javaweb開發之Filter實現過濾非法文字

1、概述

在論壇或者網站中，咱們會發現一些用戶發表一些不文明或者非法的文字。這樣可能致使論壇的不文明和諧，甚至還可能帶來一些法律上的糾紛。咱們能夠使用過濾器來幫助咱們過濾掉這些不文明的文字。

2、思路

統一維護非法文字，爲了提升程序運行效率，能夠將其緩存到內存中。當用戶提交請求後，利用過濾器對指定程序（如發表言論）請求的內容進行過濾。發現有非法字符後替換成合法字符（如「*」）。

3、具體實現

keyword.properties

討哥=**
盪漾=xx

這裏咱們使用properties文件保存非法字符。

key是非法文字，value是要被替換後的文字。

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：獲得提交數據，替換，從新設置進去
		//使用包裝對象來包裹原請求對象
		//若是是第一次請求，則加載關鍵字,緩存到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;

/**
 * 使用裝飾模式，來修改getParameter方法返回的參數值
 * 
 * @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是要過濾的請求參數名稱
		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;
	}

}