javax.servlet.Filter 的应用

最新推荐文章于 2025-03-13 11:35:28 发布

gnemy

最新推荐文章于 2025-03-13 11:35:28 发布

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分类专栏： java 文章标签： filter import exception string login session

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本文介绍如何使用Java的Filter实现字符编码过滤及登录验证功能。通过实现Filter接口并配置web.xml，可以轻松实现请求编码转换及未授权访问拦截。

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Filter过滤器的使用
本篇文章是介绍javax.servlet包中Filter的几个功能,一是字符编码过滤,二是拦截指文件夹中的文件,实现登录验证.实现以上两个功能需以下几个步骤:
1、实现javax.servlet.Filter接口，编写两个类，如下：

/**
* 作用：过滤编码
*/
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挂参初始化
    }
    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 "对请求进行编码过滤");
        filterchain.doFilter(servletrequest, servletresponse);
    }
    public void setFilterConfig(FilterConfig filterconfig)
    {
        filterConfig = filterconfig;
    }
    public void destroy()
    {
        filterConfig = null;
    }
}

/**
* 作用：过滤外界非法的进入页面
* 注意：使用该功能时，一定要把登录页与被过滤文件夹设为同级，否则会出现循环
*/
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
        {
            //通过验证时在session中存的一个标志
     key = (String) session.getAttribute("key");


            if (key!= null&&key.equals("ok"))
            {

                filterchain.doFilter(servletrequest, servletresponse);
            }
            else
            {
                response.sendRedirect(LOGIN_PAGE);
                System.out.println("被拦截一个未认证的请求");
            }
        }
        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中做一些设置

     code
     filter.EncodingFilter

     manage
     filter.ManageFilter

     code
     /*

     manage
     
     /servlets-examples/*