Injecting into a Jersey Resource class

Question

I did try going through the following links How to wire in a collaborator into a Jersey resource? and Access external objects in Jersey Resource class But still i am unable

Answer 1

This solution works well and I wanted to share what I found to enable CDI on jersey resources.

Here is the simplest bean ever :

package fr.test;

import javax.annotation.PostConstruct;
import javax.enterprise.context.RequestScoped;

@RequestScoped
public class Test {

    private int i;

    @PostConstruct
    public void create() {
        i = 6;
    }

    public int getI() {
        return i;
    }
}

In your resource class, we just inject this bean, as we would do in a any normal context :

package fr.test;

import javax.inject.Inject;
import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;

@Path("/login")
public class LoginApi {

    @Inject
    private Test test;

    @GET 
    @Produces("text/plain")
    public String getIt() {
        return "Hi there!" + test;
    }
}

And here is the key. We define a Jersey "InjectionProvider" which will be responsible of beans' resolution :

package fr.test;

import javax.inject.Inject;

import java.lang.reflect.Type;
import javax.ws.rs.ext.Provider;

import com.sun.jersey.core.spi.component.ComponentContext;
import com.sun.jersey.core.spi.component.ComponentScope;
import com.sun.jersey.spi.inject.Injectable;
import com.sun.jersey.spi.inject.InjectableProvider;

import fr.xxxxxxxxxx.ApplicationBeans;

@Provider
public class InjectionProvider implements InjectableProvider<Inject, Type> {

    public ComponentScope getScope() {
        // CDI will handle scopes for us
        return ComponentScope.Singleton;
    }

    @Override
    public Injectable<?> getInjectable(ComponentContext context,
            Inject injectAnno, Type t) {
        if (!(t instanceof Class))
            throw new RuntimeException("not injecting a class type ?");

        Class<?> clazz = (Class<?>) t;

        final Object instance = ApplicationBeans.get(clazz);

        return new Injectable<Object>() {
            public Object getValue() {
                return instance;
            }
        };
    }
}

InjectableProvider is typed with the kind of annotation we are handling, and the context type (here, normal java type)

ApplicationBeans is just a simple helper for bean resolution. Here is its content :

package fr.xxxxxxxxxx;

import java.lang.annotation.Annotation;
import java.util.Arrays;
import java.util.Collection;
import java.util.Set;

import javax.enterprise.context.ApplicationScoped;
import javax.enterprise.context.spi.CreationalContext;
import javax.enterprise.inject.spi.Bean;
import javax.enterprise.inject.spi.BeanManager;
import javax.inject.Inject;
import javax.naming.InitialContext;
import javax.naming.NamingException;

import fr.xxxxxxxxxxxxx.UnexpectedException;

/**
 * Gives direct access to managed beans - Designed to be used from unmanaged code
 * 
 * @author lgrignon
 * 
 */
@ApplicationScoped
public class ApplicationBeans
{

  protected static ApplicationBeans instance;

  @Inject
  private BeanManager beanManager;

  /**
   * Gets instance
   * 
   * @return Instance from managed environment
   */
  public static ApplicationBeans instance()
  {
    if (instance == null)
    {
      BeanManager beanManager;
      InitialContext ctx = null;
      try
      {
        ctx = new InitialContext();
        beanManager = (BeanManager)ctx.lookup("java:comp/BeanManager");
      }catch(NamingException e)
      {
        try
        {
          beanManager = (BeanManager)ctx.lookup("java:app/BeanManager");
        }catch(NamingException ne)
        {
          throw new UnexpectedException("Unable to obtain BeanManager.", ne);
        }
      }

      instance = getBeanFromManager(beanManager, ApplicationBeans.class);
    }

    return instance;
  }

  /**
   * Gets bean instance from context
   * 
   * @param <T>
   *          Bean's type
   * @param beanType
   *          Bean's type
   * @param annotations
   *          Bean's annotations
   * @return Bean instance or null if no
   */
  public static <T> T get(final Class<T> beanType, Annotation... annotations)
  {
    return instance().getBean(beanType, annotations);
  }

  /**
   * Gets bean instance from context
   * 
   * @param <T>
   *          Bean's type
   * @param beanType
   *          Bean's type
   * @param annotations
   *          Bean's annotations
   * @return Bean instance or null if no
   */
  public <T> T getBean(final Class<T> beanType, Annotation... annotations)
  {
    return getBeanFromManager(beanManager, beanType, annotations);
  }

  @SuppressWarnings("unchecked")
  private static <T> T getBeanFromManager(BeanManager beanManager, final Class<T> beanType, Annotation... annotations)
  {
    Set<Bean<?>> beans = beanManager.getBeans(beanType, annotations);
    if (beans.size() > 1)
    {
      throw new UnexpectedException("Many bean declarations found for type %s (%s)", beanType.getSimpleName(), beansToString(beans));
    }

    if (beans.isEmpty())
    {
      throw new UnexpectedException("No bean declaration found for type %s", beanType.getSimpleName());
    }

    final Bean<T> bean = (Bean<T>)beans.iterator().next();
    final CreationalContext<T> context = beanManager.createCreationalContext(bean);
    return (T)beanManager.getReference(bean, beanType, context);
  }

  private static String beansToString(Collection<Bean<?>> beans)
  {
    String[] beansLabels = new String[beans.size()];
    int i = 0;
    for (final Bean<?> bean : beans)
    {
      beansLabels[i++] = bean.getName();
    }

    return Arrays.toString(beansLabels);
  }

}

Hope this will help those who want to enable CDI injection in their Jersey resources.

Bye !

Answer 2

Your InjectableProvider is not implemented correctly. The second type parameter should not be the type of the field you are trying to inject - instead it should be the context - either java.lang.reflect.Type class or com.sun.jersey.api.model.Parameter class. In your case, you would use Type. So, your InjectableProvider implementation should look as follows:

package resource;

import javax.ws.rs.ext.Provider;
import com.sun.jersey.core.spi.component.ComponentContext;
import com.sun.jersey.core.spi.component.ComponentScope;
import com.sun.jersey.spi.inject.Injectable;
import com.sun.jersey.spi.inject.InjectableProvider;
import java.lang.reflect.Type;

@Provider
public class MyResourceProvider implements InjectableProvider<MyResource, Type> {

    @Override
    public ComponentScope getScope() {
        return ComponentScope.PerRequest;
    }

    @Override
    public Injectable getInjectable(final ComponentContext arg0, final MyResource arg1, final Type arg2) {
        if (Integer.class.equals(arg2)) {
            return new Injectable<Integer>() {

                @Override
                public Integer getValue() {
                    return new Integer(99);
                }
            };
        } else {
            return null;
        }
    }
}

There is a helper class for per-request injectable providers (PerRequestTypeInjectableProvider) as well as singleton injectable providers (SingletonTypeInjectableProvider), so you can further simplify it by inheriting from that:

package resource;

import javax.ws.rs.ext.Provider;
import com.sun.jersey.core.spi.component.ComponentContext;
import com.sun.jersey.spi.inject.Injectable;
import com.sun.jersey.spi.inject.PerRequestTypeInjectableProvider;

@Provider
public class MyResourceProvider extends PerRequestTypeInjectableProvider<MyResource, Integer> {
    public MyResourceProvider() {
        super(Integer.class);
    }

    @Override
    public Injectable<Integer> getInjectable(ComponentContext ic, MyResource a) {
        return new Injectable<Integer>() {
            @Override
            public Integer getValue() {
                return new Integer(99);
            }
        };
    }
}

Note that for these helper classes the second type parameter is the type of the field.

And one more thing - the injection happens after the constructor is called, so the constructor of your resource will still print out ...constructor called :null, but if you change your resource method to return foo, you'll see the response you'll get will be 99.