A Simple Server3.0 Example

因为好多年没做web开发，所以也一直木有关注JEE新版本的特性了。虽然老早听说Servet3.0可以异步化了，但是一直米有写过例子来跑过。最近思考异步化问题偏向于jvm层面如何保存执行中的栈和恢复栈，对异步化整体缺乏整理的考虑。

现在想来，天天面对的系统主要是接受请求，处理，发起一堆远程调用，接受远程调用结果，处理，构造响应结果，输出，没有太多深层次的业务处理。细化下去就要考虑接受请求、发起远程调用、接受调用结果、构造响应结果这块了。先从接受请求这块开始，就先了解下Servlet的异步化吧。

昨天查了下Servlet3.0的资料，写了个例子，惊奇的发现，竟然不用配置web.xml。虽然从原理上考虑，Annotation这种方式完全可以完成web.xml要实现的功能，但是现在真是这样的时候，还是有点小惊讶的，当然这只是跟记忆中web应用结构的对比后产生的，而不是对其新的实现方式产生的---Spring也有强大的Annotation呢，虽然我的记忆还停留在当年配置文件上......

另外，之前大多用myEclipse开发web应用，所以一时间都不知道怎么写了。。。不能自动发布，没有jee包的导入....淡定中，自己写ant文件拷贝，拷贝到tomcat目录下的时候，拷成webapp的接口即可，jee包从tomcat下边拷！

从tomcat的lib目录下拷servlet-api.jar

写build.xml文件：

<?xml version="1.0" encoding="GB2312"?>
<!DOCTYPE project>
<project name="async" default="autoCopy" basedir=".">
	<property name="targetDir" value="J:\java_tools\apache-tomcat-7.0.28\webapps\async"/>
	<property name="autoCompileClassDir" value="bin"/>
	<property name="webappDir" value="web"/>
	
	<target name="autoCopy" depends="copyClass,copyWeb">
	</target>
	<target name="copyClass">
		<echo message="=====Copying Class Files====="/>  
		<copy todir="${targetDir}/WEB-INF/classes">
			<fileset dir="${autoCompileClassDir}">
				<include name="**/*.class"></include>
			</fileset>
		</copy>
	</target>
	<target name="copyWeb">
		<echo message="=====Copying Web Files====="/>
		<copy todir="${targetDir}">
			<fileset dir="${webappDir}">
				<include name="**/*.xml"></include>
				<include name="**/*.properties"></include>
				<include name="**/*.jsp"></include>
				<include name="**/*.html"></include> 
			</fileset>
		</copy> 
	</target> 
</project>

 拷到我tomcat/webapps目录下了。

Servlet定义：

package com.tmall.buy.web;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.AsyncContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebInitParam;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet(asyncSupported = true, name = "asyncServlet", urlPatterns = { "/asyncServlet" }, initParams = {
		@WebInitParam(name = "hello", value = "world"),
		@WebInitParam(name = "gun", value = "dan") })
public class AsyncServlet extends HttpServlet {
	private static final long serialVersionUID = 133332222222L;

	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		doAsync(req, resp);
	}

	@Override
	protected void doPost(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		doAsync(req, resp);
	}
	
	private void doAsync(HttpServletRequest req,HttpServletResponse resp) throws IOException{
		resp.setContentType("text/html");
		System.out.println("req.isAsyncSupported = " + req.isAsyncSupported());
		final AsyncContext ctx = req.startAsync();
		new Thread(new Runnable(){
			@Override
			public void run() {
				PrintWriter out = null;
				try {
					out = ctx.getResponse().getWriter();
					Thread.sleep(1000);
					System.out.println("Async Thread~~");
					out.write("<br>Async Write ~~~<br>");
					out.flush();
				} catch (Exception e) {
					e.printStackTrace();
				}finally{
					ctx.complete();
				}
			}
			
		}).start();
	}	
}

 详细参考这里

另外蛋疼写了个Filter：

package com.tmall.buy.web.filter;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;

@WebFilter(asyncSupported = true, filterName = "commonFilter", urlPatterns = { "*" })
public class CommonFilter implements Filter {

	@Override
	public void destroy() {

	}

	@Override
	public void doFilter(ServletRequest arg0, ServletResponse arg1,
			FilterChain arg2) throws IOException, ServletException {
		System.out.println(arg0.getServerName());
		arg2.doFilter(arg0, arg1);
	}

	@Override
	public void init(FilterConfig arg0) throws ServletException {

	}
}

 然后，没了，整个应用就这么多东西了。

只是刚开始Filter的syncSupported属性没设置，于是乎异步就出错了，页面的异常堆栈：

java.lang.IllegalStateException: Not supported.
	org.apache.catalina.connector.Request.startAsync(Request.java:1664)
	org.apache.catalina.connector.Request.startAsync(Request.java:1657)
	org.apache.catalina.connector.RequestFacade.startAsync(RequestFacade.java:1023)
	com.tmall.buy.web.AsyncServlet.doAsync(AsyncServlet.java:35)
	com.tmall.buy.web.AsyncServlet.doGet(AsyncServlet.java:23)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
	com.tmall.buy.web.filter.CommonFilter.doFilter(CommonFilter.java:25)

在Filter的@WebFilter标注上加了asyncSupported=true之后，就ok了 

 

评论

1 楼 zys0523 2013-01-08  

膜拜麦大牛