07_Response

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 {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        process(req, resp);
    }

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        process(req, resp);
    }

    private void process(HttpServletRequest request, HttpServletResponse resp) {
        String operation = null;
        // /demo1/user/login
        String 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 {
    @SneakyThrows
    public 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 {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        process(req, resp);
    }

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        process(req, resp);
    }

    private void process(HttpServletRequest request, HttpServletResponse resp) {
        String operation = null;
        // /demo1/user/login
        String 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 {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse response)
            throws ServletException, IOException {
        response.setStatus(302);
    }
}

---

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 {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse response)
            throws ServletException, IOException {
        // 第一个参数是key，第二个参数是value
        response.setHeader("custom-header","aaaaaa");
    }
}

---

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 {
    @Override
    protected 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-8859-1
        response.getWriter().println("hello world");
    }
}

• 字节流举例

@WebServlet("/body2")
public class BodyServlet2 extends HttpServlet {

    // http://localhost:8080/demo1/body2?pic=1.jpg
    @Override
    protected 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 {
    @Override
    protected 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 {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse response)
            throws ServletException, IOException {
        // 指3s之后去访问demo2/hello.jsp
        response.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 {
    @Override
    protected 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-disposition
        response.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 {
    @Override
    protected 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：

1. 包含登录表单的 login.html文件，放在webapp目录下
2. 开发UserServlet
   1. /user/login对应的处理方法，使用MyBatis做查询
   2. /user/info对应的处理方法
3. 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 {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        process(req, resp);
    }

    @Override
    protected 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;
        }
    }

    @SneakyThrows
    private void info(HttpServletRequest request, HttpServletResponse response) {
        Object user = request.getAttribute("user");
        response.getWriter().println(user);
    }

    @SneakyThrows
    private void login(HttpServletRequest request, HttpServletResponse response) {
        // 1. 首先获得username和password
        String 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>