Simple Example of Filter

Simple Example of Filter

we are simply displaying information that filter is invoked automatically after the post processing of the request.

index.html

1.     <a href="servlet1">click here</a>  

MyFilter.java

1.     import java.io.IOException;  

2.     import java.io.PrintWriter;  

3.       

4.     import javax.servlet.*;  

5.       

6.     public class MyFilter implements Filter{  

7.       

8.     public void init(FilterConfig arg0) throws ServletException {}  

9.           

10.   public void doFilter(ServletRequest req, ServletResponse resp,  

11.       FilterChain chain) throws IOException, ServletException {  

12.             

13.       PrintWriter out=resp.getWriter();  

14.       out.print("filter is invoked before");  

15.             

16.       chain.doFilter(req, resp);//sends request to next resource  

17.             

18.       out.print("filter is invoked after");  

19.       }  

20.       public void destroy() {}  

21.   }  

HelloServlet.java

1.     import java.io.IOException;  

2.     import java.io.PrintWriter;  

3.       

4.     import javax.servlet.ServletException;  

5.     import javax.servlet.http.*;  

6.       

7.     public class HelloServlet extends HttpServlet {  

8.         public void doGet(HttpServletRequest request, HttpServletResponse response)  

9.                 throws ServletException, IOException {  

10.     

11.           response.setContentType("text/html");  

12.           PrintWriter out = response.getWriter();  

13.         

14.           out.print("<br>welcome to servlet<br>");  

15.             

16.       }  

17.     

18.   }  

web.xml

For defining the filter, filter element of web-app must be defined just like servlet.

1.     <web-app>  

2.       

3.     <servlet>  

4.     <servlet-name>s1</servlet-name>  

5.     <servlet-class>HelloServlet</servlet-class>  

6.     </servlet>  

7.       

8.     <servlet-mapping>  

9.     <servlet-name>s1</servlet-name>  

10.   <url-pattern>/servlet1</url-pattern>  

11.   </servlet-mapping>  

12.     

13.   <filter>  

14.   <filter-name>f1</filter-name>  

15.   <filter-class>MyFilter</filter-class>  

16.   </filter>  

17.      

18.   <filter-mapping>  

19.   <filter-name>f1</filter-name>  

20.   <url-pattern>/servlet1</url-pattern>  

21.   </filter-mapping>  

22.     

23.     

24.   </web-app>  

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