code: /*
   * Copyright (C) 2011 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 tools.com.google.gson.internal;
  
  import java.lang.reflect.Constructor;
  import java.lang.reflect.InvocationTargetException;
  import java.lang.reflect.ParameterizedType;
  import java.lang.reflect.Type;
  import java.util.ArrayDeque;
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.EnumSet;
  import java.util.LinkedHashMap;
  import java.util.LinkedHashSet;
  import java.util.Map;
  import java.util.Queue;
  import java.util.Set;
  import java.util.SortedMap;
  import java.util.SortedSet;
  import java.util.TreeMap;
  import java.util.TreeSet;
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.ConcurrentMap;
  import java.util.concurrent.ConcurrentNavigableMap;
  import java.util.concurrent.ConcurrentSkipListMap;
  
  import tools.com.google.gson.InstanceCreator;
  import tools.com.google.gson.JsonIOException;
  import tools.com.google.gson.reflect.TypeToken;
  
  /**
   * Returns a function that can construct an instance of a requested type.
   */
  public final class ConstructorConstructor {
    private final Map<Type, InstanceCreator<?>> instanceCreators;
  
    public ConstructorConstructor(Map<Type, InstanceCreator<?>> instanceCreators) {
      this.instanceCreators = instanceCreators;
    }
  
    public <T> ObjectConstructor<T> get(TypeToken<T> typeToken) {
      final Type type = typeToken.getType();
      final Class<? super T> rawType = typeToken.getRawType();
  
      // first try an instance creator
  
      @SuppressWarnings("unchecked") // types must agree
      final InstanceCreator<T> typeCreator = (InstanceCreator<T>) instanceCreators.get(type);
      if (typeCreator != null) {
        return new ObjectConstructor<T>() {
          @Override public T construct() {
            return typeCreator.createInstance(type);
          }
        };
      }
  
      // Next try raw type match for instance creators
      @SuppressWarnings("unchecked") // types must agree
      final InstanceCreator<T> rawTypeCreator =
          (InstanceCreator<T>) instanceCreators.get(rawType);
      if (rawTypeCreator != null) {
        return new ObjectConstructor<T>() {
          @Override public T construct() {
            return rawTypeCreator.createInstance(type);
          }
        };
      }
  
      ObjectConstructor<T> defaultConstructor = newDefaultConstructor(rawType);
      if (defaultConstructor != null) {
        return defaultConstructor;
      }
  
      ObjectConstructor<T> defaultImplementation = newDefaultImplementationConstructor(type, rawType);
      if (defaultImplementation != null) {
        return defaultImplementation;
      }
  
      // finally try unsafe
      return newUnsafeAllocator(type, rawType);
    }
  
    private <T> ObjectConstructor<T> newDefaultConstructor(Class<? super T> rawType) {
      try {
        final Constructor<? super T> constructor = rawType.getDeclaredConstructor();
        if (!constructor.isAccessible()) {
          constructor.setAccessible(true);
        }
        return new ObjectConstructor<T>() {
          @SuppressWarnings("unchecked") // T is the same raw type as is requested
          @Override public T construct() {
            try {
              Object[] args = null;
              return (T) constructor.newInstance(args);
            } catch (InstantiationException e) {
              // TODO: JsonParseException ?
              throw new RuntimeException("Failed to invoke " + constructor + " with no args", e);
            } catch (InvocationTargetException e) {
              // TODO: don't wrap if cause is unchecked!
              // TODO: JsonParseException ?
              throw new RuntimeException("Failed to invoke " + constructor + " with no args",
                  e.getTargetException());
            } catch (IllegalAccessException e) {
              throw new AssertionError(e);
            }
          }
        };
      } catch (NoSuchMethodException e) {
        return null;
      }
    }
  
    /**
     * Constructors for common interface types like Map and List and their
     * subtypes.
     */
    @SuppressWarnings("unchecked") // use runtime checks to guarantee that 'T' is what it is
    private <T> ObjectConstructor<T> newDefaultImplementationConstructor(
        final Type type, Class<? super T> rawType) {
      if (Collection.class.isAssignableFrom(rawType)) {
        if (SortedSet.class.isAssignableFrom(rawType)) {
          return new ObjectConstructor<T>() {
            @Override public T construct() {
              return (T) new TreeSet<Object>();
            }
          };
        } else if (EnumSet.class.isAssignableFrom(rawType)) {
          return new ObjectConstructor<T>() {
            @SuppressWarnings("rawtypes")
            @Override public T construct() {
              if (type instanceof ParameterizedType) {
                Type elementType = ((ParameterizedType) type).getActualTypeArguments()[0];
                if (elementType instanceof Class) {
                  return (T) EnumSet.noneOf((Class)elementType);
                } else {
                  throw new JsonIOException("Invalid EnumSet type: " + type.toString());
                }
              } else {
                throw new JsonIOException("Invalid EnumSet type: " + type.toString());
              }
            }
          };
        } else if (Set.class.isAssignableFrom(rawType)) {
          return new ObjectConstructor<T>() {
            @Override public T construct() {
              return (T) new LinkedHashSet<Object>();
            }
          };
        } else if (Queue.class.isAssignableFrom(rawType)) {
          return new ObjectConstructor<T>() {
            @Override public T construct() {
              return (T) new ArrayDeque<Object>();
            }
          };
        } else {
          return new ObjectConstructor<T>() {
            @Override public T construct() {
              return (T) new ArrayList<Object>();
            }
          };
        }
      }
  
      if (Map.class.isAssignableFrom(rawType)) {
        if (ConcurrentNavigableMap.class.isAssignableFrom(rawType)) {
          return new ObjectConstructor<T>() {
            @Override public T construct() {
              return (T) new ConcurrentSkipListMap<Object, Object>();
            }
          };
        } else if (ConcurrentMap.class.isAssignableFrom(rawType)) {
          return new ObjectConstructor<T>() {
            @Override public T construct() {
              return (T) new ConcurrentHashMap<Object, Object>();
            }
          };
        } else if (SortedMap.class.isAssignableFrom(rawType)) {
          return new ObjectConstructor<T>() {
            @Override public T construct() {
              return (T) new TreeMap<Object, Object>();
            }
          };
        } else if (type instanceof ParameterizedType && !(String.class.isAssignableFrom(
            TypeToken.get(((ParameterizedType) type).getActualTypeArguments()[0]).getRawType()))) {
          return new ObjectConstructor<T>() {
            @Override public T construct() {
              return (T) new LinkedHashMap<Object, Object>();
            }
          };
        } else {
          return new ObjectConstructor<T>() {
            @Override public T construct() {
              return (T) new LinkedTreeMap<String, Object>();
            }
          };
        }
      }
  
      return null;
    }
  
    private <T> ObjectConstructor<T> newUnsafeAllocator(
        final Type type, final Class<? super T> rawType) {
      return new ObjectConstructor<T>() {
        private final UnsafeAllocator unsafeAllocator = UnsafeAllocator.create();
        @SuppressWarnings("unchecked")
        @Override public T construct() {
          try {
            Object newInstance = unsafeAllocator.newInstance(rawType);
            return (T) newInstance;
          } catch (Exception e) {
            throw new RuntimeException(("Unable to invoke no-args constructor for " + type + ". "
                + "Register an InstanceCreator with Gson for this type may fix this problem."), e);
          }
        }
      };
    }
  
    @Override public String toString() {
      return instanceCreators.toString();
    }
  }
  