人员管理信息系统-2.编码过滤器和核心控制器

1. java编码过滤器的作用：
   　java过滤器能够对目标资源的请求和响应进行截取，过滤信息执行的优先级高于servlet。
2. java过滤器的使用：
   　　（1）编写一个普通的java类，实现Filter接口

package com.imooc.sm.global;

import javax.servlet.*;
import java.io.IOException;

public class EncodingFilter implements Filter {
    private String encoding = "UTF-8";
    public void init(FilterConfig filterConfig) throws ServletException {
        if (filterConfig.getInitParameter("ENCODING") != null)
            encoding = filterConfig.getInitParameter("ENCODING");
    }

    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        servletRequest.setCharacterEncoding(encoding);
        servletResponse.setCharacterEncoding(encoding);
        filterChain.doFilter(servletRequest, servletResponse);
    }

    public void destroy() {
        encoding = null;
    }
}

（2） 在web.xml文件中进行配置：主要有两个属性filter和filter-mapping

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
         version="3.1">

  <filter>
    <filter-name>Encoding</filter-name>
    <filter-class>com.imooc.sm.global.EncodingFilter</filter-class>
    <init-param>
      <param-name>ENCODING</param-name>
      <param-value>UTF-8</param-value>
    </init-param>
  </filter>

  <filter-mapping>
    <filter-name>Encoding</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>

</web-app>

3. 核心控制器Servlet：
   作用：当用户向web容器发送一个请求的时候，web容器会根据用户请求的url来判断是否应该由Servlet进行处理，然后应该由哪个Servlet进行处理，判断出来以后，构造这个Servlet对象，然后进行初始化，最后调用service对象对这次请求进行实际处理。
   

步骤：

• 解析URL
• 创建applicationcontext对象，得到相应的bean对象
• 根据bean对象得到相应的方法，然后得到执行

public class DispatchServlet extends GenericServlet {

    private  ApplicationContext context;
    public void init() throws ServletException {
        context = new ClassPathXmlApplicationContext("spring.xml");
    }

    public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {
        HttpServletRequest request = (HttpServletRequest)servletRequest;
        HttpServletResponse response = (HttpServletResponse)servletResponse;

    /*
    *   /staff/add.do       /login.do
    *   staffcontroller
    *   public void add(HttpServletRequest,HttpServletResponse) {}
    * */

        String path = request.getServletPath().substring(1); //去掉第一个斜杠，得到staff/add.do
        String beanName = null;
        String methodName = null;

        int index = path.indexOf('/');
        if (index != -1) {
            beanName = path.substring(0,index) + "controller";
            methodName = path.substring(index + 1,path.indexOf(".do"));
        } else {
            beanName = "selfController";
            methodName = path.substring(0,path.indexOf(".do"));
        }

        Object obj = context.getBean(beanName);
        try {
            Method method = obj.getClass().getMethod(methodName,HttpServletRequest.class,HttpServletResponse.class);
            method.invoke(obj,request,response);
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            e.printStackTrace();
        }

    }

因为所有的Servlet对象要在web.xml文件中进行配置，所以要进行Servlet配置

<servlet>
    <servlet-name>Global</servlet-name>
    <servlet-class>com.imooc.sm.global.DispatchServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>Global</servlet-name>
    <url-pattern>*.do</url-pattern>
  </servlet-mapping>

4.测试

• 在controller包中创建一个测试类

  public class TestController {
  
    //      test/show.do            show.jsp是在根目录底下的，所以上一层的show.jsp
    public void show(HttpServletRequest request, HttpServletResponse response) {
        request.setAttribute("NAME","张三");
        try {
            request.getRequestDispatcher("../show.jsp").forward(request,response);
        } catch (ServletException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
  }

• 在根目录底下（webapp）创建一个show.jsp

  <%@ page contentType="text/html;charset=UTF-8" language="java" %>
  <html>
  <head>
    <title>Title</title>
  </head>
  <body>
  你好，世界！ ${NAME}
  </body>
  </html>
  

```

• 访问页面为：http://localhost:8080/test/show.do