JsonDeserializerExceptionWrapper.java

/*
 * 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,
 * 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.smartandroid.sa.json;

import java.lang.reflect.Type;

import com.smartandroid.sa.json.internal.$Gson$Preconditions;

/**
 * Decorators a {@code JsonDeserializer} instance with exception handling. This
 * wrapper class ensures that a {@code JsonDeserializer} will not propagate any
 * exception other than a {@link JsonParseException}.
 * 
 * @param <T>
 *            type of the deserializer being wrapped.
 * 
 * @author Inderjeet Singh
 * @author Joel Leitch
 */
final class JsonDeserializerExceptionWrapper<T> implements JsonDeserializer<T> {

	private final JsonDeserializer<T> delegate;

	/**
	 * Returns a wrapped {@link JsonDeserializer} object that has been decorated
	 * with {@link JsonParseException} handling.
	 * 
	 * @param delegate
	 *            the {@code JsonDeserializer} instance to be wrapped.
	 * @throws IllegalArgumentException
	 *             if {@code delegate} is {@code null}.
	 */
	JsonDeserializerExceptionWrapper(JsonDeserializer<T> delegate) {
		this.delegate = $Gson$Preconditions.checkNotNull(delegate);
	}

	public T deserialize(JsonElement json, Type typeOfT,
			JsonDeserializationContext context) throws JsonParseException {
		try {
			return delegate.deserialize(json, typeOfT, context);
		} catch (JsonParseException e) {
			// just rethrow the exception
			throw e;
		} catch (Exception e) {
			// rethrow as a JsonParseException
			StringBuilder errorMsg = new StringBuilder()
					.append("The JsonDeserializer ").append(delegate)
					.append(" failed to deserialize json object ").append(json)
					.append(" given the type ").append(typeOfT);
			throw new JsonParseException(errorMsg.toString(), e);
		}
	}

	@Override
	public String toString() {
		return delegate.toString();
	}
}