07_Response-编程知识

文章目录

- 案例（请求分发案例）
Response
- 响应行
- 响应头
- 响应体
- 特殊响应头
- - refresh
  - Content-type
  - Content-disposition
  - location
- 案例（登录案例）

案例（请求分发案例）

场景：有多个请求
- Http://localhost:8080/user/login → 登录
- Http://localhost:8080/user/register → 注册
- Http://localhost:8080/user/info → 查看用户信息

eg：

/*** localhost:8080/demo1/user/login* localhost:8080/demo1/user/register* localhost:8080/demo1/user/info*///@WebServlet(value = {"/user/login", "/user/register", "/user/info"})
@WebServlet("/user1/*")
public class UserServlet extends HttpServlet {@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException {process(req, resp);}@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException {process(req, resp);}private void process(HttpServletRequest request, HttpServletResponse resp) {String operation = null;// /demo1/user/loginString requestURI = request.getRequestURI();operation = requestURI.substring(requestURI.lastIndexOf("/") + 1);
//        if("login".equals(operation)) {
//            login(request,resp);
//        } else if("info".equals(operation)) {
//            info(request,resp);
//        }switch (operation) {case "login":login(request, resp);break;case "info":info(request, resp);break;case "register":register(request, resp);break;case "remove":remove(request, resp);break;}}private void remove(HttpServletRequest request, HttpServletResponse resp) {}private void register(HttpServletRequest request, HttpServletResponse resp) {}private void info(HttpServletRequest request, HttpServletResponse resp) {}private void login(HttpServletRequest request, HttpServletResponse resp) {}
}

优化版本：

eg：

DispatchUtil.java
- 通过反射的方式，实现其通用性

public class DispatchUtil {@SneakyThrowspublic static void dispatch(String operation, HttpServletRequest request, HttpServletResponse response, HttpServlet instance) {// java.lang.Class.getDeclaredMethod()方法返回一个Method对象，
// 它反映此Class对象所表示的类或接口的指定已声明方法。
// name 参数是一个字符串，指定所需的方法的简单名称，
// parameterTypes 参数是一个数组的Class对象识别方法的形参类型，在声明的顺序Method method = instance.getClass().getDeclaredMethod(operation, HttpServletRequest.class, HttpServletResponse.class);method.setAccessible(true);method.invoke(instance, new Object[]{request, response});}
}

//@WebServlet(value = {"/user/login", "/user/register", "/user/info"})
@WebServlet("/user2/*")
public class UserServlet2 extends HttpServlet {@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException {process(req, resp);}@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException {process(req, resp);}private void process(HttpServletRequest request, HttpServletResponse resp) {String operation = null;// /demo1/user/loginString requestURI = request.getRequestURI();operation = requestURI.substring(requestURI.lastIndexOf("/") + 1);
//        if("login".equals(operation)) {
//            login(request,resp);
//        } else if("info".equals(operation)) {
//            info(request,resp);
//        }// 不需要再switch判断，直接写方法名函数就可以DispatchUtil.dispatch(operation, request, resp, this);}private void remove(HttpServletRequest request, HttpServletResponse resp) {}private void register(HttpServletRequest request, HttpServletResponse resp) {}private void info(HttpServletRequest request, HttpServletResponse resp) {}private void login(HttpServletRequest request, HttpServletResponse resp) {}private void logout(HttpServletRequest request, HttpServletResponse resp) {System.out.println("logout");}
}

Response

响应报文的封装，设置响应报文

eg：

HTTP/1.1 200
Vary: accept-encoding,origin,access-control-request-headers,access-control-request-method,accept-encoding
Set-Cookie: rememberMe=deleteMe; Path=/; Max-Age=0; Expires=Sun, 12-Feb-2023 06:51:56 GMT
Set-Cookie: JSESSIONID=24287278-5ebb-407d-a3f7-56b74782c4c7; Path=/; HttpOnly
Access-Control-Allow-Origin: *
Content-Type: application/json;charset=UTF-8
Date: Mon, 13 Feb 2023 06:51:56 GMT
Content-Length: 200{"errno":0,"data":{"adminInfo":
{"nickName":"admin123","avatar":"https://wpimg.wallstcn.com/f778738c-e4f8-4870-b634-56703b4acafe.gif"},
"token":"24287278-5ebb-407d-a3f7-56b74782c4c7"},"errmsg":"成功"}

响应行

设置一下响应状态码

方法名	参数	说明
`setStatus(int)`	参数就是状态码	设置响应状态码

eg：

/*** 常用的响应状态码：200、404、302、400、500* 响应行中的响应状态码*/
@WebServlet("/line")
public class LineServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse response)throws ServletException, IOException {response.setStatus(302);}
}

在这里插入图片描述

响应头

响应头是key：value的格式，提供了通用的方法，可以设置响应头的key和value
提供了一些特定的方法，特定的方法做的事情，就是设置特定响应头的值

方法	参数	说明
`setHeader(String,String)`	参数1提供key，参数2提供value	通用的方法

eg：

@WebServlet("/header")
public class HeaderServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse response)throws ServletException, IOException {// 第一个参数是key，第二个参数是valueresponse.setHeader("custom-header","aaaaaa");}
}

在这里插入图片描述

响应体

可以使用字符流，也可以使用字节流
场景：
- 字符流：响应文本数据，最主要的场景就是前后端分离之后，通过字符流响应Json数据
- 字节流：响应图片、文件，也通常在文件下载的场景下使用

方法	返回值	描述
`getWriter()`	PrintWriter	字符流
`getOutputStream()`	ServletOutputStream	字节流

eg：

字符流举例

@WebServlet("/body1")
public class BodyServlet1 extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse response)throws ServletException, IOException {// response.getWriter().write("hello world");// 如果把响应体里的字符以utf-8的方式编码，不一定能解决中文乱码的问题// 因为浏览器不一定以utf-8的方式来解码// 从根本上解决这个问题通知浏览器以utf-8的方式解码// content-type:指响应体里的正文类型response.setHeader("content-type","text/html;charset=utf-8");// response.getWriter().write("hello world");// 默认的编码：iso-8859-1response.getWriter().println("hello world");}
}

在这里插入图片描述

字节流举例

@WebServlet("/body2")
public class BodyServlet2 extends HttpServlet {// http://localhost:8080/demo1/body2?pic=1.jpg@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {String pic = request.getParameter("pic");String path = "D:\\test_photo";File file = new File(path, pic);// 要显示图片，需要在响应体中提供其字节数据 -> 浏览器就会显示图片ServletOutputStream outputStream = response.getOutputStream();FileInputStream inputStream = new FileInputStream(file);int length = 0;byte[] bytes = new byte[1024];while((length = inputStream.read(bytes)) != -1) {outputStream.write(bytes, 0 ,length);}inputStream.close();outputStream.close();}
}

特殊响应头

特殊的几个响应头：
1. refresh → 定时刷新、跳转
2. content-type → 限定响应的正文（也可以解决中文乱码问题）
3. content-disposition → 文件下载
4. location → 重定向

refresh

eg：

/*** 自动显示当前的时间*/
@WebServlet("/refresh")
public class RefreshServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse response)throws ServletException, IOException {response.setHeader("refresh", "1");String pattern = "yyyy-MM-dd HH:mm:ss";SimpleDateFormat simpleDateFormat = new SimpleDateFormat(pattern);String dateStr = simpleDateFormat.format(new Date());response.getWriter().println(dateStr);}
}

@WebServlet("/refresh2")
public class RefreshServlet2 extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse response)throws ServletException, IOException {// 指3s之后去访问demo2/hello.jspresponse.setHeader("refresh", "3;url=/demo1/hello.jsp");response.setContentType("text/html;charset=utf-8");response.getWriter().println("请稍后马上跳转到欢迎页面");}
}

Content-type

通常不需要设置
比如我们响应Json数据给前端，我们可以设置Content-Type：application/json
我们要在这里做字符集的设置，如果没有做有可能出现中文乱码

Content-disposition

下载的场景会使用
- eg：content-disposition: attachment;filename=1.jpg
- 以1.jpg来下载正文

eg：

@WebServlet("/download")
public class ContentDispositionServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {String pic = request.getParameter("pic");String path = "D:\\test_photo";// 如果代码没有这行内容，那么就是显示该图片// 如果做下载，需要设置header content-dispositionresponse.setHeader("content-disposition", "attachment;" + pic);FileInputStream inputStream = new FileInputStream(new File(path, pic));ServletOutputStream outputStream = response.getOutputStream();int length = 0;byte[] bytes = new byte[1024];while ((length = inputStream.read(bytes)) != -1) {outputStream.write(bytes, 0, length);}inputStream.close();}
}

location

重定向
状态码：302

eg：

@WebServlet("/location")
public class LocationServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException {System.out.println("访问到LocationServlet");resp.setStatus(302);resp.setHeader("location","http://localhost:8080/demo1/refresh");}
}

案例（登录案例）

这个请求由登录页面提供，我们可以通过html提供一个登录表单，该表单会发出请求
http://localhost:8080/user/login→ Servlet → 检查用户名和密码是否正确（使用一下MyBatis） →
如果正确，那么就提示登录成功
如果错误，那么刷新登录页面

任务拆解：

包含登录表单的 login.html文件，放在webapp目录下
开发UserServlet
/user/login对应的处理方法，使用MyBatis做查询
/user/info对应的处理方法

整合MyBatis，在应用程序中维护SqlSessionFactory实例

Mybatis的配置：

public interface UserMapper {List<User> selectByUserNameAndPassword(@Param("username") String username, @Param("password") String password);User selectByPrimaryKey(Integer id);
}

<mapper namespace="com.coo1heisenberg.demo2.mapper.UserMapper"><select id="selectByUserNameAndPassword" resultType="com.coo1heisenberg.demo2.bean.User">select id, username, password, age, birthday, createDate, mobile from test_user<where>username = #{username} and password = #{password}</where></select><select id="selectByPrimaryKey" resultType="com.coo1heisenberg.demo2.bean.User">select id, username, password, age, birthday, createDate, mobile from test_user<where>id = #{id}</where></select>
</mapper>

Servlet的配置

@WebServlet("/user/*")
public class UserServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException {process(req, resp);}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException {process(req, resp);}private void process(HttpServletRequest request, HttpServletResponse response) {String requestURI = request.getRequestURI();String operation = null;operation = requestURI.substring(requestURI.lastIndexOf("/") + 1);switch (operation) {case "login":login(request, response);break;case "info":info(request, response);break;}}@SneakyThrowsprivate void info(HttpServletRequest request, HttpServletResponse response) {Object user = request.getAttribute("user");response.getWriter().println(user);}@SneakyThrowsprivate void login(HttpServletRequest request, HttpServletResponse response) {// 1. 首先获得username和passwordString username = request.getParameter("username");String password = request.getParameter("password");// 2. 查询user记录UserMapper userMapper = MybatisUtil.getSqlSession().getMapper(UserMapper.class);List<User> users = userMapper.selectByUserNameAndPassword(username, password);// 3. 根据user记录判断登录状态response.setContentType("text/html;charset=utf-8");// 4. 判断登录状态 user的list是否为空if (users == null || users.size() == 0) {// 如果登陆失败（list == null || list.size() == 0）// 刷新到refresh --> 2;url=/demo2/login.html// 响应登录失败信息response.getWriter().println("登录失败，即将跳转登录页面");response.setHeader("refresh", "2;url=/demo2/login.html");} else {// 如果登录成功（list.size > 0）// 响应登录成功信息response.getWriter().println("登录成功");request.setAttribute("user", users.get(0));request.getRequestDispatcher("/user/info").forward(request, response);// 跳转到info -> 分享user的id信息（直接分享user信息）}}
}

HTML的配置

<body>
<h1>登录页面</h1>
<!--action：表示当前表单中的内容提交给哪个页面进行处理-->
<!--method:表示当前表单提交的方式，常见的有get和post方式，默认是get提交-->
<form action="/demo2/user/login" method="post">用户名：<input type="text" name="username"><br>密码：<input type="password" name="password"><br><input type="submit">
</form></body>