学着用Filter

学着用Filter

　　使用Filter目的是让所有的页面都先通过一个文件处理一下。
　　
　　实例1：EncodingFilter.java －关于编码的Filter

package  com.english.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  EncodingFilter  implements  Filter  {

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

    }

    @Override
    public void doFilter(ServletRequest arg0, ServletResponse arg1, FilterChain arg2) throws IOException,
            ServletException {
        arg0.setCharacterEncoding("UTF-8");
        arg1.setCharacterEncoding("UTF-8");
        arg2.doFilter(arg0, arg1);

    }

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

    }

}

同时，要在web.xml中进行Filter 的配置：

 
< filter >
       < filter - name > encodingFilter </ filter - name >
       < filter - class > com.english.filter.EncodingFilter </ filter - class >
   </ filter >
   < filter - mapping >
       < filter - name > encodingFilter </ filter - name >
     < url - pattern > / /*</url-pattern>  
  </filter-mapping>

　　实例2　SessionFilter.java －关于Session 判断的一个Filter，这个文件要过滤一些文件，而让另一些文件通过，所以加了url 的判断。

package  com.english.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;
import  javax.servlet.http.HttpServletRequest;
import  javax.servlet.http.HttpServletResponse;
import  javax.servlet.http.HttpSession;

public   class  SessionFilter  implements  Filter  {
    private static String[] passUrls = { "login.view", "login.do", "logout.do", "index.do", "index.view",
            "register.view", "register.do", ".jpg", ".js", "testId.do", ".css" };

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

    }

    @Override
    public void doFilter(ServletRequest arg0, ServletResponse arg1, FilterChain chain) throws IOException,
            ServletException {
        HttpServletResponse resp = (HttpServletResponse) arg1;
        HttpServletRequest req = (HttpServletRequest) arg0;
        HttpSession session = req.getSession();
        String url = req.getRequestURI();
        boolean pass = false;
        for (String passUrl : passUrls) {
            if (url.endsWith(passUrl) || session.getAttribute("englishUser") != null) {
                pass = true;
            }
        }
        if (pass) {
            chain.doFilter(arg0, arg1);
        } else {
            req.getRequestDispatcher("/login.view").forward(arg0, arg1);
        }
    }

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

    }

}