lazy: Implement Lazy<T>, very much like Dagger's.

5 files changed, 450 insertions, 0 deletions

diff --git a/sangria-lazy/src/main/java/com/tavianator/sangria/lazy/Lazy.java b/sangria-lazy/src/main/java/com/tavianator/sangria/lazy/Lazy.java
new file mode 100644
index 0000000..adf531c
--- /dev/null
+++ b/sangria-lazy/src/main/java/com/tavianator/sangria/lazy/Lazy.java
@@ -0,0 +1,81 @@
+/****************************************************************************
+ * Sangria                                                                  *
+ * Copyright (C) 2014 Tavian Barnes <tavianator@tavianator.com>             *
+ *                                                                          *
+ * 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.tavianator.sangria.lazy;
+
+import javax.inject.Inject;
+import javax.inject.Provider;
+
+/**
+ * A lazily-loaded dependency. Like a {@link Provider}, calling {@link #get()} will produce an instance of {@code T}.
+ * Unlike a {@link Provider}, the same instance will be returned for every future call to {@link #get()}. Different
+ * {@code Lazy} instances are independent and will return different instances from {@link #get()}.
+ *
+ * <p>
+ * {@link Lazy} works automatically for unqualified bindings, as long as just-in-time bindings are enabled. For
+ * qualified bindings, or if explicit bindings are requred, use {@link LazyBinder}:
+ * </p>
+ *
+ * <pre>
+ * // Either separately...
+ * bind(Dependency.class)
+ *         .annotatedWith(Names.named("name"))
+ *         .to(RealDependency.class);
+ *
+ * LazyBinder.create(binder())
+ *         .bind(Dependency.class)
+ *         .annotatedWith(Names.named("name"));
+ *
+ * // ... or in one go
+ * LazyBinder.create(binder())
+ *         .bind(Dependency.class)
+ *         .annotatedWith(Names.named("name"))
+ *         .to(RealDependency.class);
+ *
+ * ...
+ *
+ * {@literal @}Inject {@literal @}Named("name") Lazy&lt;Dependency&gt; lazy;
+ * </pre>
+ *
+ * @author Tavian Barnes (tavianator@tavianator.com)
+ * @version 1.2
+ * @since 1.2
+ */
+public final class Lazy<T> {
+    private final Provider<T> provider;
+    private volatile T instance = null;
+
+    @Inject
+    Lazy(Provider<T> provider) {
+        this.provider = provider;
+    }
+
+    /**
+     * @return A lazily-produced value of type {@code T}.
+     */
+    public T get() {
+        // Double-checked locking
+        if (instance == null) {
+            synchronized (this) {
+                if (instance == null) {
+                    instance = provider.get();
+                }
+            }
+        }
+        return instance;
+    }
+}
diff --git a/sangria-lazy/src/main/java/com/tavianator/sangria/lazy/LazyBinder.java b/sangria-lazy/src/main/java/com/tavianator/sangria/lazy/LazyBinder.java
new file mode 100644
index 0000000..26d3848
--- /dev/null
+++ b/sangria-lazy/src/main/java/com/tavianator/sangria/lazy/LazyBinder.java
@@ -0,0 +1,273 @@
+/****************************************************************************
+ * Sangria                                                                  *
+ * Copyright (C) 2014 Tavian Barnes <tavianator@tavianator.com>             *
+ *                                                                          *
+ * 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.tavianator.sangria.lazy;
+
+import java.lang.annotation.Annotation;
+import java.lang.reflect.Constructor;
+
+import javax.inject.Provider;
+
+import com.google.inject.Binder;
+import com.google.inject.Key;
+import com.google.inject.Scope;
+import com.google.inject.TypeLiteral;
+import com.google.inject.binder.AnnotatedBindingBuilder;
+import com.google.inject.binder.LinkedBindingBuilder;
+import com.google.inject.binder.ScopedBindingBuilder;
+import com.google.inject.spi.BindingTargetVisitor;
+import com.google.inject.spi.ProviderInstanceBinding;
+import com.google.inject.spi.ProviderWithExtensionVisitor;
+import com.google.inject.util.Types;
+
+import com.tavianator.sangria.core.PotentialAnnotation;
+
+/**
+ * Binder for {@link Lazy} instances.
+ *
+ * @author Tavian Barnes (tavianator@tavianator.com)
+ * @version 1.2
+ * @since 1.2
+ */
+public class LazyBinder {
+    private static final Class<?>[] SKIPPED_SOURCES = {
+            LazyBinder.class,
+            BindingAnnotator.class,
+            LazyBindingBuilder.class,
+    };
+
+    private final Binder binder;
+
+    private LazyBinder(Binder binder) {
+        this.binder = binder;
+    }
+
+    /**
+     * Create a {@link LazyBinder}.
+     *
+     * @param binder The {@link Binder} to use.
+     * @return A {@link LazyBinder} instance.
+     */
+    public static LazyBinder create(Binder binder) {
+        return new LazyBinder(binder.skipSources(SKIPPED_SOURCES));
+    }
+
+    @SuppressWarnings("unchecked")
+    private static <T> TypeLiteral<Lazy<T>> lazyOf(TypeLiteral<T> type) {
+        return (TypeLiteral<Lazy<T>>)TypeLiteral.get(Types.newParameterizedType(Lazy.class, type.getType()));
+    }
+
+    /**
+     * See the EDSL examples at {@link Lazy}.
+     */
+    public <T> AnnotatedBindingBuilder<T> bind(Class<T> type) {
+        return bind(TypeLiteral.get(type));
+    }
+
+    /**
+     * See the EDSL examples at {@link Lazy}.
+     */
+    public <T> AnnotatedBindingBuilder<T> bind(TypeLiteral<T> type) {
+        AnnotatedBindingBuilder<Lazy<T>> lazyBinding = binder.bind(lazyOf(type));
+        return new LazyBindingBuilder<>(binder, type, lazyBinding, PotentialAnnotation.none());
+    }
+
+    /**
+     * Applies an annotation to an {@link AnnotatedBindingBuilder}.
+     */
+    private static class BindingAnnotator<T> implements PotentialAnnotation.Visitor<LinkedBindingBuilder<T>> {
+        private final AnnotatedBindingBuilder<T> builder;
+
+        BindingAnnotator(AnnotatedBindingBuilder<T> builder) {
+            this.builder = builder;
+        }
+
+        @Override
+        public LinkedBindingBuilder<T> visitNoAnnotation() {
+            return builder;
+        }
+
+        @Override
+        public LinkedBindingBuilder<T> visitAnnotationType(Class<? extends Annotation> annotationType) {
+            return builder.annotatedWith(annotationType);
+        }
+
+        @Override
+        public LinkedBindingBuilder<T> visitAnnotationInstance(Annotation annotation) {
+            return builder.annotatedWith(annotation);
+        }
+    }
+
+    /**
+     * See the EDSL examples at {@link Lazy}.
+     */
+    public <T> LinkedBindingBuilder<T> bind(Key<T> key) {
+        TypeLiteral<T> type = key.getTypeLiteral();
+        PotentialAnnotation potentialAnnotation = PotentialAnnotation.from(key);
+        return potentialAnnotation.accept(new BindingAnnotator<>(bind(type)));
+    }
+
+    /**
+     * Actual binder implementation.
+     */
+    private static class LazyBindingBuilder<T> implements AnnotatedBindingBuilder<T> {
+        private final Binder binder;
+        private final TypeLiteral<T> type;
+        private final AnnotatedBindingBuilder<Lazy<T>> lazyBinding;
+        private final PotentialAnnotation potentialAnnotation;
+
+        LazyBindingBuilder(
+                Binder binder,
+                TypeLiteral<T> type,
+                AnnotatedBindingBuilder<Lazy<T>> lazyBinding,
+                PotentialAnnotation potentialAnnotation) {
+            this.binder = binder;
+            this.type = type;
+            this.lazyBinding = lazyBinding;
+            this.potentialAnnotation = potentialAnnotation;
+        }
+
+        @Override
+        public LinkedBindingBuilder<T> annotatedWith(Class<? extends Annotation> annotationType) {
+            PotentialAnnotation newAnnotation = potentialAnnotation.annotatedWith(annotationType);
+            Key<T> key = newAnnotation.getKey(type);
+
+            lazyBinding.annotatedWith(annotationType)
+                    .toProvider(new LazyProvider<>(binder.getProvider(key), key));
+
+            return new LazyBindingBuilder<>(binder, type, null, newAnnotation);
+        }
+
+        @Override
+        public LinkedBindingBuilder<T> annotatedWith(Annotation annotation) {
+            PotentialAnnotation newAnnotation = potentialAnnotation.annotatedWith(annotation);
+            Key<T> key = newAnnotation.getKey(type);
+
+            lazyBinding.annotatedWith(annotation)
+                    .toProvider(new LazyProvider<>(binder.getProvider(key), key));
+
+            return new LazyBindingBuilder<>(binder, type, null, newAnnotation);
+        }
+
+        /**
+         * @return A binding builder for the underlying binding.
+         */
+        private LinkedBindingBuilder<T> makeBinder() {
+            return binder.bind(potentialAnnotation.getKey(type));
+        }
+
+        @Override
+        public ScopedBindingBuilder to(Class<? extends T> implementation) {
+            return makeBinder().to(implementation);
+        }
+
+        @Override
+        public ScopedBindingBuilder to(TypeLiteral<? extends T> implementation) {
+            return makeBinder().to(implementation);
+        }
+
+        @Override
+        public ScopedBindingBuilder to(Key<? extends T> targetKey) {
+            return makeBinder().to(targetKey);
+        }
+
+        @Override
+        public void toInstance(T instance) {
+            makeBinder().toInstance(instance);
+        }
+
+        @Override
+        public ScopedBindingBuilder toProvider(com.google.inject.Provider<? extends T> provider) {
+            return makeBinder().toProvider(provider);
+        }
+
+        @Override
+        public ScopedBindingBuilder toProvider(Provider<? extends T> provider) {
+            return makeBinder().toProvider(provider);
+        }
+
+        @Override
+        public ScopedBindingBuilder toProvider(Class<? extends Provider<? extends T>> providerType) {
+            return makeBinder().toProvider(providerType);
+        }
+
+        @Override
+        public ScopedBindingBuilder toProvider(TypeLiteral<? extends Provider<? extends T>> providerType) {
+            return makeBinder().toProvider(providerType);
+        }
+
+        @Override
+        public ScopedBindingBuilder toProvider(Key<? extends Provider<? extends T>> providerKey) {
+            return makeBinder().toProvider(providerKey);
+        }
+
+        @Override
+        public <S extends T> ScopedBindingBuilder toConstructor(Constructor<S> constructor) {
+            return makeBinder().toConstructor(constructor);
+        }
+
+        @Override
+        public <S extends T> ScopedBindingBuilder toConstructor(Constructor<S> constructor, TypeLiteral<? extends S> type) {
+            return makeBinder().toConstructor(constructor, type);
+        }
+
+        @Override
+        public void in(Class<? extends Annotation> scopeAnnotation) {
+            makeBinder().in(scopeAnnotation);
+        }
+
+        @Override
+        public void in(Scope scope) {
+            makeBinder().in(scope);
+        }
+
+        @Override
+        public void asEagerSingleton() {
+            makeBinder().asEagerSingleton();
+        }
+    }
+
+    private static class LazyProvider<T> implements LazyBinding<T>, ProviderWithExtensionVisitor<Lazy<T>> {
+        private final Provider<T> provider;
+        private final Key<T> key;
+
+        LazyProvider(Provider<T> provider, Key<T> key) {
+            this.provider = provider;
+            this.key = key;
+        }
+
+        @Override
+        public Lazy<T> get() {
+            return new Lazy<>(provider);
+        }
+
+        @Override
+        public Key<T> getTargetKey() {
+            return key;
+        }
+
+        @SuppressWarnings("unchecked") // B must be Lazy<T>
+        @Override
+        public <B, V> V acceptExtensionVisitor(BindingTargetVisitor<B, V> visitor, ProviderInstanceBinding<? extends B> binding) {
+            if (visitor instanceof LazyBindingVisitor) {
+                return ((LazyBindingVisitor<T, V>)visitor).visit(this);
+            } else {
+                return visitor.visit(binding);
+            }
+        }
+    }
+}
diff --git a/sangria-lazy/src/main/java/com/tavianator/sangria/lazy/LazyBinding.java b/sangria-lazy/src/main/java/com/tavianator/sangria/lazy/LazyBinding.java
new file mode 100644
index 0000000..518ae57
--- /dev/null
+++ b/sangria-lazy/src/main/java/com/tavianator/sangria/lazy/LazyBinding.java
@@ -0,0 +1,34 @@
+/****************************************************************************
+ * Sangria                                                                  *
+ * Copyright (C) 2014 Tavian Barnes <tavianator@tavianator.com>             *
+ *                                                                          *
+ * 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.tavianator.sangria.lazy;
+
+import com.google.inject.Key;
+
+/**
+ * SPI for {@link LazyBinder} bindings.
+ *
+ * @author Tavian Barnes (tavianator@tavianator.com)
+ * @version 1.2
+ * @since 1.2
+ */
+public interface LazyBinding<T> {
+    /**
+     * @return The key wrapped by the {@link Lazy Lazy&lt;T&gt;} binding.
+     */
+    Key<T> getTargetKey();
+}
diff --git a/sangria-lazy/src/main/java/com/tavianator/sangria/lazy/LazyBindingVisitor.java b/sangria-lazy/src/main/java/com/tavianator/sangria/lazy/LazyBindingVisitor.java
new file mode 100644
index 0000000..ef95a0c
--- /dev/null
+++ b/sangria-lazy/src/main/java/com/tavianator/sangria/lazy/LazyBindingVisitor.java
@@ -0,0 +1,37 @@
+/****************************************************************************
+ * Sangria                                                                  *
+ * Copyright (C) 2014 Tavian Barnes <tavianator@tavianator.com>             *
+ *                                                                          *
+ * 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.tavianator.sangria.lazy;
+
+import com.google.inject.spi.BindingTargetVisitor;
+
+/**
+ * Visitor interface for the lazy binding SPI.
+ *
+ * @author Tavian Barnes (tavianator@tavianator.com)
+ * @version 1.2
+ * @since 1.2
+ */
+public interface LazyBindingVisitor<T, V> extends BindingTargetVisitor<T, V> {
+    /**
+     * Visit a {@link LazyBinding}.
+     *
+     * @param binding The binding to visit.
+     * @return A value of type {@code V}.
+     */
+    V visit(LazyBinding<? extends T> binding);
+}
diff --git a/sangria-lazy/src/main/java/com/tavianator/sangria/lazy/package-info.java b/sangria-lazy/src/main/java/com/tavianator/sangria/lazy/package-info.java
new file mode 100644
index 0000000..15b5b1a
--- /dev/null
+++ b/sangria-lazy/src/main/java/com/tavianator/sangria/lazy/package-info.java
@@ -0,0 +1,25 @@
+/****************************************************************************
+ * Sangria                                                                  *
+ * Copyright (C) 2014 Tavian Barnes <tavianator@tavianator.com>             *
+ *                                                                          *
+ * 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.                                           *
+ ****************************************************************************/
+
+/**
+ * Lazy loading.
+ *
+ * @author Tavian Barnes (tavianator@tavianator.com)
+ * @version 1.2
+ * @since 1.2
+ */
+package com.tavianator.sangria.lazy;