Filter-过滤器基础

过滤器基础

过滤器实现的过程及配置过滤器
执行完第一过滤器，再执行第二过滤器

HelloFilter.java

public class HelloFilter implements Filter{

    //创建实例
    public HelloFilter(){
        System.out.println("1.创建过滤器实例");
    }

    //初始化方法，在服务器启动时执行
    //
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        // TODO Auto-generated method stub
        System.out.println("2.执行过滤器初始化方法");

        /*
        //获取过滤器在web.xml中配置的初始化参数
        String encoding = filterConfig.getInitParameter("encoding");
        System.out.println(encoding);
        */

        //获取过滤器在web.xml中配种的所有初始化参数
        Enumeration<String> enums = filterConfig.getInitParameterNames();
        while(enums.hasMoreElements()){
            //获取所有参数
            String name = enums.nextElement();
            //获取名称对应的值
            String value = filterConfig.getInitParameter(name);
            System.out.println(name+":"+value);
        }
    }

    //过滤器业务处理方法，在请求到达servlet之前县进入此方法处理公用的业务逻辑操作
    //FilterChain   过滤器链参数；一个个过滤器形成一个执行链
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {
        // TODO Auto-generated method stub
        System.out.println("3.执行过滤器业务处理方法");
        //执行下一个过滤器或放行（去到servlet）
        chain.doFilter(request, response);
        //如果有下一个过滤器，进入下一个过滤器，否则就执行访问servlet
        System.out.println("5.Servlet处理完成，又回到过滤器");
    }

    //销毁过滤器实例时候调用
    @Override
    public void destroy() {
        // TODO Auto-generated method stub
        System.out.println("6.销毁过滤器实例");
    }

}

HelloFilter2.java

public class HelloFilter2 implements Filter{

    @Override
    public void destroy() {
        // TODO Auto-generated method stub

    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {
        // TODO Auto-generated method stub
        System.out.println("第二个过滤器");
        //放行（去到servlet）
        chain.doFilter(request, response);
        //如果有下一个过滤器，进入下一个过滤器，否则就执行访问servlet
        System.out.println("第二个过滤器执行结束");
    }

    @Override
    public void init(FilterConfig arg0) throws ServletException {
        // TODO Auto-generated method stub

    }

}

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="3.0"
    xmlns="http://java.sun.com/xml/ns/javaee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd">

  <!-- 过滤器配置 -->
  <filter>
    <filter-name>encoding</filter-name>
    <filter-class>Filter.EncodingFilter.java</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>encoding</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>

  <filter>
    <!-- 配置初始化参数 -->
    <init-param>
        <param-name>encoding</param-name>
        <param-value>UTF-8</param-value>
    </init-param>
    <init-param>
        <param-name>path</param-name>
        <param-value>c:/...</param-value>
    </init-param>
    <!-- filter内部名称 -->
    <filter-name>hello_filter</filter-name>
    <!-- 过滤器类的全名 -->
    <filter-class>a_filter_hello.HelloFilter</filter-class>
  </filter>
  <filter-mapping>
    <!-- filter内部名称 -->
    <filter-name>hello_filter</filter-name>
    <!-- 拦截所有资源 -->
    <url-pattern>/*</url-pattern>
  </filter-mapping>

  <!-- 配置第二个过滤器 -->
  <filter>
    <!-- filter内部名称 -->
    <filter-name>hello_filter2</filter-name>
    <!-- 过滤器类的全名 -->
    <filter-class>a_filter_hello.HelloFilter2</filter-class>
  </filter>
  <!-- 拦截指定的请求 -->
  <filter-mapping>
    <!-- filter内部名称 -->
    <filter-name>hello_filter2</filter-name>

    <!-- 
    1.拦截所有资源 
    <url-pattern>/*</url-pattern>
    -->

    <!-- 2.拦截指定的jsp -->
    <url-pattern>/index.jsp</url-pattern>
    <url-pattern>/list.jsp</url-pattern>
    <url-pattern>*.jsp</url-pattern>

    <!-- 3.根据servlet的内部名称拦截 -->
    <servlet-name>IndexServlet</servlet-name>
    <url-pattern>/IndexServlet</url-pattern>

    <!-- 4.拦截指定的类型 
    REQUEST：默认拦截的类型
    FORWARD：拦截转发
    INCLUDE：拦截包含的页面
    ERROR：拦截声明式异常
    -->

    <dispatcher>REQUEST</dispatcher>
    <dispatcher>FORWARD</dispatcher>
    <dispatcher>INCLUDE</dispatcher>
    <dispatcher>ERROR</dispatcher>
  </filter-mapping>

  <servlet>
    <description>This is the description of my J2EE component</description>
    <display-name>This is the display name of my J2EE component</display-name>
    <servlet-name>IndexServlet</servlet-name>
    <servlet-class>a_filter_hello.IndexServlet</servlet-class>
  </servlet>

  <servlet-mapping>
    <servlet-name>IndexServlet</servlet-name>
    <url-pattern>/IndexServlet</url-pattern>
  </servlet-mapping>

</web-app>