servlet过滤器入门

源码请见共享目录CSDN/JavaEE基础/1. SimpleFilter.zip

一、目标

书写过滤器，过滤指定的地址

二、说明

编写的过滤器，要实现javax.servlet.Filter接口！Filter接口的生命周期如下：

每个过滤器随着jvm的启动而初始化，jvm的关闭而关闭，在程序执行过程中负责拦截请求，用户可以定义规则判断是否调用chain.doFilter(request, response)去做相应servlet操作。

三、代码

1. 增加servlet依赖

<dependency>    <groupId>javax.servlet</groupId>    <artifactId>javax.servlet-api</artifactId>    <version>3.1.0</version>    <scope>provided</scope></dependency>

1. 编写过滤器

public class MyFilter implements Filter{    public void destroy() {        System.out.println("destroy");    }    public void doFilter(ServletRequest arg0, ServletResponse arg1,            FilterChain chain) throws IOException, ServletException {        System.out.println("doFilter");        chain.doFilter(arg0, arg1);    }    public void init(FilterConfig arg0) throws ServletException {        System.out.println("init");    }}

1. 编写servlet

public class Test extends HttpServlet{    @Override    protected void doGet(HttpServletRequest req, HttpServletResponse resp)            throws ServletException, IOException {        System.out.println("Hello,GET!");    }    @Override    protected void doPost(HttpServletRequest req, HttpServletResponse resp)            throws ServletException, IOException {        System.out.println("Hello,POST!");    }}

1. 配置servlet和filter

<!DOCTYPE web-app PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN" "http://java.sun.com/dtd/web-app_2_3.dtd" ><web-app>  <display-name>Archetype Created Web Application</display-name>  <servlet>    <servlet-name>Test</servlet-name>    <servlet-class>Controller.Test</servlet-class>  </servlet>  <servlet-mapping>    <servlet-name>Test</servlet-name>    <url-pattern>/test</url-pattern>  </servlet-mapping>    <filter>        <filter-name>MyFilter</filter-name>        <filter-class>Filter.MyFilter</filter-class>    </filter>      <filter-mapping>        <filter-name>MyFilter</filter-name>        <!--拦截所有/test开始的url-->        <url-pattern>/test/*</url-pattern>      </filter-mapping></web-app>

四、总结

用户可以自定义多个Filter，每个Filter可以拦截1个或多个URL请求（分POST、GET等请求），这些Filter系统会链接在一起，形成FilterChain。
，方便访问某个URL时调用。