servlet中service doGet doPost 的关系
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; errArgs = 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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