JavaWeb入门

项目结构

web.xml文件的初始配置

  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. </web-app>

pom.xml文件的配置解读

  1. <?xml version="1.0" encoding="UTF-8"?>
  3. <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  4.          xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  5.     <modelVersion>4.0.0</modelVersion>
  7.     <!--  创建项目时选择的信息-->
  8.     <groupId>com.william</groupId>
  9.     <artifactId>javaweb-maven-01</artifactId>
  10.     <version>1.0-SNAPSHOT</version>
  12.     <!--  项目的打包方式:
  13.       jar: java项目
  14.       war: javaweb项目
  15.       -->
  16.     <packaging>war</packaging>
  18.     <name>javaweb-maven-01 Maven Webapp</name>
  19.     <!-- FIXME change it to the project's website -->
  20.     <url>http://www.example.com</url>
  22.     <!--  配置-->
  23.     <properties>
  24.         <!--      项目的默认构建编码-->
  25.         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  26.         <!--        编码版本-->
  27.         <maven.compiler.source>1.7</maven.compiler.source>
  28.         <maven.compiler.target>1.7</maven.compiler.target>
  29.     </properties>
  31.     <!--    项目依赖 从仓库中下载jar包的信息-->
  32.     <dependencies>
  33.         <dependency>
  34.             <groupId>junit</groupId>
  35.             <artifactId>junit</artifactId>
  36.             <version>4.11</version>
  37.             <scope>test</scope>
  38.         </dependency>
  40.     </dependencies>
  42.     <!--    项目构建的信息-->
  43.     <build>
  44.         <finalName>javaweb-maven-01</finalName>
  45.         <pluginManagement><!-- lock down plugins versions to avoid using Maven defaults (may be moved to parent pom) -->
  46.             <plugins>
  47.                 <plugin>
  48.                     <artifactId>maven-clean-plugin</artifactId>
  49.                     <version>3.1.0</version>
  50.                 </plugin>
  51.                 <!-- see http://maven.apache.org/ref/current/maven-core/default-bindings.html#Plugin_bindings_for_war_packaging -->
  52.                 <plugin>
  53.                     <artifactId>maven-resources-plugin</artifactId>
  54.                     <version>3.0.2</version>
  55.                 </plugin>
  56.                 <plugin>
  57.                     <artifactId>maven-compiler-plugin</artifactId>
  58.                     <version>3.8.0</version>
  59.                 </plugin>
  60.                 <plugin>
  61.                     <artifactId>maven-surefire-plugin</artifactId>
  62.                     <version>2.22.1</version>
  63.                 </plugin>
  64.                 <plugin>
  65.                     <artifactId>maven-war-plugin</artifactId>
  66.                     <version>3.2.2</version>
  67.                 </plugin>
  68.                 <plugin>
  69.                     <artifactId>maven-install-plugin</artifactId>
  70.                     <version>2.5.2</version>
  71.                 </plugin>
  72.                 <plugin>
  73.                     <artifactId>maven-deploy-plugin</artifactId>
  74.                     <version>2.8.2</version>
  75.                 </plugin>
  76.             </plugins>
  77.         </pluginManagement>
  78.     </build>
  79. </project>

Servlet

mapping

  1.     <!--    注册servlet-->
  2.     <servlet>
  3.         <servlet-name>hello</servlet-name>
  4.         <servlet-class>com.william.servlet.HelloServlet</servlet-class>
  5.     </servlet>
  6.     <!--    servlet请求的映射名和请求路径-->
  7.     <servlet-mapping>
  8.         <servlet-name>hello</servlet-name>
  9.         <url-pattern>/hello</url-pattern>
  10.     </servlet-mapping>

ServletContext

  1. // GetContext.class
  2. public class GetContext extends HttpServlet {
  3.     @Override
  4.     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  5.         ServletContext context = this.getServletContext();
  6.         String username = (String) context.getAttribute("username");
  8.         resp.setContentType("text/html");
  9.         resp.setCharacterEncoding("utf-8");
  10.         resp.getWriter().print("名字:" +username);
  11.     }
  13.     @Override
  14.     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  15.         doGet(req, resp);
  16.     }
  17. }
  20. // HelloServlet.class
  21. public class HelloServlet extends HttpServlet {
  22.     @Override
  23.     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  24.         ServletContext context = this.getServletContext();
  25.         String username = "william";
  26.         context.setAttribute("username", username);
  28.     }
  30.     @Override
  31.     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  32.         doPost(req, resp);
  33.     }
  34. }

HttpServletReponse

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);
  3.     void setContentLength(int var1);
  5.     void setContentLengthLong(long var1);
  7.     void setContentType(String var1);
  9.     void setBufferSize(int var1);

常用响应的状态码

  1.     int SC_OK = 200;
  2.     int SC_MULTIPLE_CHOICES = 300; // 重定向
  3.     int SC_NOT_FOUND = 404;
  4.     int SC_BAD_GATEWAY = 502; // 网关错误

常见应用

  1. 向浏览器发送消息

  2. 下载文件

    1. public class FileServlet extends HttpServlet {
    2.  @Override
    3.  protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    4.      //1.获取文件的下载路径
    5.      // String realPath = this.getServletContext().getRealPath("/1.png"); 这个路径是web服务器(Tomcat)下的路径,找不到目标文件
    6.      String realPath = "D:\\MyProject\\javeweb-servlet-01\\response\\target\\classes\\1.png";
    8.      System.out.println("文件的下载路径是" + realPath);
    10.      //2.下载的文件名
    11.      String fileName = realPath.substring(realPath.lastIndexOf("//") + 1);
    12. /*        小技巧: 用lastIndexOf找出文件路径最后一个/的下标+1后
    13.      得到文件名第一个字的下标后使用substring得出文件名*/
    15.      //3.设置浏览器响应头
    16.      resp.setHeader("Content-Disposition", "attachment; filename=" + URLEncoder.encode(fileName, "utf-8"));
    18.      //4.获取文件的输入流
    19.      FileInputStream in = new FileInputStream(realPath);
    21.      //5.创建缓冲区
    22.      int len = 0;
    23.      byte[] buffer = new byte[1024];
    25.      //6.获取OutputStream对象
    26.      ServletOutputStream out = resp.getOutputStream();
    28.      //7.将FileInputStream流写入缓冲区,使用ServletOutputStream将缓冲区数据输出到客户端
    29.      while ((len = in.read(buffer)) > 0) {
    30.          out.write(buffer, 0, len);
    31.      }
    33.      //9.关闭流
    34.      out.close();
    35.      in.close();
    36.  }
    38.  @Override
    39.  protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    40.      doGet(req, resp);
    41.  }
    42. }

应用:生成验证码图片

  1. public class ImageServlet extends HttpServlet {
  2.     @Override
  3.     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  4.         //设置浏览器自动刷新
  5.         resp.setHeader("refresh","5");
  7.         //在内存中创建一个图片对象
  8.         BufferedImage image = new BufferedImage(80,20,BufferedImage.TYPE_INT_RGB);
  10.         //得到笔
  11.         Graphics2D graphics = (Graphics2D) image.getGraphics();
  13.         //设置笔的颜色,填充图片背景
  14.         graphics.setColor(Color.WHITE);
  15.         graphics.fillRect(0,0,80,20);
  17.         //写字
  18.         graphics.setColor(Color.BLACK);
  19.         graphics.setFont(new Font(null, Font.BOLD,20));
  20.         graphics.drawString(makeNum(), 0, 20);
  22.         //设置浏览器
  23.         resp.setContentType("image/jpeg");
  24.         resp.setDateHeader("expires",-1);
  25.         resp.setHeader("Cache-Control", "no-cache");
  26.         resp.setHeader("pragma", "no-cache");
  28.         //把图片写给浏览器
  29.         ImageIO.write(image, "jpeg", resp.getOutputStream());
  31.     }
  33.     @Override
  34.     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  35.         doGet(req, resp);
  36.     }
  38.     /*生成随机数*/
  39.     private String makeNum() {
  40.         Random random = new Random();
  41.         String num = random.nextInt(9999999) + "";
  42.         StringBuffer stringBuffer = new StringBuffer();
  43.         //保证返回的字符串是7位
  44.         for (int i = 0; i < 7 - num.length(); i++) {
  45.             stringBuffer.append("0");
  46.         }
  47.         num = stringBuffer.toString() + num;
  48.         return num;
  49.     }
  50. }

重定向

  1.     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  2.         resp.sendRedirect("/response_war/image");
  3.         /*      
  4.         相当于  
  5.         resp.setHeader("Location","/response_war/image");
  6.         resp.setStatus(HttpServletResponse.SC_FOUND);
  7.         */
  8.     }

重定向和转发的区别

相同

  • 页面都会实现跳转

不同点

  • 请求转发时,URL不会变 307
  • 重定向,URL会改变 302

HttpServletRequest

  1. package com.william.servlet;
  3. import javax.servlet.ServletException;
  4. import javax.servlet.http.HttpServlet;
  5. import javax.servlet.http.HttpServletRequest;
  6. import javax.servlet.http.HttpServletResponse;
  7. import java.io.IOException;
  8. import java.util.Arrays;
  10. public class LoginServlet extends HttpServlet {
  11.     @Override
  12.     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  13.         //防止中文乱码
  14.         req.setCharacterEncoding("utf-8");
  15.         resp.setCharacterEncoding("utf-8");
  17.         String username = req.getParameter("username");
  18.         String password = req.getParameter("password");
  19.         //多个属性用getParameterValues()获取
  20.         String[] hobbies = req.getParameterValues("hobbies");
  21.         System.out.println("================================");
  22.         System.out.println("username = " + username);
  23.         System.out.println("password = " + password);
  24.         System.out.println("hobbies = " + Arrays.toString(hobbies));
  25.         System.out.println("================================");
  27.         //通过请求转发实现跳转
  28.         // /代表当前web应用
  29.         req.getRequestDispatcher("/success.jsp").forward(req, resp);
  31.     }
  33.     @Override
  34.     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  35.         doGet(req, resp);
  36.     }
  37. }

Cookie Session

保存会话的两种技术

Cookie

  • 客户端技术

Session

  • 服务器技术
  1. package com.william;
  3. import javax.servlet.ServletException;
  4. import javax.servlet.http.Cookie;
  5. import javax.servlet.http.HttpServlet;
  6. import javax.servlet.http.HttpServletRequest;
  7. import javax.servlet.http.HttpServletResponse;
  8. import java.io.IOException;
  9. import java.io.PrintWriter;
  10. import java.util.Date;
  12. //保存用户上一次登录的时间
  13. public class CookieDemo01 extends HttpServlet {
  14.     @Override
  15.     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  16.         //解决中文乱码
  17.         req.setCharacterEncoding("utf-8");
  18.         resp.setCharacterEncoding("utf-8");
  20.         PrintWriter out = resp.getWriter();
  22.         //服务端从客户端获取cookie
  23.         Cookie[] cookies = req.getCookies();
  25.         //判断cookie是否为空
  26.         if (cookies != null) {
  27.             out.print("last login time: ");
  29.             for (Cookie cookie : cookies) {
  30.                 if (cookie.getName().equals("last_time")) {
  31.                     String value = cookie.getValue();
  32.                     //    cookie值转换为时间输出
  33.                     long l = Long.parseLong(value);
  34.                     Date date = new Date(l);
  35.                     out.print(date.toString());
  36.                 }
  37.             }
  39.         } else {
  40.             out.print("this is your first time for login");
  41.         }
  43.         //    第一次访问则服务器给客户端一个cookie
  44.         //     不是第一次也更新cookie
  45.         Cookie cookie = new Cookie("last_time", System.currentTimeMillis() + "");
  46.         //设置cookie有效期
  47.         cookie.setMaxAge(24 * 60 * 60);
  48.         //设置有效期为0则删除
  49.         resp.addCookie(cookie);
  50.     }
  52.     @Override
  53.     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  54.         doGet(req, resp);
  55.     }
  56. }

JSP

基本语法

  1. <%--JSP表达式用于将程序的输出输出至客户端--%>
  2. <%= new java.util.Date()%>
  3. <%--JSP脚本片段--%>
  4. <%
  5.     int sum = 0;
  6.     for (int i = 0; i < 10; i++) {
  7.         sum += i;
  8.     }
  9.     out.print("<h1>sum=" + sum + "</h1>");
  11. %>

JSP声明

会将代码转换为生成的类中.

其他的会生成到_jspService方法中

  1. <%!
  2.     static {
  3.         System.out.println("entry servlet");
  4.     }
  6. %>

Filter过滤器

  1. 导包

  2. 编写过滤器

    1. 实现接口
    2. 重写方法
  3. 在web.xml中注册

Listener监听器

与过滤器类似