javaweb开发之Filter实现过滤非法文字

1、概述

在论坛或者网站中，咱们会发现一些用户发表一些不文明或者非法的文字。这样可能致使论坛的不文明和谐，甚至还可能带来一些法律上的纠纷。咱们能够使用过滤器来帮助咱们过滤掉这些不文明的文字。

2、思路

统一维护非法文字，为了提升程序运行效率，能够将其缓存到内存中。当用户提交请求后，利用过滤器对指定程序（如发表言论）请求的内容进行过滤。发现有非法字符后替换成合法字符（如“*”）。

3、具体实现

keyword.properties

讨哥=**
荡漾=xx

这里咱们使用properties文件保存非法字符。

key是非法文字，value是要被替换后的文字。

ContentFilter.java

package cn.heimar.filter.contentfilter.util;

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.HttpServletResponse;

public class ContentFilter implements Filter {

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

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

		//思路：获得提交数据，替换，从新设置进去
		//使用包装对象来包裹原请求对象
		//若是是第一次请求，则加载关键字,缓存到ServletContext
		ContentReplaceHttpServletRequestWapper wapper=new ContentReplaceHttpServletRequestWapper(request);
		chain.doFilter(wapper, resp);
	}

	@Override
	public void destroy() {
		// TODO Auto-generated method stub
	}

}

ContentReplaceHttpServletRequestWapper.java

package cn.heimar.filter.contentfilter.util;

import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.util.Properties;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;

/**
 * 使用装饰模式，来修改getParameter方法返回的参数值
 * 
 * @author yan
 * 
 */
public class ContentReplaceHttpServletRequestWapper extends
		HttpServletRequestWrapper {
	private static Properties keywords;

	static {
		keywords = new Properties();
		try {
			keywords.load(ContentReplaceHttpServletRequestWapper.class
					.getClassLoader().getResourceAsStream("keyword.properties"));
		} catch (IOException e) {
			e.printStackTrace();
		}
	}

	public ContentReplaceHttpServletRequestWapper(HttpServletRequest request) {
		super(request);
	}

	@Override
	public String getParameter(String name) {
        //content和name是要过滤的请求参数名称
		if ("content".equals(name) || "title".equals(name)) {
			String old = super.getParameter(name);
			old = doFilter(old);
			return old;
		}
		return super.getParameter(name);
	}

	private String doFilter(String old) {
		for (Object temp : keywords.keySet()) {
			try {
				String key = new String(((String) temp).getBytes("ISO-8859-1"),"UTF-8");
				old = old.replaceAll(key, keywords.getProperty((String)temp));
			} catch (UnsupportedEncodingException e) {
				e.printStackTrace();
			}
		}
		return old;
	}

}