ServletContext

web容器在启动的时候，它会为每一个web程序创建一个对应的ServletContext对象，它代表了当前的web应用；

1、共享数据

我在这个Servlet中保存的数据，可以在另外一个servlet中拿到；

 1 package com.kuang.servlet;
 2 
 3 import javax.servlet.ServletContext;
 4 import javax.servlet.ServletException;
 5 import javax.servlet.http.HttpServlet;
 6 import javax.servlet.http.HttpServletRequest;
 7 import javax.servlet.http.HttpServletResponse;
 8 import java.io.IOException;
 9 
10 public class HelloServlet extends HttpServlet {
11     @Override
12     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
13 
14         //this.getInitParameter()     初始化参数
15         //this.getServletConfig()     Servlet配置
16         //this.getServletContext()    Servlet上下文
17         ServletContext context = this.getServletContext();
18 
19         String username = "王刘"; //数据
20         context.setAttribute("username",username); //将一个数据保存在了ServletContext中，名字为：username，值username
21 
22 
23     }
24 
25     @Override
26     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
27         doGet(req, resp);
28     }
29 }

获取数据：

 1 package com.kuang.servlet;
 2 
 3 import javax.servlet.ServletContext;
 4 import javax.servlet.ServletException;
 5 import javax.servlet.http.HttpServlet;
 6 import javax.servlet.http.HttpServletRequest;
 7 import javax.servlet.http.HttpServletResponse;
 8 import java.io.IOException;
 9 
10 public class GetServlet extends HttpServlet {
11     @Override
12     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
13         ServletContext context = this.getServletContext();
14         String username = (String) context.getAttribute("username");
15 
16         resp.setContentType("text/html");
17         resp.setCharacterEncoding("utf-8");
18         resp.getWriter().print("名字："+username);
19     }
20 
21     @Override
22     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
23         doGet(req, resp);
24     }
25 }

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
 3          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 4          xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
 5                       http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
 6          version="4.0"
 7          metadata-complete="true">
 8 
 9     <servlet>
10         <servlet-name>hello</servlet-name>
11         <servlet-class>com.kuang.servlet.HelloServlet</servlet-class>
12     </servlet>
13     <servlet-mapping>
14         <servlet-name>hello</servlet-name>
15         <url-pattern>/hello</url-pattern>
16     </servlet-mapping>
17 
18     <servlet>
19         <servlet-name>getc</servlet-name>
20         <servlet-class>com.kuang.servlet.GetServlet</servlet-class>
21     </servlet>
22     <servlet-mapping>
23         <servlet-name>getc</servlet-name>
24         <url-pattern>/getc</url-pattern>
25     </servlet-mapping>
26 
27 
28 </web-app>

2、获取初始化参数

1     <!--配置一些web应用初始化参数-->
2     <context-param>
3         <param-name>url</param-name>
4         <param-value>jdbc:mysql://localhost:3306/mybatis</param-value>
5     </context-param>

1     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
2         ServletContext context = this.getServletContext();
3         String url = context.getInitParameter("url");
4         resp.getWriter().print(url);
5     }

3、请求转发

1     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
2         ServletContext context = this.getServletContext();
3         System.out.println("进入了ServletDemo04");
4         //RequestDispatcher requestDispatcher = context.getRequestDispatcher("/gp"); //转发的请求路劲
5         //requestDispatcher.forward(req,resp); //调用forward实现请求转发；
6         context.getRequestDispatcher("/gp").forward(req,resp);
7     }

4、读取资源文件

Properties

在java目录下新建properties
在resources目录下新建properties

发现：都被打包到了同一个路劲下：classes，我们俗称这个路劲为classpath:

思路：需要一个文件流；

db.properties

username=root
password=123456

 1 public class ServletDemo05 extends HttpServlet {
 2     @Override
 3     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
 4         InputStream is = this.getServletContext().getResourceAsStream("/WEB-INF/classes/db.properties");
 5         Properties prop = new Properties();
 6         prop.load(is);
 7         String user = prop.getProperty("username");
 8         String pwd = prop.getProperty("password");
 9 
10         resp.getWriter().print(user + ":" + pwd);
11     }
12 
13     @Override
14     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
15         doGet(req, resp);
16     }
17 }

访问测试即可；

6.6、HttpServletResponse

web服务器接收到客户端的http请求，针对这个请求，分别创建一个代表请求的HttpServletRequest

对象，代表响应的一个HttpServletResponse;

如果要获取客户端请求过来的参数：找HttpServletRequest
如果要给客户端响应一些信息：找HttpServletResponse

1、简单分类

负责向浏览器发送数据的方法

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

负责向浏览器发送响应头的方法

1     void setCharacterEncoding(String var1);
2 
3     void setContentLength(int var1);
4 
5     void setContentLengthLong(long var1);
6 
7     void setContentType(String var1);

 1     void setDateHeader(String var1, long var2);
 2 
 3     void addDateHeader(String var1, long var2);
 4 
 5     void setHeader(String var1, String var2);
 6 
 7     void addHeader(String var1, String var2);
 8 
 9     void setIntHeader(String var1, int var2);
10 
11     void addIntHeader(String var1, int var2);

响应的状态

 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

要获取下载文件的路径
下载文件名是啥？
设置想办法让浏览器能够支持下载我们需要的东西
获取下载文件的输入流
创建缓冲区
获取OutputStream对象
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！

 1 public class FileServlet extends HttpServlet {
 2     @Override
 3     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
 4 
 5 //        要获取下载文件的路径
 6         String realPath = "F:\\develop\\workspace\\JavaWeb\\javaweb-02-servlet\\response\\target\\classes\\王刘.jpg";
 7         System.out.println("下载文件的路径:"+realPath);
 8 //        下载文件名是啥？
 9         String fileName = realPath.substring(realPath.lastIndexOf("\\") + 1);
10 //        设置想办法让浏览器能够支持(Content-Disposition)下载我们需要的东西,中文文件名URLEncoder.encode进行编码，否则有可能乱码
11         resp.setHeader("Content-Disposition","attachment;filename="+ URLEncoder.encode(fileName,"utf-8"));
12 //        获取下载文件的输入流
13         FileInputStream in = new FileInputStream(realPath);
14 //        创建缓冲区
15         int len = 0;
16         byte[] buffer = new byte[1024];
17 //        获取OutputStream对象
18         ServletOutputStream out= resp.getOutputStream();
19 //        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！
20         while ((in.read(buffer))!=-1) {
21             out.write(buffer,0,len);
22         }
23 
24         in.close();
25         out.close();
26     }

3、验证码的功能

验证码怎么来的？

前端实现
后端实现，需要用到java的图片类，生成一个图片

 1 public class ImageServlet extends HttpServlet {
 2     @Override
 3     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
 4 
 5         //如何让浏览器5秒自动刷新一次；
 6         resp.setHeader("refresh","3");
 7 
 8         //在内存中创建一个图片
 9         BufferedImage image = new BufferedImage(80,20,BufferedImage.TYPE_INT_RGB);
10         //得到图片
11         Graphics2D g = (Graphics2D) image.getGraphics(); //笔
12         //设置图片的背景颜色
13         g.setColor(Color.WHITE);
14         g.fillRect(0,0,80,20);
15         //给图片写数据
16         g.setColor(Color.blue);
17         g.setFont(new Font(null, Font.BOLD,20));
18         g.drawString(makeNum(),0,20);
19 
20         //告诉浏览器这个请求用图片的方式打开
21         resp.setContentType("image/jpg");
22         //网站存在缓存，不让浏览器缓存
23         resp.setDateHeader("expires", -1);
24         resp.setHeader("Cache-Control","no-cache");
25         resp.setHeader("Pragma","no-cache");
26 
27         //把图片写给浏览器
28         boolean write = ImageIO.write(image,"jpg", resp.getOutputStream());
29     }
30 
31     //生成随机数
32     private String makeNum(){
33         Random random = new Random();
34         String num = random.nextInt(9999999) + "";
35         StringBuffer sb = new StringBuffer();
36         for (int i = 0; i < 7-num.length(); i++) {
37             sb.append("0");
38         }
39         num = sb.toString() + num;
40         return num;
41     }
42 
43     @Override
44     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
45         doGet(req, resp);
46     }
47 }

4、实现重定向

B一个web资源收到客户端请求后，B他会通知A客户端去访问另外一个web资源C，这个过程叫重定向

常见场景：

用户登录

1 void sendRedirect(String var1) throws IOException;

测试

1 public class RedirectServlet extends HttpServlet {
2     @Override
3     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
4         resp.sendRedirect("/r/img"); //重定向
5 
6     }

面试提：请你聊聊重定向和转发的区别？

相同点

页面都会跳转

不同点

请求转发的时候，url不会产生变化
重定向的时候,url地址栏会发生变化；

 1 public class RequestTest extends HttpServlet {
 2     @Override
 3     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
 4         //处理请求
 5         String username = req.getParameter("username");
 6         String password = req.getParameter("password");
 7 
 8         System.out.println(username+":"+password);
 9 
10         //重定向的时候一定要注意，路径问题，否则404；
11         resp.sendRedirect("/r/success.jsp");
12     }
13 
14     @Override
15     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
16         doGet(req, resp);
17     }
18 }

 1 <html>
 2 <body>
 3 <h2>Hello World!</h2>
 4 
 5 <%--这里提交的路径，需要寻找到项目的路径--%>
 6 <%--${pageContext.request.contextPath}代表当前的项目--%>
 7 <form action="${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" value="提交">
11 </form>
12 
13 </body>
14 </html>

 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>

6.7、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，通过这个HttpServletRequest，获取客户端的所有信息

1、获取参数,请求转发

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

面试提：请你聊聊重定向和转发的区别？

相同点

页面都会跳转

不同点

请求转发的时候，url不会产生变化；307
重定向的时候,url地址栏会发生变化；302

posted @ 2020-12-13 17:33 王刘study 阅读(109) 评论(0) 收藏举报

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