分布式 - Jetty架构

Connectors

For each accepted TCP connection, the Connector asks a ConnectionFactory to create a Connection object that handles the network traffic on that TCP connection, parsing and generating bytes for a specific protocol.

比如：a ServerConnector configured with three factories: ProxyConnectionFactory, SslConnectionFactory and HttpConnectionFactory. Such connector will be able to handle PROXY protocol bytes coming from a load balancer such as HAProxy (with the ProxyConnectionFactory), then handle TLS bytes (with SslConnectionFactory) and therefore decrypting/encrypting the bytes from/to a remote client, and finally handling HTTP/1.1 bytes (with HttpConnectionFactory).

可以自己自定义ConnectionFactory实现来处理自定义的协议。

Handlers

// org.eclipse.jetty.server.Handler的方法：
public void handle(String target, Request baseRequest, HttpServletRequest request, HttpServletResponse response)
        throws IOException, ServletException;

Handlers有两种模型：

• Sequential handlers，即handlers依赖定义的顺序，而上一个handler不依赖于下一个handler的调用。实现为org.eclipse.jetty.server.handler.HandlerCollection
• Nested handlers，即 before/invokeNext/after 模式(上一个handler依赖于下一个handler的调用)，比如常见的FilterChain就是这种模式。实现为org.eclipse.jetty.server.handler.HandlerWrapper

ServletHandler、ServletContextHandler

最基层的handler，常见的就是spring的DispacherServlet + 一些Filter。ServletHandler会被 ServletContextHandler 所持有。ServletContextHandler与ServletHandler是一对一的，逻辑上就是 web application context ，即SessionHandler、SecurityHandler、ServletHandler、GzipHandler的组合，常见的就是web.xml。

Server启动

1. new Server(int port) -> 实例化QueuedThreadPool和ServerConnector
2. Server#setHandler 设置运行时处理流程:
   通常会实例化一个ServletContextHandler，注意ServletContextHandler的构造方法最终会调用ServletContextHandler#relinkHandlers
   依次将SessionHandler、SecurityHandler、GzipHandler、ServletHandler构成责任链（因为这4个handler连同ServletContextHandler都是HandlerWrapper
   类型）。
3. Server#start即AbstractLifeCycle#start -> Server#doStart。以下步骤是Server#doStart
4. 设置ErrorHandler
5. ShutdownThread通过Runtime.getRuntime().addShutdownHook(Thread)使得jvm关闭时会唤起ShutdownThread来stop Server
6. 启动ShutdownMonitor来监听远端stop指令，可以设置STOP.HOST、STOP.PORT、STOP.KEY来启用。
7. 内部所有connector（ServerConnector等）执行Connector#start 即AbstractLifeCycle#start。
8. AbstractNetworkConnector#doStart -> ServerConnector#open -> ServerConnector#openAcceptChannel 即绑定host、port到ServerSocket

Server运行时

由于Server继承HandlerWrapper，运行时由其内部托管的handler实现（比如ServletContextHandler）。

• HttpChannel#handle -> Server#handle(target, request, request, response)即HandlerWrapper的handle方法

注意：Server、ServletContextHandler、SessionHandler、SecurityHandler、GzipHandler、ServletHandler都是HandlerWrapper，即都在一条责任链上。
注意：ServletContextHandler、SessionHandler、ServletHandler继承ScopedHandler，即调用链上是 ScopedHandler#handle(target, request, request, response) -> ScopedHandler#doScope入参略 -> ScopedHandler#doHandle

所以最后请求request会传递到ServletHandler，通常会设置spring的DispatcherServlet作为ServletHandler的Servlet。