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Java example source code file (BoundFieldModule.java)

This example Java source code file (BoundFieldModule.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

annotatedbindingbuilder, annotation, bind, boundfieldexception, boundfieldinfo, boundfieldmodule, class, field, linkedbindingbuilder, object, optional, override, provider, reflection, suppresswarnings, typeliteral

The BoundFieldModule.java Java example source code

/*
 * Copyright (C) 2014 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.testing.fieldbinder;

import com.google.common.base.Optional;
import com.google.common.base.Preconditions;
import com.google.inject.Binder;
import com.google.inject.BindingAnnotation;
import com.google.inject.Module;
import com.google.inject.Provider;
import com.google.inject.TypeLiteral;
import com.google.inject.binder.AnnotatedBindingBuilder;
import com.google.inject.binder.LinkedBindingBuilder;
import com.google.inject.internal.Annotations;
import com.google.inject.internal.Nullability;
import com.google.inject.spi.Message;
import com.google.inject.util.Providers;

import java.lang.annotation.Annotation;
import java.lang.reflect.Field;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;

/**
 * Automatically creates Guice bindings for fields in an object annotated with {@link Bind}.
 *
 * <p>This module is intended for use in tests to reduce the code needed to bind local fields
 * (usually mocks) for injection.
 *
 * <p>The following rules are followed in determining how fields are bound using this module:
 *
 * <ul>
 * <li>
 * For each {@link Bind} annotated field of an object and its superclasses, this module will bind
 * that field's type to that field's value at injector creation time. This includes both instance
 * and static fields.
 * </li>
 * <li>
 * If {@link Bind#to} is specified, the field's value will be bound to the class specified by
 * {@link Bind#to} instead of the field's actual type.
 * </li>
 * <li>
 * If a {@link BindingAnnotation} or {@link javax.inject.Qualifier} is present on the field,
 * that field will be bound using that annotation via {@link AnnotatedBindingBuilder#annotatedWith}.
 * For example, {@code bind(Foo.class).annotatedWith(BarAnnotation.class).toInstance(theValue)}.
 * It is an error to supply more than one {@link BindingAnnotation} or
 * {@link javax.inject.Qualifier}.
 * </li>
 * <li>
 * If the field is of type {@link Provider}, the field's value will be bound as a {@link Provider}
 * using {@link LinkedBindingBuilder#toProvider} to the provider's parameterized type. For example,
 * {@code Provider<Integer>} binds to {@link Integer}. Attempting to bind a non-parameterized
 * {@link Provider} without a {@link Bind#to} clause is an error.
 * </li>
 * </ul>
 *
 * <p>Example use:
 * <pre>
 * public class TestFoo {
 *   // bind(new TypeLiteral{@code <List}() {}).toInstance(listOfObjects);
 *   {@literal @}Bind private List{@code <Object>} listOfObjects = Lists.of();
 *
 *   // bind(String.class).toProvider(new Provider() { public String get() { return userName; }});
 *   {@literal @}Bind(lazy = true) private String userName;
 *
 *   // bind(SuperClass.class).toInstance(aSubClass);
 *   {@literal @}Bind(to = SuperClass.class) private SubClass aSubClass = new SubClass();
 *
 *   // bind(String.class).annotatedWith(MyBindingAnnotation.class).toInstance(myString);
 *   {@literal @}Bind
 *   {@literal @}MyBindingAnnotation
 *   private String myString = "hello";
 *
 *   // bind(Object.class).toProvider(myProvider);
 *   {@literal @}Bind private Provider{@code <Object>} myProvider = getProvider();
 *
 *   {@literal @}Before public void setUp() {
 *     Guice.createInjector(BoundFieldModule.of(this)).injectMembers(this);
 *   }
 * }
 * </code>
* * @see Bind * @author eatnumber1@google.com (Russ Harmon) */ public final class BoundFieldModule implements Module { private final Object instance; // Note that binder is not initialized until configure() is called. private Binder binder; private BoundFieldModule(Object instance) { this.instance = instance; } /** * Create a BoundFieldModule which binds the {@link Bind} annotated fields of {@code instance}. * * @param instance the instance whose fields will be bound. * @return a module which will bind the {@link Bind} annotated fields of {@code instance}. */ public static BoundFieldModule of(Object instance) { return new BoundFieldModule(instance); } private static class BoundFieldException extends RuntimeException { private final Message message; BoundFieldException(Message message) { super(message.getMessage()); this.message = message; } } private class BoundFieldInfo { /** The field itself. */ final Field field; /** * The actual type of the field. * * <p>For example, {@code @Bind(to = Object.class) Number one = new Integer(1);} will be * {@link Number}. */ final TypeLiteral<?> type; /** The {@link Bind} annotation which is present on the field. */ final Bind bindAnnotation; /** * The type this field will bind to. * * <p>For example, {@code @Bind(to = Object.class) Number one = new Integer(1);} will be * {@link Object} and {@code @Bind Number one = new Integer(1);} will be {@link Number}. */ final TypeLiteral<?> boundType; /** * The "natural" type of this field. * * <p>For example, {@code @Bind(to = Object.class) Number one = new Integer(1);} will be * {@link Number}, and {@code @Bind(to = Object.class) Provider<Number> one = new Integer(1);} * will be {@link Number}. * * @see #getNaturalFieldType */ final Optional<TypeLiteral naturalType; BoundFieldInfo( Field field, Bind bindAnnotation, TypeLiteral<?> fieldType) { this.field = field; this.type = fieldType; this.bindAnnotation = bindAnnotation; field.setAccessible(true); this.naturalType = getNaturalFieldType(); this.boundType = getBoundType(); } private TypeLiteral<?> getBoundType() { Class<?> bindClass = bindAnnotation.to(); // Bind#to's default value is Bind.class which is used to represent that no explicit binding // type is requested. if (bindClass == Bind.class) { Preconditions.checkState(naturalType != null); if (!this.naturalType.isPresent()) { throwBoundFieldException( field, "Non parameterized Provider fields must have an explicit " + "binding class via @Bind(to = Foo.class)"); } return this.naturalType.get(); } else { return TypeLiteral.get(bindClass); } } /** * Retrieves the type this field binds to naturally. * * <p>A field's "natural" type specifically ignores the to() method on the @Bind annotation, is * the parameterized type if the field's actual type is a parameterized {@link Provider}, is * {@link Optional#absent()} if this field is a non-parameterized {@link Provider} and otherwise * is the field's actual type. * * @return the type this field binds to naturally, or {@link Optional#absent()} if this field is * a non-parameterized {@link Provider}. */ private Optional<TypeLiteral getNaturalFieldType() { if (isTransparentProvider(type.getRawType())) { Type providerType = type.getType(); if (providerType instanceof Class) { return Optional.absent(); } Preconditions.checkState(providerType instanceof ParameterizedType); Type[] providerTypeArguments = ((ParameterizedType) providerType).getActualTypeArguments(); Preconditions.checkState(providerTypeArguments.length == 1); return Optional.<TypeLiteralof(TypeLiteral.get(providerTypeArguments[0])); } else { return Optional.<TypeLiteralof(type); } } Object getValue() { try { return field.get(instance); } catch (IllegalAccessException e) { // Since we called setAccessible(true) on this field in the constructor, this is a // programming error if it occurs. throw new AssertionError(e); } } /** Returns whether a binding supports null values. */ boolean allowsNull() { return !isTransparentProvider(type.getRawType()) && Nullability.allowsNull(field.getAnnotations()); } } private static boolean hasInject(Field field) { return field.isAnnotationPresent(javax.inject.Inject.class) || field.isAnnotationPresent(com.google.inject.Inject.class); } /** * Retrieve a {@link BoundFieldInfo}. * * <p>This returns a {@link BoundFieldInfo} if the field has a {@link Bind} annotation. * Otherwise it returns {@link Optional#absent()}. */ private Optional<BoundFieldInfo> getBoundFieldInfo( TypeLiteral<?> containingClassType, Field field) { Bind bindAnnotation = field.getAnnotation(Bind.class); if (bindAnnotation == null) { return Optional.absent(); } if (hasInject(field)) { throwBoundFieldException( field, "Fields annotated with both @Bind and @Inject are illegal."); } return Optional.of( new BoundFieldInfo( field, bindAnnotation, containingClassType.getFieldType(field))); } private LinkedBindingBuilder<?> verifyBindingAnnotations( Field field, AnnotatedBindingBuilder<?> annotatedBinder) { LinkedBindingBuilder<?> binderRet = annotatedBinder; for (Annotation annotation : field.getAnnotations()) { Class<? extends Annotation> annotationType = annotation.annotationType(); if (Annotations.isBindingAnnotation(annotationType)) { // not returning here ensures that annotatedWith will be called multiple times if this field // has multiple BindingAnnotations, relying on the binder to throw an error in this case. binderRet = annotatedBinder.annotatedWith(annotation); } } return binderRet; } /** * Determines if {@code clazz} is a "transparent provider". * * <p>A transparent provider is a {@link com.google.inject.Provider} or * {@link javax.inject.Provider} which binds to it's parameterized type when used as the argument * to {@link Binder#bind}. * * <p>A {@link Provider} is transparent if the base class of that object is {@link Provider}. In * other words, subclasses of {@link Provider} are not transparent. As a special case, if a * {@link Provider} has no parameterized type but is otherwise transparent, then it is considered * transparent. * * <p>Subclasses of {@link Provider} are not considered transparent in order to allow users to * bind those subclasses directly, enabling them to inject the providers themselves. */ private static boolean isTransparentProvider(Class<?> clazz) { return com.google.inject.Provider.class == clazz || javax.inject.Provider.class == clazz; } private void bindField(final BoundFieldInfo fieldInfo) { if (fieldInfo.naturalType.isPresent()) { Class<?> naturalRawType = fieldInfo.naturalType.get().getRawType(); Class<?> boundRawType = fieldInfo.boundType.getRawType(); if (!boundRawType.isAssignableFrom(naturalRawType)) { throwBoundFieldException( fieldInfo.field, "Requested binding type \"%s\" is not assignable from field binding type \"%s\"", boundRawType.getName(), naturalRawType.getName()); } } AnnotatedBindingBuilder<?> annotatedBinder = binder.bind(fieldInfo.boundType); LinkedBindingBuilder<?> binder = verifyBindingAnnotations(fieldInfo.field, annotatedBinder); // It's unfortunate that Field.get() just returns Object rather than the actual type (although // that would be impossible) because as a result calling binder.toInstance or binder.toProvider // is impossible to do without an unchecked cast. This is safe if fieldInfo.naturalType is // present because compatibility is checked explicitly above, but is _unsafe_ if // fieldInfo.naturalType is absent which occurrs when a non-parameterized Provider is used with // @Bind(to = ...) @SuppressWarnings("unchecked") AnnotatedBindingBuilder<Object> binderUnsafe = (AnnotatedBindingBuilder) binder; if (isTransparentProvider(fieldInfo.type.getRawType())) { if (fieldInfo.bindAnnotation.lazy()) { binderUnsafe.toProvider( new Provider<Object>() { @Override // @Nullable public Object get() { // This is safe because we checked that the field's type is Provider above. @SuppressWarnings("unchecked") javax.inject.Provider<?> provider = (javax.inject.Provider<?>) getFieldValue(fieldInfo); return provider.get(); } }); } else { // This is safe because we checked that the field's type is Provider above. @SuppressWarnings("unchecked") javax.inject.Provider<?> fieldValueUnsafe = (javax.inject.Provider<?>) getFieldValue(fieldInfo); binderUnsafe.toProvider(fieldValueUnsafe); } } else if (fieldInfo.bindAnnotation.lazy()) { binderUnsafe.toProvider( new Provider<Object>() { @Override // @Nullable public Object get() { return getFieldValue(fieldInfo); } }); } else { Object fieldValue = getFieldValue(fieldInfo); if (fieldValue == null) { binderUnsafe.toProvider(Providers.of(null)); } else { binderUnsafe.toInstance(fieldValue); } } } // @Nullable /** * Returns the field value to bind, throwing for non-{@code @Nullable} fields with null values, * and for null "transparent providers". */ private Object getFieldValue(final BoundFieldInfo fieldInfo) { Object fieldValue = fieldInfo.getValue(); if (fieldValue == null && !fieldInfo.allowsNull()) { if (isTransparentProvider(fieldInfo.type.getRawType())) { throwBoundFieldException( fieldInfo.field, "Binding to null is not allowed. Use Providers.of(null) if this is your intended " + "behavior.", fieldInfo.field.getName()); } else { throwBoundFieldException( fieldInfo.field, "Binding to null values is only allowed for fields that are annotated @Nullable.", fieldInfo.field.getName()); } } return fieldValue; } private void throwBoundFieldException(Field field, String format, Object... args) { Preconditions.checkNotNull(binder); String source = String.format( "%s field %s", field.getDeclaringClass().getName(), field.getName()); throw new BoundFieldException(new Message(source, String.format(format, args))); } @Override public void configure(Binder binder) { binder = binder.skipSources(BoundFieldModule.class); this.binder = binder; TypeLiteral<?> currentClassType = TypeLiteral.get(instance.getClass()); while (currentClassType.getRawType() != Object.class) { for (Field field : currentClassType.getRawType().getDeclaredFields()) { try { Optional<BoundFieldInfo> fieldInfoOpt = getBoundFieldInfo(currentClassType, field); if (fieldInfoOpt.isPresent()) { bindField(fieldInfoOpt.get()); } } catch (BoundFieldException e) { // keep going to try to collect as many errors as possible binder.addError(e.message); } } currentClassType = currentClassType.getSupertype(currentClassType.getRawType().getSuperclass()); } } }

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