整體架構

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核心在于TypeAdapter，它定義了類型和字節(jié)之間的相互轉(zhuǎn)換

TypeAdapter

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public abstract class TypeAdapter<T> {

  public abstract void write(JsonWriter out, T value) throws IOException;

  public abstract T read(JsonReader in) throws IOException;

  ...
}

看Json代碼示例

{
            "test1": "wx9fdb8ble7ce3c68f",
            "test2": 123456789,
            "testData1": {   
                "testdatason1": "97895455"
                "testdatason2":3,
             }
}

解析Json睬澡，當解析到value的時候固额，會去獲取對應的TypeAdapter，具體是到一個List<TypeAdapter>按序匹配煞聪，如果沒有名字斗躏，采用反射

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  Gson(final Excluder excluder, final FieldNamingStrategy fieldNamingStrategy,
      final Map<Type, InstanceCreator<?>> instanceCreators, boolean serializeNulls,
      boolean complexMapKeySerialization, boolean generateNonExecutableGson, boolean htmlSafe,
      boolean prettyPrinting, boolean lenient, boolean serializeSpecialFloatingPointValues,
      LongSerializationPolicy longSerializationPolicy, String datePattern, int dateStyle,
      int timeStyle, List<TypeAdapterFactory> builderFactories,
      List<TypeAdapterFactory> builderHierarchyFactories,
      List<TypeAdapterFactory> factoriesToBeAdded) {
    ...
    ...
    ...

    List<TypeAdapterFactory> factories = new ArrayList<TypeAdapterFactory>();

    // built-in type adapters that cannot be overridden
    factories.add(TypeAdapters.JSON_ELEMENT_FACTORY);
    factories.add(ObjectTypeAdapter.FACTORY);

    // the excluder must precede all adapters that handle user-defined types
    factories.add(excluder);

    // users type adapters
    factories.addAll(factoriesToBeAdded);

    // type adapters for basic platform types
    factories.add(TypeAdapters.STRING_FACTORY);
    factories.add(TypeAdapters.INTEGER_FACTORY);
    factories.add(TypeAdapters.BOOLEAN_FACTORY);
    factories.add(TypeAdapters.BYTE_FACTORY);
    factories.add(TypeAdapters.SHORT_FACTORY);
    TypeAdapter<Number> longAdapter = longAdapter(longSerializationPolicy);
    factories.add(TypeAdapters.newFactory(long.class, Long.class, longAdapter));
    factories.add(TypeAdapters.newFactory(double.class, Double.class,
            doubleAdapter(serializeSpecialFloatingPointValues)));
    factories.add(TypeAdapters.newFactory(float.class, Float.class,
            floatAdapter(serializeSpecialFloatingPointValues)));
    factories.add(TypeAdapters.NUMBER_FACTORY);
    factories.add(TypeAdapters.ATOMIC_INTEGER_FACTORY);
    factories.add(TypeAdapters.ATOMIC_BOOLEAN_FACTORY);
    factories.add(TypeAdapters.newFactory(AtomicLong.class, atomicLongAdapter(longAdapter)));
    factories.add(TypeAdapters.newFactory(AtomicLongArray.class, atomicLongArrayAdapter(longAdapter)));
    factories.add(TypeAdapters.ATOMIC_INTEGER_ARRAY_FACTORY);
    factories.add(TypeAdapters.CHARACTER_FACTORY);
    factories.add(TypeAdapters.STRING_BUILDER_FACTORY);
    factories.add(TypeAdapters.STRING_BUFFER_FACTORY);
    factories.add(TypeAdapters.newFactory(BigDecimal.class, TypeAdapters.BIG_DECIMAL));
    factories.add(TypeAdapters.newFactory(BigInteger.class, TypeAdapters.BIG_INTEGER));
    factories.add(TypeAdapters.URL_FACTORY);
    factories.add(TypeAdapters.URI_FACTORY);
    factories.add(TypeAdapters.UUID_FACTORY);
    factories.add(TypeAdapters.CURRENCY_FACTORY);
    factories.add(TypeAdapters.LOCALE_FACTORY);
    factories.add(TypeAdapters.INET_ADDRESS_FACTORY);
    factories.add(TypeAdapters.BIT_SET_FACTORY);
    factories.add(DateTypeAdapter.FACTORY);
    factories.add(TypeAdapters.CALENDAR_FACTORY);
    factories.add(TimeTypeAdapter.FACTORY);
    factories.add(SqlDateTypeAdapter.FACTORY);
    factories.add(TypeAdapters.TIMESTAMP_FACTORY);
    factories.add(ArrayTypeAdapter.FACTORY);
    factories.add(TypeAdapters.CLASS_FACTORY);

    // type adapters for composite and user-defined types
    factories.add(new CollectionTypeAdapterFactory(constructorConstructor));
    factories.add(new MapTypeAdapterFactory(constructorConstructor, complexMapKeySerialization));
    this.jsonAdapterFactory = new JsonAdapterAnnotationTypeAdapterFactory(constructorConstructor);
    factories.add(jsonAdapterFactory);
    factories.add(TypeAdapters.ENUM_FACTORY);
    // 注意，ReflectiveTypeAdapterFactor是要最后添加的
    factories.add(new ReflectiveTypeAdapterFactory(
        constructorConstructor, fieldNamingStrategy, excluder, jsonAdapterFactory));

    this.factories = Collections.unmodifiableList(factories);
  }

對于自定義對象其實就是通過ReflectiveTypeAdapterFactory來做的
內(nèi)部其實還是調(diào)用的基本數(shù)據(jù)類型TypeAdapter

總結

1米绕、整體分為2部分瑟捣，一個是TypeAdapter，定義寫入寫出栅干；一個是容器，用于存放JSON
2捐祠、對于自定義對象解析碱鳞，需要反射獲取對象字段，然后挑選具體的TypeAdapter
3踱蛀、對于自定義對象循環(huán)嵌套的情況窿给，使用FutureTypeAdapter，單個對象只需解析一次
4率拒、對于多線程情況崩泡，用ThreadLocal支持

后記

有什么寫得錯誤、讓人費解或遺漏的地方猬膨，希望可以不吝賜教角撞，我會馬上更改

學習自

https://mp.weixin.qq.com/s/j-klYVIjJxeWWIGfdeBsEw
https://blog.csdn.net/chunqiuwei/article/details/49401733