core/src/com/google/inject/internal/ProviderMethod.java

/**
 * Copyright (C) 2008 Google 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.google.inject.internal;

import com.google.common.base.Objects;
import com.google.common.collect.ImmutableSet;
import com.google.inject.Binder;
import com.google.inject.Exposed;
import com.google.inject.Key;
import com.google.inject.PrivateBinder;
import com.google.inject.Provider;
import com.google.inject.internal.util.StackTraceElements;
import com.google.inject.spi.Dependency;
import com.google.inject.spi.ProviderWithDependencies;

import java.lang.annotation.Annotation;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.List;
import java.util.Set;

/**
 * A provider that invokes a method and returns its result.
 *
 * @author jessewilson@google.com (Jesse Wilson)
 */
public class ProviderMethod<T> implements ProviderWithDependencies<T> {
  private final Key<T> key;
  private final Class<? extends Annotation> scopeAnnotation;
  private final Object instance;
  private final Method method;
  private final ImmutableSet<Dependency<?>> dependencies;
  private final List<Provider<?>> parameterProviders;
  private final boolean exposed;

  /**
   * @param method the method to invoke. It's return type must be the same type as {@code key}.
   */
  ProviderMethod(Key<T> key, Method method, Object instance,
      ImmutableSet<Dependency<?>> dependencies, List<Provider<?>> parameterProviders,
      Class<? extends Annotation> scopeAnnotation) {
    this.key = key;
    this.scopeAnnotation = scopeAnnotation;
    this.instance = instance;
    this.dependencies = dependencies;
    this.method = method;
    this.parameterProviders = parameterProviders;
    this.exposed = method.isAnnotationPresent(Exposed.class);

    method.setAccessible(true);
  }

  public Key<T> getKey() {
    return key;
  }

  public Method getMethod() {
    return method;
  }

  // exposed for GIN
  public Object getInstance() {
    return instance;
  }

  public void configure(Binder binder) {
    binder = binder.withSource(method);

    if (scopeAnnotation != null) {
      binder.bind(key).toProvider(this).in(scopeAnnotation);
    } else {
      binder.bind(key).toProvider(this);
    }

    if (exposed) {
      // the cast is safe 'cause the only binder we have implements PrivateBinder. If there's a
      // misplaced @Exposed, calling this will add an error to the binder's error queue
      ((PrivateBinder) binder).expose(key);
    }
  }

  public T get() {
    Object[] parameters = new Object[parameterProviders.size()];
    for (int i = 0; i < parameters.length; i++) {
      parameters[i] = parameterProviders.get(i).get();
    }

    try {
      // We know this cast is safe becase T is the method's return type.
      @SuppressWarnings({ "unchecked", "UnnecessaryLocalVariable" })
      T result = (T) method.invoke(instance, parameters);
      return result;
    } catch (IllegalAccessException e) {
      throw new AssertionError(e);
    } catch (InvocationTargetException e) {
      throw Exceptions.rethrowCause(e);
    }
  }

  public Set<Dependency<?>> getDependencies() {
    return dependencies;
  }

  @Override public String toString() {
    return "@Provides " + StackTraceElements.forMember(method).toString();
  }
  
  @Override
  public boolean equals(Object obj) {
    if (obj instanceof ProviderMethod) {
      ProviderMethod o = (ProviderMethod)obj;
      return method.equals(o.method)
         && instance.equals(o.instance);
    } else {
      return false;
    }
  }
  
  @Override
  public int hashCode() {
    // Avoid calling hashCode on 'instance', which is a user-object
    // that might not be expecting it.
    // (We need to call equals, so we do.  But we can avoid hashCode.)
    return Objects.hashCode(method);
  }
}