Java Servlet常用到的几个Filter

一、使浏览器不缓存页面的过滤器

public class ForceNoCacheFilter implements Filter {

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

}

 二、检测用户是否登陆的过滤器

/**
 * 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 CheckLoginFilter implements Filter {
	protected FilterConfig filterConfig = null;
	private String redirectURL = null;
	private List notCheckURLList = new ArrayList();
	private String sessionKey = null;
	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());
			}
		}
	}
	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);
	}
	private boolean checkRequestURIIntNotFilterList(HttpServletRequest request) {
		String uri = request.getServletPath()
				+ (request.getPathInfo() == null ? "" : request.getPathInfo());
		return notCheckURLList.contains(uri);
	}
	public void destroy() {
		notCheckURLList.clear();
	}
	
}

三、字符编码的过滤器

/**
 * 用于设置 HTTP 请求字符编码的过滤器，通过过滤器参数encoding指明使用何种字符编码,用于处理Html Form请求参数的中文问题
 */
public class CharacterEncodingFilter implements Filter {
	protected FilterConfig filterConfig = null;
	protected String encoding = "";
	public void init(FilterConfig filterConfig) throws ServletException {
		this.filterConfig = filterConfig;
		this.encoding = filterConfig.getInitParameter("encoding");

	}
	public void doFilter(ServletRequest servletRequest,
			ServletResponse servletResponse, FilterChain filterChain)
			throws IOException, ServletException {
		if (encoding != null)
			servletRequest.setCharacterEncoding(encoding);
		filterChain.doFilter(servletRequest, servletResponse);
	}

	public void destroy() {
		filterConfig = null;
		encoding = null;
	}
}

 四 利用Filter限制用户浏览权限

public class RightFilter implements Filter {

	public void init(FilterConfig arg0) throws ServletException {
	}

	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
		}
	}

	public void destroy() {
	}
}

 <!-- 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>