/*
 * Copyright 2002-2018 the original author or authors.
 *
 * 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 org.springframework.http.converter.json;

import java.io.Reader;
import java.io.Writer;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;

import com.google.gson.Gson;

import org.springframework.lang.Nullable;
import org.springframework.util.Assert;

Implementation of HttpMessageConverter that can read and write JSON using the Google Gson library.
This converter can be used to bind to typed beans or untyped HashMaps. By default, it supports application/json and application/*+json with UTF-8 character set. 
Tested against Gson 2.8; compatible with Gson 2.0 and higher.
Author:
Roy Clarkson, Juergen Hoeller
See Also:
Gson
GsonBuilder
setGson
Since:
4.1/**
 * Implementation of {@link org.springframework.http.converter.HttpMessageConverter}
 * that can read and write JSON using the
 * <a href="https://code.google.com/p/google-gson/">Google Gson</a> library.
 *
 * <p>This converter can be used to bind to typed beans or untyped {@code HashMap}s.
 * By default, it supports {@code application/json} and {@code application/*+json} with
 * {@code UTF-8} character set.
 *
 * <p>Tested against Gson 2.8; compatible with Gson 2.0 and higher.
 *
 * @author Roy Clarkson
 * @author Juergen Hoeller
 * @since 4.1
 * @see com.google.gson.Gson
 * @see com.google.gson.GsonBuilder
 * @see #setGson
 */
public class GsonHttpMessageConverter extends AbstractJsonHttpMessageConverter {

	private Gson gson;


	
Construct a new GsonHttpMessageConverter with default configuration. /**
	 * Construct a new {@code GsonHttpMessageConverter} with default configuration.
	 */
	public GsonHttpMessageConverter() {
		this.gson = new Gson();
	}

	
Construct a new GsonHttpMessageConverter with the given delegate. 
Params:
gson – the Gson instance to use
Since:
5.0/**
	 * Construct a new {@code GsonHttpMessageConverter} with the given delegate.
	 * @param gson the Gson instance to use
	 * @since 5.0
	 */
	public GsonHttpMessageConverter(Gson gson) {
		Assert.notNull(gson, "A Gson instance is required");
		this.gson = gson;
	}


	
Set the Gson instance to use. If not set, a default Gson instance will be used. 
Setting a custom-configured Gson is one way to take further control of the JSON serialization process. 
See Also:
GsonHttpMessageConverter(Gson)/**
	 * Set the {@code Gson} instance to use.
	 * If not set, a default {@link Gson#Gson() Gson} instance will be used.
	 * <p>Setting a custom-configured {@code Gson} is one way to take further
	 * control of the JSON serialization process.
	 * @see #GsonHttpMessageConverter(Gson)
	 */
	public void setGson(Gson gson) {
		Assert.notNull(gson, "A Gson instance is required");
		this.gson = gson;
	}

	
Return the configured Gson instance for this converter. /**
	 * Return the configured {@code Gson} instance for this converter.
	 */
	public Gson getGson() {
		return this.gson;
	}


	@Override
	protected Object readInternal(Type resolvedType, Reader reader) throws Exception {
		return getGson().fromJson(reader, resolvedType);
	}

	@Override
	protected void writeInternal(Object o, @Nullable Type type, Writer writer) throws Exception {
		// In Gson, toJson with a type argument will exclusively use that given type,
		// ignoring the actual type of the object... which might be more specific,
		// e.g. a subclass of the specified type which includes additional fields.
		// As a consequence, we're only passing in parameterized type declarations
		// which might contain extra generics that the object instance doesn't retain.
		if (type instanceof ParameterizedType) {
			getGson().toJson(o, type, writer);
		}
		else {
			getGson().toJson(o, writer);
		}
	}

}