GuiceJustInTimeResolver.java

/*
 * Copyright 2014-2016 Squarespace, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.squarespace.jersey2.guice;

import java.lang.annotation.Annotation;
import java.lang.reflect.Type;
import java.util.Set;

import org.glassfish.hk2.api.Injectee;
import org.glassfish.hk2.api.JustInTimeInjectionResolver;
import org.glassfish.hk2.api.ServiceLocator;
import org.glassfish.hk2.utilities.ServiceLocatorUtilities;

import com.google.inject.Binding;
import com.google.inject.Guice;
import com.google.inject.Injector;
import com.google.inject.Key;
import com.google.inject.internal.MoreTypes;

/**
 * A {@link JustInTimeInjectionResolver} that is backed by {@link Guice}.
 */
class GuiceJustInTimeResolver implements JustInTimeInjectionResolver {
  
  private final ServiceLocator locator;
  
  private final Injector injector;
  
  public GuiceJustInTimeResolver(ServiceLocator locator, Injector injector) {
    this.locator = locator;
    this.injector = injector;
  }

  @Override
  public boolean justInTimeResolution(Injectee injectee) {
    Type type = injectee.getRequiredType();
    Class<?> clazz = MoreTypes.getRawType(type);
    
    if (clazz != null) {
      Binding<?> binding = findBinding(injectee);
      if (binding != null) {
        Key<?> key = binding.getKey();
        Set<Annotation> qualifiers = BindingUtils.getQualifiers(key);
        
        GuiceBindingDescriptor<?> descriptor = new GuiceBindingDescriptor<>(
            type, clazz, qualifiers, binding);
        ServiceLocatorUtilities.addOneDescriptor(locator, descriptor);
        return true;
      }
    }
    
    
    return false;
  }
  
  /**
   * Returns a {@link Guice} {@link Binding} for the given HK2 {@link Injectee}
   * or {@code null} if there is no such binding (i.e. Guice doesn't have it and
   * doesn't know how to build it).
   */
  private Binding<?> findBinding(Injectee injectee) {
    Key<?> key = BindingUtils.toKey(injectee);
    if (key == null) {
      return null;
    }
    
    // We can't do anything about HK2 @Contracts
    if (BindingUtils.isHk2Contract(injectee)) {
      return null;
    }
    
    // Classes with a @Contract annotation are SPIs. They either exist or
    // not. They must be explicit bindings in the world of Guice.
    if (BindingUtils.isJerseyContract(injectee)) {
      return injector.getExistingBinding(key);
    }
    
    // We've to use Injector#getBinding() to cover Just-In-Time bindings
    // which may fail with an Exception because Guice doesn't know how to
    // construct the requested object.
    return injector.getBinding(key);
  }
}