4.Servlet的Response和Request

一.综述

  • web服务器接受到客户端的HTTP请求，对于这个请求分别创建一个代表请求的对象HttpServletRequest和一个代表响应的对象HttpServletResponse。

    • 如果要获得客户端请求过来的参数：找HttpServletRequest

    • 如果要给客户端响应一些参数信息：找HttpServletResponse

二.HttpServletResponse

 1.简单分类

负责向浏览器发送数据的方法

1 public ServletOutputStream getOutputStream() throws IOException;
2 public PrintWriter getWriter() throws IOException;

负责向浏览器发送响应头的方法

 1 public void setCharacterEncoding(String charset);
 2 public void setContentLength(int len);
 3 public void setContentLengthLong(long len);
 4 public void setContentType(String type);
 5 public void setBufferSize(int size);
 6 public void setLocale(Locale loc);
 7 
 8 public void setDateHeader(String name, long date);
 9 public void addDateHeader(String name, long date);
10 public void setHeader(String name, String value);
11 public void addHeader(String name, String value);
12 public void setIntHeader(String name, int value);
13 public void addIntHeader(String name, int value);
14 public void setStatus(int sc);

 响应的状态码常量

 1 int SC_CONTINUE = 100;
 2 int SC_SWITCHING_PROTOCOLS = 101;
 3 int SC_OK = 200;
 4 int SC_CREATED = 201;
 5 int SC_ACCEPTED = 202;
 6 int SC_NON_AUTHORITATIVE_INFORMATION = 203;
 7 int SC_NO_CONTENT = 204;
 8 int SC_RESET_CONTENT = 205;
 9 int SC_PARTIAL_CONTENT = 206;
10 int SC_MULTIPLE_CHOICES = 300;
11 int SC_MOVED_PERMANENTLY = 301;
12 int SC_MOVED_TEMPORARILY = 302;
13 int SC_FOUND = 302;
14 int SC_SEE_OTHER = 303;
15 int SC_NOT_MODIFIED = 304;
16 int SC_USE_PROXY = 305;
17 int SC_TEMPORARY_REDIRECT = 307;
18 int SC_BAD_REQUEST = 400;
19 int SC_UNAUTHORIZED = 401;
20 int SC_PAYMENT_REQUIRED = 402;
21 int SC_FORBIDDEN = 403;
22 int SC_NOT_FOUND = 404;
23 int SC_METHOD_NOT_ALLOWED = 405;
24 int SC_NOT_ACCEPTABLE = 406;
25 int SC_PROXY_AUTHENTICATION_REQUIRED = 407;
26 int SC_REQUEST_TIMEOUT = 408;
27 int SC_CONFLICT = 409;
28 int SC_GONE = 410;
29 int SC_LENGTH_REQUIRED = 411;
30 int SC_PRECONDITION_FAILED = 412;
31 int SC_REQUEST_ENTITY_TOO_LARGE = 413;
32 int SC_REQUEST_URI_TOO_LONG = 414;
33 int SC_UNSUPPORTED_MEDIA_TYPE = 415;
34 int SC_REQUESTED_RANGE_NOT_SATISFIABLE = 416;
35 int SC_EXPECTATION_FAILED = 417;
36 int SC_INTERNAL_SERVER_ERROR = 500;
37 int SC_NOT_IMPLEMENTED = 501;
38 int SC_BAD_GATEWAY = 502;
39 int SC_SERVICE_UNAVAILABLE = 503;
40 int SC_GATEWAY_TIMEOUT = 504;
41 int SC_HTTP_VERSION_NOT_SUPPORTED = 505;

2.常见应用

  1. 向浏览器输出消息

  2. 下载文件

    1. 获得要下载文件的路径和文件名

    2. 设置浏览器能够支持下载

    3. 获取下载文件的输入流

    4. 创建缓冲区

    5. 获取OutputStream对象

    6. 将FileOutputStream流写入到buffer缓冲区中

    7. 使用OutputStream将缓冲区中的数据输出到客户端

  3. 验证码功能

  4. 实现重定向：使用场景用户登陆

注：

  • 重定向的 / 表示：http://服务器ip:端口/    ，重定向编码302

  • 请求转发的 / 表示：http://服务器ip:端口/项目名  ，请求转发编码307

 

下载文件代码：

 1 public class FileServlet extends HttpServlet {
 2     @Override
 3     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
 4         //1.获取要下载的文件路径
 5         String realPath = "F:\java_code\ServletCode\Servlet-response\src\main\resources\1.jpg";
 6         System.out.println("下载文件的路径：" + realPath);
 7 
 8         //2.获取下载文件名
 9         String fileName = realPath.substring(realPath.lastIndexOf("\") + 1);
10 
11         //3.设置浏览器支持，设置将文件名进行编码，防止中文乱码
12         resp.setHeader("Content-Disposition", "attachment;filename=" + URLEncoder.encode(fileName, "UTF-8"));
13 
14         //4.获取下载文件的输入流
15         FileInputStream in = new FileInputStream(realPath);
16 
17         //5.创建缓冲区
18         int len = 0;
19         byte[] buffer = new byte[1024];
20 
21         //6.获取OutputStream对象
22         ServletOutputStream out = resp.getOutputStream();
23 
24         //7.将FileOutputStream流写入到buffer缓冲区，使用OutputStream将缓冲区中的数据输出到客户端
25         while ((len = in.read(buffer)) > 0) {
26             out.write(buffer, 0, len);
27         }
28 
29         in.close();
30         out.close();
31 
32 
33     }
34 
35     @Override
36     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
37         doGet(req, resp);
38     }
39 }

验证码功能：

 1 public class ImageServlet extends HttpServlet {
 2     @Override
 3     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException {
 4 
 5         //设置浏览器3秒刷新一次
 6         resp.setHeader("refresh","3");
 7 
 8         //在内存中建立一个图片
 9         BufferedImage image = new BufferedImage(80,20,BufferedImage.TYPE_INT_RGB);
10 
11         //得到图片
12         Graphics2D g = (Graphics2D) image.getGraphics();
13 
14         //设置图片样式
15         g.setColor(Color.gray);
16         g.fillRect(0,0,80,20);
17 
18         //给图片填充数据
19         g.setColor(Color.orange);
20         g.setFont(new Font(null,Font.BOLD,20));
21         g.drawString(makeNum(7),0,20);
22 
23         //设置浏览器打开图片的方式
24         resp.setContentType("image/jpeg");
25         //设置浏览器不缓存
26         resp.setDateHeader("expires",-1);
27         resp.setHeader("Cache-Control","no-cache");
28         resp.setHeader("Pragma","no-cache");
29 
30         //将图片写给浏览器
31         ImageIO.write(image,"jpg",resp.getOutputStream());
32 
33     }
34 
35     //生成随机数
36     private String makeNum(int len) {
37         Random random = new Random();
38         StringBuffer num = new StringBuffer();
39         while (len > 0) {
40             num.append(random.nextInt(9) + "");
41             len--;
42         }
43         return num.toString();
44     }
45 
46     @Override
47     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
48         doGet(req, resp);
49     }
50 }

重定向实现

 1 public class RedirectServlet extends HttpServlet {
 2     @Override
 3     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
 4 
 5         /*
 6         传入参数为项目打包的路径名（sr1）+重定向的路径名（image）
 7         resp.sendRedirect("/sr1/image");
 8         等价于下面语句
 9         resp.setHeader("Location","/sr1/image");
10         resp.setStatus(302);
11         */
12 
13 
14         resp.sendRedirect("/sr1/image");
15     }
16 
17     @Override
18     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
19         doGet(req, resp);
20     }
21 }

重定向案例：登陆后重定向

  1. 在index.jsp中登陆
  2. 在RequestTestServlet中处理，然后重定向
  3. 重定向到Success.jsp中

RequestTestServlet：

 1 public class RequestTestServlet extends HttpServlet {
 2 
 3     @Override
 4     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
 5 
 6         String username = req.getParameter("username");
 7         String password = req.getParameter("password");
 8 
 9         System.out.println(username + ":" + password);
10 
11         resp.sendRedirect("/sr1/success.jsp");
12     }
13 
14     @Override
15     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
16         doGet(req, resp);
17     }
18 }

index.jsp：

 1 <%@ page contentType="text/html;charset=UTF-8" language="java" %>
 2 <html>
 3 <body>
 4 <h2>Hello World!</h2>
 5 
 6 <%--${pageContext.request.contextPath}代表当前的项目名，login为web.xml中注册绑定的处理Servlet--%>
 7 <form action="${pageContext.request.contextPath}/login" method="get">
 8     用户名：<input type="text" name="username"> <br>
 9     密码：<input type="password" name="password"> <br>
10     <input type="submit">
11 </form>
12 
13 
14 </body>
15 </html>

success.jsp：

 1 <%@ page contentType="text/html;charset=UTF-8" language="java" %>
 2 <html>
 3 <head>
 4     <title>Title</title>
 5 </head>
 6 <body>
 7 
 8 <h1>Success</h1>
 9 
10 </body>
11 </html>

二.HttpServletRequest

HttpServletRequest代表客户端的请求，用户通过Http协议访问服务器，HTTP请求中的所有信息会被封装到HttpServletRequest，通过HttpServletRequest的方法，获得客户端的所有信息

1.HttpServletRequest中的一些方法：

2.主要应用

  1. 获取前端传递的参数（主要是两个方法）

    1.  public String getParameter(String name); 

    2.  public String[] getParameterValues(String name); 

  2. 请求转发

请求转发案例：前端提交登录表单，Servlet处理并转发

LoginServlet：

 1 public class LoginServlet extends HttpServlet {
 2 
 3     @Override
 4     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
 5 
 6         req.setCharacterEncoding("utf-8");
 7         resp.setCharacterEncoding("utf-8");
 8 
 9         String username = req.getParameter("username");
10 
11         String password = req.getParameter("password");
12 
13         String[] hobbys = req.getParameterValues("hobbys");
14 
15         System.out.println(username);
16         System.out.println(password);
17         System.out.println(Arrays.toString(hobbys));
18 
19 
20         //通过请求转发
21         req.getRequestDispatcher("/success.jsp").forward(req, resp);
22 
23     }
24 
25     @Override
26     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
27         doGet(req, resp);
28     }
29 }

登录页面：index.jsp

 1 <%@ page contentType="text/html;charset=UTF-8" language="java" %>
 2 <html>
 3 <head>
 4     <title>登录</title>
 5 </head>
 6 <body>
 7 
 8 
 9 <h1>登录</h1>
10 <div>
11     <form action="${pageContext.request.contextPath}/login" method="post">
12         用户名：<input type="text" name="username"> <br>
13         密码：<input type="password" name="password"> <br>
14         爱好：
15         <input type="checkbox" name="hobbys" value="打篮球"> 打篮球
16         <input type="checkbox" name="hobbys" value="写代码"> 写代码
17         <input type="checkbox" name="hobbys" value="玩游戏"> 玩游戏
18         <input type="checkbox" name="hobbys" value="看电影"> 看电影
19         <br>
20 
21         <input type="submit">
22     </form>
23 </div>
24 
25 </body>
26 </html>

成功登录页面：success.jsp

 1 <%@ page contentType="text/html;charset=UTF-8" language="java" %>
 2 <html>
 3 <head>
 4     <title>Success</title>
 5 </head>
 6 <body>
 7 
 8 <h1>登录成功</h1>
 9 </body>
10 </html>
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原文地址：https://www.cnblogs.com/zhihaospace/p/11950933.html