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：
[GS=JAVA]/**
* 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;
}
}[/GS]
[GS=JAVA]/**
* 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;
}
}[/GS]
2、在web.xml中做一些设置
[GS=XML]