本文详细介绍了StandardServer在Tomcat结构中的核心地位与职责，包括其作为Server接口的标准实现，如何通过JNDI加载资源、注册监听器、初始化与启动流程。着重阐述了StandardServer与生命周期管理接口Lifecycle的交互，以及如何通过MBeanRegistration接口与JMX进行交互，实现组件状态的监控与管理。此外，文章还深入探讨了StandardServer在启动、运行与停止过程中的关键步骤与方法，为理解和优化Tomcat服务提供了理论依据。
2013-09-13
####StandardServer是什么 StandardServer标准实现Server接口，从tomcat结构层次图中知道，Server处于最外层，其他组件在其内部,起统领做，像一家公司的CEO，负责管理整个公司，Server代表完整的Servlet容器,管理维护Server和全局resource，在各个组件中共享StandardServer资源。在tomcat启动过程中由Catalina通过Digester库加载解析server.xml，创建StandardServer对象，并初始化和启动Server,Server将自己注册到JMX上面，通过tomcat管理页面查看Server状态。StandardServer除了实现Server接口以外，还使用下列组件来完成功能。
Lifecycle StandardServer实现Lifecycle接口，Lifecycle是tomcat中关于组件生命周期状态监控操作监听的接口，通过Lifecycle提供的9个状态和5个方法，使得监控组件的状态更新和在组件不同生命周期阶段操作成为可能。
9的状态：指示组件状态
- BEFORE_INIT
- AFTER_INIT
- BEFORE_START
- START
- AFTER_START
- BEFORE_STOP
- STOP
- AFTER_STOP
- BEFORE_DESTROY
- AFTER_DESTROY
- PERIODIC
- CONFIG_START
- CONFIG_STOP
5个方法： 更新组件状态和添加监听组件状态变更通知组件
- addLifecycleListener(LifecycleListener)
- findLifecycleListeners()
- removeLifecycleListener(LifecycleListener)
- start()
- stop()
addLifecycleListener(LifecycleListener)是注册LifecycleEvent事件监听器。LifecycleListener是监听Lifecycle组件状态变更触发的LifecycleEvent事件，当LifecycleListener监听到LifecycleEvent事件事件时，会调用LifecycleListener方法lifecycleEvent(LifecycleEvent)响应事件。
MBeanRegistration
StandardServer实现MBeanRegistration接口。MBeanRegistration接口是JMX的MBean方法的内容，实现该接口的目的是将StandardServer组件注册到JMX中，通过JMX可以实现对StandardServer的控制。
LifecycleSupport
StandardServer的属性，它的作用就是负责管理Lifecycle接口实现类的LifecycleListener，只有一个到参的构造器，必须在创建对象时传入Lifecycle，在StandardServer中创建对象时同时将StandardServer自身传入，private LifecycleSupport lifecycle = new LifecycleSupport(this);
LifecycleSupport 管理注册在StandardServer上的监听器，当监听到LifecycleEvent，LifecycleSupport 马上调用方法fireLifecycleEvent(String, Object)遍历监听器响应事件，属性state指明了当前Lifecycle的状态。
javax.naming.Context
StandardServer的属性，是JNDI中的内容，不了解，只知道它提供命名服务，也就是根据名字获取对象以及对象属性信息等，通过给定资源路径，然后就可以获取资源路径下面对象，在server.xml中关于资源的配置，从配置信息中可以看到配置的是tomcat管理页面登陆账号权限信息。
<!-- Global JNDI resources Documentation at /docs/jndi-resources-howto.html -->
<GlobalNamingResources>
<!-- Editable user database that can also be used by UserDatabaseRealm
to authenticate users -->
<Resource name="UserDatabase" auth="Container"
type="org.apache.catalina.UserDatabase" description="User database that can be updated and saved"
factory="org.apache.catalina.users.MemoryUserDatabaseFactory"
pathname="conf/tomcat-users.xml" />
</GlobalNamingResources>
。java和第三方交互时经常使用，例如数据库驱动，mysql的JDBC和ODBC,java不用关心其实现部分。JNDI理解例子，来自博客lujin55
NamingContextListener
StandardServer的属性，是JNDI中的内容，不了解，比较复杂，只知道是负责监听javax.naming.Context资源事件。NamingContextListener实现了LifecycleListener、ContainerListener、PropertyChangeListener3个接口，具备监听Lifecycle组件，Container组件、PropertyChange的事件能力。
NamingResources
StandardServer的属性，是JNDI中的内容，不了解，比较复杂，知道它管理命名资源，将要加载的资源封装成对象，可以直接从NamingResources获取对象了。
PropertyChangeSupport
StandardServer的属性，参照LifecycleSupport的理解不难看出，PropertyChangeSupport管理对象属性变化监听器，跟LifecycleSupport的使命一样，监听PropertyChangeEvent事件，然后响应。
StandardServer通过JNDI加载server.xml中配置的资源，完成资源配置，注册监听器来监听事件，同时将自己注册到ServerFactory 上。StandardServer再次完成资源加载后调用init()方法初始化，实践调用的是initialize()，在tomcat启动中，调用初始化方法是由Catalina来完成。在initialize()方法中分4步完成
- 第一步首先判断是否已经初始化
- 第二部触发INIT_EVENT事件，标记已经初始化(initialized = true)
- 第三步注册到MBeanServer服务器，添加监控，可以在tomcat管理页面管理Server
- 第四步遍历services数组，挨个调用initialize()初始化
/**
* Invoke a pre-startup initialization. This is used to allow connectors to
* bind to restricted ports under Unix operating environments.
*/
public void initialize() throws LifecycleException {
if (initialized) {
log.info(sm.getString("standardServer.initialize.initialized"));
return;
}
lifecycle.fireLifecycleEvent(INIT_EVENT, null);
initialized = true;
if (oname == null) {
try {
oname = new ObjectName("Catalina:type=Server");
Registry.getRegistry(null, null).registerComponent(this, oname,
null);
} catch (Exception e) {
log.error("Error registering ", e);
}
}
// Register global String cache
try {
ObjectName oname2 = new ObjectName(oname.getDomain()
+ ":type=StringCache");
Registry.getRegistry(null, null).registerComponent(
new StringCache(), oname2, null);
} catch (Exception e) {
log.error("Error registering ", e);
}
// Initialize our defined Services
for (int i = 0; i < services.length; i++) {
services[i].initialize();
}
}
StandardServer初始化完成后，调用start()方法启动Server，在start()方法分4步完成
- 第一步首先判断Server是否已经启动
- 第二部触发BEFORE_START_EVENT，START_EVENT事件，标记已经启动(started = true)
- 第三步遍历services数组，挨个调用start()初始化
- 第四步触发AFTER_START_EVENT事件,通知监听器
/**
* Prepare for the beginning of active use of the public methods of this
* component. This method should be called before any of the public methods
* of this component are utilized. It should also send a LifecycleEvent of
* type START_EVENT to any registered listeners.
*
* @exception LifecycleException
* if this component detects a fatal error that prevents this
* component from being used
*/
public void start() throws LifecycleException {
// Validate and update our current component state
if (started) {
log.debug(sm.getString("standardServer.start.started"));
return;
}
// Notify our interested LifecycleListeners
lifecycle.fireLifecycleEvent(BEFORE_START_EVENT, null);
lifecycle.fireLifecycleEvent(START_EVENT, null);
started = true;
// Start our defined Services
synchronized (services) {//同步
for (int i = 0; i < services.length; i++) {
if (services[i] instanceof Lifecycle)
((Lifecycle) services[i]).start();
System.out.println(i+":"+services[i].hashCode());//自己加的，为了验证catalina是否在Server的services列表中，最后事实证明catalina不在列表中
}
}
// Notify our interested LifecycleListeners
lifecycle.fireLifecycleEvent(AFTER_START_EVENT, null);
}
StandardServer完成启动后，Catalina在start()方法中调用await()方法，await()中调用StandardServer的await()，StandardServer的await()方法主要完成的功能非常简单：启动ServerSocket监听网络端口请求关闭Server的请求,从代码中可以看出StandardServer使用一个死循环不断监听端口，当接收到"SHUTDOWN"命令时跳出循环，回到Catalina的start()方法中。
/**
* Wait until a proper shutdown command is received, then return. This keeps
* the main thread alive - the thread pool listening for http connections is
* daemon threads.
*/
public void await() {
// Negative values - don't wait on port - tomcat is embedded or we just
// don't like ports
if (port == -2) {
// undocumented yet - for embedding apps that are around, alive.
return;
}
if (port == -1) {
try {
awaitThread = Thread.currentThread();//当前线程
while (!stopAwait) {
try {
Thread.sleep(10000);
} catch (InterruptedException ex) {
// continue and check the flag
}
}
} finally {
awaitThread = null;
}
return;
}
// Set up a server socket to wait on
try {
awaitSocket = new ServerSocket(port, 1,
InetAddress.getByName("localhost"));
} catch (IOException e) {
log.error("StandardServer.await: create[" + port + "]: ", e);
return;
}
try {
awaitThread = Thread.currentThread();//当前线程
// Loop waiting for a connection and a valid command
while (!stopAwait) {
ServerSocket serverSocket = awaitSocket;
if (serverSocket == null) {
break;
}
// Wait for the next connection
Socket socket = null;
StringBuilder command = new StringBuilder();
try {
InputStream stream = null;
try {
socket = serverSocket.accept();
socket.setSoTimeout(10 * 1000); // Ten seconds
stream = socket.getInputStream();
} catch (AccessControlException ace) {
log.warn("StandardServer.accept security exception: "
+ ace.getMessage(), ace);
continue;
} catch (IOException e) {
if (stopAwait) {
// Wait was aborted with socket.close()
break;
}
log.error("StandardServer.await: accept: ", e);
break;
}
// Read a set of characters from the socket
int expected = 1024; // Cut off to avoid DoS attack
while (expected < shutdown.length()) {
if (random == null)
random = new Random();
expected += (random.nextInt() % 1024);
}
while (expected > 0) {
int ch = -1;
try {
ch = stream.read();
} catch (IOException e) {
log.warn("StandardServer.await: read: ", e);
ch = -1;
}
if (ch < 32) // Control character or EOF terminates loop
break;
command.append((char) ch);
expected--;
}
} finally {
// Close the socket now that we are done with it
try {
if (socket != null) {
socket.close();
}
} catch (IOException e) {
// Ignore
}
}
// Match against our command string
boolean match = command.toString().equals(shutdown);
if (match) {
break;
} else
log.warn("StandardServer.await: Invalid command '"
+ command.toString() + "' received");
}
} finally {
ServerSocket serverSocket = awaitSocket;
awaitThread = null;
awaitSocket = null;
// Close the server socket and return
if (serverSocket != null) {
try {
serverSocket.close();
} catch (IOException e) {
// Ignore
}
}
}
}
在StandardServer调出awaite()方法循环回到Catalina的start()方法中，紧跟在awaite()方法后的是stop()方法，也即停止Server的方法，在StandardServer的stop()方法中主要完成停止Server的任务，分5步完成
- 第一步首先判断Server是否已经启动
- 第二部触发BEFORE_STOP_EVENT，STOP_EVENT事件，标记已经停止(started = false)
- 第三步遍历services数组，挨个调用stop()初始化
- 第四步触发AFTER_STOP_EVENT事件,通知监听器
- 第五步调用stopAwait(),关闭ServerSocket，调用interrupt()退出线程。
/**
* Gracefully terminate the active use of the public methods of this
* component. This method should be the last one called on a given instance
* of this component. It should also send a LifecycleEvent of type
* STOP_EVENT to any registered listeners.
*
* @exception LifecycleException
* if this component detects a fatal error that needs to be
* reported
*/
public void stop() throws LifecycleException {
// Validate and update our current component state
if (!started)
return;
// Notify our interested LifecycleListeners
lifecycle.fireLifecycleEvent(BEFORE_STOP_EVENT, null);
lifecycle.fireLifecycleEvent(STOP_EVENT, null);
started = false;
// Stop our defined Services
for (int i = 0; i < services.length; i++) {
if (services[i] instanceof Lifecycle)
((Lifecycle) services[i]).stop();
}
// Notify our interested LifecycleListeners
lifecycle.fireLifecycleEvent(AFTER_STOP_EVENT, null);
stopAwait();
}
至此，StandardServer的初始化，启动，停止的内容完成了，StandardServer的认识也清晰了很多，StandardServer先从server.xml中加载资源完成配置，提供监听StandardServer状态方法，已经才不同生命周期操作StandardServer；在初始化中触发事件，初始化services，注册到MBeanServer，标记已经初始化，在启动中，触发启动事件，启动services，启动完成后，在由Catalina触发awaite()方法，启动ServerSocket监听请求关闭Server命令，在停止Server stop()方法中，触发停止Server事件，停止services，清除资源。注册在StandardServer上的监听器有点复杂，以后在看看是什么回事。
经过检测Catalian不在StandardServer的services列表中，那Catalian为何要实现Service接口呢？ 感觉JNDI有点意思，有时间好好看看!
啊啊啊...终于写完了，好累哦，欢迎吐槽...
专一而精，要记得坚持
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