servlet中的service()方法重写与不重写

来源：互联网发布：bim造价软件编辑：程序博客网时间：2024/05/21 20:21

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：

原代码：

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[i]+"<br>"); } }}

那么当你提交数据后的输出结果是:this is the service