servlet中service doGet doPost 的关系

jzinfo · 发表于 2013-2-7 15:50:01

在servlet中默认情况下，无论你是get还是post 提交过来都会经过service（）方法来处理，然后转向到doGet
或是doPost方法，可以看HttpServlet 类的service方法：
protected void service(HttpServletRequest req, HttpServletResponse resp)       throws ServletException, IOException {       String method = req.getMethod();       if(method.equals("GET"))       {          long lastModified = getLastModified(req);          if(lastModified == -1L)          {             doGet(req, resp);          } else          {             long ifModifiedSince = req.getDateHeader("If-Modified-Since");             if(ifModifiedSince < (lastModified / 1000L) * 1000L)             {                   maybeSetLastModified(resp, lastModified);                   doGet(req, resp);             } else             {                   resp.setStatus(304);             }          }       } else       if(method.equals("HEAD"))       {          long lastModified = getLastModified(req);          maybeSetLastModified(resp, lastModified);          doHead(req, resp);       } else       if(method.equals("POST"))          doPost(req, resp);       else       if(method.equals("PUT"))          doPut(req, resp);       else       if(method.equals("DELETE"))          doDelete(req, resp);       else       if(method.equals("OPTIONS"))          doOptions(req, resp);       else       if(method.equals("TRACE"))       {          doTrace(req, resp);       } else       {          String errMsg = lStrings.getString("http.method_not_implemented");          Object errArgs[] = new Object[1];          errArgs[0] = method;          errMsg = MessageFormat.format(errMsg, errArgs);          resp.sendError(501, errMsg);       } }
从上面可以看出这里的service是用来转向的，但是如果你在自己的servlet类中覆盖了service方法，比如说你的service是这样的：

public void service(ServletRequest req, ServletResponse res)                throws ServletException, IOException {       res.getOutputStream().print(       "image is <img src='images/downcoin.gif'></img><br>"); }
那么这时service就不是用来转向的，而是用来处理业务的，现在不论你的客户端是用pos还是get来请求此servlet
都会执行service方法也只能执行servlet方法，不会去执行doPost或是doGet方法。

比如说：你的客户端代码是：
<%@page contentType="text/html; charset=utf-8"%><html><head><title>选择</title></head><body>请选择你喜欢的水果：<br><form action = "Test" method = "post"><input type="checkbox" name="fruit" value ="apple" >苹果<br><input type="checkbox" name="fruit" value ="orange">桔子<br><input type="checkbox" name="fruit" value ="mango">芒果<br><input type="submit" value="提交"></form></body></html>服务端servlet是：Test类import java.io.IOException;import javax.servlet.ServletException;import javax.servlet.ServletOutputStream;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;/** * 演示service方法 */public class Test extends HttpServlet { public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException {          res.getOutputStream().print("This is the service"); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {  doPost(request,response); } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {  ServletOutputStream out=response.getOutputStream();  String[] args=(String[])request.getParameterValues("fruit");  for(int i=0;i<args.length;i++){ out.print(args+"<br>");  } }}

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servlet中service doGet doPost 的关系

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