Java 开发中用到的几种过滤器

在Java中有时会遇见乱码的情况，这里提供了几种转换方法

（一）Java中的编码转换

（二）可以在web.xml文件中配置的自己写的过滤器

第一种方法最简单也最方便，但是只能用在少量的地方或是偶尔一两次转码，如果大面积使用就不方便了，也大大增加了编码量，如果你的项目里没有用Spring的框架开发，用web.xml配置自定义过滤器可以一劳永逸的解决

1.首先要编写自己的过滤器类(实现了javax.servlet.Filter)：

package fck.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 CodeFilter implements Filter {

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

	}

	public void doFilter(ServletRequest request, ServletResponse response,
			FilterChain filter) throws IOException, ServletException {
		// TODO Auto-generated method stub
			request.setCharacterEncoding("utf-8"); 
			filter.doFilter(request, response); 
	}

	public void init(FilterConfig arg0) throws ServletException {
		// TODO Auto-generated method stub

	}

}

2.在web.xml文件中编写过滤器配置：

<filter>
  <!--CodeFilter是自己随便取的名字-->
  <filter-name>CodeFilter</filter-name>
  <!--写好对应的过滤器类的路径-->
  <filter-class>fck.filter.CodeFilter</filter-class>
 </filter>
 <filter-mapping>
  <filter-name>CodeFilter</filter-name>
  <!--“/*”代表所有的请求都经过过滤-->
  <url-pattern>/*</url-pattern>
 </filter-mapping>

之后不用再做什么代码的改变，过滤器就将所有的访问都转码了

(三)使浏览器不缓存页面的过滤器

import javax.servlet.*; 
import javax.servlet.http.HttpServletResponse; 
import java.io.IOException; 

/** *//** 
* 用于的使 Browser 不缓存页面的过滤器 
*/ 
public class ForceNoCacheFilter implements Filter { 

	public void doFilter(ServletRequest request, ServletResponse response, 
		FilterChain filterChain) throws IOException, ServletException{ 
		((HttpServletResponse) response).setHeader("Cache-Control","no-cache"); 
		((HttpServletResponse) response).setHeader("Pragma","no-cache"); 
		((HttpServletResponse) response).setDateHeader ("Expires", -1); 
		filterChain.doFilter(request, response); 
	} 

	public void destroy() { 
	} 

	public void init(FilterConfig filterConfig) throws ServletException { 
	} 
} 

(四)检测用户是否登陆的过滤器

import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.util.List;
import java.util.ArrayList;
import java.util.StringTokenizer;
import java.io.IOException;

/** */
/**
 * 用于检测用户是否登陆的过滤器，如果未登录，则重定向到指的登录页面
 * 配置参数
 * checkSessionKey 需检查的在 Session 中保存的关键字
 * redirectURL 如果用户未登录，则重定向到指定的页面，URL不包括 ContextPath
 * notCheckURLList 不做检查的URL列表，以分号分开，并且 URL 中不包括 ContextPath
 */
public class T implements Filter {
	protected FilterConfig filterConfig = null;
	private String redirectURL = null;
	private List notCheckURLList = new ArrayList();
	private String sessionKey = null;

	public void doFilter(ServletRequest servletRequest,
			ServletResponse servletResponse, FilterChain filterChain)
			throws IOException, ServletException {

		HttpServletRequest request = (HttpServletRequest) servletRequest;
		HttpServletResponse response = (HttpServletResponse) servletResponse;

		HttpSession session = request.getSession();
		if (sessionKey == null) {
			filterChain.doFilter(request, response);
			return;
		}
		if ((!checkRequestURIIntNotFilterList(request))
				&& session.getAttribute(sessionKey) == null) {
			response.sendRedirect(request.getContextPath() + redirectURL);
			return;
		}
		filterChain.doFilter(servletRequest, servletResponse);
	}

	public void destroy() {
		notCheckURLList.clear();
	}

	private boolean checkRequestURIIntNotFilterList(HttpServletRequest request) {
		String uri = request.getServletPath()
				+ (request.getPathInfo() == null ? "" : request.getPathInfo());
		return notCheckURLList.contains(uri);
	}

	public void init(FilterConfig filterConfig) throws ServletException {
		this.filterConfig = filterConfig;
		redirectURL = filterConfig.getInitParameter("redirectURL");
		sessionKey = filterConfig.getInitParameter("checkSessionKey");

		String notCheckURLListStr = filterConfig.getInitParameter("notCheckURLList");

		if (notCheckURLListStr != null) {
			StringTokenizer st = new StringTokenizer(notCheckURLListStr, ";");
			notCheckURLList.clear();
			while (st.hasMoreTokens()) {
				notCheckURLList.add(st.nextToken());
			}
		}
	}
}

(五)资源保护过滤器

import javax.servlet.Filter;
import javax.servlet.FilterConfig;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import java.io.IOException;
import java.util.Iterator;
import java.util.Set;
import java.util.HashSet; // 
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/** */
/**
 * This Filter class handle the security of the application.
 * 
 * It should be configured inside the web.xml.
 * 
 * @author Derek Y. Shen
 */
public class SecurityFilter implements Filter {
	// the login page uri
	private static final String LOGIN_PAGE_URI = "login.jsf";

	// the logger object
	private Log logger = LogFactory.getLog(this.getClass());

	// a set of restricted resources
	private Set restrictedResources;

	/** */
	/**
	 * Initializes the Filter.
	 */
	public void init(FilterConfig filterConfig) throws ServletException {
		this.restrictedResources = new HashSet();
		this.restrictedResources.add("/createProduct.jsf");
		this.restrictedResources.add("/editProduct.jsf");
		this.restrictedResources.add("/productList.jsf");
	}

	/** */
	/**
	 * Standard doFilter object.
	 */
	public void doFilter(ServletRequest req, ServletResponse res,
			FilterChain chain) throws IOException, ServletException {
		this.logger.debug("doFilter");

		String contextPath = ((HttpServletRequest) req).getContextPath();
		String requestUri = ((HttpServletRequest) req).getRequestURI();

		this.logger.debug("contextPath = " + contextPath);
		this.logger.debug("requestUri = " + requestUri);

		if (this.contains(requestUri, contextPath)
				&& !this.authorize((HttpServletRequest) req)) {
			this.logger.debug("authorization failed");
			((HttpServletRequest) req).getRequestDispatcher(LOGIN_PAGE_URI)
					.forward(req, res);
		} else {
			this.logger.debug("authorization succeeded");
			chain.doFilter(req, res);
		}
	}

	public void destroy() {
	}

	private boolean contains(String value, String contextPath) {
		Iterator ite = this.restrictedResources.iterator();

		while (ite.hasNext()) {
			String restrictedResource = (String) ite.next();

			if ((contextPath + restrictedResource).equalsIgnoreCase(value)) {
				return true;
			}
		}

		return false;
	}

	private boolean authorize(HttpServletRequest req) {

		// 处理用户登录
		/**//*
			 * UserBean user =
			 * (UserBean)req.getSession().getAttribute(BeanNames.USER_BEAN);
			 * 
			 * if (user != null && user.getLoggedIn()) { //user logged in return
			 * true; } else { return false; }
			 */
	}
}

(六) 利用Filter限制用户浏览权限

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;

public class T implements Filter {

	public void destroy() {

	}

	public void doFilter(ServletRequest sreq, ServletResponse sres,
			FilterChain arg2) throws IOException, ServletException {
		// 获取uri地址
		HttpServletRequest request = (HttpServletRequest) sreq;
		String uri = request.getRequestURI();
		String ctx = request.getContextPath();
		uri = uri.substring(ctx.length());
		// 判断admin级别网页的浏览权限
		if (uri.startsWith("/admin")) {
			if (request.getSession().getAttribute("admin") == null) {
				request.setAttribute("message", "您没有这个权限");
				request.getRequestDispatcher("/login.jsp").forward(sreq, sres);
				return;
			}
		}
		// 判断manage级别网页的浏览权限
		if (uri.startsWith("/manage")) {
			// 这里省去
		}
	}

	// 下面还可以添加其他的用户权限，省去。

	public void init(FilterConfig arg0) throws ServletException {

	}

}

配置文件写入：

<!-- 判断页面的访问权限 --> 
<filter> 
<filter-name>RightFilter</filter-name> 
<filter-class>cn.itkui.filter.RightFilter</filter-class> 
</filter> 
<filter-mapping> 
<filter-name>RightFilter</filter-name> 
<url-pattern>/admin/**//*</url-pattern> 
</filter-mapping> 
<filter-mapping> 
<filter-name>RightFilter</filter-name> 
<url-pattern>/manage/*</url-pattern> 
</filter-mapping>

最简单也是可以少量用的方法就是在java类中使用的编码方式转换

比如在项目中输出String Name；是“&#（）@（￥*@”乱码，那么可以采用：

String strNew = ""; //转化后的字符串
strNew = new String(str.getBytes("iso8859-1"),"utf-8");

这样得到的strNew就是转换成“utf-8”后的编码