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Java example source code file (ProviderMethodsModule.java)

This example Java source code file (ProviderMethodsModule.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, injectionpoint, key, list, method, moduleannotatedmethodscanner, object, override, providermethodsmodule, provides_builder, reflection, signature, string, typeliteral, util

The ProviderMethodsModule.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 static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.base.Optional;
import com.google.common.collect.HashMultimap;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Lists;
import com.google.common.collect.Multimap;
import com.google.inject.Binder;
import com.google.inject.Key;
import com.google.inject.Module;
import com.google.inject.Provider;
import com.google.inject.Provides;
import com.google.inject.TypeLiteral;
import com.google.inject.spi.Dependency;
import com.google.inject.spi.InjectionPoint;
import com.google.inject.spi.Message;
import com.google.inject.spi.ModuleAnnotatedMethodScanner;
import com.google.inject.util.Modules;

import java.lang.annotation.Annotation;
import java.lang.reflect.Member;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.util.Arrays;
import java.util.List;
import java.util.Set;

/**
 * Creates bindings to methods annotated with {@literal @}{@link Provides}. Use the scope and
 * binding annotations on the provider method to configure the binding.
 *
 * @author crazybob@google.com (Bob Lee)
 * @author jessewilson@google.com (Jesse Wilson)
 */
public final class ProviderMethodsModule implements Module {

  private static ModuleAnnotatedMethodScanner PROVIDES_BUILDER =
      new ModuleAnnotatedMethodScanner() {
        @Override
        public <T> Key prepareMethod(
            Binder binder, Annotation annotation, Key<T> key, InjectionPoint injectionPoint) {
          return key;
        }

        @Override
        public Set<? extends Class annotationClasses() {
          return ImmutableSet.of(Provides.class);
        }
      };

  private final Object delegate;
  private final TypeLiteral<?> typeLiteral;
  private final boolean skipFastClassGeneration;
  private final ModuleAnnotatedMethodScanner scanner;

  private ProviderMethodsModule(Object delegate, boolean skipFastClassGeneration,
      ModuleAnnotatedMethodScanner scanner) {
    this.delegate = checkNotNull(delegate, "delegate");
    this.typeLiteral = TypeLiteral.get(this.delegate.getClass());
    this.skipFastClassGeneration = skipFastClassGeneration;
    this.scanner = scanner;
  }

  /**
   * Returns a module which creates bindings for provider methods from the given module.
   */
  public static Module forModule(Module module) {
    return forObject(module, false, PROVIDES_BUILDER);
  }

  /**
   * Returns a module which creates bindings methods in the module that match the scanner.
   */
  public static Module forModule(Object module, ModuleAnnotatedMethodScanner scanner) {
    return forObject(module, false, scanner);
  }

  /**
   * Returns a module which creates bindings for provider methods from the given object.
   * This is useful notably for <a href="http://code.google.com/p/google-gin/">GIN
   *
   * <p>This will skip bytecode generation for provider methods, since it is assumed that callers
   * are only interested in Module metadata.
   */
  public static Module forObject(Object object) {
    return forObject(object, true, PROVIDES_BUILDER);
  }

  private static Module forObject(Object object, boolean skipFastClassGeneration,
      ModuleAnnotatedMethodScanner scanner) {
    // avoid infinite recursion, since installing a module always installs itself
    if (object instanceof ProviderMethodsModule) {
      return Modules.EMPTY_MODULE;
    }

    return new ProviderMethodsModule(object, skipFastClassGeneration, scanner);
  }

  public Object getDelegateModule() {
    return delegate;
  }

  @Override
  public synchronized void configure(Binder binder) {
    for (ProviderMethod<?> providerMethod : getProviderMethods(binder)) {
      providerMethod.configure(binder);
    }
  }

  public List<ProviderMethod getProviderMethods(Binder binder) {
    List<ProviderMethod result = Lists.newArrayList();
    Multimap<Signature, Method> methodsBySignature = HashMultimap.create();
    for (Class<?> c = delegate.getClass(); c != Object.class; c = c.getSuperclass()) {
      for (Method method : c.getDeclaredMethods()) {
        // private/static methods cannot override or be overridden by other methods, so there is no
        // point in indexing them.
        // Skip synthetic methods and bridge methods since java will automatically generate
        // synthetic overrides in some cases where we don't want to generate an error (e.g.
        // increasing visibility of a subclass).
        if (((method.getModifiers() & (Modifier.PRIVATE | Modifier.STATIC)) == 0)
            && !method.isBridge() && !method.isSynthetic()) {
          methodsBySignature.put(new Signature(method), method);
        }
        Optional<Annotation> annotation = isProvider(binder, method);
        if (annotation.isPresent()) {
          result.add(createProviderMethod(binder, method, annotation.get()));
        }
      }
    }
    // we have found all the providers and now need to identify if any were overridden
    // In the worst case this will have O(n^2) in the number of @Provides methods, but that is only
    // assuming that every method is an override, in general it should be very quick.
    for (ProviderMethod<?> provider : result) {
      Method method = provider.getMethod();
      for (Method matchingSignature : methodsBySignature.get(new Signature(method))) {
        // matching signature is in the same class or a super class, therefore method cannot be
        // overridding it.
        if (matchingSignature.getDeclaringClass().isAssignableFrom(method.getDeclaringClass())) {
          continue;
        }
        // now we know matching signature is in a subtype of method.getDeclaringClass()
        if (overrides(matchingSignature, method)) {
          String annotationString = provider.getAnnotation().annotationType() == Provides.class
              ? "@Provides" : "@" + provider.getAnnotation().annotationType().getCanonicalName();
          binder.addError(
              "Overriding " + annotationString + " methods is not allowed."
                  + "\n\t" + annotationString + " method: %s\n\toverridden by: %s",
              method,
              matchingSignature);
          break;
        }
      }
    }
    return result;
  }

  /**
   * Returns true if the method is a provider.
   *
   * Synthetic bridge methods are excluded. Starting with JDK 8, javac copies annotations onto
   * bridge methods (which always have erased signatures).
   */
  private Optional<Annotation> isProvider(Binder binder, Method method) {
    if (method.isBridge() || method.isSynthetic()) {
      return Optional.absent();
    }
    Annotation annotation = null;
    for (Class<? extends Annotation> annotationClass : scanner.annotationClasses()) {
      Annotation foundAnnotation = method.getAnnotation(annotationClass);
      if (foundAnnotation != null) {
        if (annotation != null) {
          binder.addError("More than one annotation claimed by %s on method %s."
              + " Methods can only have one annotation claimed per scanner.",
              scanner, method);
          return Optional.absent();
        }
        annotation = foundAnnotation;
      }
    }
    return Optional.fromNullable(annotation);
  }

  private final class Signature {
    final Class<?>[] parameters;
    final String name;
    final int hashCode;

    Signature(Method method) {
      this.name = method.getName();
      // We need to 'resolve' the parameters against the actual class type in case this method uses
      // type parameters.  This is so we can detect overrides of generic superclass methods where
      // the subclass specifies the type parameter.  javac implements these kinds of overrides via
      // bridge methods, but we don't want to give errors on bridge methods (but rather the target
      // of the bridge).
      List<TypeLiteral resolvedParameterTypes = typeLiteral.getParameterTypes(method);
      this.parameters = new Class<?>[resolvedParameterTypes.size()];
      int i = 0;
      for (TypeLiteral<?> type : resolvedParameterTypes) {
        parameters[i] = type.getRawType();
      }
      this.hashCode = name.hashCode() + 31 * Arrays.hashCode(parameters);
    }

    @Override public boolean equals(Object obj) {
      if (obj instanceof Signature) {
        Signature other = (Signature) obj;
        return other.name.equals(name) && Arrays.equals(parameters, other.parameters);
      }
      return false;
    }

    @Override public int hashCode() {
      return hashCode;
    }
  }

  /** Returns true if a overrides b, assumes that the signatures match */
  private static boolean overrides(Method a, Method b) {
    // See JLS section 8.4.8.1
    int modifiers = b.getModifiers();
    if (Modifier.isPublic(modifiers) || Modifier.isProtected(modifiers)) {
      return true;
    }
    if (Modifier.isPrivate(modifiers)) {
      return false;
    }
    // b must be package-private
    return a.getDeclaringClass().getPackage().equals(b.getDeclaringClass().getPackage());
  }

  private <T> ProviderMethod createProviderMethod(Binder binder, Method method,
      Annotation annotation) {
    binder = binder.withSource(method);
    Errors errors = new Errors(method);

    // prepare the parameter providers
    InjectionPoint point = InjectionPoint.forMethod(method, typeLiteral);
    List<Dependency dependencies = point.getDependencies();
    List<Provider parameterProviders = Lists.newArrayList();
    for (Dependency<?> dependency : point.getDependencies()) {
      parameterProviders.add(binder.getProvider(dependency));
    }

    @SuppressWarnings("unchecked") // Define T as the method's return type.
    TypeLiteral<T> returnType = (TypeLiteral) typeLiteral.getReturnType(method);
    Key<T> key = getKey(errors, returnType, method, method.getAnnotations());
    try {
      key = scanner.prepareMethod(binder, annotation, key, point);
    } catch(Throwable t) {
      binder.addError(t);
    }
    Class<? extends Annotation> scopeAnnotation
        = Annotations.findScopeAnnotation(errors, method.getAnnotations());
    for (Message message : errors.getMessages()) {
      binder.addError(message);
    }
    return ProviderMethod.create(key, method, delegate, ImmutableSet.copyOf(dependencies),
        parameterProviders, scopeAnnotation, skipFastClassGeneration, annotation);
  }

  <T> Key getKey(Errors errors, TypeLiteral type, Member member, Annotation[] annotations) {
    Annotation bindingAnnotation = Annotations.findBindingAnnotation(errors, member, annotations);
    return bindingAnnotation == null ? Key.get(type) : Key.get(type, bindingAnnotation);
  }

  @Override public boolean equals(Object o) {
    return o instanceof ProviderMethodsModule
        && ((ProviderMethodsModule) o).delegate == delegate
        && ((ProviderMethodsModule) o).scanner == scanner;
  }

  @Override public int hashCode() {
    return delegate.hashCode();
  }
}

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