Useful Filter Examples

There is given some useful examples of filter.

Example of sending response by filter only

MyFilter.java

1. import java.io.*;  
2. import javax.servlet.*;  
3.   
4. public class MyFilter implements Filter{  
5.     public void init(FilterConfig arg0) throws ServletException {}  
6.   
7.     public void doFilter(ServletRequest req, ServletResponse res,  
8.             FilterChain chain) throws IOException, ServletException {  
9.       
10.         PrintWriter out=res.getWriter();  
11.           
12.         out.print("<br/>this site is underconstruction..");  
13.         out.close();  
14.           
15.     }  
16.     public void destroy() {}  
17. }  

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Example of counting number of visitors for a single page

MyFilter.java

1. import java.io.*;  
2. import javax.servlet.*;  
3.   
4. public class MyFilter implements Filter{  
5.     static int count=0;  
6.     public void init(FilterConfig arg0) throws ServletException {}  
7.   
8.     public void doFilter(ServletRequest req, ServletResponse res,  
9.             FilterChain chain) throws IOException, ServletException {  
10.       
11.         PrintWriter out=res.getWriter();  
12.         chain.doFilter(request,response);  
13.           
14.         out.print("<br/>Total visitors "+(++count));  
15.         out.close();  
16.           
17.     }  
18.     public void destroy() {}  
19. }  

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Example of checking total response time in filter

MyFilter.java

1. import java.io.*;  
2. import javax.servlet.*;  
3.   
4. public class MyFilter implements Filter{  
5.     static int count=0;  
6.     public void init(FilterConfig arg0) throws ServletException {}  
7.   
8.     public void doFilter(ServletRequest req, ServletResponse res,  
9.             FilterChain chain) throws IOException, ServletException {  
10.       
11.         PrintWriter out=res.getWriter();  
12.         long before=System.currentTimeMillis();  
13.   
14.         chain.doFilter(request,response);  
15.           
16.         long after=System.currentTimeMillis();  
17.         out.print("<br/>Total response time "+(after-before)+" miliseconds");  
18.         out.close();  
19.           
20.     }  
21.     public void destroy() {}  
22. }