javaWEB總結(7):HttpServlet和HttpServletRequest

時間  2019-11-22
標籤 javaweb 總結 httpservlet httpservletrequest 欄目 Java 简体版
原文   原文鏈接

前言:HttpServletRequest對象封裝了客戶端進行HTTP協議請求時的全部信息，HttpServletRequest繼承了ServletRequest，因此和ServletRequest同樣，是由tomcat服務器提供實現的。具體過程以下:html

1）Web客戶向Servlet容器發出Http請求；java

2）Servlet容器解析Web客戶的Http請求；web

3）Servlet容器建立一個HttpRequest對象，在這個對象中封裝Http請求信息；api


1.HttpServlet
瀏覽器

說到HttpServletRequest就不得不說一下HttpServlet,下面看它的API:tomcat

javax.servlet.http
Class HttpServlet

java.lang.Object
  javax.servlet.GenericServlet
      javax.servlet.http.HttpServlet
All Implemented Interfaces:
Serializable, Servlet, ServletConfig
Method Summary
protected  void doDelete(HttpServletRequest req,HttpServletResponse resp)
          Called by the server (via the service method) to allow a servlet to handle a DELETE request.
protected  void doGet(HttpServletRequest req,HttpServletResponse resp)
          Called by the server (via the service method) to allow a servlet to handle a GET request.
protected  void doHead(HttpServletRequest req,HttpServletResponse resp)
          Receives an HTTP HEAD request from the protected service method and handles the request.
protected  void doOptions(HttpServletRequest req,HttpServletResponse resp)
          Called by the server (via the service method) to allow a servlet to handle a OPTIONS request.
protected  void doPost(HttpServletRequest req,HttpServletResponse resp)
          Called by the server (via the service method) to allow a servlet to handle a POST request.
protected  void doPut(HttpServletRequest req,HttpServletResponse resp)
          Called by the server (via the service method) to allow a servlet to handle a PUT request.
protected  void doTrace(HttpServletRequest req,HttpServletResponse resp)
          Called by the server (via the service method) to allow a servlet to handle a TRACE request.
protected  long getLastModified(HttpServletRequest req)
          Returns the time the HttpServletRequest object was last modified, in milliseconds since midnight January 1, 1970 GMT.
protected  void service(HttpServletRequest req,HttpServletResponse resp)
          Receives standard HTTP requests from the public service method and dispatches them to thedoXXX methods defined in this class.
 void service(ServletRequest req,ServletResponse res)
          Dispatches client requests to the protected service method.
能夠看到HttpServlet實現了servlet接口，因此其中的service(ServletRequest req,ServletResponse res)方法和servlet中的一致，在每次請求時調用。只抽取部分方法，概要信息以下:

(1).doGet(HttpServletRequest req,HttpServletResponse resp):接收HTTP的GET請求；服務器

(2).doPost(HttpServletRequest req,HttpServletResponse resp):接收HTTP的POST請求；cookie

(3).service(HttpServletRequest req,HttpServletResponse resp):接收HTTP請求，並把它分配到doXXX方法中；網絡



2.HttpServletRequest的API:session

javax.servlet.http
Interface HttpServletRequest

All Superinterfaces:
ServletRequest
All Known Implementing Classes:
HttpServletRequestWrapper
 String getAuthType()
          Returns the name of the authentication scheme used to protect the servlet.
 String getContextPath()
          Returns the portion of the request URI that indicates the context of the request.
 Cookie[] getCookies()
          Returns an array containing all of the Cookie objects the client sent with this request.
 long getDateHeader(String name)
          Returns the value of the specified request header as a long value that represents aDate object.
 String getHeader(String name)
          Returns the value of the specified request header as a String.
 Enumeration getHeaderNames()
          Returns an enumeration of all the header names this request contains.
 Enumeration getHeaders(String name)
          Returns all the values of the specified request header as an Enumeration ofString objects.
 int getIntHeader(String name)
          Returns the value of the specified request header as an int.
 String getMethod()
          Returns the name of the HTTP method with which this request was made, for example, GET, POST, or PUT.
 String getPathInfo()
          Returns any extra path information associated with the URL the client sent when it made this request.
 String getPathTranslated()
          Returns any extra path information after the servlet name but before the query string, and translates it to a real path.
 String getQueryString()
          Returns the query string that is contained in the request URL after the path.
 String getRemoteUser()
          Returns the login of the user making this request, if the user has been authenticated, ornull if the user has not been authenticated.
 String getRequestedSessionId()
          Returns the session ID specified by the client.
 String getRequestURI()
          Returns the part of this request's URL from the protocol name up to the query string in the first line of the HTTP request.
 StringBuffer getRequestURL()
          Reconstructs the URL the client used to make the request.
 String getServletPath()
          Returns the part of this request's URL that calls the servlet.
 HttpSession getSession()
          Returns the current session associated with this request, or if the request does not have a session, creates one.
 HttpSession getSession(boolean create)
          Returns the current HttpSession associated with this request or, if there is no current session andcreate is true, returns a new session.
 Principal getUserPrincipal()
          Returns a java.security.Principal object containing the name of the current authenticated user.
 boolean isRequestedSessionIdFromCookie()
          Checks whether the requested session ID came in as a cookie.
 boolean isRequestedSessionIdFromUrl()
          Deprecated. As of Version 2.1 of the Java Servlet API, useisRequestedSessionIdFromURL() instead.
 boolean isRequestedSessionIdFromURL()
          Checks whether the requested session ID came in as part of the request URL.
 boolean isRequestedSessionIdValid()
          Checks whether the requested session ID is still valid.
 boolean isUserInRole(String role)
          Returns a boolean indicating whether the authenticated user is included in the specified logical "role".

這裏只列舉經常使用的幾個方法(有些API中沒有列舉到的，是在ServletRequest中已有的方法):

(1)得到客戶機信息                                                                       

getRequestURL():返回客戶端發出請求時的完整URL。
getRequestURI():返回請求行中的資源名部分。
getQueryString() :返回請求行中的參數部分。
getRemoteAddr():返回發出請求的客戶機的IP地址。
getRemoteHost() :返回發出請求的客戶機的完整主機名。
getRemotePort():返回客戶機所使用的網絡端口號。
getLocalAddr() :返回WEB服務器的IP地址。
getLocalName():返回WEB服務器的主機名。


(2)得到客戶機請求頭                                                                    

getHeaders(String name):得到請求頭信息組成的Enumeration。


(3)得到客戶機請求參數(客戶端提交的數據)                                            

getParameterMap():獲取參數名和參數值的String[]組成的鍵值對，即返回的類型爲Map(String,String[])，用於多參數值。



3.項目的目錄結構




4.web.xml


<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
  <display-name>javaWeb_07</display-name>
  <welcome-file-list>
    <welcome-file>login.jsp</welcome-file>
  </welcome-file-list>
  <servlet>
    <servlet-name>httpRequestDemo</servlet-name>
    <servlet-class>com.dao.chu.HttpRequestDemo</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>httpRequestDemo</servlet-name>
    <url-pattern>/httpRequest</url-pattern>
  </servlet-mapping>
</web-app>

5.login.jsp


<%@ page language="java" contentType="text/html; charset=utf-8"
    pageEncoding="utf-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<title>登錄頁</title>
</head>
<body>

	<!-- 相對路徑寫action="httpRequest"; -->
	<!-- 絕對路徑寫action="/javaWeb_07/httpRequest"; -->
	
	<form action="httpRequest" method="get">
		用戶名：<input type="text" name="user">
		<br><br>
		密碼  <input type="password" name="password">
		<br><br>
		
		
		<!-- 一組信息 -->
		interesting:
		<input type="checkbox" name="interesting" value="reading">Reading
		<input type="checkbox" name="interesting" value="writing">Writing
		<input type="checkbox" name="interesting" value="football">Football
		<input type="checkbox" name="interesting" value="game">Game
		<input type="checkbox" name="interesting" value="shopping">Shopping
		<input type="checkbox" name="interesting" value="party">Party
		<input type="checkbox" name="interesting" value="TV">TV
		
		<br><br>
		
		<input type="submit" value="提交">
	</form>
	
</body>
</html>

6.HttpRequestDemo.java,分三種狀況，對應後面的三種現象

(1)只寫一個service方法


package com.dao.chu;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.Enumeration;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * 
 * <p>
 * Title: HttpRequestDemo Description:繼承了HttpServlet的測試類
 * </p>
 */
public class HttpRequestDemo extends HttpServlet {

	/** serialVersionUID */
	private static final long serialVersionUID = 1L;

	// 獲得請求的URL地址
	String requestUrl = "";
	// 獲得請求行中的資源部分
	String requestUri = "";
	// 獲得請求的URL地址中附帶的參數
	String queryString = "";
	// 獲得來訪者的IP地址
	String remoteAddr = "";
	// 來訪者主機名
	String remoteHost = "";
	// 客戶機所使用的網絡端口號
	int remotePort = 0;
	// 獲得請求方式GET/POST
	String method = "";
	// 獲取WEB服務器的IP地址
	String localAddr = "";
	// 獲取WEB服務器的主機名
	String localName = "";

	/**
	 * 繼承了HttpServlet的service方法
	 */
	@Override
	protected void service(HttpServletRequest request,
			HttpServletResponse response) throws ServletException, IOException {
		
		//調用公共輸出方法
		commonPrint(request, response);
		
	}
	

	/**
	 * Title: commonPrint
	 * Description:公共輸出方法
	 * @param request
	 * @param response
	 */
	private void commonPrint(HttpServletRequest request,
			HttpServletResponse response) {

		// 設置將字符以"UTF-8"編碼輸出到客戶端瀏覽器
		response.setCharacterEncoding("UTF-8");
		// 經過設置響應頭控制瀏覽器以UTF-8的編碼顯示數據，若是不加這句話，那麼瀏覽器顯示的將是亂碼
		response.setHeader("content-type", "text/html;charset=UTF-8");
		
		requestUrl = request.getRequestURL().toString();
		requestUri = request.getRequestURI();
		queryString = request.getQueryString();
		remoteAddr = request.getRemoteAddr();
		method = request.getMethod();
		localAddr = request.getLocalAddr();
		localName = request.getLocalName();

		PrintWriter out;
		try {
			out = response.getWriter();

			out.write("<hr/>");
			out.write("（1）獲取客戶機信息：");
			out.write("<br/>");
			out.write("請求的URL地址：" + requestUrl);
			out.write("<br/>");
			out.write("請求的資源：" + requestUri);
			out.write("<br/>");
			out.write("請求的URL地址中附帶的參數：" + queryString);
			out.write("<br/>");
			out.write("來訪者的IP地址：" + remoteAddr);
			out.write("<br/>");
			out.write("來訪者的主機名：" + remoteHost);
			out.write("<br/>");
			out.write("使用的端口號：" + remotePort);
			out.write("<br/>");
			out.write("請求的方式：" + method);
			out.write("<br/>");
			out.write("服務器的IP地址：" + localAddr);
			out.write("<br/>");
			out.write("服務器的主機名：" + localName);

			// 獲取的客戶機的請求頭信息
			out.write("<br/>");
			out.write("<hr/>");
			out.write("（2）獲取客戶機的請求頭信息：");
			out.write("<br/>");

			// 獲得全部請求頭名組成的Enumeration
			Enumeration<String> headerNames = request.getHeaderNames();

			// 循環
			while (headerNames.hasMoreElements()) {

				// 獲得全部的請求頭名
				String headerName = (String) headerNames.nextElement();
				// 根據請求頭名獲得全部請求頭值
				String headerValue = request.getParameter(headerName);
				out.write(headerName + ": " + headerValue);
				out.write("<br/>");
			}

			// 獲取的客戶機的請求信息
			out.write("<br/>");
			out.write("<hr/>");
			out.write("（3）獲取客戶機的請求信息：");
			out.write("<br/>");

			// 獲取參數名和參數值的String[]組成的鍵值對
			Map<String, String[]> map = request.getParameterMap();
			Set<Entry<String, String[]>> entrySet = map.entrySet();
			for (Entry<String, String[]> entry : entrySet) {

				out.write(entry.getKey() + "： "
						+ Arrays.asList(entry.getValue()));
				out.write("<br/>");
			}
			
		} catch (IOException e) {
			e.printStackTrace();
		}

	}

}


(2)寫有service方法，doget方法，dopost方法


package com.dao.chu;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.Enumeration;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * 
 * <p>
 * Title: HttpRequestDemo Description:繼承了HttpServlet的測試類
 * </p>
 */
public class HttpRequestDemo extends HttpServlet {

	/** serialVersionUID */
	private static final long serialVersionUID = 1L;

	// 獲得請求的URL地址
	String requestUrl = "";
	// 獲得請求行中的資源部分
	String requestUri = "";
	// 獲得請求的URL地址中附帶的參數
	String queryString = "";
	// 獲得來訪者的IP地址
	String remoteAddr = "";
	// 來訪者主機名
	String remoteHost = "";
	// 客戶機所使用的網絡端口號
	int remotePort = 0;
	// 獲得請求方式GET/POST
	String method = "";
	// 獲取WEB服務器的IP地址
	String localAddr = "";
	// 獲取WEB服務器的主機名
	String localName = "";

	/**
	 * 繼承了HttpServlet的service方法
	 */
	@Override
	protected void service(HttpServletRequest request,
			HttpServletResponse response) throws ServletException, IOException {
		
		System.out.println("調用了service方法");
		//調用公共輸出方法
		commonPrint(request, response);
		
	}
	
	/**
	 * 繼承了HttpServlet的doGet方法
	 */
	@Override
	protected void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		
		System.out.println("調用了doGet方法");
		//調用公共輸出方法
		commonPrint(request, response);
	}
	
	/**
	 * 繼承了HttpServlet的doPost方法
	 */
	@Override
	protected void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		
		System.out.println("調用了doPost方法");
		//調用公共輸出方法
		commonPrint(request, response);
	}
	

	/**
	 * Title: commonPrint
	 * Description:公共輸出方法
	 * @param request
	 * @param response
	 */
	private void commonPrint(HttpServletRequest request,
			HttpServletResponse response) {

		// 設置將字符以"UTF-8"編碼輸出到客戶端瀏覽器
		response.setCharacterEncoding("UTF-8");
		// 經過設置響應頭控制瀏覽器以UTF-8的編碼顯示數據，若是不加這句話，那麼瀏覽器顯示的將是亂碼
		response.setHeader("content-type", "text/html;charset=UTF-8");
		
		requestUrl = request.getRequestURL().toString();
		requestUri = request.getRequestURI();
		queryString = request.getQueryString();
		remoteAddr = request.getRemoteAddr();
		method = request.getMethod();
		localAddr = request.getLocalAddr();
		localName = request.getLocalName();

		PrintWriter out;
		try {
			out = response.getWriter();

			out.write("<hr/>");
			out.write("（1）獲取客戶機信息：");
			out.write("<br/>");
			out.write("請求的URL地址：" + requestUrl);
			out.write("<br/>");
			out.write("請求的資源：" + requestUri);
			out.write("<br/>");
			out.write("請求的URL地址中附帶的參數：" + queryString);
			out.write("<br/>");
			out.write("來訪者的IP地址：" + remoteAddr);
			out.write("<br/>");
			out.write("來訪者的主機名：" + remoteHost);
			out.write("<br/>");
			out.write("使用的端口號：" + remotePort);
			out.write("<br/>");
			out.write("請求的方式：" + method);
			out.write("<br/>");
			out.write("服務器的IP地址：" + localAddr);
			out.write("<br/>");
			out.write("服務器的主機名：" + localName);

			// 獲取的客戶機的請求頭信息
			out.write("<br/>");
			out.write("<hr/>");
			out.write("（2）獲取客戶機的請求頭信息：");
			out.write("<br/>");

			// 獲得全部請求頭名組成的Enumeration
			Enumeration<String> headerNames = request.getHeaderNames();

			// 循環
			while (headerNames.hasMoreElements()) {

				// 獲得全部的請求頭名
				String headerName = (String) headerNames.nextElement();
				// 根據請求頭名獲得全部請求頭值
				String headerValue = request.getParameter(headerName);
				out.write(headerName + ": " + headerValue);
				out.write("<br/>");
			}

			// 獲取的客戶機的請求信息
			out.write("<br/>");
			out.write("<hr/>");
			out.write("（3）獲取客戶機的請求信息：");
			out.write("<br/>");

			// 獲取參數名和參數值的String[]組成的鍵值對
			Map<String, String[]> map = request.getParameterMap();
			Set<Entry<String, String[]>> entrySet = map.entrySet();
			for (Entry<String, String[]> entry : entrySet) {

				out.write(entry.getKey() + "： "
						+ Arrays.asList(entry.getValue()));
				out.write("<br/>");
			}
			
		} catch (IOException e) {
			e.printStackTrace();
		}

	}

}

(3)寫有service方法，doget方法，dopost方法,且service方法調用了父類的service(HttpServletRequest req,HttpServletResponse resp)方法。


package com.dao.chu;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.Enumeration;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * 
 * <p>
 * Title: HttpRequestDemo Description:繼承了HttpServlet的測試類
 * </p>
 */
public class HttpRequestDemo extends HttpServlet {

	/** serialVersionUID */
	private static final long serialVersionUID = 1L;

	// 獲得請求的URL地址
	String requestUrl = "";
	// 獲得請求行中的資源部分
	String requestUri = "";
	// 獲得請求的URL地址中附帶的參數
	String queryString = "";
	// 獲得來訪者的IP地址
	String remoteAddr = "";
	// 來訪者主機名
	String remoteHost = "";
	// 客戶機所使用的網絡端口號
	int remotePort = 0;
	// 獲得請求方式GET/POST
	String method = "";
	// 獲取WEB服務器的IP地址
	String localAddr = "";
	// 獲取WEB服務器的主機名
	String localName = "";

	/**
	 * 繼承了HttpServlet的service方法
	 */
	@Override
	protected void service(HttpServletRequest request,
			HttpServletResponse response) throws ServletException, IOException {
		
		System.out.println("調用了service方法");
		//調用公共輸出方法
		commonPrint(request, response);
		
		//依舊調用父類的方法
		super.service(request, response);

	}
	
	/**
	 * 繼承了HttpServlet的doGet方法
	 */
	@Override
	protected void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		
		System.out.println("調用了doGet方法");
		//調用公共輸出方法
		commonPrint(request, response);
	}
	
	/**
	 * 繼承了HttpServlet的doPost方法
	 */
	@Override
	protected void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		
		System.out.println("調用了doPost方法");
		//調用公共輸出方法
		commonPrint(request, response);
	}
	

	/**
	 * Title: commonPrint
	 * Description:公共輸出方法
	 * @param request
	 * @param response
	 */
	private void commonPrint(HttpServletRequest request,
			HttpServletResponse response) {

		// 設置將字符以"UTF-8"編碼輸出到客戶端瀏覽器
		response.setCharacterEncoding("UTF-8");
		// 經過設置響應頭控制瀏覽器以UTF-8的編碼顯示數據，若是不加這句話，那麼瀏覽器顯示的將是亂碼
		response.setHeader("content-type", "text/html;charset=UTF-8");
		
		requestUrl = request.getRequestURL().toString();
		requestUri = request.getRequestURI();
		queryString = request.getQueryString();
		remoteAddr = request.getRemoteAddr();
		method = request.getMethod();
		localAddr = request.getLocalAddr();
		localName = request.getLocalName();

		PrintWriter out;
		try {
			out = response.getWriter();

			out.write("<hr/>");
			out.write("（1）獲取客戶機信息：");
			out.write("<br/>");
			out.write("請求的URL地址：" + requestUrl);
			out.write("<br/>");
			out.write("請求的資源：" + requestUri);
			out.write("<br/>");
			out.write("請求的URL地址中附帶的參數：" + queryString);
			out.write("<br/>");
			out.write("來訪者的IP地址：" + remoteAddr);
			out.write("<br/>");
			out.write("來訪者的主機名：" + remoteHost);
			out.write("<br/>");
			out.write("使用的端口號：" + remotePort);
			out.write("<br/>");
			out.write("請求的方式：" + method);
			out.write("<br/>");
			out.write("服務器的IP地址：" + localAddr);
			out.write("<br/>");
			out.write("服務器的主機名：" + localName);

			// 獲取的客戶機的請求頭信息
			out.write("<br/>");
			out.write("<hr/>");
			out.write("（2）獲取客戶機的請求頭信息：");
			out.write("<br/>");

			// 獲得全部請求頭名組成的Enumeration
			Enumeration<String> headerNames = request.getHeaderNames();

			// 循環
			while (headerNames.hasMoreElements()) {

				// 獲得全部的請求頭名
				String headerName = (String) headerNames.nextElement();
				// 根據請求頭名獲得全部請求頭值
				String headerValue = request.getParameter(headerName);
				out.write(headerName + ": " + headerValue);
				out.write("<br/>");
			}

			// 獲取的客戶機的請求信息
			out.write("<br/>");
			out.write("<hr/>");
			out.write("（3）獲取客戶機的請求信息：");
			out.write("<br/>");

			// 獲取參數名和參數值的String[]組成的鍵值對
			Map<String, String[]> map = request.getParameterMap();
			Set<Entry<String, String[]>> entrySet = map.entrySet();
			for (Entry<String, String[]> entry : entrySet) {

				out.write(entry.getKey() + "： "
						+ Arrays.asList(entry.getValue()));
				out.write("<br/>");
			}
			
		} catch (IOException e) {
			e.printStackTrace();
		}

	}

}


7.填寫jsp頁面表單，發出HTTP請求



8.三種狀況的現象

(1)頁面顯示



控制檯無輸出，說明成功調用了service方法。


(2)頁面顯示





控制檯輸出:


說明雖然寫了dopost和doget方法，可是卻沒有接收到請求。


(3)頁面顯示



控制檯打印:


很顯然此次接收到了doGET方法


8.爲了追求根源，咱們找到HttpServlet的service方法的源碼:

/**
	 * <p>Title: HttpServlet的service方法的源碼</p>
	 * <p>Description: </p>
	 * @throws ServletException
	 * @throws IOException
	 */
	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;
				try {
					ifModifiedSince = req.getDateHeader("If-Modified-Since");
				} catch (IllegalArgumentException iae) {
					ifModifiedSince = -1L;
				}
				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);
		}
	}

咱們能夠看到

String method = req.getMethod();if (method.equals("GET")){doGet(req, resp);}等

的確有接收請求的方式，根據判斷的請求方式轉到相應的方法。而咱們在(2)中繼承了HttpServlet，覆蓋了service方法，沒有調用原來父類的方法，因此即便寫了doget和dopost也接收不到請求。



附:

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