Filter過濾器的使用

本篇文章是介紹javax.servlet包中Filter的幾個功能,一是字符編碼過濾,二是攔截指文件夾中的文件,實現登錄驗證.實現以上兩個功能需以下幾個步驟:

1、實現javax.servlet.Filter接口，編寫兩個類，如下：

/**
 * 作用：過濾編碼
 */

package filter;
import java.io.IOException;
import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;

public class EncodingFilter implements Filter
{

    protected FilterConfig filterConfig;
    private String targetEncoding;

    public EncodingFilter()
    {
        targetEncoding = "gb2312";//直接初始化0912
    }

    public void init(FilterConfig filterconfig) throws ServletException
    {
        filterConfig = filterconfig;
        //targetEncoding = filterconfig.getInitParameter("encoding");//web.xml掛參初始化
    }

    public void doFilter(ServletRequest servletrequest, ServletResponse servletresponse, FilterChain filterchain)
        throws IOException, ServletException
    {
        HttpServletRequest httpservletrequest = (HttpServletRequest)servletrequest;
        httpservletrequest.setCharacterEncoding(targetEncoding);
        System.out.println("使用" targetEncoding "對請求進行編碼過濾");
        filterchain.doFilter(servletrequest, servletresponse);
    }

    public void setFilterConfig(FilterConfig filterconfig)
    {
        filterConfig = filterconfig;
    }

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

/**
 * 作用：過濾外界非法的進入頁面
 * 注意：使用該功能時，一定要把登錄頁與被過濾文件夾設爲同級，否則會出現循環
 */
package filter;
import java.io.IOException;
import javax.servlet.*;
import javax.servlet.http.*;

public class ManageFilter implements Filter
{

    String LOGIN_PAGE;
    protected FilterConfig filterConfig;

    public ManageFilter()
    {
        LOGIN_PAGE = "/login.jsp";
    }

    public void doFilter(ServletRequest servletrequest, ServletResponse servletresponse, FilterChain filterchain)
        throws IOException, ServletException
    {
        HttpServletRequest request = (HttpServletRequest) servletrequest;
        HttpServletResponse response = (HttpServletResponse) servletresponse;
        HttpSession session = request.getSession();
        String key = "";
        try
        {
            //通過驗證時在session中存的一個標誌
     key = (String) session.getAttribute("key");
          
           
            if (key!= null&&key.equals("ok"))
            {
              
                filterchain.doFilter(servletrequest, servletresponse);
            }
            else
            {
                response.sendRedirect(LOGIN_PAGE);
                System.out.println("被攔截一個未認證的請求");
            }
        }
        catch (Exception exception)
        {
            exception.printStackTrace();
        }
    }

    public void setFilterConfig(FilterConfig filterconfig)
    {
        filterConfig = filterconfig;
    }

    public void destroy()
    {
        filterConfig = null;
    }

    public void init(FilterConfig filterconfig)
        throws ServletException
    {
        filterConfig = filterconfig;
    }
}

2、在web.xml中做一些設置
 <filter>
     <filter-name>code</filter-name>
     <filter-class>filter.EncodingFilter</filter-class>
 </filter>
 
 <filter>
     <filter-name>manage</filter-name>
     <filter-class>filter.ManageFilter</filter-class>
 </filter>

 <filter-mapping>
     <filter-name>code</filter-name>
     <url-pattern>/*</url-pattern>
 </filter-mapping>
 
 <filter-mapping>
     <filter-name>manage</filter-name>
     <!-- <url-pattern>/ShuiBaoRHPWK_NEW/system/ruhepaiwukou/*</url-pattern>-->
     <url-pattern>/servlets-examples/*</url-pattern>
 </filter-mapping>
  
   OK，基本FILTER應該做的基本就這樣，你只需要在程序中驗證通過時，在session中存個標誌進去，好讓ManageFilter可以找到，就可以了！