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servlet中service() doGet() doPost() 方法

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08/31
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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：

    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
  1. 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);
        }
    }
    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：
  1. Java代码
  2. 1. public void service(ServletRequest req, ServletResponse res)
  3. 2.                    throws ServletException, IOException {
  4. 3.          res.getOutputStream().print(
  5. 4.          "image is <img src='images/downcoin.gif'></img><br>");
  6. 5.      }
  7. Java代码
  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. 29. */
  36. 30. public class Test extends HttpServlet {
  37. 31.
  38. 32. public void service(ServletRequest req, ServletResponse res)
  39. 33.    throws ServletException, IOException {
  40. 34.             res.getOutputStream().print("This is the service");
  41. 35.
  42. 36. }
  43. 37.
  44. 38. protected void doGet(HttpServletRequest request,
  45. 39.     HttpServletResponse response) throws ServletException, IOException {
  46. 40.    doPost(request,response);
  47. 41.
  48. 42. }
  49. 43. protected void doPost(HttpServletRequest request,
  50. 44.     HttpServletResponse response) throws ServletException, IOException {
  51. 45.    ServletOutputStream out=response.getOutputStream();
  52. 46.    String[] args=(String[])request.getParameterValues("fruit");
  53. 47.   for(int i=0;i<args.length;i++){
  54. 48.     out.print(args[i]+"<br>");
  55. 49.    }
  56. 50.
  57. 51. }
  58. 52. }
  59. 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。