JAVA WEB过滤器Filter使用总结

1.过滤器的作用

(1)对所有请求的内容进行统一编码，防止乱码

(2)过滤或屏蔽一些非法字符

(3)判断用户是否登录，就是判断session是否存在

2.如何编写过滤器？

(1)所在的类必须实现Filter接口(它含有三个抽象方法)

publib interface Filter{

pulbic void init(FilterConfig config) throws ServletException;

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

public void destroy();

}

3.常见的过滤器的写法

(1)SetCharacterEncodingFilter.java(统一编码)

package filter;
import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
public class SetCharacterEncodingFilter implements Filter {
	protected String encoding = null;
	protected FilterConfig filterConfig = null;
	public void init(FilterConfig config) throws ServletException {
		System.out.println("过滤器初始化!");
		this.filterConfig = config;
		this.encoding = filterConfig.getInitParameter("encoding");
	}
	public void doFilter(ServletRequest request, ServletResponse response,
			FilterChain chain) throws IOException, ServletException {
		String encoding = this.encoding;
		if (encoding != null) {
			request.setCharacterEncoding(encoding);
		} else {
			request.setCharacterEncoding("UTF-8");
		}
		chain.doFilter(request, response);
	}
	public void destroy() {
		System.out.println("过滤器销毁!");
		this.encoding = null;
		this.filterConfig = null;
	}
}

(2)SessionFilter.java(session是否生效)

package filter;
import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;
//是否登陆进行过滤
public class SessionFilter implements Filter {
	public void init(FilterConfig config) throws ServletException {
		System.out.println("过滤器初始化!");
	}
	public void doFilter(ServletRequest request, ServletResponse response,
			FilterChain chain) throws IOException, ServletException {
		HttpServletRequest req = (HttpServletRequest) request;
		HttpSession session = req.getSession();
		// 如果session不为空，则跳转到其它页面,否则转到登陆页面
		if (session.getAttribute("user") != null) {
			chain.doFilter(request, response);
		} else {
			request.getRequestDispatcher("login.jsp")
					.forward(request, response);
		}
	}
	public void destroy() {
		System.out.println("过滤器销毁!");
	}
}

(3)CharFilter .java(过滤非法字符)

package filter;
import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
//过滤非法字符
public class CharFilter implements Filter{
	public void init(FilterConfig config){
		System.out.println("过滤器初始化!");
	}
	public void doFilter(ServletRequest request,ServletResponse response,FilterChain chain)throws IOException,ServletException{
		String content=request.getParameter("content");
		if(content!=null){
			if(content.indexOf("<script")==-1){
				chain.doFilter(request,response);
			}else{
				System.out.println("有非法字符!");
			}
		}else{
			chain.doFilter(request, response);
		}
	}
    public void destroy(){
    	System.out.println("过滤器销毁!");
    }
}

另附，以上三种过滤器的web.xml配置

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" 
	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_2_5.xsd">
    <!--统一字符编码过滤器-->
	<filter>
		<filter-name>SetCharacterEncoding</filter-name>
		<filter-class>
			filter.SetCharacterEncodingFilter
		</filter-class>
		<init-param>
			<param-name>encoding</param-name>
			<param-value>UTF-8</param-value>
		</init-param>
	</filter>
	<filter-mapping>
		<filter-name>SetCharacterEncoding</filter-name>
		<url-pattern>/*</url-pattern>
		<dispatcher>FORWARD</dispatcher>
		<dispatcher>REQUEST</dispatcher>
	</filter-mapping>
    <!--过滤非法字符-->
    <filter>
		<filter-name>CharFilter</filter-name>
		<filter-class>
			filter.CharFilter
		</filter-class>
	</filter>
	<filter-mapping>
		<filter-name>CharFilter</filter-name>
		<url-pattern>/*</url-pattern>
	</filter-mapping>
	<!-- 是否登陆进行过滤 -->
	<filter>
		<filter-name>SessionFilter</filter-name>
		<filter-class>
			filter.SessionFilter
		</filter-class>
	</filter>
	<filter-mapping>
		<filter-name>SessionFilter</filter-name>
		<url-pattern>/*</url-pattern>
	</filter-mapping>
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
</web-app>