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Java example source code file (Scoping.java)

This example Java source code file (Scoping.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

annotation, class, eager_singleton, errors, injectorimpl, internalfactory, override, provider, scope, scoping, singleton_annotation, singleton_instance, string, unscoped

The Scoping.java Java example source code

/**
 * 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.inject.Key;
import com.google.inject.Provider;
import com.google.inject.Scope;
import com.google.inject.Scopes;
import com.google.inject.Singleton;
import com.google.inject.Stage;
import com.google.inject.binder.ScopedBindingBuilder;
import com.google.inject.spi.BindingScopingVisitor;
import com.google.inject.spi.ScopeBinding;

import java.lang.annotation.Annotation;
import java.lang.ref.WeakReference;

/**
 * References a scope, either directly (as a scope instance), or indirectly (as a scope annotation).
 * The scope's eager or laziness is also exposed.
 *
 * @author jessewilson@google.com (Jesse Wilson)
 */
public abstract class Scoping {

  /**
   * No scoping annotation has been applied. Note that this is different from {@code
   * in(Scopes.NO_SCOPE)}, where the 'NO_SCOPE' has been explicitly applied.
   */
  public static final Scoping UNSCOPED = new Scoping() {
    @Override public <V> V acceptVisitor(BindingScopingVisitor visitor) {
      return visitor.visitNoScoping();
    }

    @Override public Scope getScopeInstance() {
      return Scopes.NO_SCOPE;
    }

    @Override public String toString() {
      return Scopes.NO_SCOPE.toString();
    }

    @Override public void applyTo(ScopedBindingBuilder scopedBindingBuilder) {
      // do nothing
    }
  };

  public static final Scoping SINGLETON_ANNOTATION = new Scoping() {
    @Override public <V> V acceptVisitor(BindingScopingVisitor visitor) {
      return visitor.visitScopeAnnotation(Singleton.class);
    }

    @Override public Class<? extends Annotation> getScopeAnnotation() {
      return Singleton.class;
    }

    @Override public String toString() {
      return Singleton.class.getName();
    }

    @Override public void applyTo(ScopedBindingBuilder scopedBindingBuilder) {
      scopedBindingBuilder.in(Singleton.class);
    }
  };

  public static final Scoping SINGLETON_INSTANCE = new Scoping() {
    @Override public <V> V acceptVisitor(BindingScopingVisitor visitor) {
      return visitor.visitScope(Scopes.SINGLETON);
    }

    @Override public Scope getScopeInstance() {
      return Scopes.SINGLETON;
    }

    @Override public String toString() {
      return Scopes.SINGLETON.toString();
    }

    @Override public void applyTo(ScopedBindingBuilder scopedBindingBuilder) {
      scopedBindingBuilder.in(Scopes.SINGLETON);
    }
  };

  public static final Scoping EAGER_SINGLETON = new Scoping() {
    @Override public <V> V acceptVisitor(BindingScopingVisitor visitor) {
      return visitor.visitEagerSingleton();
    }

    @Override public Scope getScopeInstance() {
      return Scopes.SINGLETON;
    }

    @Override public String toString() {
      return "eager singleton";
    }

    @Override public void applyTo(ScopedBindingBuilder scopedBindingBuilder) {
      scopedBindingBuilder.asEagerSingleton();
    }
  };

  public static Scoping forAnnotation(final Class<? extends Annotation> scopingAnnotation) {
    if (scopingAnnotation == Singleton.class
        || scopingAnnotation == javax.inject.Singleton.class) {
      return SINGLETON_ANNOTATION;
    }

    return new Scoping() {
      @Override public <V> V acceptVisitor(BindingScopingVisitor visitor) {
        return visitor.visitScopeAnnotation(scopingAnnotation);
      }

      @Override public Class<? extends Annotation> getScopeAnnotation() {
        return scopingAnnotation;
      }

      @Override public String toString() {
        return scopingAnnotation.getName();
      }

      @Override public void applyTo(ScopedBindingBuilder scopedBindingBuilder) {
        scopedBindingBuilder.in(scopingAnnotation);
      }
    };
  }

  public static Scoping forInstance(final Scope scope) {
    if (scope == Scopes.SINGLETON) {
      return SINGLETON_INSTANCE;
    }

    return new Scoping() {
      @Override public <V> V acceptVisitor(BindingScopingVisitor visitor) {
        return visitor.visitScope(scope);
      }

      @Override public Scope getScopeInstance() {
        return scope;
      }

      @Override public String toString() {
        return scope.toString();
      }

      @Override public void applyTo(ScopedBindingBuilder scopedBindingBuilder) {
        scopedBindingBuilder.in(scope);
      }
    };
  }

  /**
   * Returns true if this scope was explicitly applied. If no scope was explicitly applied then the
   * scoping annotation will be used.
   */
  public boolean isExplicitlyScoped() {
    return this != UNSCOPED;
  }

  /**
   * Returns true if this is the default scope. In this case a new instance will be provided for
   * each injection.
   */
  public boolean isNoScope() {
    return getScopeInstance() == Scopes.NO_SCOPE;
  }

  /**
   * Returns true if this scope is a singleton that should be loaded eagerly in {@code stage}.
   */
  public boolean isEagerSingleton(Stage stage) {
    if (this == EAGER_SINGLETON) {
      return true;
    }

    if (stage == Stage.PRODUCTION) {
      return this == SINGLETON_ANNOTATION || this == SINGLETON_INSTANCE;
    }

    return false;
  }

  /**
   * Returns the scope instance, or {@code null} if that isn't known for this instance.
   */
  public Scope getScopeInstance() {
    return null;
  }

  /**
   * Returns the scope annotation, or {@code null} if that isn't known for this instance.
   */
  public Class<? extends Annotation> getScopeAnnotation() {
    return null;
  }
  
  @Override
  public boolean equals(Object obj) {
    if(obj instanceof Scoping) {
      Scoping o = (Scoping)obj;
      return Objects.equal(getScopeAnnotation(), o.getScopeAnnotation())
        && Objects.equal(getScopeInstance(), o.getScopeInstance());
    } else {
      return false;
    }
  }
  
  @Override
  public int hashCode() {
    return Objects.hashCode(getScopeAnnotation(), getScopeInstance());
  }

  public abstract <V> V acceptVisitor(BindingScopingVisitor visitor);

  public abstract void applyTo(ScopedBindingBuilder scopedBindingBuilder);

  private Scoping() {}

  /** Scopes an internal factory. */
  static <T> InternalFactory scope(Key key, InjectorImpl injector,
      InternalFactory<? extends T> creator, Object source, Scoping scoping) {

    if (scoping.isNoScope()) {
      return creator;
    }

    Scope scope = scoping.getScopeInstance();

    // SingletonScope needs access to the injector's thread-specific InternalContext
    SingletonScope.currentInjector.set(new WeakReference<InjectorImpl>(injector));
    Provider<T> scoped
        = scope.scope(key, new ProviderToInternalFactoryAdapter<T>(injector, creator));
    return new InternalFactoryToProviderAdapter<T>(scoped, source);
  }

  /**
   * Replaces annotation scopes with instance scopes using the Injector's annotation-to-instance
   * map. If the scope annotation has no corresponding instance, an error will be added and unscoped
   * will be retuned.
   */
  static Scoping makeInjectable(Scoping scoping, InjectorImpl injector, Errors errors) {
    Class<? extends Annotation> scopeAnnotation = scoping.getScopeAnnotation();
    if (scopeAnnotation == null) {
      return scoping;
    }

    ScopeBinding scope = injector.state.getScopeBinding(scopeAnnotation);
    if (scope != null) {
      return forInstance(scope.getScope());
    }

    errors.scopeNotFound(scopeAnnotation);
    return UNSCOPED;
  }
}

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