home | career | drupal | java | mac | mysql | perl | scala | uml | unix  

Java example source code file (FactoryProvider2.java)

This example Java source code file (FactoryProvider2.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, assistdata, assistedinject, class, constructor, errors, injector, key, list, log, logging, method, methodhandlewrapper, object, override, reflection, set, typeliteral, util

The FactoryProvider2.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,
 * See the License for the specific language governing permissions and
 * limitations under the License.

package com.google.inject.assistedinject;

import static com.google.common.base.Preconditions.checkState;
import static com.google.common.collect.Iterables.getOnlyElement;

import com.google.common.base.MoreObjects;
import com.google.common.base.Objects;
import com.google.common.collect.HashMultimap;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Iterables;
import com.google.common.collect.Lists;
import com.google.common.collect.Multimap;
import com.google.common.collect.Sets;
import com.google.inject.AbstractModule;
import com.google.inject.Binder;
import com.google.inject.Binding;
import com.google.inject.ConfigurationException;
import com.google.inject.Inject;
import com.google.inject.Injector;
import com.google.inject.Key;
import com.google.inject.Module;
import com.google.inject.Provider;
import com.google.inject.ProvisionException;
import com.google.inject.Scopes;
import com.google.inject.TypeLiteral;
import com.google.inject.internal.Annotations;
import com.google.inject.internal.BytecodeGen;
import com.google.inject.internal.Errors;
import com.google.inject.internal.ErrorsException;
import com.google.inject.internal.UniqueAnnotations;
import com.google.inject.internal.util.Classes;
import com.google.inject.spi.BindingTargetVisitor;
import com.google.inject.spi.Dependency;
import com.google.inject.spi.HasDependencies;
import com.google.inject.spi.InjectionPoint;
import com.google.inject.spi.Message;
import com.google.inject.spi.ProviderInstanceBinding;
import com.google.inject.spi.ProviderWithExtensionVisitor;
import com.google.inject.spi.Toolable;
import com.google.inject.util.Providers;

import java.lang.annotation.Annotation;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.lang.reflect.Proxy;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.logging.Level;
import java.util.logging.Logger;

 * The newer implementation of factory provider. This implementation uses a child injector to
 * create values.
 * @author jessewilson@google.com (Jesse Wilson)
 * @author dtm@google.com (Daniel Martin)
 * @author schmitt@google.com (Peter Schmitt)
 * @author sameb@google.com (Sam Berlin)
final class FactoryProvider2 <F> implements InvocationHandler,
    ProviderWithExtensionVisitor<F>, HasDependencies, AssistedInjectBinding {

  /** A constant annotation to denote the return value, instead of creating a new one each time. */
  static final Annotation RETURN_ANNOTATION = UniqueAnnotations.create();

  // use the logger under a well-known name, not FactoryProvider2
  static final Logger logger = Logger.getLogger(AssistedInject.class.getName());

  /** if a factory method parameter isn't annotated, it gets this annotation. */
  static final Assisted DEFAULT_ANNOTATION = new Assisted() {
    public String value() {
      return "";

    public Class<? extends Annotation> annotationType() {
      return Assisted.class;

    @Override public boolean equals(Object o) {
      return o instanceof Assisted && ((Assisted) o).value().isEmpty();

    @Override public int hashCode() {
      return 127 * "value".hashCode() ^ "".hashCode();

    @Override public String toString() {
      return "@" + Assisted.class.getName() + "(value=)";

  /** All the data necessary to perform an assisted inject. */
  private static class AssistData implements AssistedMethod {
    /** the constructor the implementation is constructed with. */
    final Constructor<?> constructor;
    /** the return type in the factory method that the constructor is bound to. */
    final Key<?> returnType;
    /** the parameters in the factory method associated with this data. */
    final ImmutableList<Key paramTypes;
    /** the type of the implementation constructed */
    final TypeLiteral<?> implementationType;

    /** All non-assisted dependencies required by this method. */
    final Set<Dependency dependencies;
    /** The factory method associated with this data*/
    final Method factoryMethod;

    /** true if {@link #isValidForOptimizedAssistedInject} returned true. */
    final boolean optimized;
    /** the list of optimized providers, empty if not optimized. */
    final List<ThreadLocalProvider> providers;
    /** used to perform optimized factory creations. */
    volatile Binding<?> cachedBinding; // TODO: volatile necessary?

    AssistData(Constructor<?> constructor, Key returnType, ImmutableList> paramTypes,
        TypeLiteral<?> implementationType, Method factoryMethod,
        Set<Dependency dependencies,
        boolean optimized, List<ThreadLocalProvider> providers) {
      this.constructor = constructor;
      this.returnType = returnType;
      this.paramTypes = paramTypes;
      this.implementationType = implementationType;
      this.factoryMethod = factoryMethod;
      this.dependencies = dependencies;
      this.optimized = optimized;
      this.providers = providers;

    public String toString() {
      return MoreObjects.toStringHelper(getClass())
        .add("ctor", constructor)
        .add("return type", returnType)
        .add("param type", paramTypes)
        .add("implementation type", implementationType)
        .add("dependencies", dependencies)
        .add("factory method", factoryMethod)
        .add("optimized", optimized)
        .add("providers", providers)
        .add("cached binding", cachedBinding)

    public Set<Dependency getDependencies() {
      return dependencies;

    public Method getFactoryMethod() {
      return factoryMethod;

    public Constructor<?> getImplementationConstructor() {
      return constructor;

    public TypeLiteral<?> getImplementationType() {
      return implementationType;

  /** Mapping from method to the data about how the method will be assisted. */
  private final ImmutableMap<Method, AssistData> assistDataByMethod;

  /** Mapping from method to method handle, for generated default methods. */
  private final ImmutableMap<Method, MethodHandleWrapper> methodHandleByMethod;

  /** the hosting injector, or null if we haven't been initialized yet */
  private Injector injector;

  /** the factory interface, implemented and provided */
  private final F factory;
  /** The key that this is bound to. */
  private final Key<F> factoryKey;
  /** The binding collector, for equality/hashing purposes. */
  private final BindingCollector collector;

   * @param factoryKey a key for a Java interface that defines one or more create methods.
   * @param collector binding configuration that maps method return types to
   *    implementation types.
  FactoryProvider2(Key<F> factoryKey, BindingCollector collector) {
    this.factoryKey = factoryKey;
    this.collector = collector;

    TypeLiteral<F> factoryType = factoryKey.getTypeLiteral();
    Errors errors = new Errors();

    @SuppressWarnings("unchecked") // we imprecisely treat the class literal of T as a Class<T>
    Class<F> factoryRawType = (Class) (Class) factoryType.getRawType();

    try {
      if(!factoryRawType.isInterface()) {
        throw errors.addMessage("%s must be an interface.", factoryRawType).toException();

      Multimap<String, Method> defaultMethods = HashMultimap.create();
      Multimap<String, Method> otherMethods = HashMultimap.create();
      ImmutableMap.Builder<Method, AssistData> assistDataBuilder = ImmutableMap.builder();
      // TODO: also grab methods from superinterfaces
      for (Method method : factoryRawType.getMethods()) {
        // Skip static methods
        if (Modifier.isStatic(method.getModifiers())) {

        // Skip default methods that java8 may have created.
        if (isDefault(method) && (method.isBridge() || method.isSynthetic())) {
          // Even synthetic default methods need the return type validation...
          // unavoidable consequence of javac8. :-(
          validateFactoryReturnType(errors, method.getReturnType(), factoryRawType);
          defaultMethods.put(method.getName(), method);
        otherMethods.put(method.getName(), method);

        TypeLiteral<?> returnTypeLiteral = factoryType.getReturnType(method);
        Key<?> returnType;
        try {
          returnType = Annotations.getKey(returnTypeLiteral, method, method.getAnnotations(), errors);
        } catch(ConfigurationException ce) {
          // If this was an error due to returnTypeLiteral not being specified, rephrase
          // it as our factory not being specified, so it makes more sense to users.
          if(isTypeNotSpecified(returnTypeLiteral, ce)) {
            throw errors.keyNotFullySpecified(TypeLiteral.get(factoryRawType)).toException();
          } else {
            throw ce;
        validateFactoryReturnType(errors, returnType.getTypeLiteral().getRawType(), factoryRawType);
        List<TypeLiteral params = factoryType.getParameterTypes(method);
        Annotation[][] paramAnnotations = method.getParameterAnnotations();
        int p = 0;
        List<Key keys = Lists.newArrayList();
        for (TypeLiteral<?> param : params) {
          Key<?> paramKey = Annotations.getKey(param, method, paramAnnotations[p++], errors);
          Class<?> underlylingType = paramKey.getTypeLiteral().getRawType();
          if (underlylingType.equals(Provider.class)
              || underlylingType.equals(javax.inject.Provider.class)) {
            errors.addMessage("A Provider may not be a type in a factory method of an AssistedInject."
                    + "\n  Offending instance is parameter [%s] with key [%s] on method [%s]",
                    p, paramKey, method);
          keys.add(assistKey(method, paramKey, errors));
        ImmutableList<Key immutableParamList = ImmutableList.copyOf(keys);

        // try to match up the method to the constructor
        TypeLiteral<?> implementation = collector.getBindings().get(returnType);
        if(implementation == null) {
          implementation = returnType.getTypeLiteral();
        Class<? extends Annotation> scope =
            Annotations.findScopeAnnotation(errors, implementation.getRawType());
        if (scope != null) {
          errors.addMessage("Found scope annotation [%s] on implementation class "
              + "[%s] of AssistedInject factory [%s].\nThis is not allowed, please"
              + " remove the scope annotation.",
              scope, implementation.getRawType(), factoryType);
        InjectionPoint ctorInjectionPoint;
        try {
          ctorInjectionPoint =
            findMatchingConstructorInjectionPoint(method, returnType, implementation, immutableParamList);
        } catch(ErrorsException ee) {

        Constructor<?> constructor = (Constructor) ctorInjectionPoint.getMember();
        List<ThreadLocalProvider> providers = Collections.emptyList();
        Set<Dependency deps = getDependencies(ctorInjectionPoint, implementation);
        boolean optimized = false;
        // Now go through all dependencies of the implementation and see if it is OK to
        // use an optimized form of assistedinject2.  The optimized form requires that
        // all injections directly inject the object itself (and not a Provider of the object,
        // or an Injector), because it caches a single child injector and mutates the Provider
        // of the arguments in a ThreadLocal.
        if(isValidForOptimizedAssistedInject(deps, implementation.getRawType(), factoryType)) {
          ImmutableList.Builder<ThreadLocalProvider> providerListBuilder = ImmutableList.builder();
          for(int i = 0; i < params.size(); i++) {
            providerListBuilder.add(new ThreadLocalProvider());
          providers = providerListBuilder.build();
          optimized = true;

        AssistData data = new AssistData(constructor,
        assistDataBuilder.put(method, data);

      factory = factoryRawType.cast(Proxy.newProxyInstance(
          BytecodeGen.getClassLoader(factoryRawType), new Class<?>[] {factoryRawType}, this));

      // Now go back through default methods. Try to use MethodHandles to make things
      // work.  If that doesn't work, fallback to trying to find compatible method
      // signatures.
      Map<Method, AssistData> dataSoFar = assistDataBuilder.build();
      ImmutableMap.Builder<Method, MethodHandleWrapper> methodHandleBuilder = ImmutableMap.builder();
      for (Map.Entry<String, Method> entry : defaultMethods.entries()) {
        Method defaultMethod = entry.getValue();
        MethodHandleWrapper handle = MethodHandleWrapper.create(defaultMethod, factory);
        if (handle != null) {
          methodHandleBuilder.put(defaultMethod, handle);
        } else {
          boolean foundMatch = false;
          for (Method otherMethod : otherMethods.get(defaultMethod.getName())) {
            if (dataSoFar.containsKey(otherMethod) && isCompatible(defaultMethod, otherMethod)) {
              if (foundMatch) {
                errors.addMessage("Generated default method %s with parameters %s is"
                    + " signature-compatible with more than one non-default method."
                    + " Unable to create factory. As a workaround, remove the override"
                    + " so javac stops generating a default method.",
                    defaultMethod, Arrays.asList(defaultMethod.getParameterTypes()));
              } else {
                assistDataBuilder.put(defaultMethod, dataSoFar.get(otherMethod));
                foundMatch = true;
          if (!foundMatch) {
            throw new IllegalStateException("Can't find method compatible with: " + defaultMethod);

      // If we generated any errors (from finding matching constructors, for instance), throw an exception.
      if(errors.hasErrors()) {
        throw errors.toException();

      assistDataByMethod = assistDataBuilder.build();
      methodHandleByMethod = methodHandleBuilder.build();
    } catch (ErrorsException e) {
      throw new ConfigurationException(e.getErrors().getMessages());

  static boolean isDefault(Method method) {
    // Per the javadoc, default methods are non-abstract, public, non-static.
    // They're also in interfaces, but we can guarantee that already since we only act
    // on interfaces.
    return (method.getModifiers() & (Modifier.ABSTRACT | Modifier.PUBLIC | Modifier.STATIC))
        == Modifier.PUBLIC;

  private boolean isCompatible(Method src, Method dst) {
    if (!src.getReturnType().isAssignableFrom(dst.getReturnType())) {
      return false;
    Class<?>[] srcParams = src.getParameterTypes();
    Class<?>[] dstParams = dst.getParameterTypes();
    if (srcParams.length != dstParams.length) {
      return false;
    for (int i = 0; i < srcParams.length; i++) {
      if (!srcParams[i].isAssignableFrom(dstParams[i])) {
        return false;
    return true;

  public F get() {
    return factory;

  public Set<Dependency getDependencies() {
    Set<Dependency combinedDeps = new HashSet>();
    for(AssistData data : assistDataByMethod.values()) {
    return ImmutableSet.copyOf(combinedDeps);
  public Key<F> getKey() {
    return factoryKey;

  // Safe cast because values are typed to AssistedData, which is an AssistedMethod, and
  // the collection is immutable.
  public Collection<AssistedMethod> getAssistedMethods() {
    return (Collection<AssistedMethod>) (Collection) assistDataByMethod.values();

  public <T, V> V acceptExtensionVisitor(BindingTargetVisitor visitor,
      ProviderInstanceBinding<? extends T> binding) {
    if (visitor instanceof AssistedInjectTargetVisitor) {
      return ((AssistedInjectTargetVisitor<T, V>)visitor).visit((AssistedInjectBinding)this);
    return visitor.visit(binding);

  private void validateFactoryReturnType(Errors errors, Class<?> returnType, Class factoryType) {
    if (Modifier.isPublic(factoryType.getModifiers())
        && !Modifier.isPublic(returnType.getModifiers())) {
      errors.addMessage("%s is public, but has a method that returns a non-public type: %s. "
          + "Due to limitations with java.lang.reflect.Proxy, this is not allowed. "
          + "Please either make the factory non-public or the return type public.",
          factoryType, returnType);

   * Returns true if the ConfigurationException is due to an error of TypeLiteral not being fully
   * specified.
  private boolean isTypeNotSpecified(TypeLiteral<?> typeLiteral, ConfigurationException ce) {
    Collection<Message> messages = ce.getErrorMessages();
    if (messages.size() == 1) {
      Message msg = Iterables.getOnlyElement(
          new Errors().keyNotFullySpecified(typeLiteral).getMessages());
      return msg.getMessage().equals(Iterables.getOnlyElement(messages).getMessage());
    } else {
      return false;

   * Finds a constructor suitable for the method.  If the implementation contained any constructors
   * marked with {@link AssistedInject}, this requires all {@link Assisted} parameters to exactly
   * match the parameters (in any order) listed in the method.  Otherwise, if no
   * {@link AssistedInject} constructors exist, this will default to looking for an
   * {@literal @}{@link Inject} constructor.
  private <T> InjectionPoint findMatchingConstructorInjectionPoint(
      Method method, Key<?> returnType, TypeLiteral implementation, List> paramList)
      throws ErrorsException {
    Errors errors = new Errors(method);
    if(returnType.getTypeLiteral().equals(implementation)) {
      errors = errors.withSource(implementation);
    } else {
      errors = errors.withSource(returnType).withSource(implementation);

    Class<?> rawType = implementation.getRawType();
    if (Modifier.isInterface(rawType.getModifiers())) {
          "%s is an interface, not a concrete class.  Unable to create AssistedInject factory.",
      throw errors.toException();
    } else if (Modifier.isAbstract(rawType.getModifiers())) {
          "%s is abstract, not a concrete class.  Unable to create AssistedInject factory.",
      throw errors.toException();
    } else if (Classes.isInnerClass(rawType)) {
      throw errors.toException();

    Constructor<?> matchingConstructor = null;
    boolean anyAssistedInjectConstructors = false;
    // Look for AssistedInject constructors...
    for (Constructor<?> constructor : rawType.getDeclaredConstructors()) {
      if (constructor.isAnnotationPresent(AssistedInject.class)) {
        anyAssistedInjectConstructors = true;
        if (constructorHasMatchingParams(implementation, constructor, paramList, errors)) {
          if (matchingConstructor != null) {
                    "%s has more than one constructor annotated with @AssistedInject"
                        + " that matches the parameters in method %s.  Unable to create "
                        + "AssistedInject factory.",
                    implementation, method);
            throw errors.toException();
          } else {
            matchingConstructor = constructor;

    if(!anyAssistedInjectConstructors) {
      // If none existed, use @Inject.
      try {
        return InjectionPoint.forConstructorOf(implementation);
      } catch(ConfigurationException e) {
        throw errors.toException();
    } else {
      // Otherwise, use it or fail with a good error message.
      if(matchingConstructor != null) {
          // safe because we got the constructor from this implementation.
          InjectionPoint ip = InjectionPoint.forConstructor(
              (Constructor<? super T>) matchingConstructor, implementation);
          return ip;
      } else {
            "%s has @AssistedInject constructors, but none of them match the"
            + " parameters in method %s.  Unable to create AssistedInject factory.",
            implementation, method);
        throw errors.toException();

   * Matching logic for constructors annotated with AssistedInject.
   * This returns true if and only if all @Assisted parameters in the
   * constructor exactly match (in any order) all @Assisted parameters
   * the method's parameter.
  private boolean constructorHasMatchingParams(TypeLiteral<?> type,
      Constructor<?> constructor, List> paramList, Errors errors)
      throws ErrorsException {
    List<TypeLiteral params = type.getParameterTypes(constructor);
    Annotation[][] paramAnnotations = constructor.getParameterAnnotations();
    int p = 0;
    List<Key constructorKeys = Lists.newArrayList();
    for (TypeLiteral<?> param : params) {
      Key<?> paramKey = Annotations.getKey(param, constructor, paramAnnotations[p++],
    // Require that every key exist in the constructor to match up exactly.
    for (Key<?> key : paramList) {
      // If it didn't exist in the constructor set, we can't use it.
      if (!constructorKeys.remove(key)) {
        return false;
    // If any keys remain and their annotation is Assisted, we can't use it.
    for (Key<?> key : constructorKeys) {
      if (key.getAnnotationType() == Assisted.class) {
        return false;
    // All @Assisted params match up to the method's parameters.
    return true;

  /** Calculates all dependencies required by the implementation and constructor. */
  private Set<Dependency getDependencies(InjectionPoint ctorPoint, TypeLiteral implementation) {
    ImmutableSet.Builder<Dependency builder = ImmutableSet.builder();
    if (!implementation.getRawType().isInterface()) {
      for (InjectionPoint ip : InjectionPoint.forInstanceMethodsAndFields(implementation)) {
    return builder.build();

  /** Return all non-assisted dependencies. */
  private Set<Dependency removeAssistedDeps(Set> deps) {
    ImmutableSet.Builder<Dependency builder = ImmutableSet.builder();
    for(Dependency<?> dep : deps) {
      Class<?> annotationType = dep.getKey().getAnnotationType();
      if (annotationType == null || !annotationType.equals(Assisted.class)) {
    return builder.build();

   * Returns true if all dependencies are suitable for the optimized version of AssistedInject. The
   * optimized version caches the binding & uses a ThreadLocal Provider, so can only be applied if
   * the assisted bindings are immediately provided. This looks for hints that the values may be
   * lazily retrieved, by looking for injections of Injector or a Provider for the assisted values.
  private boolean isValidForOptimizedAssistedInject(Set<Dependency dependencies,
      Class<?> implementation, TypeLiteral factoryType) {
    Set<Dependency badDeps = null; // optimization: create lazily
    for (Dependency<?> dep : dependencies) {
      if (isInjectorOrAssistedProvider(dep)) {
        if (badDeps == null) {
          badDeps = Sets.newHashSet();
    if (badDeps != null && !badDeps.isEmpty()) {
      logger.log(Level.WARNING, "AssistedInject factory {0} will be slow "
          + "because {1} has assisted Provider dependencies or injects the Injector. "
          + "Stop injecting @Assisted Provider<T> (instead use @Assisted T) "
          + "or Injector to speed things up. (It will be a ~6500% speed bump!)  "
          + "The exact offending deps are: {2}",
          new Object[] {factoryType, implementation, badDeps} );
      return false;
    return true;

   * Returns true if the dependency is for {@link Injector} or if the dependency
   * is a {@link Provider} for a parameter that is {@literal @}{@link Assisted}.
  private boolean isInjectorOrAssistedProvider(Dependency<?> dependency) {
    Class<?> annotationType = dependency.getKey().getAnnotationType();
    if (annotationType != null && annotationType.equals(Assisted.class)) { // If it's assisted..
      if (dependency.getKey().getTypeLiteral().getRawType().equals(Provider.class)) { // And a Provider...
        return true;
    } else if (dependency.getKey().getTypeLiteral().getRawType().equals(Injector.class)) { // If it's the Injector...
      return true;
    return false;

   * Returns a key similar to {@code key}, but with an {@literal @}Assisted binding annotation.
   * This fails if another binding annotation is clobbered in the process. If the key already has
   * the {@literal @}Assisted annotation, it is returned as-is to preserve any String value.
  private <T> Key assistKey(Method method, Key key, Errors errors) throws ErrorsException {
    if (key.getAnnotationType() == null) {
      return Key.get(key.getTypeLiteral(), DEFAULT_ANNOTATION);
    } else if (key.getAnnotationType() == Assisted.class) {
      return key;
    } else {
          "Only @Assisted is allowed for factory parameters, but found @%s",
      throw errors.toException();

   * At injector-creation time, we initialize the invocation handler. At this time we make sure
   * all factory methods will be able to build the target types.
  @Inject @Toolable
  void initialize(Injector injector) {
    if (this.injector != null) {
      throw new ConfigurationException(ImmutableList.of(new Message(FactoryProvider2.class,
          "Factories.create() factories may only be used in one Injector!")));

    this.injector = injector;

    for (Map.Entry<Method, AssistData> entry : assistDataByMethod.entrySet()) {
      Method method = entry.getKey();
      AssistData data = entry.getValue();
      Object[] args;
      if(!data.optimized) {
        args = new Object[method.getParameterTypes().length];
        Arrays.fill(args, "dummy object for validating Factories");
      } else {
        args = null; // won't be used -- instead will bind to data.providers.
      getBindingFromNewInjector(method, args, data); // throws if the binding isn't properly configured

   * Creates a child injector that binds the args, and returns the binding for the method's result.
  public Binding<?> getBindingFromNewInjector(
      final Method method, final Object[] args, final AssistData data) {
    checkState(injector != null,
        "Factories.create() factories cannot be used until they're initialized by Guice.");

    final Key<?> returnType = data.returnType;

    // We ignore any pre-existing binding annotation.
    final Key<?> returnKey = Key.get(returnType.getTypeLiteral(), RETURN_ANNOTATION);

    Module assistedModule = new AbstractModule() {
        "unchecked", "rawtypes"}) // raw keys are necessary for the args array and return value
      protected void configure() {
        Binder binder = binder().withSource(method);

        int p = 0;
        if(!data.optimized) {
          for (Key<?> paramKey : data.paramTypes) {
            // Wrap in a Provider to cover null, and to prevent Guice from injecting the parameter
            binder.bind((Key) paramKey).toProvider(Providers.of(args[p++]));
        } else {
          for (Key<?> paramKey : data.paramTypes) {
            // Bind to our ThreadLocalProviders.
            binder.bind((Key) paramKey).toProvider(data.providers.get(p++));

        Constructor constructor = data.constructor;
        // Constructor *should* always be non-null here,
        // but if it isn't, we'll end up throwing a fairly good error
        // message for the user.
        if(constructor != null) {
              .toConstructor(constructor, (TypeLiteral)data.implementationType)
              .in(Scopes.NO_SCOPE); // make sure we erase any scope on the implementation type

    Injector forCreate = injector.createChildInjector(assistedModule);
    Binding<?> binding = forCreate.getBinding(returnKey);
    // If we have providers cached in data, cache the binding for future optimizations.
    if(data.optimized) {
      data.cachedBinding = binding;
    return binding;

   * When a factory method is invoked, we create a child injector that binds all parameters, then
   * use that to get an instance of the return type.
  public Object invoke(Object proxy, final Method method, final Object[] args) throws Throwable {
    // If we setup a method handle earlier for this method, call it.
    // This is necessary for default methods that java8 creates, so we
    // can call the default method implementation (and not our proxied version of it).
    if (methodHandleByMethod.containsKey(method)) {
      return methodHandleByMethod.get(method).invokeWithArguments(args);

    if (method.getDeclaringClass().equals(Object.class)) {
      if ("equals".equals(method.getName())) {
        return proxy == args[0];
      } else if ("hashCode".equals(method.getName())) {
        return System.identityHashCode(proxy);
      } else {
        return method.invoke(this, args);

    AssistData data = assistDataByMethod.get(method);
    checkState(data != null, "No data for method: %s", method);
    Provider<?> provider;
    if(data.cachedBinding != null) { // Try to get optimized form...
      provider = data.cachedBinding.getProvider();
    } else {
      provider = getBindingFromNewInjector(method, args, data).getProvider();
    try {
      int p = 0;
      for(ThreadLocalProvider tlp : data.providers) {
      return provider.get();
    } catch (ProvisionException e) {
      // if this is an exception declared by the factory method, throw it as-is
      if (e.getErrorMessages().size() == 1) {
        Message onlyError = getOnlyElement(e.getErrorMessages());
        Throwable cause = onlyError.getCause();
        if (cause != null && canRethrow(method, cause)) {
          throw cause;
      throw e;
    } finally {
      for(ThreadLocalProvider tlp : data.providers) {

  @Override public String toString() {
    return factory.getClass().getInterfaces()[0].getName();
  public int hashCode() {
    return Objects.hashCode(factoryKey, collector);

  @Override public boolean equals(Object obj) {
    if (!(obj instanceof FactoryProvider2)) {
      return false;
    FactoryProvider2<?> other = (FactoryProvider2) obj;
    return factoryKey.equals(other.factoryKey) && Objects.equal(collector, other.collector);

  /** Returns true if {@code thrown} can be thrown by {@code invoked} without wrapping. */
  static boolean canRethrow(Method invoked, Throwable thrown) {
    if (thrown instanceof Error || thrown instanceof RuntimeException) {
      return true;

    for (Class<?> declared : invoked.getExceptionTypes()) {
      if (declared.isInstance(thrown)) {
        return true;

    return false;

  // not <T> because we'll never know and this is easier than suppressing warnings.
  private static class ThreadLocalProvider extends ThreadLocal<Object> implements Provider {
    protected Object initialValue() {
      throw new IllegalStateException(
          "Cannot use optimized @Assisted provider outside the scope of the constructor."
              + " (This should never happen.  If it does, please report it.)");

  /** Wrapper around MethodHandles/MethodHandle, so we can compile+run on java6. */
  private static class MethodHandleWrapper {
    static final int ALL_MODES = Modifier.PRIVATE
        | Modifier.STATIC /* package */
        | Modifier.PUBLIC
        | Modifier.PROTECTED;
    static final Method unreflectSpecial;
    static final Method bindTo;
    static final Method invokeWithArguments;
    static final Constructor<?> lookupCxtor;
    static final boolean valid;

    static {
      Method unreflectSpecialTmp = null;
      Method bindToTmp = null;
      Method invokeWithArgumentsTmp = null;
      boolean validTmp = false;
      Constructor<?> lookupCxtorTmp = null;
      try {
        Class<?> lookupClass = Class.forName("java.lang.invoke.MethodHandles$Lookup");
        unreflectSpecialTmp = lookupClass.getMethod("unreflectSpecial", Method.class, Class.class);
        Class<?> methodHandleClass = Class.forName("java.lang.invoke.MethodHandle");
        bindToTmp = methodHandleClass.getMethod("bindTo", Object.class);
        invokeWithArgumentsTmp = methodHandleClass.getMethod("invokeWithArguments", Object[].class);
        lookupCxtorTmp = lookupClass.getDeclaredConstructor(Class.class, int.class);
        validTmp = true;
      } catch (Exception invalid) {
        // Ignore the exception, store the values & exit early in create(..) if invalid.

      // Store refs to later.
      valid = validTmp;
      unreflectSpecial = unreflectSpecialTmp;
      bindTo = bindToTmp;
      invokeWithArguments = invokeWithArgumentsTmp;
      lookupCxtor = lookupCxtorTmp;

    static MethodHandleWrapper create(Method method, Object proxy) {
      if (!valid) {
        return null;
      try {
        Class<?> declaringClass = method.getDeclaringClass();
        // Note: this isn't a public API, but we need to use it in order to call default methods.
        Object lookup = lookupCxtor.newInstance(declaringClass, ALL_MODES);
        // These are part of the public API, but we use reflection since we run on java6
        // and they were introduced in java7.
        lookup = unreflectSpecial.invoke(lookup, method, declaringClass);
        Object handle = bindTo.invoke(lookup, proxy);
        return new MethodHandleWrapper(handle);
      } catch (InvocationTargetException ite) {
        return null;
      } catch (IllegalAccessException iae) {
        return null;
      } catch (InstantiationException ie) {
        return null;

    final Object handle;

    MethodHandleWrapper(Object handle) {
      this.handle = handle;

    Object invokeWithArguments(Object[] args) throws Exception {
      // We must cast the args to an object so the Object[] is the first param,
      // as opposed to each individual varargs param.
      return invokeWithArguments.invoke(handle, (Object) args);

    @Override public String toString() {
      return handle.toString();

Other Java examples (source code examples)

Here is a short list of links related to this Java FactoryProvider2.java source code file:

my book on functional programming


new blog posts


Copyright 1998-2021 Alvin Alexander, alvinalexander.com
All Rights Reserved.

A percentage of advertising revenue from
pages under the /java/jwarehouse URI on this website is
paid back to open source projects.