Java Request和Response对象 - Request篇

小灰灰 2023-09-23 15:11 68阅读 0赞

#### 文章目录 ####

*   *  Request
     *   *  Request继承体系
         *  Request获取请求数据
         *   *  获取请求数据基本使用
             *  通用方式获取请求参数
             *  Request请求参数中文乱码处理
         *  请求转发

### Request ###

> Request: 使用 request对象来获取请求数据
> 
> Response: 使用 response对象来设置响应数据

#### Request继承体系 ####

**Request的继承体系如下**

> Tomcat需要解析请求数据，封装为request对象，并且创建request对象传递到service方法中; 因此Tomcat需要实现HttpServletRequest接口
> 
> 学习实现类RequestFacade的使用，可以查阅JavaEE API文档的HttpServletRequest接口

![在这里插入图片描述][60af378e683045b88b507001219c0a2b.png_pic_center]

#### Request获取请求数据 ####

##### 获取请求数据基本使用 #####

**请求数据分为三部分**:

> 请求头
> 
> 请求行
> 
> 请求体

**获取请求头的方法如下**:

<table> 
 <thead> 
  <tr> 
   <th>方法名</th> 
   <th>描述</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>String getHeader(String name)</td> 
   <td>根据请求头名称，获取值</td> 
  </tr> 
 </tbody> 
</table>

**获取请求行的方法如下**:

<table> 
 <thead> 
  <tr> 
   <th>方法名</th> 
   <th>描述</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>String getMethod()</td> 
   <td>获取的请求方式</td> 
  </tr> 
  <tr> 
   <td>String getContextPath()</td> 
   <td>获取虚拟目录(项目访问路径)</td> 
  </tr> 
  <tr> 
   <td>StringBuffer getRequestURL()</td> 
   <td>获取URL(统一资源定位符)</td> 
  </tr> 
  <tr> 
   <td>String getRequestURI()</td> 
   <td>获取URI(统一资源标识符)</td> 
  </tr> 
  <tr> 
   <td>String getQueryString()</td> 
   <td>获取请求参数(GET方式)</td> 
  </tr> 
 </tbody> 
</table>

> 演示代码: 启动服务器后通过查询字符串传递参数, 访问URL: `http://localhost:8080/request-demo/req?name=chenyq&age=18`

@WebServlet("/req")
    public class RequestDemo extends HttpServlet {
        
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        
            // 获取请求的方式
            String method = req.getMethod();
            System.out.println(method); // GET
    
            // 获取虚拟目录(项目访问路径)
            String contextPath = req.getContextPath();
            System.out.println(contextPath); // /request-demo
    
            // 获取URL统一资源定位符
            StringBuffer requestURL = req.getRequestURL();
            System.out.println(requestURL.toString()); // http://localhost:8080/request-demo/req
    
            // 获取URI统一资源标识符
            String requestURI = req.getRequestURI();
            System.out.println(requestURI); // /request-demo/req
    
            // 获取请求参数
            String queryString = req.getQueryString();
            System.out.println(queryString); // name=chenyq&age=18
        }
    }

**获取请求体(*post请求才有请求体*)的方法如下**:

<table> 
 <thead> 
  <tr> 
   <th>方法名</th> 
   <th>描述</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>ServletInputStream getInputStream()</td> 
   <td>获取字节输入流</td> 
  </tr> 
  <tr> 
   <td>BufferedReader getReader()</td> 
   <td>获取字符输入流</td> 
  </tr> 
 </tbody> 
</table>

> 我们编写一个html文件, 在文件中使用表单模拟post请求

<form method="post" action="http://localhost:8080/request-demo/req">
      <div>
        <span>请输入账号: </span>
        <input type="text" name="username">
      </div>
      <div>
        <span>请输入密码: </span>
        <input type="password" name="password">
      </div>
      <input type="submit" value="提交">
    </form>

> 通过post获取到请求体

@WebServlet("/req")
    public class RequestDemo extends HttpServlet {
        
        @Override
        protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        
            // 获取post请求体(post的请求的参数)
            // 1. 获取字符输入流
            BufferedReader br = req.getReader();
            // 2. 读取数据
            String line = br.readLine();
            System.out.println(line); // username=admin&password=1234
        }
    }

##### 通用方式获取请求参数 #####

**上面我们说了请求参数获取方式**:

> GET 方式：`String getQueryString()`
> 
> POST 方式: `BufferedReader getReader()`

**思考**:

> GET 请求方式 和 POST 请求方式 区别主要在于获取请求参数的方式不一样，是否可以提供一种统一获取请求参数的方式，从而统一doGet 和 doPost方法内的代码？

**Request 通用获取请求参数的方法如下**:

> 通用指的是: 获取参数的方法既可以被用于Get, 又可以被用于Post请求;
> 
> 既然有了统一获取参数的方法, 那么我们doPost方法中直接调用doGet即可, 无需再编写重复逻辑的代码

<table> 
 <thead> 
  <tr> 
   <th>方法名</th> 
   <th>描述</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>Map&lt;String, String[ ]&gt; getParameterMap()</td> 
   <td>获取所有参数Map集合, 如果key相同, 会将值放入一个数组中</td> 
  </tr> 
  <tr> 
   <td>String[ ] getParameterValues(String name)</td> 
   <td>根据名称获取一个参数值的数组</td> 
  </tr> 
  <tr> 
   <td>String getParameter(String name)</td> 
   <td>根据名称获取一个单个参数值</td> 
  </tr> 
 </tbody> 
</table>

**示例代码**:

> 获取所有参数Map集合

@WebServlet("/req2")
    public class RequestDemo2 extends HttpServlet {
        
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        
          	// 获取所有参数Map集合
            Map<String, String[]> map = req.getParameterMap();
            // 遍历展示
            for (String key : map.keySet()) {
        
                String[] values = map.get(key);
                System.out.print(key + ":");
                for (String value : values) {
        
                    System.out.print(value + " ");
                }
                System.out.println();
            }
        }
    
        @Override
        protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        
          	// 调用doGet方法, 避免编写重复逻辑
            this.doGet(req, resp);
        }
    }

> 根据名称获取一个参数值的数组

@WebServlet("/req2")
    public class RequestDemo2 extends HttpServlet {
        
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        
            // 根据名称获取一个参数值的数组
            String[] hobbies = req.getParameterValues("hobby");
            // 遍历展示
            for (String hobby : hobbies) {
        
                System.out.println(hobby);
            }
        @Override
        protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        
          	// 调用doGet方法, 避免编写重复逻辑
            this.doGet(req, resp);
        }
    }

> 根据名称获取一个单个参数值

@WebServlet("/req2")
    public class RequestDemo2 extends HttpServlet {
        
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        
            // 根据名称获取一个单个参数值
            String username = req.getParameter("username");
            System.out.println(username);
        }
    
        @Override
        protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        
          	// 调用doGet方法, 避免编写重复逻辑
            this.doGet(req, resp);
        }
    }

##### Request请求参数中文乱码处理 #####

> 请求参数如果存在中文数据，是会出现乱码问题的

**POST请求解决方案**:

> 设置输入流的编码为"UTF-8"

request.setCharacterEncoding("UTF-8");

> 演示代码

@WebServlet("/req3")
    public class RequestDemo3 extends HttpServlet {
        
        @Override
        protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        
            // 1. 解决Post乱码
            request.setCharacterEncoding("UTF-8"); // 设置字符输入流的编码为UTF-8
    
            // 2. 获取username
            String username = request.getParameter("username");
            System.out.println(username);
        }
    
        @Override
        protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        
            this.doGet(request, response);
        }
    }

**GET和POST的通用方式**

> 浏览器进行URL编码默认使用的是UTF-8, 而Tomcat进行URL解码默认的是ISO-8859-1;
> 
> 所以我们需要拿到Tomcat解码的结果, 对其先编码，再解码;
> 
> Tomcat 8.0 之后，已将GET请求乱码问题解决，设置默认的解码方式为UTF-8

new String(username.getBytes("ISO-8859-1"),"UTF-8");

> 演示代码

@WebServlet("/req3")
    public class RequestDemo3 extends HttpServlet {
        
        @Override
        protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        
            // 1. 获取username参数
            String username = request.getParameter("username");
    
            // 2. 对获取到的username先通过ISO-8859-1编码再通过UTF-8解码
            username = new String(username.getBytes("ISO-8859-1"), "UTF-8");
    
            System.out.println(username);
        }
    
        @Override
        protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        
            this.doGet(request, response);
        }
    }

#### 请求转发 ####

**请求转发(forward)：一种在服务器内部的资源跳转方式**

> 例如下图, 浏览器向Tomcat请求资源A; 资源A又将请求转发给资源B

![在这里插入图片描述][c4c9be9456734ae0862283681aa6ffa6.png_pic_center]

**实现方式**：

req.getRequestDispatcher("资源B路径").forward(req,resp);

**示例代码如下**:

> 分别创建一个RequestDemo4, 访问路径为/req4和一个RequestDemo5, 访问路径为/req5

@WebServlet("/req4")
    public class RequestDemo4 extends HttpServlet {
        
        @Override
        protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        
            System.out.println("demo4...");
        }
    
        @Override
        protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        
            this.doGet(request, response);
        }
    }

@WebServlet("/req5")
    public class RequestDemo5 extends HttpServlet {
        
        @Override
        protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        
            System.out.println("demo5...");
        }
    
        @Override
        protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        
            this.doGet(request, response);
        }
    }

> 再在demo4中将请求转发发哦demo5中

@WebServlet("/req4")
    public class RequestDemo4 extends HttpServlet {
        
        @Override
        protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        
            System.out.println("demo4...");
    
            // 请求转发, 将请求转发到/req5
            request.getRequestDispatcher("/req5").forward(request, response);
        }
    
        @Override
        protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        
            this.doGet(request, response);
        }
    }

> 访问/req4的打印结果

demo4...
    demo5...

**在很多时候, 我们通常是在资源A中处理一部分数据, 然后再转发给资源B继续处理; 那么就需要请求转发资源间数据共享: 转发资源间数据共享使用的是request对象, request对象提供了如下数据共享常用的方法**:

<table> 
 <thead> 
  <tr> 
   <th>方法名</th> 
   <th>描述</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>void setAttribute(String name, Object o)</td> 
   <td>存储数据到 request域中</td> 
  </tr> 
  <tr> 
   <td>Object getAttribute(String name)</td> 
   <td>根据 key，获取值</td> 
  </tr> 
  <tr> 
   <td>void removeAttribute(String name)</td> 
   <td>根据 key，删除该键值对</td> 
  </tr> 
 </tbody> 
</table>

> 示例代码:

@WebServlet("/req4")
    public class RequestDemo4 extends HttpServlet {
        
        @Override
        protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        
            System.out.println("demo4...");
    
            // 向request域中存储数据
            request.setAttribute("name", "chenyq");
    
            // 请求转发, 将请求转发到/req5
            request.getRequestDispatcher("/req5").forward(request, response);
        }
    
        @Override
        protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        
            this.doGet(request, response);
        }
    }

@WebServlet("/req5")
    public class RequestDemo5 extends HttpServlet {
        
        @Override
        protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        
            System.out.println("demo5...");
    
            // 从request中获取数据
            Object message = request.getAttribute("name");
            System.out.println(message); // chenyq
        }
    
        @Override
        protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        
            this.doGet(request, response);
        }
    }

**请求转发的特点**:

> 请求转发后, 浏览器地址栏路径不发生变化
> 
> 只能转发到当前服务器的内部资源
> 
> 一次请求，可以在转发的资源间使用request共享数据

[60af378e683045b88b507001219c0a2b.png_pic_center]: https://img-blog.csdnimg.cn/60af378e683045b88b507001219c0a2b.png#pic_center
[c4c9be9456734ae0862283681aa6ffa6.png_pic_center]: https://img-blog.csdnimg.cn/c4c9be9456734ae0862283681aa6ffa6.png#pic_center