servlet中service() doGet() doPost() 方法

HttpServlet 里的三个方法:service(HttpServletRequest req, HttpServletResponse resp) ,doGet(HttpServletRequest req, HttpServletResponse resp), doPost(HttpServletRequest req, HttpServletResponse res)的区别和联系:
  1. 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 
  2. 或是doPost方法,我们可以查看HttpServlet 类的service方法:  我在tomcat的lib目录下,解压servlet-api.jar,然后用反编译软件把lib\javax\servlet\http下的HttpServlet.class反编译,看里头的service()方法的原代码:
  3. 注意,sun只是定义了servlet接口,而实现servlet接口的就是类似于tomcat的服务器,所以我是在tomcat的安装目录下找到实现的类。
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);
        }
    }
  1. 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: 
  2.  
  3. Java代码 
  4.  
  5.    1. public void service(ServletRequest req, ServletResponse res)    
  6.    2.                    throws ServletException, IOException {    
  7.    3.          res.getOutputStream().print(    
  8.    4.          "image is <img src='images/downcoin.gif'></img><br>");    
  9.    5.      }   
    1. 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 
    2.  
    3. 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。 
    4.  
    5. 比如说:你的客户端代码是: 
    6. Java代码 
    7.  
    8.    1. <%@page contentType="text/html; charset=utf-8"%>    
    9.    2. <html>    
    10.    3. <head><title>选择</title></head>    
    11.    4. <body>    
    12.    5. 请选择你喜欢的水果:<br>    
    13.    6. <form action = "Test" method = "post">    
    14.    7. <input type="checkbox" name="fruit" value ="apple" >苹果<br>    
    15.    8. <input type="checkbox" name="fruit" value ="orange">桔子<br>    
    16.    9. <input type="checkbox" name="fruit" value ="mango">芒果<br>    
    17.   10. <input type="submit" value="提交">    
    18.   11. </form>    
    19.   12. </body>    
    20.   13. </html>    
    21.   14.    
    22.   15. 服务端servlet是:Test类    
    23.   16.    
    24.   17. import java.io.IOException;    
    25.   18.    
    26.   19. import javax.servlet.ServletException;    
    27.   20. import javax.servlet.ServletOutputStream;    
    28.   21. import javax.servlet.ServletRequest;    
    29.   22. import javax.servlet.ServletResponse;    
    30.   23. import javax.servlet.http.HttpServlet;    
    31.   24. import javax.servlet.http.HttpServletRequest;    
    32.   25. import javax.servlet.http.HttpServletResponse;    
    33.   26.    
    34.   27. /**
    35.   28. * 演示service方法
    36.   29. */   
    37.   30. public class Test extends HttpServlet {    
    38.   31.    
    39.   32. public void service(ServletRequest req, ServletResponse res)    
    40.   33.    throws ServletException, IOException {    
    41.   34.             res.getOutputStream().print("This is the service");    
    42.   35.    
    43.   36. }    
    44.   37.    
    45.   38. protected void doGet(HttpServletRequest request,    
    46.   39.     HttpServletResponse response) throws ServletException, IOException {    
    47.   40.    doPost(request,response);    
    48.   41.    
    49.   42. }    
    50.   43. protected void doPost(HttpServletRequest request,    
    51.   44.     HttpServletResponse response) throws ServletException, IOException {    
    52.   45.    ServletOutputStream out=response.getOutputStream();    
    53.   46.    String[] args=(String[])request.getParameterValues("fruit");    
    54.   47.   for(int i=0;i<args.length;i++){    
    55.   48.     out.print(args[i]+"<br>");    
    56.   49.    }    
    57.   50.       
    58.   51. }    
    59.   52. }   
    60. 点击提交后:页面输出结果为“This is the service“;

    61. 所以,我们在写servlet的时候,一般都是重写doGet或doPost方法,不会管service方法。

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