【Servlet】Filter过滤器的编写和配置

2022-10-22 11:20:32

Servlet的Filter介绍

在Servlet作为过滤器使用时，它可以对客户的请求进行过滤处理，当它处理完成后，它会交给下一个过滤器处理，就这样，客户的请求在过滤链里一个个处理，直到请求发送到目标.如果过滤器不成功，则将试图转发到指定页面.

过滤器就像一扇门，客户端要和服务端的某个目标交互，必须通过这扇门.

典型filter应用

1 设置统一字符集解决中文乱码问题.

request.setCharacterEncoding(“UTF-8");

post/get默认传输编码都是ISO8859-1

2 权限,比如检查会话是否有效。

如何编写Filter

开发一个自定义的Filter，需要实现Filter接口，Filter接口定义了以下的方法：

	//由Web容器调用，销毁此Filter

	destroy()

	 //由Web容器调用，初始化此Filter

	init(FilterConfig filterConfig)

	//具体过滤处理代码

	doFilter(ServletRequest request, ServletResponse response, FilterChain chain)

如何配置Filter

在web.xml文件中配置filter逻辑名初始参数及拦截哪些pattern的请求。

<filter>

	<filter-name>EncodingFilter</filter-name>

	<filter-class>com.lessons.filter.EncodingFilter</filter-class>

	<init-param>

		<param-name>encoding</param-name>

		<param-value>utf-8</param-value>

	</init-param>//通过FilterConfig类的getInitParameter("paramName")

</filter>

<filter-mapping>

	<filter-name>EncodingFilter</filter-name>

	<url-pattern>/*</url-pattern>

</filter-mapping>

过滤器范例：设置请求编码的过滤器

package com.app.servlet;

import java.io.IOException;

import javax.servlet.Filter;

import javax.servlet.FilterChain;

import javax.servlet.FilterConfig;

import javax.servlet.ServletContext;

import javax.servlet.ServletException;

import javax.servlet.ServletRequest;

import javax.servlet.ServletResponse;

import javax.servlet.http.HttpServletRequest;

/**

 * 设置请求编码的过滤器

 * @author user

 */

public class EncodingFilter implements Filter {

	ServletContext application;

	private String basePath;

	public void destroy() {

		// TODO Auto-generated method stub

	}

	public void doFilter(ServletRequest req, ServletResponse response,

			FilterChain chain) throws IOException, ServletException {

		// TODO Auto-generated method stub

		HttpServletRequest request = (HttpServletRequest)req;

		request.setCharacterEncoding("utf-8");

		String path = request.getContextPath();

		basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";

		application.setAttribute("bashPath", basePath);

		chain.doFilter(req, response);//交给下一个过滤器

	}

	public void init(FilterConfig config) throws ServletException {

		// TODO Auto-generated method stub

		application = config.getServletContext();

	}

}

XML文件的配置

	<filter>

		<filter-name>EncodingFilter</filter-name>

		<filter-class>com.app.servlet.EncodingFilter</filter-class>

	</filter>

	<filter-mapping>

		<filter-name>EncodingFilter</filter-name>

		<url-pattern>/*</url-pattern>

	</filter-mapping>

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