001/* 002 * Copyright 2002-2020 the original author or authors. 003 * 004 * Licensed under the Apache License, Version 2.0 (the "License"); 005 * you may not use this file except in compliance with the License. 006 * You may obtain a copy of the License at 007 * 008 * https://www.apache.org/licenses/LICENSE-2.0 009 * 010 * Unless required by applicable law or agreed to in writing, software 011 * distributed under the License is distributed on an "AS IS" BASIS, 012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 013 * See the License for the specific language governing permissions and 014 * limitations under the License. 015 */ 016 017package org.springframework.http.converter.json; 018 019import java.io.Reader; 020import java.io.Writer; 021import java.lang.reflect.ParameterizedType; 022import java.lang.reflect.Type; 023 024import com.google.gson.Gson; 025 026import org.springframework.lang.Nullable; 027import org.springframework.util.Assert; 028 029/** 030 * Implementation of {@link org.springframework.http.converter.HttpMessageConverter} 031 * that can read and write JSON using the 032 * <a href="https://code.google.com/p/google-gson/">Google Gson</a> library. 033 * 034 * <p>This converter can be used to bind to typed beans or untyped {@code HashMap}s. 035 * By default, it supports {@code application/json} and {@code application/*+json} with 036 * {@code UTF-8} character set. 037 * 038 * <p>Tested against Gson 2.8; compatible with Gson 2.0 and higher. 039 * 040 * @author Roy Clarkson 041 * @author Juergen Hoeller 042 * @since 4.1 043 * @see com.google.gson.Gson 044 * @see com.google.gson.GsonBuilder 045 * @see #setGson 046 */ 047public class GsonHttpMessageConverter extends AbstractJsonHttpMessageConverter { 048 049 private Gson gson; 050 051 052 /** 053 * Construct a new {@code GsonHttpMessageConverter} with default configuration. 054 */ 055 public GsonHttpMessageConverter() { 056 this.gson = new Gson(); 057 } 058 059 /** 060 * Construct a new {@code GsonHttpMessageConverter} with the given delegate. 061 * @param gson the Gson instance to use 062 * @since 5.0 063 */ 064 public GsonHttpMessageConverter(Gson gson) { 065 Assert.notNull(gson, "A Gson instance is required"); 066 this.gson = gson; 067 } 068 069 070 /** 071 * Set the {@code Gson} instance to use. 072 * If not set, a default {@link Gson#Gson() Gson} instance will be used. 073 * <p>Setting a custom-configured {@code Gson} is one way to take further 074 * control of the JSON serialization process. 075 * @see #GsonHttpMessageConverter(Gson) 076 */ 077 public void setGson(Gson gson) { 078 Assert.notNull(gson, "A Gson instance is required"); 079 this.gson = gson; 080 } 081 082 /** 083 * Return the configured {@code Gson} instance for this converter. 084 */ 085 public Gson getGson() { 086 return this.gson; 087 } 088 089 090 @Override 091 protected Object readInternal(Type resolvedType, Reader reader) throws Exception { 092 return getGson().fromJson(reader, resolvedType); 093 } 094 095 @Override 096 protected void writeInternal(Object object, @Nullable Type type, Writer writer) throws Exception { 097 // In Gson, toJson with a type argument will exclusively use that given type, 098 // ignoring the actual type of the object... which might be more specific, 099 // e.g. a subclass of the specified type which includes additional fields. 100 // As a consequence, we're only passing in parameterized type declarations 101 // which might contain extra generics that the object instance doesn't retain. 102 if (type instanceof ParameterizedType) { 103 getGson().toJson(object, type, writer); 104 } 105 else { 106 getGson().toJson(object, writer); 107 } 108 } 109 110}