Java filter过滤器在项目开发中的应用.doc

过滤器在项目开发中的应用javaee过滤器在项目怒开发中通常有三种应用：应用一：统一项目的字符编码：我们新建一个名为Encode.java的文件，内容是：package 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 Encode implements Filter public void destroy() / TODO Auto-generated method stubpublic void doFilter(ServletRequest request, ServletResponse response,FilterChain chain) throws IOException, ServletException request.setCharacterEncoding(utf-8); response.setCharacterEncoding(utf-8); chain.doFilter(request, response);public void init(FilterConfig arg0) throws ServletException / TODO Auto-generated method stub程序在dofilter的方法中设置了request和response的编码为utf-8，这样便可以解决开发中的乱码问题，配置文件web.xml这样写: encoding filter.Encode encoding /* 应用二：限制所有未经登陆的用户通过地址直接请求资源。我们的项目文件结构如图：所有的页面文件都在pages的文件夹下（包括第一个登陆页面）。先建一个Unlogin,java，内容为：package filter;/防止未登录访问页面的过滤器import java.io.IOException;import javax.servlet.Filter;import javax.servlet.FilterChain;import javax.servlet.FilterConfig;import javax.servlet.RequestDispatcher;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;public class Unlogin implements Filter public void destroy() / TODO Auto-generated method stubpublic void doFilter(ServletRequest request, ServletResponse response,FilterChain chain) throws IOException, ServletException RequestDispatcher dispatcher = request.getRequestDispatcher(/pages/login.jsp);/这里设置如果没有登陆将要转发到的页面 HttpServletRequest req = (HttpServletRequest) request; HttpServletResponse res = (HttpServletResponse) response; HttpSession session = req.getSession(true); /排除登陆页面不被过滤 String request_uri = req.getRequestURI(); String ctx_path = req.getContextPath(); /这里假设是排除登陆页面login.jsp 。排除文件夹是一样的，例如排除admin文件夹：/admin if(request_uri.substring(ctx_path.length().equals( /pages/login.jsp) chain.doFilter(request,response); return; / 从session里取的用户名信息 String username = (String) session.getAttribute(name);/这里获取session，为了检查session里有没有保存用户信息，没有的话回转发到登陆页面 System.out.println(username); / 判断如果没有取到用户信息,就跳转到登陆页面 if (username = null | .equals(username) / 跳转到登陆页面 dispatcher.forward(request,response); / System.out.println(用户没有登陆，不允许操作); res.setHeader(Cache-Control,no-store); res.setDateHeader(Expires,0); res.setHeader(Pragma,no-cache); else / 已经登陆,继续此次请求 chain.doFilter(request,response); / System.out.println(用户已经登陆，允许操作); public void init(FilterConfig arg0) throws ServletException / TODO Auto-generated method stub注意在doFilter方法中先进行了对象的强制转换。设置好未登录将被转发到的请求页面，然后排除login.jsp不被过滤，注意这种用法，也可用于排除某个目录不被过滤。Web.xml这样配置： unlogin filter.Unlogin unlogin /pages/*表示所有对pages下的页面请求都会接受过滤。应用三：防止已经登陆的用户越权访问不该自己访问的目录。新建一个Bosscheck.java，用于拦截普通用户强行访问管理员的页面。管理员的页面在pages/usermanage文件夹下，内容如下：package filter;import java.io.IOException;import javax.servlet.Filter;import javax.servlet.FilterChain;import javax.servlet.FilterConfig;import javax.servlet.RequestDispatcher;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;public class Bosscheck implements Filter public void destroy() / TODO Auto-generated method stubpublic void doFilter(ServletRequest request, ServletResponse response,FilterChain chain) throws IOException, ServletException HttpServletRequest req = (HttpServletRequest) request; HttpServletResponse res = (HttpServletResponse) response; HttpSession session = req.getSession(true); String user=(String)session.getAttribute(usertype); if(boss.equals(user) chain.doFilter(request,response); return; RequestDispatcher dispatcher = request.getRequestDisp