屏蔽非法字符就这么简单

package com.zhangkai.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 FilterToWord implements Filter {
	//销毁，当服务器关闭的时候，也就destroy了。
	@Override
	public void destroy() {		
	}
	//过滤
	@Override
	public void doFilter(ServletRequest request, ServletResponse response,
			FilterChain chain) throws IOException, ServletException {
		//首先拿到你输入的字符
		String content = request.getParameter("content");
		//第二步，判断一下拿到的值是不是空值
		if (content != null) {
		//比如我们规定含有XX的是非法字符
		if (content.indexOf("AAA") == -1) {
			//如果不包含，则继续往下操作
			chain.doFilter(request, response);
		} else {
			//反之，就提示用户，输入有误
			System.out.println("有非法文字");
			//如果有需要依然可以使用request.getRequestDispatcher跳转
			}
		} else {
			//如果是空值，则继续操作
			chain.doFilter(request, response);
		}		
	}
	//初始化，服务器一打开就init。
	@Override
	public void init(FilterConfig arg0) throws ServletException {	
	}	
}

<form action="demo011.jsp">
<input type = "text" name = "content"/>
<input type = "submit" value = "提交"/>

<%=request.getParameter("content")%>