白痴与Servlet的深入交流（二）内含请求重定向等知识点

其他 2021-01-29 14:07:30 阅读次数: 0

请求重定向

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在某些情况下，针对客户端的请求，一个Servlet类可能无法完成全部工作。这时，可以使用请求重定向来完成。所谓请求重定向，指的是Web服务器接收到客户端的请求后，可能由于某些条件限制，不能访问当前请求URL所指向的Web资源，而是指定了一个新的资源路径，让客户端重新发送请求。

为了实现请求重定向，在HttpServletResponse接口中，定义了一个sendRedirect()方法，该方法用于生成302响应码和Location响应头，从而通知客户端重新访问Location响应头中指定的URL，sendRedirect()方法的完整语法如下所示：
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sendRedirect()方法的工作原理

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入门小案例——登陆案例

login.html

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
	<h1>登录页面</h1>
	<font color="red">用户或密码错误，请重新输入</font><br />
	<form action="http://localhost:8080/Review4/login" method="get">
		<table>
			<tr>
				<td>用户名：</td>
				<td><input type="text" name="username" /></td>
			</tr>
			<tr>
				<td>密码：</td>
				<td><input type="password" name="pwd" /></td>
			</tr>
			<tr>
				<td colspan="2" align="center">
				<input type="submit" name="submit" value="登陆" />
				</td>
			</tr>
		</table>
	</form>
	
</body>
</html>

welcome.html

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>User,Welcome!</title>
</head>
<body>
	<h1>登陆成功！</h1>
	<h2>いらっしゃいませ</h2><br />
	<h2>欢迎光临</h1>
</body>
</html>

LoginServlet.java


import java.io.IOException;

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

/**
 * Servlet implementation class LoginServlet
 */
public class LoginServlet extends HttpServlet {
    
    
	private static final long serialVersionUID = 1L;

	/**
	 * @see HttpServlet#HttpServlet()
	 */
	public LoginServlet() {
    
    
		super();
		// TODO Auto-generated constructor stub
	}

	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
	 *      response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
    
    
		// TODO Auto-generated method stub
		// 1.获取登陆的用户名和密码
		String nameString = request.getParameter("username");
		String passwordString = request.getParameter("pwd");

		// 2.判断用户名和密码是否正确
		if (nameString.equals("admin") && passwordString.equals("123")) {
    
    
			response.sendRedirect("/Review4/welcome.html");
		} else {
    
    
			response.sendRedirect("/Review4/login.html");
		}
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse
	 *      response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
    
    
		// TODO Auto-generated method stub
		doGet(request, response);
	}

}

全局配置：
在这里插入图片描述
运行部分效果：
在这里插入图片描述
在这里插入图片描述
原理图如下：
在这里插入图片描述

HttpServletRequest

在Servlet API中，定义了一个HttpServletRequest接口，它继承自ServletRequest接口，专门用来封装HTTP请求消息。由于HTTP请求消息分为请求行、请求消息头和请求消息体三部分，因此，在HttpServletRequest接口中定义了获取请求行、请求头和请求消息体的相关方法

获取请求行的相关方法（部分）

当访问Servlet时，会在请求消息的请求行中，包含请求方法、请求资源名、请求路径等信息，为了获取这些信息，在HttpServletRequest接口中，定义了一系列用于获取请求行的方法，如表所示。
在这里插入图片描述
在这里插入图片描述
在这里插入图片描述

入门小案例

RequestLineServlet.java

package Request;

import java.io.IOException;

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

/**
 * Servlet implementation class RequestLineServlet
 */
public class RequestLineServlet extends HttpServlet {
    
    
	private static final long serialVersionUID = 1L;

	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
	 *      response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
    
    
		// TODO Auto-generated method stub
		// 1.获取请求提交的方式
		String methodString = request.getMethod();
		System.out.println("请求方式：" + methodString);
		// 2.获取请求的协议
		String protocolString = request.getProtocol();
		System.out.println("请求的协议：" + protocolString);
		// 3.获取项目路径
		String contextPathString = request.getContextPath();
		System.out.println("项目路径：" + contextPathString);
		// 4.获取servlet路径
		String servletPathString = request.getServletPath();
		System.out.println("servlet路径：" + servletPathString);
		// 5.获取请求的路径
		String pathURI = request.getRequestURI();
		StringBuffer pathURL = request.getRequestURL();
		System.out.println("URI对应的值：" + pathURI + "   URL路径对应的值：" + pathURL);
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse
	 *      response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
    
    
		// TODO Auto-generated method stub
		doGet(request, response);
	}

}

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_2_5.xsd" id="WebApp_ID" version="2.5">
  <display-name>Review4</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  <servlet>
    <servlet-name>PrintServlet</servlet-name>
    <servlet-class>PrintServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>PrintServlet</servlet-name>
    <url-pattern>/ps</url-pattern>
  </servlet-mapping>
  <servlet>
    <description></description>
    <display-name>ChineseServlet</display-name>
    <servlet-name>ChineseServlet</servlet-name>
    <servlet-class>ChineseServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>ChineseServlet</servlet-name>
    <url-pattern>/cs</url-pattern>
  </servlet-mapping>
  <servlet>
    <description></description>
    <display-name>ChineseServlet2</display-name>
    <servlet-name>ChineseServlet2</servlet-name>
    <servlet-class>ChineseServlet2</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>ChineseServlet2</servlet-name>
    <url-pattern>/cs2</url-pattern>
  </servlet-mapping>
  <servlet>
    <description></description>
    <display-name>refreshServlet</display-name>
    <servlet-name>refreshServlet</servlet-name>
    <servlet-class>refreshServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>refreshServlet</servlet-name>
    <url-pattern>/rs</url-pattern>
  </servlet-mapping>
  <servlet>
    <description></description>
    <display-name>LoginServlet</display-name>
    <servlet-name>LoginServlet</servlet-name>
    <servlet-class>LoginServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>LoginServlet</servlet-name>
    <url-pattern>/login</url-pattern>
  </servlet-mapping>
  <servlet>
    <description></description>
    <display-name>RequestLineServlet</display-name>
    <servlet-name>RequestLineServlet</servlet-name>
    <servlet-class>Request.RequestLineServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>RequestLineServlet</servlet-name>
    <url-pattern>/line</url-pattern>
  </servlet-mapping>
</web-app>

全局配置：
在这里插入图片描述
运行结果：
在这里插入图片描述
URI对应的值：/项目名称/servlet路径
URL对应的值是完整的：如上图，http://localhost:8080/Review4/line

获取请求头的相关方法

当请求Servlet时，需要通过请求头向服务器传递附加信息，例如，客户端可以接收的数据类型，压缩方式，语言等等。为此，在HttpServletRequest接口中，定义了一系列用于获取HTTP请求头字段的方法，如表所示。
在这里插入图片描述
在这里插入图片描述

入门小案例

RequestHeaderServlet.java

package Request;

import java.io.IOException;
import java.util.Enumeration;

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

/**
 * Servlet implementation class RequestHeaderServlet
 */
public class RequestHeaderServlet extends HttpServlet {
    
    
	private static final long serialVersionUID = 1L;

	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
	 *      response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
    
    
		// TODO Auto-generated method stub
		 
		// 1.获取所有的消息头名称
		Enumeration<String> enumeration = request.getHeaderNames();
		// 2.遍历
		while (enumeration.hasMoreElements()) {
    
    
			// 3.获取消息头
			String nameString = enumeration.nextElement();
			// 4.获取消息头对应的值
			String valueString = request.getHeader(nameString);
			response.getWriter().print("消息头：" + nameString + " " + valueString + "<br />");
		}
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse
	 *      response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
    
    
		// TODO Auto-generated method stub
		doGet(request, response);
	}

}

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_2_5.xsd" id="WebApp_ID" version="2.5">
  <display-name>Review4</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  <servlet>
    <servlet-name>PrintServlet</servlet-name>
    <servlet-class>PrintServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>PrintServlet</servlet-name>
    <url-pattern>/ps</url-pattern>
  </servlet-mapping>
  <servlet>
    <description></description>
    <display-name>ChineseServlet</display-name>
    <servlet-name>ChineseServlet</servlet-name>
    <servlet-class>ChineseServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>ChineseServlet</servlet-name>
    <url-pattern>/cs</url-pattern>
  </servlet-mapping>
  <servlet>
    <description></description>
    <display-name>ChineseServlet2</display-name>
    <servlet-name>ChineseServlet2</servlet-name>
    <servlet-class>ChineseServlet2</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>ChineseServlet2</servlet-name>
    <url-pattern>/cs2</url-pattern>
  </servlet-mapping>
  <servlet>
    <description></description>
    <display-name>refreshServlet</display-name>
    <servlet-name>refreshServlet</servlet-name>
    <servlet-class>refreshServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>refreshServlet</servlet-name>
    <url-pattern>/rs</url-pattern>
  </servlet-mapping>
  <servlet>
    <description></description>
    <display-name>LoginServlet</display-name>
    <servlet-name>LoginServlet</servlet-name>
    <servlet-class>LoginServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>LoginServlet</servlet-name>
    <url-pattern>/login</url-pattern>
  </servlet-mapping>
  <servlet>
    <description></description>
    <display-name>RequestLineServlet</display-name>
    <servlet-name>RequestLineServlet</servlet-name>
    <servlet-class>Request.RequestLineServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>RequestLineServlet</servlet-name>
    <url-pattern>/line</url-pattern>
  </servlet-mapping>
  <servlet>
    <description></description>
    <display-name>RequestHeaderServlet</display-name>
    <servlet-name>RequestHeaderServlet</servlet-name>
    <servlet-class>Request.RequestHeaderServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>RequestHeaderServlet</servlet-name>
    <url-pattern>/header</url-pattern>
  </servlet-mapping>
  <servlet>
    <description></description>
    <display-name>DownLoadServlet</display-name>
    <servlet-name>DownLoadServlet</servlet-name>
    <servlet-class>Request.DownLoadServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>DownLoadServlet</servlet-name>
    <url-pattern>/download</url-pattern>
  </servlet-mapping>
</web-app>

全局配置：
在这里插入图片描述
运行结果：
乱码
在这里插入图片描述
在servlet中加入代码

response.setContentType("text/html;charset=utf-8");

即可解决
在这里插入图片描述
运行结果：
在这里插入图片描述

防盗链的小案例

需求：
在这里插入图片描述
在这里插入图片描述
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_2_5.xsd" id="WebApp_ID" version="2.5">
  <display-name>Review4</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  <servlet>
    <servlet-name>PrintServlet</servlet-name>
    <servlet-class>PrintServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>PrintServlet</servlet-name>
    <url-pattern>/ps</url-pattern>
  </servlet-mapping>
  <servlet>
    <description></description>
    <display-name>ChineseServlet</display-name>
    <servlet-name>ChineseServlet</servlet-name>
    <servlet-class>ChineseServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>ChineseServlet</servlet-name>
    <url-pattern>/cs</url-pattern>
  </servlet-mapping>
  <servlet>
    <description></description>
    <display-name>ChineseServlet2</display-name>
    <servlet-name>ChineseServlet2</servlet-name>
    <servlet-class>ChineseServlet2</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>ChineseServlet2</servlet-name>
    <url-pattern>/cs2</url-pattern>
  </servlet-mapping>
  <servlet>
    <description></description>
    <display-name>refreshServlet</display-name>
    <servlet-name>refreshServlet</servlet-name>
    <servlet-class>refreshServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>refreshServlet</servlet-name>
    <url-pattern>/rs</url-pattern>
  </servlet-mapping>
  <servlet>
    <description></description>
    <display-name>LoginServlet</display-name>
    <servlet-name>LoginServlet</servlet-name>
    <servlet-class>LoginServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>LoginServlet</servlet-name>
    <url-pattern>/login</url-pattern>
  </servlet-mapping>
  <servlet>
    <description></description>
    <display-name>RequestLineServlet</display-name>
    <servlet-name>RequestLineServlet</servlet-name>
    <servlet-class>Request.RequestLineServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>RequestLineServlet</servlet-name>
    <url-pattern>/line</url-pattern>
  </servlet-mapping>
  <servlet>
    <description></description>
    <display-name>RequestHeaderServlet</display-name>
    <servlet-name>RequestHeaderServlet</servlet-name>
    <servlet-class>Request.RequestHeaderServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>RequestHeaderServlet</servlet-name>
    <url-pattern>/header</url-pattern>
  </servlet-mapping>
  <servlet>
    <description></description>
    <display-name>DownLoadServlet</display-name>
    <servlet-name>DownLoadServlet</servlet-name>
    <servlet-class>Request.DownLoadServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>DownLoadServlet</servlet-name>
    <url-pattern>/download</url-pattern>
  </servlet-mapping>
</web-app>

DownLoadServlet.java

package Request;

import java.io.IOException;

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

/**
 * Servlet implementation class DownLoadServlet
 */
public class DownLoadServlet extends HttpServlet {
    
    
	private static final long serialVersionUID = 1L;

	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
	 *      response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
    
    
		// TODO Auto-generated method stub
		// 1.获取Referer请求头：Referer=http://localhost:8080/Review4/download
		String refererString = request.getHeader("Referer");
		// 2.获取服务器名称
		String serverNameString = request.getServerName();
		// 3.判断是否是从本网站发起的下载请求
		if (refererString != null && refererString.contains(serverNameString)) {
    
    
			response.getWriter().print("download......");
		} else {
    
    
			response.sendRedirect("/Review4/download.html");
		}
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse
	 *      response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
    
    
		// TODO Auto-generated method stub
		doGet(request, response);
	}

}

download.html

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
	<a href="/Review4/download">从这个网站的页面打开，才能下载！</a>
</body>
</html>

全局配置：
在这里插入图片描述
运行结果如下：
在这里插入图片描述
在这里插入图片描述
由于这里没有另一个服务器，所以就无法演示盗链的情况，但是基本原理就是上面那样的

之后我会持续更新，如果喜欢我的文章，请记得一键三连哦，点赞关注收藏，你的每一个赞每一份关注每一次收藏都将是我前进路上的无限动力 ！！！↖(▔▽▔)↗感谢支持！

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