Tomcat从socket到java Servlet

整体架构图

一. 启动阶段

BootStrap的main方法加载server.xml配置文件，封装成Server,Service,Connector,Engine等java对象

Server初始化==>Service初始化==>Connector初始化==>Engine初始化==>Host初始化==>Context初始化 WAR解压 创建Servlet

Connector初始化:绑定端口,创建BIO NIO NIO2线程池

Connector.setProtocol是在解析server.xml配置文件时绑定关系

启动Connector initInternal() ===>ProtocolHandler.init() ==> Endpoint.init()-->Endpoint.bind()

Connector作用(接收请求时):

ServerSocket(Channel)接收socket请求创建Socket, 并将Socket.InputStream中的内容封装成javax.servlet.http.HttpServletRequest的实现类, 经过多个valve filter之后传递到Container的Servlet(SpringMVC)中, servlet.doService完成之后由HttpServletResponse（持有请求时创建的socket?）.outputStream回写内容到socket中

Protocol 配置在server.xml的<connector >标签的属性中, 作用:根据配置创建不同的Endpoint

tomcat8.5

Endpoint 具体协议的实现， 完成绑定端口及创建线程池

tomcat8.5

tomcat8.0 

tomcat 7.0

Endpoint.startInternal()

7.0默认使用JIOEndpoint, 8.0以上默认使用NIOEndpoint

//搞懂NIO NIO2===>

二、接收浏览器HTTP请求

整体流程：

NIOEndpoint ---> Http11Processor(创建Request, Response) ---> CoyoteAdapter --> Container -->

PipeLine(StandardEngineValve, StandardHostValve, StandardContextValve, StandardWrapperValve)--> Servlet.doService

2.1 Endpoint中request创建

JIOEndpoint在接收socket请求后,直接将Request交给了worker线程

NIOEndpoint.Acceptor在接收到请求后（while循环一直监听），将PollerEvent事件注册到NIOEndpoint.Poller（持有selector对象）的事件队列中，并调用selector.waitup() 只调用一次,

private void addEvent(PollerEvent event) {
            events.offer(event);
            if ( wakeupCounter.incrementAndGet() == 0 ) selector.wakeup();
}

Poller的while循环中查找到PollerEvent, 调用processKey()方法-->AbstractEndpoint#processSocket()在这里创建SocketProcessor(Runable)并提交给Executor线程池处理。

SocketProcessor --> Http11Processor.service() readsocket&buildRequest-->CoyoteAdatper.service()

2.2 CoyoteAdapter中处理Request

Servlet3.1 异步Request, 在Servlet里面设置.isAsync， coyoteAdapter invoke服务方法后直接返回，socket并没有释放

org.apache.catalina.connector.CoyoteAdapter#service

             if (postParseSuccess) {
                 //check valves if we support async
                 request.setAsyncSupported(
                         connector.getService().getContainer().getPipeline().isAsyncSupported());
                 // Calling the container  调用filter servlet
                 connector.getService().getContainer().getPipeline().getFirst().invoke(
                         request, response);
             }
             if (request.isAsync()) {
                 async = true;
                 ReadListener readListener = req.getReadListener();
                 if (readListener != null && request.isFinished()) {
                     // Possible the all data may have been read during service()
                     // method so this needs to be checked here
                     ClassLoader oldCL = null;
                     try {
                         oldCL = request.getContext().bind(false, null);
                         if (req.sendAllDataReadEvent()) {
                             req.getReadListener().onAllDataRead();
                         }
                     } finally {
                         request.getContext().unbind(false, oldCL);
                     }
                 }

                 Throwable throwable =
                         (Throwable) request.getAttribute(RequestDispatcher.ERROR_EXCEPTION);

                 // If an async request was started, is not going to end once
                 // this container thread finishes and an error occurred, trigger
                 // the async error process
                 if (!request.isAsyncCompleting() && throwable != null) {
                     request.getAsyncContextInternal().setErrorState(throwable, true);
                 }
             } else {
                 request.finishRequest(); // 非异步的请求处理之后, 会释放socket
                 response.finishResponse();
             }

session创建时机， 在Request.getSession时根据请求中的JSESSIONID查找，如果id为null,首次创建，新的请求中就携带了JSESSIONID

Connector创建的是org.apache.catalina.connector.Request

org.apache.catalina.core.StandardWrapperValve --> 具体某个Servlet (DispatchServlet),  初始化FilterChain, 然后调用各个filter, 最后到Servlet.doService

filterChain.doFilter
    (request.getRequest(), response.getResponse()); 

压缩版的两个默认Servlet: DefaultServlet处理静态资源，JSPServlet创建HttpServletRequest，对connector.Request又包一层

2.3 Response的socket WRITE，CLOSE事件在NIOEndpoint中的处理

和socket OPEN_READ事件基本一致

其他参考:

Http中socket长连接短连接使用场景 http://www.cnblogs.com/0201zcr/p/4694945.html

程序中设置为长连接 1. socket.setKeepAlive(true)   2.socketChannel.setOption(StandardSocketOptions.SO_KEEPALIVE, true);

See:

http://tomcat.apache.org/tomcat-8.0-doc/architecture/requestProcess.html

http://tomcat.apache.org/tomcat-8.0-doc/config/http.html#NIO2_specific_configuration