JavaWeb_04 Servlet 下

复习！

4.5、ServletContext

web容器在启动的时候，他会为每个web程序创建一个对应的servletContext对象，它代表当前的web应用。

4个案例

1、共享数据

我在这个servlet中保存的数据，可以在另一个servlet中拿到

public class HelloServlet extends HttpServlet {
    
    
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
    
        //this.getServletContext()
        ServletContext servletContext = this.getServletContext();
        //共享数据
        String username = "hyf";
        servletContext.setAttribute("username",username);
    }
}

public class GetServlet extends HttpServlet {
    
    
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
    
        ServletContext servletContext = this.getServletContext();

        String username = String.valueOf(servletContext.getAttribute("username"));

        resp.getWriter().print("name:"+username);
    }

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

在web.xml中添加映射

  <servlet>
    <servlet-name>hello</servlet-name>
    <servlet-class>com.hao.servlet.HelloServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>hello</servlet-name>
    <url-pattern>/hello</url-pattern>
  </servlet-mapping>

  <servlet>
    <servlet-name>getname</servlet-name>
    <servlet-class>com.hao.servlet.GetServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>getname</servlet-name>
    <url-pattern>/getname</url-pattern>
  </servlet-mapping>

2、获取初始化参数

//获取初始化参数
public class ServletDemo03 extends HttpServlet {
    
    
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
    
        ServletContext servletContext = this.getServletContext();

        String url = servletContext.getInitParameter("url");
        resp.getWriter().print(url);
    }

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

  <!--配置一些web应用初始化参数-->
  <context-param>
    <param-name>url</param-name>
    <param-value>jdbc:mysql://localhost:3306/mybatis</param-value>
  </context-param>
  
  <servlet>
    <servlet-name>gp</servlet-name>
    <servlet-class>com.hao.servlet.ServletDemo03</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>gp</servlet-name>
    <url-pattern>/gp</url-pattern>
  </servlet-mapping>

3、请求转发

//请求转发
public class ServletDemo04 extends HttpServlet {
    
    
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
    
        ServletContext servletContext = this.getServletContext();

        RequestDispatcher requestDispatcher = servletContext.getRequestDispatcher("/gp");//转发的请求路径
        requestDispatcher.forward(req,resp);//调用forward实现请求转发
    }

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

在web.xml中添加映射，略

4、读取资源文件

/*
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：都被打包到了同一路径下classes，我们俗称这个路径为classpath
**/

public class ServletDemo05 extends HttpServlet {
    
    

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
    
        ServletContext servletContext = this.getServletContext();

        InputStream asStream = servletContext.getResourceAsStream("/WEB-INF/classes/com/hao/servlet/aa.properties");
        Properties properties = new Properties();
        properties.load(asStream);
        String user = properties.getProperty("username");
        String pwd = properties.getProperty("password");

        resp.getWriter().print(user+":"+pwd);
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
    
        doGet(req, resp);
    }
}

会出现资源导出失败问题，需要在pom.xml中 build里添加

	  <resources>
            <resource>
                <directory>src/main/resources</directory>
                <excludes>
                    <exclude>**/*.properties</exclude>
                    <exclude>**/*.xml</exclude>
                </excludes>
                <filtering>true</filtering>
            </resource>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>true</filtering>
            </resource>
        </resources>

添加映射

4.6、HttpServletResponse

1、下载文件

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HttpServletResponse对象，代表响应一个HttpServletResponse

public class FileServletTest extends HttpServlet {
    
    
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
    
// 1、获取下载文件路径
        //F:\idea-workspace\javaweb-02-servlet\response\src\main\resources\tx.jpg
        String realPath = "F:\\idea-workspace\\javaweb-02-servlet\\response\\src\\main\\resources\\tx.jpg";
        //String realPath = this.getServletContext().getRealPath("/tx.jpg");
        System.out.println("下载文件的路径："+realPath);
// 2、文件名
        String fileName = realPath.substring(realPath.lastIndexOf("\\" )+1);
// 3、想办法设置让浏览器能够支持(Content-Disposition)下载我们需要的东西
        //"attachment:filename"是查看，分号是实现下载
        resp.setHeader("Content-Disposition","attachment;filename"+fileName);
// 4、获取下载文件输入流
        FileInputStream in = new FileInputStream(realPath);
// 5、创建缓冲区buffer
        int len = 0;
        byte[] buffer = new byte[1024];
// 6、获取OutputStream对象
        ServletOutputStream os = resp.getOutputStream();
// 7、将FileOutputStream流写入到buffer缓冲区
// 8、使用OutputStream将缓冲区的数据传输到客户端
        while(in.read(buffer)>0){
    
    
            os.write(buffer,0,len);
        }

        in.close();
        os.close();
    }

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

2、验证码实现

//验证码实现
public class ImageServlet extends HttpServlet {
    
    
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
    

        //让浏览器自动3秒刷新一次就生成一个验证码
        resp.setHeader("refresh","3");

        //在内存中创建一个图片
        BufferedImage image = new BufferedImage(80,20,BufferedImage.TYPE_INT_BGR);

        //画图，得到一个图片
        Graphics2D g = (Graphics2D) image.getGraphics();//笔

        //设置图片背景色
        g.setColor(Color.lightGray);
        g.fillRect(0,0,80,20);

        //给图片写数据
        g.setColor(Color.blue);
        g.setFont(new Font(null,Font.ITALIC,20));
        g.drawString(makeNum(),0,20);

        //告诉浏览器，请求用图片的方式打开
        resp.setContentType("image/jpg");
        //不让浏览器缓存
        resp.setDateHeader("expires",-1);
        resp.setHeader("Cache-Control","no-cache");
        resp.setHeader("Pragma","no-cache");

        //图片写给浏览器
        ImageIO.write(image,"jpg",resp.getOutputStream());
    }

    //生成随机数
    private String makeNum(){
    
    
        Random random = new Random();
        String num = random.nextInt(9999)+"";
        StringBuffer sb = new StringBuffer();
        for (int i=0;i<4-num.length();i++){
    
    
            sb.append("0");
        }
        num = sb.toString()+num;
        return num;
    }

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

3、重定向

//重定向
public class SendRedirectServlet extends HttpServlet {
    
    
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
    
        resp.sendRedirect("/response_war/img");
        //重定向：status code：302           location

        //重定向  VS 请求转发307
        /*
        相同点：都会跳转
        不同：  请求转发，url不会变化
               重定向   url变化
        * */
    }

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

jsp文件

<!--这个提交路径,需要找项目路径-->
<%--${pageContext.request.contextPath}代表当前项目--%>
<form action="${pageContext.request.contextPath}/login" method="get">
用户名：<input type="text" name="user"><br>
密码：<input type="password" name="password"><br>
    <input type="submit">
</form>

public class RequestTest extends HttpServlet {
    
    
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
    
        System.out.println("进入了这个请求");

        //处理请求
        String user = req.getParameter("user");
        String password = req.getParameter("password");

        System.out.println(user+":"+password);

        //重定向
        resp.sendRedirect("/response_war/success.jsp");

    }

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

4.7、HttpServletRequest

获取前端传递的参数、请求转发

public class loginServlet extends HttpServlet {
    
    
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
    

        String user = req.getParameter("user");
        String password = req.getParameter("password");
        String[] hobbies = req.getParameterValues("hobby");
        System.out.println("=============");
        System.out.println(user+":"+password);
        
        System.out.println(Arrays.toString(hobbies));

        //通过请求转发   307
        //转发跟重定向不一样，转发，/就是当前项目
        req.getRequestDispatcher("/success.jsp").forward(req,resp);
    }

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

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