src/com/demo/filter/HtmlFilter.java

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package com.demo.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.HttpServletRequestWrapper;
import javax.servlet.http.HttpServletResponse;

/**
 * 过滤器-http过滤器
 * 可以过滤url的字符
 * @author shao
 */
public class HtmlFilter implements Filter {

	@Override
	public void doFilter(ServletRequest req, ServletResponse resp,
			FilterChain chain) throws IOException, ServletException {
		HttpServletRequest request = (HttpServletRequest) req;
		HttpServletResponse response = (HttpServletResponse) resp;
		
		chain.doFilter(new MyRequest2(request), response);
	}

	@Override
	public void init(FilterConfig arg0) throws ServletException {}
	@Override
	public void destroy() {}
}

class MyRequest2 extends HttpServletRequestWrapper{

	private HttpServletRequest request;
	public MyRequest2(HttpServletRequest request) {
		super(request);
		this.request = request;
	}
	@Override
	public String getParameter(String name) {
		String value = this.request.getParameter(name);
		if(value == null) return null;
		return filter(value);	
	}
	
	public String filter(String message) {

        if (message == null)
            return (null);

        char content[] = new char[message.length()];
        message.getChars(0, message.length(), content, 0);
        StringBuilder result = new StringBuilder(content.length + 50);
        for (int i = 0; i < content.length; i++) {
            switch (content[i]) {