Apache Felix Filter Issue

Question

I'm developing an Apache Sling WCMS application. I need to filter all requests sent to the server and set some headers in response object. I implemented filter and bundle activator class according to Felix Http Filter Sample and installed as bundle to sling.

Fileter class:

import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class HeaderFilter implements Filter {
    private final String name;

    public HeaderFilter(String name) {
        this.name = name;
    }

    public void init(FilterConfig config) throws ServletException {
        doLog("Init with config [" + config + "]");
    }

    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain)
            throws IOException, ServletException {
        try {
            HttpServletResponse response = (HttpServletResponse) res;
            HttpServletRequest request = (HttpServletRequest) req;
            doLog("Filter request [" + request + "]");
            response.setHeader("Cache-Control", "no-cache");
            response.setHeader("Expires", "-1");
            chain.doFilter(req, response);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public void destroy() {
        doLog("Destroyed filter");
    }

    private void doLog(String message) {
        System.out.println("## [" + this.name + "] " + message);
    }
}

Bundle Activator class:

import org.apache.felix.http.api.ExtHttpService;
import org.osgi.framework.BundleActivator;
import org.osgi.framework.BundleContext;
import org.osgi.framework.ServiceReference;
import org.osgi.util.tracker.ServiceTracker;

import java.util.Dictionary;
import java.util.Hashtable;

public class Activator implements BundleActivator {
    private ServiceTracker tracker;
    private HeaderFilter filter1 = new HeaderFilter("filter1");
    Dictionary hashTable = new Hashtable<Object, Object>();

    public void start(BundleContext context) throws Exception {
        try {
            this.tracker = new ServiceTracker(context, ExtHttpService.class.getName(), null) {
                @Override
                public Object addingService(ServiceReference ref) {
                    Object service = super.addingService(ref);
                    serviceAdded((ExtHttpService) service);
                    return service;
                }

                @Override
                public void removedService(ServiceReference ref, Object service) {
                    serviceRemoved((ExtHttpService) service);
                    super.removedService(ref, service);
                }
            };

            this.tracker.open();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public void stop(BundleContext context)
            throws Exception {
        this.tracker.close();
    }

    private void serviceAdded(ExtHttpService service) {
        try {
            hashTable.put("filter.scope", new String[]{"request", "forward", "include"});
            service.registerFilter(this.filter1, ".*", hashTable, 0, null);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private void serviceRemoved(ExtHttpService service) {
        service.unregisterFilter(this.filter1);
    }
}

The is a problem with the code above. It's not working and no request will be filtered.

Any help is appreciated in advance.

Answer 1

I found that my filter is not tracked by the service tracker, so by passing parameter 'true' to tracker.open() the filter was tracked:

this.tracker.open(true);

Answer 2

Note that you can implement this in a much simpler way using Sling Filters implemented as OSGi Declarative Services (DS).

You'll then just need a few annotations in your Filter, no Activator and the correct pom.xml setup for the Maven plugins that handle the DS annotations.

The documentation is at https://sling.apache.org/documentation/the-sling-engine/filters.html and it points to the NoPropertyFilter example from the Sling integration tests.