Spark HistoryServer之Jetty简单使用

这两天在看Spark HistoryServer的代码，发现里面使用了Jetty，下面简单描述下Jetty的使用

有两个Servlet：HelloServlet和WorldServlet

package com.luogankun.servlet;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class HelloServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;  

    private String msg = "hello";  

    public HelloServlet() {
    }  

    public HelloServlet(String msg) {
        this.msg = "hello: "+ msg;
    }  

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.getWriter().println(msg);
    }
}  

package com.luogankun.servlet;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class WorldServlet  extends HttpServlet{
    private static final long serialVersionUID = 1L;

    private String msg = "world";

    public WorldServlet() {
    }

    public WorldServlet(String msg) {
        this.msg = "world: " + msg;
    }

    protected void doGet(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        response.getWriter().println(msg);
    }
}

Jetty客户端测试：

package com.luogankun.jetty;

import org.eclipse.jetty.server.Server;
import org.eclipse.jetty.servlet.ServletContextHandler;
import org.eclipse.jetty.servlet.ServletHolder;
import com.luogankun.servlet.HelloServlet;
import com.luogankun.servlet.WorldServlet;

public class JettyServer {
    public static void main(String[] args) throws Exception {
        Server server = new Server(7798);  //指定jettyserver的启动端口

        ServletContextHandler context = new ServletContextHandler(ServletContextHandler.SESSIONS);
        context.setContextPath("/");  //设置访问路径
        server.setHandler(context);

        // http://localhost:8080/hello
        context.addServlet(new ServletHolder(new HelloServlet()), "/hello"); //当访问/hello时执行HelloServlet()
        // http://localhost:8080/hello/luogankun
        context.addServlet(new ServletHolder(new HelloServlet("luogankun")),"/hello/luogankun"); //当执行/hello/luogankun时执行HelloServlet

        // http://localhost:8080/world
        context.addServlet(new ServletHolder(new WorldServlet()), "/world"); //当执行/world时执行WorldServlet
        // http://localhost:8080/world/luogankun
        context.addServlet(new ServletHolder(new WorldServlet("luogankun")), "/world/luogankun"); //当执行/world/luogankun时执行WorldServlet

        server.start();
        server.join();
    }
}

总结：当request请求匹配到某个设定的路径时就执行某个指定的Servlet。

在浏览器中访问如下地址，注意观察执行结果

http://localhost:8080/hello

http://localhost:8080/hello/luogankun

http://localhost:8080/world

http://localhost:8080/world/luogankun

查看HistoryServer的代码

def initialize() {
    attachPage(new HistoryPage(this))
    attachHandler(createStaticHandler(SparkUI.STATIC_RESOURCE_DIR, "/static"))

    val contextHandler = new ServletContextHandler
    contextHandler.setContextPath(HistoryServer.UI_PATH_PREFIX)   //UI_PATH_PREFIX是history
    contextHandler.addServlet(new ServletHolder(loaderServlet), "/*")
    attachHandler(contextHandler)
}

private val loaderServlet = new HttpServlet {
    protected override def doGet(req: HttpServletRequest, res: HttpServletResponse): Unit = {
        val parts = Option(req.getPathInfo()).getOrElse("").split("/")
        if (parts.length < 2) {
            res.sendError(HttpServletResponse.SC_BAD_REQUEST, ......)}")
            return
        }

    　　val appId = parts(1)

    　　appCache.get(appId)
    　　res.sendRedirect(res.encodeRedirectURL(req.getRequestURI()))
    }
}

可以看到当请求为: /history/*时交由loadServlet执行，该步骤在historyserver主页中点击查看某个app历史信息时触发；

此处的req.getPathInfo()的值为/app编号，形如：/app-20141105100235-0009

刚开始看代码时，不懂jetty，死活弄不明白怎么跳转过到具体的app信息页面的，了解下jetty后明白了是按照指定的请求路径进行转发的。