Servlet – FilterConfig

Web 容器为每个过滤器创建一个 FilterConfig 对象。它可用于读取过滤器初始化参数。放置在 web.xml 文件中。如果配置信息是从 web.xml 文件中修改的，我们不需要更改过滤器。因此，如果不时修改任何特定内容，则更容易管理 Web 应用程序。

FilterConfig 接口的方法

FilterConfig 接口中有四个方法。

1. String getFilterName()：返回部署描述符中定义的此过滤器的过滤器名称。

Syntax: public String getFilterName() 

2. String getInitParameter(String name)：返回一个包含命名初始化参数值的String，如果参数不存在则返回null。

Syntax: public String getInitParameter(String name)

3. Enumeration getInitParameterNames()：如果过滤器没有初始化参数，则将过滤器初始化参数的名称作为字符串对象的枚举或空枚举返回。

Syntax: public Enumeration getInitParameterNames()

4. ServletContext getServletContext()：返回对调用者正在执行的ServletContext的引用

Syntax: public ServletContext getServletContext() 

例子

索引.html

HTML

   
       
       
       
   
    
   
       
FilterConfig Demo
   

       User name 

       Password 

       
   
   

美国广播公司。Java

Java

import static java.lang.System.out;
  
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
  
public class abc extends HttpServlet {
  
    protected void
    processRequest(HttpServletRequest request,
                   HttpServletResponse response)
        throws ServletException, IOException
    {
  
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter p = response.getWriter();
        p.println(
            "
Welcome User");
    }
  
    // 
    @Override
    protected void doGet(HttpServletRequest request,
                         HttpServletResponse response)
        throws ServletException, IOException
    {
        processRequest(request, response);
    }
  
    @Override
    protected void doPost(HttpServletRequest request,
                          HttpServletResponse response)
        throws ServletException, IOException
    {
        processRequest(request, response);
    }
  
    @Override
    public String getServletInfo()
    {
        return "Short description";
    }
}

过滤器配置演示。Java

Java

package demo;
  
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
  
public class filter_config_demo implements Filter {
  
    FilterConfig fc;
  
    @Override
    public void init(FilterConfig filterConfig)
        throws ServletException
    {
        this.fc = filterConfig;
    }
  
    @Override
    public void doFilter(ServletRequest request,
                         ServletResponse response,
                         FilterChain chain)
        throws IOException, ServletException
    {
        String un, up;
        un = request.getParameter("un");
        up = request.getParameter("up");
        PrintWriter p = response.getWriter();
        System.out.println("My filter Name is "
                          + fc.getFilterName());
        if (un.equals(fc.getInitParameter("username"))
            && up.equals(
                fc.getInitParameter("userpassword")))
  
        {
            chain.doFilter(request, response);
        }
  
        else
        {
            RequestDispatcher rd
                = request.getRequestDispatcher(
                    "/index.html");
            rd.include(request, response);
            p.println("incorrect user name and password");
        }
    }
  
    @Override
    public void destroy()
    {
        this.fc = null;
    }
}

web.xml

XML

  
   
       filter1
       demo.filter_config_demo
       
           username
           sumit
       
  
       
           userpassword
           sumit@123
       
   
  
   
       filter1
       abc
   
  
   
       abc
       abc
   
  
   
       abc
       /abc
   
  
   
       30
   
  

输出

首先，我们输入了错误的用户名和密码：

• 用户 ID - 管理员
• 密码 - 12345

现在我们输入正确的用户名和密码：

• 用户 ID – sumit
• 密码 – sumit@123