A Java servlet filter is a Java class that can be used to intercept HTTP requests and responses in a web application. Here's how you can create a Java servlet filter:

1. Create a Java class that implements the javax.servlet.Filter interface. This interface defines the init, doFilter, and destroy methods that you will need to implement.

public class MyFilter implements Filter {

  public void init(FilterConfig config) throws ServletException {
    // Initialization code here
  }

  public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
      throws IOException, ServletException {
    // Filter code here
    chain.doFilter(request, response);
  }

  public void destroy() {
    // Cleanup code here
  }

}

2. In the init method of your filter, you can perform any initialization tasks required by your filter. This method is called once when the filter is first created.

3. In the doFilter method, you can intercept incoming HTTP requests and modify the request or response as needed. You can also call the doFilter method of the FilterChain object to pass the request and response along to the next filter in the chain or to the servlet that will handle the request.

4. In the destroy method, you can perform any cleanup tasks required by your filter. This method is called once when the filter is about to be destroyed.

5. To register your filter, you need to add it to the web.xml file of your web application. Here's an example of how to add a filter mapping to the web.xml file:

<filter>
  <filter-name>MyFilter</filter-name>
  <filter-class>com.example.MyFilter</filter-class>
</filter>
<filter-mapping>
  <filter-name>MyFilter</filter-name>
  <url-pattern>/*</url-pattern>
</filter-mapping>

This will map the MyFilter filter to all requests that match the /* URL pattern.

That's it! With these steps, you can create a Java servlet filter and register it to intercept incoming HTTP requests in your web application.