Servlet API

雨点打透心脏的1/2处 2024-03-23 13:23 47阅读 0赞

**目录**

1.HttpServlet

1.doGet

2.doPost

2.HttpServletRequest

2.1方法

2.2打印请求信息

2.3获取GET请求的参数

2.4post请求body格式

1.x-www-form-urlencoded

2.json

3.HttpServletResponse

3.1方法

3.2设置状态码

3.3自动刷新

3.4构造重定向的响应

--------------------

## 1.HttpServlet ##

<table style="width:500px;"> 
 <tbody> 
  <tr> 
   <td>方法名称</td> 
   <td>调用时机</td> 
  </tr> 
  <tr> 
   <td>init</td> 
   <td>实例化后被调用一次</td> 
  </tr> 
  <tr> 
   <td>destroy</td> 
   <td>实例不使用时,调用一次</td> 
  </tr> 
  <tr> 
   <td>service</td> 
   <td>收到HTTP请求调用</td> 
  </tr> 
  <tr> 
   <td>doGet</td> 
   <td> <p>收到 GET 请求的时候调用(由 service 方法调用)</p> </td> 
  </tr> 
  <tr> 
   <td>doPost</td> 
   <td> <p>收到 POST 请求的时候调用(由 service 方法调用)</p> </td> 
  </tr> 
  <tr> 
   <td> <p>doPut/doDelete/doOptions/...</p> </td> 
   <td> <p>收到其他请求的时候调用(由 service 方法调用)</p> </td> 
  </tr> 
 </tbody> 
</table>

### 1.doGet ###

@WebServlet("/method")
    public class MethodServlet extends HttpServlet {
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            resp.setContentType("text/html;charset=utf8");
            resp.getWriter().write("Get响应");
        }
    }

## ![41a4358b1d4649b6ba534ea8068462e7.png][] ##

### 2.doPost ###

test.html

请求是相对路径,不用加/

方法是post,路径是method1,得到body

<!DOCTYPE html>
    <html lang="en">
    <head>
        <meta charset="UTF-8">
        <title>Title</title>
    </head>
    <body>
        <script src="https://cdn.bootcdn.net/ajax/libs/jquery/3.6.4/jquery.min.js"></script>
        <script>
            $.ajax({
                type:'post',
                url:'method1',
                success:function(body){
                    console.log(body);
                }
            });
        </script>
    </body>
    </html>

MethodServlet1.java

contentType:让服务器告诉浏览器它发送的数据属于什么文件类型

@WebServlet("/method1")
    public class MethodServlet1 extends HttpServlet {
        @Override
        protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            resp.setContentType("text/html;charset=utf8");
            resp.getWriter().write("post响应");
        }
    }

Fiddler捕获到两个页面

![f38ab62d9b744129a1679ea52c30642e.png][]

![ce76c60f483a41d4902f11f736682b14.png][]

## 2.HttpServletRequest ##

通过Socket API读取HTTP请求(字符串),按照HTTP协议把字符串解析成HttpServletPequest对象

### 2.1方法 ###

<table style="width:500px;"> 
 <tbody> 
  <tr> 
   <td>方法</td> 
   <td>描述</td> 
  </tr> 
  <tr> 
   <td>String getProtocol()</td> 
   <td>返回请求协议的名称和版本</td> 
  </tr> 
  <tr> 
   <td>String getMethod()</td> 
   <td>返回请求的方法</td> 
  </tr> 
  <tr> 
   <td>String getRequestURI()</td> 
   <td> <p>从协议名称直到 HTTP 请求的第一行的查询字符串中，返回该请求的URL 的一部分。</p> </td> 
  </tr> 
  <tr> 
   <td>String getContextPath()</td> 
   <td> <p>返回第一级路径</p> </td> 
  </tr> 
  <tr> 
   <td>String getQueryString()</td> 
   <td>返回查询的字符串(完整的)</td> 
  </tr> 
  <tr> 
   <td>Enumeratin getParameterNames()</td> 
   <td>解析成键值对,key用enum方式表达</td> 
  </tr> 
  <tr> 
   <td>String getParameter(String name)</td> 
   <td>解析成键值对,根据key返回value</td> 
  </tr> 
  <tr> 
   <td>String[] getParameterValues(String name)</td> 
   <td>返回请求参数的值,如果不存在返回null</td> 
  </tr> 
  <tr> 
   <td> <p>Enumeration getHeaderNames()</p> </td> 
   <td>请求报头解析成键值对,key用enum方式表达</td> 
  </tr> 
  <tr> 
   <td> <p>String getHeader(Stringname)</p> </td> 
   <td>请求报头解析成键值对,根据key返回value</td> 
  </tr> 
  <tr> 
   <td> <p>String getCharacterEncoding()</p> </td> 
   <td>返回主体中使用字符编码的名称</td> 
  </tr> 
  <tr> 
   <td> <p>String getContentType()</p> </td> 
   <td> <p>返回请求主体的 MIME 类型，如果不知道类型则返回 null</p> </td> 
  </tr> 
  <tr> 
   <td> <p>int getContentLength()</p> </td> 
   <td> <p>以字节为单位返回请求主体的长度，并提供输入流，或者如果长度未知则返回 -1。</p> </td> 
  </tr> 
  <tr> 
   <td> <p>InputStream getInputStream()</p> </td> 
   <td> <p>用于读取请求的 body 内容. 返回一个 InputStream 对象.</p> </td> 
  </tr> 
 </tbody> 
</table>

## 2.2打印请求信息 ##

创建stringBuilder对象,把api得到的结果存入,

通过write()方法,输出到页面

@WebServlet("/showRequest")
    public class showRequest extends HttpServlet {
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            //调用API,把得到的结果组织到html中,作为响应的body
    
            //把api执行的结果,放入stringbuilder中
            StringBuilder stringBuilder=new StringBuilder();
            stringBuilder.append("<h3>首行部分</h3>");
            stringBuilder.append(req.getProtocol());//协议名称和版本号
            stringBuilder.append("<br>");
            stringBuilder.append(req.getMethod());//请求的方法
            stringBuilder.append("<br>");
            stringBuilder.append(req.getRequestURI());//返回第一行查询的字符串
            stringBuilder.append("<br>");
            stringBuilder.append(req.getContextPath());//第一级路径
            stringBuilder.append("<br>");
            stringBuilder.append(req.getQueryString());//完整字符串
            stringBuilder.append("<br>");
            stringBuilder.append("<h3>header部分</h3>");
            Enumeration<String> headerNames=req.getHeaderNames();//key
            while(headerNames.hasMoreElements()){
                String headerName=headerNames.nextElement();
                String headerValue=req.getHeader(headerName);//value
                stringBuilder.append(headerName+" : "+headerValue+"<br>");
            }
            resp.setContentType("text/html;charset=utf8");
            resp.getWriter().write(stringBuilder.toString());
        }
    }

![1a65fb46d09440de8e96bb29a4ed0c64.png][]

### 2.3获取GET请求的参数 ###

在输入网址时,输入信息

用getParameter()得到信息,输出

@WebServlet("/getParameter")
    public class GetParameterServlet extends HttpServlet {
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            //预期浏览器传来一个形如这样的请求:/getParameter?userId=123&classId=456
            String userId=req.getParameter("userId");
            String classId=req.getParameter("classId");
            resp.getWriter().write("userId"+userId+",classId="+classId);
        }

网址: [localhost:8080/4/getParameter?userId=10&classId=20][localhost_8080_4_getParameter_userId_10_classId_20]

如果?后 没有信息,则都为null

## ![3caf95260804421696c7aea9f14d8a11.png][] ##

### 2.4post请求body格式 ###

#### 1.x-www-form-urlencoded ####

前端代码:

a.form表单

b.postman

前端请求:

action中写的是相对路径

点击submit后,会跳转到action中写的路径(后端代码的页面)

后端代码:

@WebServlet("/postGetParameter")
    public class postGetParameterServlet extends HttpServlet {
        @Override
        protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            //假设前端传过来的参数是userId=10&classId=20
            //服务器也通过req.getParameter来获取内容的
            String userId=req.getParameter("userId");
            String classId=req.getParameter("classId");
            resp.getWriter().write("useId:"+userId+", classId:"+classId);
    
        }
    }

先登录test.html得到信息提交,转到postGetParameter,页面显示信息

#### ![7b46343d318942398b430d131c10eb3d.png][] ####

#### ![2f01c7376f714f9b962348e3065be18e.png][] ####

#### 2.json ####

形式:

> \{
> 
> userId:zhang,
> 
> classId:123;
> 
> \}

用第三方库处理json格式==>Jackson

<dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-databind</artifactId>
        <version>2.12.7</version>
    </dependency>

前端代码:通过js构造body为json的格式请求

1.得到信息(userId,classId,submit)

2.编写点击按钮:

使用ajax:

写入:type,url,contentType,data(设置成json的格式),回调函数

<input type="text" id="userId">
            <input type="text" id="classId">
            <input type="button" value="提交" id="submit">
            
            <script src="https://cdn.bootcdn.net/ajax/libs/jquery/3.6.4/jquery.min.js"></script>
             <script>
                let userIdInput=document.querySelector('#userId');
                let classIdInput=document.querySelector('#classId');
                let button=document.querySelector('#submit');
                button.onclick=function(){
                    $.ajax({
                        type:'post',
                        url:'postJson',
                        contentType:'application/json',
                        data:JSON.stringify({
                            userId:userIdInput.value,
                            classId:classIdInput.value
                        }),
                        success:function(body){
                            console.log(body);
                        }
                    });
                }
             </script>

后端代码:

1.创建User类

2.创建jackson核心对象

3.读取body的请求,使用objectMapper解析成user.class

readValue把json格式的对象,转换成java对象

4.输出信息

遍历键值对,得到每个key,把对应的value附到User属性中

class User{
        public int userId;
        public int classId;
    }
    @WebServlet("/postJson")
    public class PostJsonServlet extends HttpServlet {
        private ObjectMapper objectMapper=new ObjectMapper();
    
        @Override
        protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            User user=objectMapper.readValue(req.getInputStream(),User.class);
            resp.getWriter().write("userId: " + user.userId + ", classId: " + user.classId);
    
        }
    }

![cde1523c4426431ca70fabc1e5ae6f11.png][]

## 3.HttpServletResponse ##

Tomcat 就会把这个 HttpServletResponse 对象按照 HTTP 协议的格式, 转成一个字符串, 并通过Socket 写回给浏览器.

### 3.1方法 ###

<table style="width:500px;"> 
 <tbody> 
  <tr> 
   <td>方法</td> 
   <td>描述</td> 
  </tr> 
  <tr> 
   <td> <p>void setStatus(int sc)</p> </td> 
   <td>设置响应码</td> 
  </tr> 
  <tr> 
   <td> <p>void setHeader(String name,String value)</p> </td> 
   <td> <p>设置有名称和值的header,</p> <p>name已有则覆盖旧的值</p> </td> 
  </tr> 
  <tr> 
   <td> <p>void addHeader(Stringname, String value)</p> </td> 
   <td>添加有名称和值的header,name已有,不覆盖新的值,添加新的键值对</td> 
  </tr> 
  <tr> 
   <td> <p>void setContentType(Stringtype)</p> </td> 
   <td>设置响应的内容类型</td> 
  </tr> 
  <tr> 
   <td> <p>void&nbsp; setCharacterEncoding(Stringcharset)</p> </td> 
   <td>设置字符编码</td> 
  </tr> 
  <tr> 
   <td> <p>void sendRedirect(Stringlocation)</p> </td> 
   <td> <p>用指定的重定向位置 URL 发送临时重定向响应到客户端</p> </td> 
  </tr> 
  <tr> 
   <td> <p>PrintWriter getWriter()</p> </td> 
   <td> <p>往 body 中写入文本格式数据.</p> </td> 
  </tr> 
  <tr> 
   <td> <p>OutputStream&nbsp; getOutputStream()</p> </td> 
   <td> <p>往 body 中写入二进制格式数据.</p> </td> 
  </tr> 
 </tbody> 
</table>

### 3.2设置状态码 ###

响应码:服务器返回的状态码,只是告诉浏览器当前响应的状态,不影响浏览器显示body

@WebServlet("/status")
    public class StatusServlet extends HttpServlet {
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            resp.setStatus(404);
            resp.getWriter().write("hello");
        }
    }

![4b2bd6baa14b415d8e61c0c493eb5382.png][]

### 3.3自动刷新 ###

@WebServlet("/autoRefresh")
    public class autoRefresh extends HttpServlet {
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            resp.setHeader("Refresh","1");
            resp.getWriter().write("timeStamp"+System.currentTimeMillis());
        }
    }

![c631fa7799764f38954ac2dd32c41604.png][]

### 3.4构造重定向的响应 ###

@WebServlet("/RedirectServlet")
    public class RedirectServlet extends HttpServlet {
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            resp.sendRedirect("https://www.bilibili.com/");
        }
    }

![34cab7a3b3f145d9867a36ae55e8e2b2.png][]

[41a4358b1d4649b6ba534ea8068462e7.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/23/7097e4cdeeaa45d39193bc98d35e352e.png
[f38ab62d9b744129a1679ea52c30642e.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/23/18314ff1333246c1913ad9188e2011b2.png
[ce76c60f483a41d4902f11f736682b14.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/23/27a45b7b3ca04d0c9145255abd90bbc3.png
[1a65fb46d09440de8e96bb29a4ed0c64.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/23/0482d6a547df4deba5ad3b391ce56ca7.png
[localhost_8080_4_getParameter_userId_10_classId_20]: http://localhost:8080/4/getParameter?userId=10&classId=20
[3caf95260804421696c7aea9f14d8a11.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/23/a981cdf83d024ca09c4983384124948c.png
[7b46343d318942398b430d131c10eb3d.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/23/d3f4c12ef1a041ebbac6989f2a8256da.png
[2f01c7376f714f9b962348e3065be18e.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/23/36ef70e5d02c44089e4b62d09abf9f0e.png
[cde1523c4426431ca70fabc1e5ae6f11.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/23/fe095bd6688c4961bdf487eade910238.png
[4b2bd6baa14b415d8e61c0c493eb5382.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/23/caf98ee38be245bdb8078f4246733495.png
[c631fa7799764f38954ac2dd32c41604.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/23/ae2abeff65c346009348ec7dc3a4370d.png
[34cab7a3b3f145d9867a36ae55e8e2b2.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/23/fde79f94200f4a1fa23e09d1aa68907b.png