代理实现过滤器例子

package cn.itcast.proxy;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

import javax.servlet.http.HttpServletRequest;

public class NameProxy implements InvocationHandler{
	private HttpServletRequest request;
	
	public NameProxy(HttpServletRequest request) {
		super();
		this.request = request;
	}
	public HttpServletRequest getNameProxy(){
		
		HttpServletRequest proxy = (HttpServletRequest) Proxy.newProxyInstance(
								request.getClass().getClassLoader(),
								request.getClass().getInterfaces(),
								this
								);
		return proxy;
	}

	public Object invoke(Object proxy, Method method, Object[] args)
			throws Throwable {
		
			if("getParameter".equals(method.getName())){
				String value = request.getParameter(args[0].toString());
				value = filterHtml(value);
				return value;
			}
		return method.invoke(request, args);
	}
	 public static String filterHtml(String message) {

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

	        char content[] = new char[message.length()];
	        message.getChars(0, message.length(), content, 0);
	        StringBuffer result = new StringBuffer(content.length + 50);
	        for (int i = 0; i < content.length; i++) {
	            switch (content[i]) {
	            case '<':
	                result.append("&lt;");
	                break;
	            case '>':
	                result.append("&gt;");
	                break;
	            case '&':
	                result.append("&amp;");
	                break;
	            case '"':
	                result.append("&quot;");
	                break;
	            default:
	                result.append(content[i]);
	            }
	        }
	        return (result.toString());

	    }
}

package cn.itcast.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 cn.itcast.proxy.NameProxy;


public class NameFilter implements Filter {

	public void doFilter(ServletRequest req, ServletResponse response,
			FilterChain chain) throws IOException, ServletException {
		//在放行之前要对提交过来的文本进行转意操作
		HttpServletRequest request =(HttpServletRequest) req;
		NameProxy  p = new NameProxy(request);
		HttpServletRequest requestp = p.getNameProxy();
		chain.doFilter(requestp, response);
	}
	public void destroy() {
		// TODO Auto-generated method stub
		
	}


	public void init(FilterConfig filterConfig) throws ServletException {
		// TODO Auto-generated method stub
		
	}

}