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Java example source code file (Parameter.java)

This example Java source code file (Parameter.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, assisted, configurationexception, key, object, override, parameterizedtype, provider, reflection, stringbuilder, type

The Parameter.java Java example source code

/**
 * Copyright (C) 2007 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.assistedinject;

import static com.google.common.base.Preconditions.checkArgument;

import com.google.inject.ConfigurationException;
import com.google.inject.Injector;
import com.google.inject.Key;
import com.google.inject.Provider;
import com.google.inject.internal.Annotations;

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

/**
 * Models a method or constructor parameter.
 *
 * @author jmourits@google.com (Jerome Mourits)
 * @author jessewilson@google.com (Jesse Wilson)
 */
class Parameter {
  
  private final Type type;
  private final boolean isAssisted;
  private final Annotation bindingAnnotation;
  private final boolean isProvider;

  private volatile Provider<? extends Object> provider;

  public Parameter(Type type, Annotation[] annotations) {
    this.type = type;
    this.bindingAnnotation = getBindingAnnotation(annotations);
    this.isAssisted = hasAssistedAnnotation(annotations);
    this.isProvider = isProvider(type);
  }

  public boolean isProvidedByFactory() {
    return isAssisted;
  }
  
  public Type getType() {
    return type;
  }

  @Override
  public String toString() {
    StringBuilder result = new StringBuilder();
    if (isAssisted) {
      result.append("@Assisted ");
    }
    if (bindingAnnotation != null) {
      result.append(bindingAnnotation).append(" ");
    }
    return result.append(type).toString();
  }

  private boolean hasAssistedAnnotation(Annotation[] annotations) {
    for (Annotation annotation : annotations) {
      if (annotation.annotationType().equals(Assisted.class)) {
        return true;
      }
    }
    return false;
  }

  /**
   * Returns the Guice {@link Key} for this parameter.
   */
  public Object getValue(Injector injector) {
    if (null == provider) {
      synchronized (this) {
        if (null == provider) {
          provider = isProvider
              ? injector.getProvider(getBindingForType(getProvidedType(type)))
              : injector.getProvider(getPrimaryBindingKey());
        }
      }
    }

    return isProvider ? provider : provider.get();
  }

  public boolean isBound(Injector injector) {
    return isBound(injector, getPrimaryBindingKey())
        || isBound(injector, fixAnnotations(getPrimaryBindingKey()));
  }

  private boolean isBound(Injector injector, Key<?> key) {
    // This method is particularly lame - we really need an API that can test
    // for any binding, implicit or explicit
    try {
      return injector.getBinding(key) != null;
    } catch (ConfigurationException e) {
      return false;
    }
  }

  /**
   * Replace annotation instances with annotation types, this is only
   * appropriate for testing if a key is bound and not for injecting.
   *
   * See Guice bug 125,
   * https://github.com/google/guice/issues/125
   */
  public Key<?> fixAnnotations(Key key) {
    return key.getAnnotation() == null
        ? key
        : Key.get(key.getTypeLiteral(), key.getAnnotation().annotationType());
  }

  Key<?> getPrimaryBindingKey() {
    return isProvider
        ? getBindingForType(getProvidedType(type))
        : getBindingForType(type);
  }

  private Type getProvidedType(Type type) {
    return ((ParameterizedType) type).getActualTypeArguments()[0];
  }

  private boolean isProvider(Type type) {
    return type instanceof ParameterizedType
        && ((ParameterizedType) type).getRawType() == Provider.class;
  }

  private Key<?> getBindingForType(Type type) {
    return bindingAnnotation != null
        ? Key.get(type, bindingAnnotation)
        : Key.get(type);
  }

  /**
   * Returns the unique binding annotation from the specified list, or
   * {@code null} if there are none.
   *
   * @throws IllegalStateException if multiple binding annotations exist.
   */
  private Annotation getBindingAnnotation(Annotation[] annotations) {
    Annotation bindingAnnotation = null;
    for (Annotation annotation : annotations) {
      if (Annotations.isBindingAnnotation(annotation.annotationType())) {
        checkArgument(bindingAnnotation == null,
            "Parameter has multiple binding annotations: %s and %s", bindingAnnotation, annotation);
        bindingAnnotation = annotation;
      }
    }
    return bindingAnnotation;
  }
}

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