How to create a servlet filter in Eclipse?

Question

I am new to the servlet technology. I set up Java 7, Tomcat8 and Eclipse. I have created several servlets on Eclipse and everything is working fine.

Today I created a simple servlet filter. But its not executing before any servlet . I can see the init method gets executed using the console messages. As per servlet 3.0 I am not using web.xml but @WebFilter("/FilterDemo") annotation.

here is the servlet filter code,

package net.codejava;

import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;

/**
 * Servlet Filter implementation class FilterDemo
 */
@WebFilter("/FilterDemo")
public class FilterDemo implements Filter {

/** 
 * Default constructor. 
 */
public FilterDemo() {
    // TODO Auto-generated constructor stub
}

/**
 * @see Filter#destroy()
 */
public void destroy() {
    // TODO Auto-generated method stub
    System.out.println("Destroy is called.");
}

/**
 * @see Filter#doFilter(ServletRequest, ServletResponse, FilterChain)
 */
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
    // TODO Auto-generated method stub
    // place your code here

    String ipAddress = request.getRemoteAddr();
    System.out.println("Do Filter is called.");
    System.out.println(ipAddress);

    // pass the request along the filter chain
    chain.doFilter(request, response);
}

/**
 * @see Filter#init(FilterConfig)
 */
public void init(FilterConfig fConfig) throws ServletException {
    // TODO Auto-generated method stub
    System.out.println("Filter Init is called."); 
}

}

Screenshot of Workspace:

Any help will be greatly appreciated.

Answer 1

Filters sit in front of servlets. In your annotation, you specified that the filter should only filter requests that go to /FilterDemo. What you'll need to do is map the filter to either the same URL as one of your servlets, or specify the names of the servlets that you want the filter to do processing for (using the servletNames parameter of the @WebFilter annotation.

Answer 2

You have to declare your filter mapping in web.xml despite the fact you are using @WebFilter annotation.

Answer 3

See how to map Servlet to the filter.

web.xml:

<filter>  
<filter-name>f1</filter-name>  
<filter-class>MyFilter</filter-class>  
</filter>  

<filter-mapping>  
<filter-name>f1</filter-name>  
<url-pattern>/servlet1</url-pattern> 
</filter-mapping>  

here /servlet1 is url pattern of your servlet(Which you want to execute).

Answer 4

As per servlet 3.0

@WebServlet("/LoginServlet")
public class LoginServlet extends HttpServlet{...}

@WebFilter(filterName="filter1", urlPatterns={ "/LoginServlet" })
public class AuthenticationFilter implements Filter {..}

but you should still keep the <url-pattern> in web.xml, because it's required as per XSD, although it can be empty:

<filter-mapping>
    <filter-name>filter1</filter-name>
    <url-pattern />
</filter-mapping>

See also Using Tomcat, @WebFilter doesn't work with inside web.xml