Java深入 - Filter过滤器

Posted 2020-09-22 jzssuanfa

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Java的1.3開始，对servlet2.3规范中增加了过滤器的支持。

过滤器可以让我们对目标资源的请求和响应进行截取。

一些filter的特性：

1. Filter是Servlet规范的规定，须要Servlet容器的支持。

2. Filter不能使用Spring框架中的资源对象。

3. Filter仅仅在Servlet前后起作用。

Filter实现

我们须要实现接口Filter中定义的方法：

/*
 * The contents of this file are subject to the terms
 * of the Common Development and Distribution License
 * (the "License").  You may not use this file except
 * in compliance with the License.
 *
 * You can obtain a copy of the license at
 * glassfish/bootstrap/legal/CDDLv1.0.txt or
 * https://glassfish.dev.java.net/public/CDDLv1.0.html.
 * See the License for the specific language governing
 * permissions and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL
 * HEADER in each file and include the License file at
 * glassfish/bootstrap/legal/CDDLv1.0.txt.  If applicable,
 * add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your
 * own identifying information: Portions Copyright [yyyy]
 * [name of copyright owner]
 *
 * Copyright 2005 Sun Microsystems, Inc. All rights reserved.
 *
 * Portions Copyright Apache Software Foundation.
 */

package javax.servlet;

import java.io.IOException;


public interface Filter {

	public void init(FilterConfig filterConfig) throws ServletException;
	
	

    public void doFilter ( ServletRequest request, ServletResponse response, FilterChain chain ) 
throws IOException, ServletException;

	public void destroy();


}

自己定义一个TestFilter

/**
 * 自己定义一个Filter
 * @author zhuli
 * @date 2014-7-20
 */
public class TestFilter implements Filter {

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("TestFiltern init"); //初始化容器的时候，这边会执行
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) 
throws IOException, ServletException {
        // TODO Auto-generated method stub
        HttpServletRequest request2 = (HttpServletRequest)request;
        String ip = IPUtil.getClientIp(request2);
        System.out.println("TestFiltern doFilter 请求前面就处理了 + ip: " + ip);
        chain.doFilter(request, response); //传递filter链
        System.out.println("业务处理完了之后。会继续调用这个filter。然后调用这边");
    }

    @Override
    public void destroy() {
        // TODO Auto-generated method stub
        System.out.println("TestFiltern destroy"); //销毁容器的时候，这边会执行
    }

}

结果：

TestFiltern doFilter 请求前面就处理了 + ip: 127.0.0.1
业务逻辑=========
业务处理完了之后，会继续调用这个filter，然后调用这边

Filter配置

在web.xml中，配置servlet前面配置Filter就可以：

url-pattern能够配置符合哪些请求的须要走这个filter

	<!-- TEST filter -->
	<filter>
		<filter-name>testFilter</filter-name>
		<filter-class>com.xxx.test.TestFilter</filter-class>
	</filter>
	<filter-mapping>
		<filter-name>testFilter</filter-name>
		<url-pattern>/*</url-pattern>
	</filter-mapping>