網頁請求過濾器Filter

學習相關資料：

Java web開發——過濾器Filter的常見使用

簡單通俗易懂的理解，就是類似於殺毒軟件對電腦系統的功能和作用。即程序中的防火牆。

過濾器運行原理：

 

若有多個過濾器，則按順序進行執行，直到最后一個過濾器通過后，才可進行下一步的請求。

項目要求和功能：

1.編碼過濾器，對亂碼進行過濾

2.登錄權限過濾器，只有用戶登陸后，才可以訪問相關頁面

項目思路：

1.在Filter中將reques和response進行強制轉換

2.將所需要過濾的東西（本體為編碼格式，和驗證用戶登錄）的相關代碼放入Filter中

3.對Filter設置適用范圍，排除不用過濾的界面

項目源碼：

對編碼格式的過濾：

package com.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.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet Filter implementation class LoginFilter
 */
@WebFilter(filterName="CodeFilter",urlPatterns="/*")//設置適用的范圍
public class CodeFilter implements Filter {

    /**
     * Default constructor. 
     */
    public CodeFilter() {
        // TODO Auto-generated constructor stub
    }

    /**
     * @see Filter#destroy()
     */
    public void destroy() {
        // TODO Auto-generated method stub
    }

    /**
     * @see Filter#doFilter(ServletRequest, ServletResponse, FilterChain)
     */
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        // TODO Auto-generated method stub
        
        HttpServletRequest req=(HttpServletRequest) request;
        HttpServletResponse res=(HttpServletResponse) response;
        
        //用戶請求編碼設置
        request.setCharacterEncoding("utf-8");
        response.setCharacterEncoding("ytf-8");
        response.setContentType("text/html;charset=utf-8");
        
        System.out.println("進入編碼過濾器......");
        chain.doFilter(request, response);
        System.out.println("退出編碼過濾器......");
        
    }

    /**
     * @see Filter#init(FilterConfig)
     */
    public void init(FilterConfig fConfig) throws ServletException {
        // TODO Auto-generated method stub
    }

}

對用戶登錄權限的過濾：

package com.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.annotation.WebFilter;
import javax.servlet.annotation.WebInitParam;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**
 * Servlet Filter implementation class LoginServlet
 */
@WebFilter(filterName="LoginFilter",
            urlPatterns="/*",
            initParams= {
                      @WebInitParam(name="noFilterUrl",value="login.jsp,LoginSErvlet")
              })//設置適用的范圍,排除登錄權限的過濾
public class LoginFilter implements Filter {

    private String[] noFilter;
    /**
     * Default constructor. 
     */
    public LoginFilter() {
        // TODO Auto-generated constructor stub
    }

    /**
     * @see Filter#destroy()
     */
    public void destroy() {
        // TODO Auto-generated method stub
    }

    /**
     * @see Filter#doFilter(ServletRequest, ServletResponse, FilterChain)
     */
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        // TODO Auto-generated method stub
        //首先強制轉換request,response
        HttpServletRequest req=(HttpServletRequest) request;
        HttpServletResponse res=(HttpServletResponse) response;
        
        //獲取sessionz中的數值
        HttpSession session=req.getSession();
        String username=(String)req.getAttribute("username");
        
        //判斷是否登錄
        if(username!=null) {
            //已登錄繼續執行
        chain.doFilter(request, response);
        }else {
            //未登錄，頁面跳轉
            String url=req.getRequestURI();//獲取用戶地址
            for(String temp:noFilter)
            {
                if(url.indexOf(temp)!=-1)
                {
                    chain.doFilter(request, response);//直接放行
                    return;
                }
            }
            res.sendRedirect("login.jsp");
        }
    }

    /**
     * @see Filter#init(FilterConfig)
     */
    public void init(FilterConfig fConfig) throws ServletException {
        //排除相關幾年的過濾，以便正常運行
        // TODO Auto-generated method stub
        noFilter=fConfig.getInitParameter("noFilerUrl").split(",");//將數組noFilerUrl用","進行分割
    }

}

servlet:

package com.servlet;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**
 * Servlet implementation class FilterServlet
 */
@WebServlet("/FilterServlet")
public class FilterServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public FilterServlet() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        
        System.out.println("進入servlet......");
        //接受用戶登錄信息
        String username=request.getParameter("username");
        String password=request.getParameter("password");
        //然后輸出
        response.getWriter().print("用戶名："+username);
        response.getWriter().print("<br/>");
        response.getWriter().print("密碼："+password);
        
        //將用戶信息放入到session中
        HttpSession session=request.getSession();
        session.setAttribute("username", username);
        //設置session的有效時間為10秒
        session.setMaxInactiveInterval(10);
        
        System.out.println("退出servlet......");
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}

運行項目跟蹤的測試順序截圖：

 

 遇到的問題：

原因：當設置用戶登錄權限的過濾器時，沒有排除非不必過濾的代碼和訪問頁面，從而造成了頁面的死循環

 

解決方法：在LoginFilter進行排除不該受權限的內容

 1.

 2.

 

 3.

 

 

 解決時間：由於初次學Filter，所以解決的時間有點長，大約20分鍾。通過查閱相關資料說，這種死循環錯誤在登錄用戶過濾器中是很常見的問題。特別注意。