Servlet过滤器示例

在本节中，给出了一个有用的过滤器示例。

这是一个仅通过过滤器发送响应的示例 -

文件：MyFilter.java

import java.io.*;  
import javax.servlet.*;  

public class MyFilter implements Filter{  
    public void init(FilterConfig arg0) throws ServletException {}  

    public void doFilter(ServletRequest req, ServletResponse res,  
            FilterChain chain) throws IOException, ServletException {  

        PrintWriter out=res.getWriter();  

        out.print("<br/>this site is underconstruction..");  
        out.close();  

    }  
    public void destroy() {}  
}

计算单页访问次数的示例

文件：MyFilter.java

import java.io.*;  
import javax.servlet.*;  

public class MyFilter implements Filter{  
    static int count=0;  
    public void init(FilterConfig arg0) throws ServletException {}  

    public void doFilter(ServletRequest req, ServletResponse res,  
            FilterChain chain) throws IOException, ServletException {  

        PrintWriter out=res.getWriter();  
        chain.doFilter(request,response);  

        out.print("<br/>Total visitors "+(++count));  
        out.close();  

    }  
    public void destroy() {}  
}

在过滤器中检查总响应时间的示例

文件：MyFilter.java

import java.io.*;  
import javax.servlet.*;  

public class MyFilter implements Filter{  
    static int count=0;  
    public void init(FilterConfig arg0) throws ServletException {}  

    public void doFilter(ServletRequest req, ServletResponse res,  
            FilterChain chain) throws IOException, ServletException {  

        PrintWriter out=res.getWriter();  
        long before=System.currentTimeMillis();  

        chain.doFilter(request,response);  

        long after=System.currentTimeMillis();  
        out.print("<br/>Total response time "+(after-before)+" miliseconds");  
        out.close();  

    }  
    public void destroy() {}  
}