servlet-2

5、HttpServletRequest 类

5.1、HttpServletRequest 类有什么作用

每次只要有请求进入 Tomcat 服务器,Tomcat服务器就会把请求过来的HTTP协议解析好封装到Request对象中。然后传递到 servlet方法(doGet 和 doPost)中给我们使用,我们可以通过 HttpServletRequest 对象,获取到所有请求的信息

5.2、HttpServletRequest 类的常用方法

getRequestURI() 获取请求的资源路径
getRequestURL() 获取请求的统一资源定位符(绝对路径)
getRemoteHost() 获取客户端 ip 地址
getHeader 获取请求头
getMethod() 获取请求方式 GET或POST

RequestAPIServlet:

package com.aiguigu.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
public class RequestAPIServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //getRequestURI()
        System.out.println("URI =>" + req.getRequestURI());
        //getRequestURL()       获取请求的统一资源定位符(绝对路径)
        System.out.println("URL =>" + req.getRequestURL());
        //getRemoteHost()       获取客户端 ip 地址
        System.out.println("客户端 ip =>" + req.getRemoteHost());
        //getHeader             获取请求头
        System.out.println("请求头 =>" + req.getHeader("User-Agent"));
        //getMethod()           获取请求方式 GET或POST
        System.out.println("请求的方式 =>" + req.getMethod());
    }
}

web.xml:

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0">
    <servlet>
        <servlet-name>RequestAPIServlet</servlet-name>
        <servlet-class>com.aiguigu.servlet.RequestAPIServlet</servlet-class>
    </servlet>

    <servlet-mapping>
        <servlet-name>RequestAPIServlet</servlet-name>
        <url-pattern>/requestAPIServlet</url-pattern>
    </servlet-mapping>
    
</web-app>

运行效果:

请求的方式 =>GET
URI =>/07_servlet/requestAPIServlet
URL =>http://localhost:8080/07_servlet/requestAPIServlet
客户端 ip =>0:0:0:0:0:0:0:1
请求头 =>Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/96.0.4664.55 Safari/537.36 Edg/96.0.1054.43

5.3、如何获取请求参数

ParameterServlet:

package com.aiguigu.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.Arrays;

public class ParameterServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String username = req.getParameter("username");
        String password = req.getParameter("password");
        String[] hobby = req.getParameterValues("hobby");


        System.out.println("用户名:" + username);
        System.out.println("密码:" + password);
        System.out.println("兴趣爱好:" + Arrays.asList(hobby));
    }
}

form.html:

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<form action="http://localhost:8080/07_servlet/parameterServlet" method="get">
    用户名:<input type="text" name="username" ><br/>
    密码:<input type="password" name="password" ><br/>
    兴趣爱好: <input type="checkbox" name="hobby" value="cpp">C++
    <input type="checkbox" name="hobby" value="java">Java
    <input type="checkbox" name="hobby" value="js">JavaScript<br/>
    <input type="submit" >

</form>
</body>
</html>

运行结果:

用户名:qwe123
密码:qwe123
兴趣爱好:[cpp, java, js]

5.3.1、 解决 Post 请求 中午乱码问题

servlet-2
代码实现:

 @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //设置请求体的字符为 UTF-8 从而解决 post 请求乱码问题
        //也要在获取请求参数之前调用才有效
        req.setCharacterEncoding("UTF-8");

        String username = req.getParameter("username");
        String password = req.getParameter("password");
        String[] hobby = req.getParameterValues("hobby");


        System.out.println("用户名:" + username);
        System.out.println("密码:" + password);
        System.out.println("兴趣爱好:" + Arrays.asList(hobby));
    }

运行效果:
servlet-2

5.4 、请求的转发

什么是请求的转发?
请求转发是指,服务器收到请求后,从一个资源跳转到另一个资源的操作叫请求转发
servlet-2
Servlet1

package com.aiguigu.servlet;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class Servlet1 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //获取请求的参数(办事的材料)查看
        String username = req.getParameter("username");
        System.out.println("在Servlet(柜台1) 中查看 参数(材料):" + username);

        //给材料 盖一个章
        req.setAttribute("key1","柜台1的章");

        //问路:S额rvlet(柜台2)怎么走

//        RequestDispatcher requestDispatcher = req.getRequestDispatcher("/servlet2");
        RequestDispatcher requestDispatcher = req.getRequestDispatcher("/WEB-INF/form.html");

        //走向 Servlet2 (柜台2)
        requestDispatcher.forward(req,resp);
    }
}

Servlet2

package com.aiguigu.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class Servlet2 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //获取请求的参数(办事的材料)查看
        String username = req.getParameter("username");
        System.out.println("在Servlet(柜台1) 中查看 参数(材料)" + username);

        //查看 柜台1 是否有盖章
        Object key1 = req.getAttribute("key1");
        System.out.println("柜台1是否有章:" + key1);

        //处理自己的业务
        System.out.println("Servlet2 处理自己的业务");
    }
}

运行结果:

在Servlet(柜台1) 中查看 参数(材料):null
在Servlet(柜台1) 中查看 参数(材料)null
柜台1是否有章:柜台1的章
Servlet2 处理自己的业务

servlet-2

5.5、base 标签的作用

index.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>首页</title>
<!--base 标签设置页面相对路径工作时参照的地址
        href 属性就是参数的地址值
-->

</head>
<body>
    这是Web下的index.html <br/>
    <a href="a/b/c.html">a/b/c.html</a>
    <a href="http://localhost:8080/07_servlet/forwardC">请求转发:a/b/c.html</a>
</body>
</html>

c.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <base href="http://localhost:8080/07_servlet/a/b/">
</head>
<body>
    这是a下的b下的c.html页面<br/>
    <a href="../../index.html">跳回首页</a>
</body>
</html>

ForwardC

package com.aiguigu.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class ForwardC extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("经过了 Forward 程序");

        req.getRequestDispatcher("/a/b/c.html").forward(req,resp);
    }
}

运行结果
servlet-2
点击上图任意一个超链接文本
servlet-2
分析:
servlet-2

5.6、Web中的相对路径和绝对路径

servlet-2

5.7、web 中 / 斜杠的不同意义

在 web 中 / 斜杠 是一种绝对路径。
/ 斜杠 如果被浏览器解析,得到的地址是:http://ip:port/
servlet-2
/ 斜杠 如果被服务器解析,得到的地址是:http://ip:port/工程路径
1、/forwardC
2、servletContext.getRealPath("/");
3、request.getRequestDispatcher("/");

特殊情况:respone.sendRediect("/");		把斜杠发生给浏览器解析。得到 http://ip:port/

6、HttpServletRespone 类

6.1、HttpServletRespone 类的作用

HttpServletRespone 类 和HttpServletRequest 类一样。每次请求进来,Tomcat服务器都会创建一个 Respone 对象传递给 Servlet 程序去使用。HttpServletResquest 表示请求过来的信息,HttpServletRespone 表示所有响应的信息,
我们如果需要设置返回给客户端的信息,都可以通过 HttpServletRespone 对象进行设置

6.2、两个输出流的说明

字节流 getOutputstream();
字符流 getWriter();
两个流同时只能使用一个。
使用了字节流,就不能使用字符流,反之亦然,否则就会报错
servlet-2

6.3、如何往客户端回传数据

要求:往客户端回传 字符串 数据。

ResponseIOServlet

package com.aiguigu.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

public class ResponseIOServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        PrintWriter writer = resp.getWriter();
        writer.write("respone context!!!");
    }
}

运行结果:
servlet-2

6.4、响应的乱码解决

输入中文会乱码:

servlet-2

解决响应乱码方案一:
ResponseIOServlet

package com.aiguigu.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

public class ResponseIOServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
        //设置服务器字符集为UTF-8
         resp.setCharacterEncoding("UTF-8");
        //通过响应头,设置浏览器也使用UTF-8字符集
   		resp.setHeader("Content-Type","text/html;charset=UTF-8 " );
        // 要求:往客户端回传 字符串 数据
        PrintWriter writer = resp.getWriter();
        writer.write("这是中文");
    }
}

解决响应乱码方案二(推荐):

//它会同时设置服务器和客户端都使用UTF-8字符集,还设置了响应头
//此方法一定要在获取流对象之前调用才有效
		resp.setContentType("text/html;charset=UTF-8");

运行效果:
servlet-2

6.5、请求重定向

请求重定向,是指客户端给服务器发请求,然后服务器告诉客户端,我给你一些地址,你去新地址访问。叫请求重定向(因为之前的地址可能已经被废弃了)
servlet-2
tip:浏览器无法直接访问 WEB-INF 目录及其下的项目

代码实现:
Response1

package com.aiguigu.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class Response1 extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("response1 到此一游");
        req.setAttribute("key1","value1");
        resp.setStatus(302);

        resp.setHeader("Location","http://localhost:8080/07_servlet/response2");
        //resp.setHeader("Location","http://localhost:8080/07_servlet/WEB-INF/form.html");

    }
}

Response2

package com.aiguigu.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class Response2 extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.getWriter().write("response2 result");
        System.out.println(req.getAttribute("key1"));
    }
}

运行结果:
1、浏览器地址栏会发生变化

servlet-2
3、不共享域中数据

response1 到此一游
null

4、不能访问WEB-INF下的资源
servlet-2

第二种方式:

resp.sendRedirect("http://localhost:8080/07_servlet/response2");

笔记来自尚硅谷JavaWeb视频教学

上一篇:阿里云物联网平台快速入门实践


下一篇:Adobe Photoshop CC 2019下载中文永久安装和破解教程