for (int i = 0; i < children.length; i++) {
children.start();
}
// Start the Valves in our pipeline (including the basic), if any
if (pipeline instanceof Lifecycle)
((Lifecycle) pipeline).start();

setState(LifecycleState.STARTING);
// Start our thread
threadStart();
}
　　Conector的initInternal和startInternal方法

@Override
protected void initInternal() throws LifecycleException {
super.initInternal();
// Initialize adapter
adapter = new CoyoteAdapter(this);
protocolHandler.setAdapter(adapter);
// Make sure parseBodyMethodsSet has a default
if( null == parseBodyMethodsSet )
setParseBodyMethods(getParseBodyMethods());
try {
protocolHandler.init();
} catch (Exception e) {
throw new LifecycleException
(sm.getString
("coyoteConnector.protocolHandlerInitializationFailed"), e);
}
// Initialize mapper listener
mapperListener.init();
}

/**
* Begin processing requests via this Connector.
*
* @exception LifecycleException if a fatal startup error occurs
*/
@Override
protected void startInternal() throws LifecycleException {
// Validate settings before starting
if (getPort() < 1) {
throw new LifecycleException(sm.getString(
"coyoteConnector.invalidPort", Integer.valueOf(getPort())));
}
setState(LifecycleState.STARTING);
try {
protocolHandler.start();
} catch (Exception e) {
String errPrefix = "";
if(this.service != null) {
errPrefix += "service.getName(): \"" + this.service.getName() + "\"; ";
}
throw new LifecycleException
(errPrefix + " " + sm.getString
("coyoteConnector.protocolHandlerStartFailed"), e);
}
mapperListener.start();
}

　　从上面的代码我们可以看出，父容器在启动时会把下面所有的组件都启动起来。Connector在启动的时候调用了protocolHandler.start();这个protocolHandler会是什么呢？它是Http11Protocol的实例，这个类就是http1.1 协议的一个实现类，就是真正解析、处理请求的地方。接下来我们会去分析一下这个类以及由它引申出来的内容。