> For the complete documentation index, see [llms.txt](https://doc.shiker.tech/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://doc.shiker.tech/spring-boot-can-kao-wen-dang/7.-he-xin-te-xing/7.7.-json.md).

# 7.7. JSON

Spring Boot 提供与三个 JSON 映射库的集成：

* gson
* Jackson
* JSON-B

Jackson 是首选的默认库。

#### 7.7.1. Jackson

提供了 Jackson 的自动配置，并且 Jackson 是`spring-boot-starter-json`. 当 Jackson 在类路径上时，`ObjectMapper`会自动配置一个 bean。提供了几个配置属性用于[自定义`ObjectMapper`](https://docs.spring.io/spring-boot/docs/current/reference/html/howto.html#howto.spring-mvc.customize-jackson-objectmapper).

**6.1.1. 自定义序列化器和反序列化器**

如果您使用 Jackson 来序列化和反序列化 JSON 数据，您可能需要编写自己的`JsonSerializer`类和`JsonDeserializer`类。自定义序列化程序通常[通过模块向 Jackson 注册](https://github.com/FasterXML/jackson-docs/wiki/JacksonHowToCustomSerializers)，但 Spring Boot 提供了一个`@JsonComponent`注解，可以更轻松地直接注册 Spring Bean。

您可以直接在`JsonSerializer` `JsonDeserializer` 或`KeyDeserializer`实现上使用`@JsonComponent`注释。您还可以在包含序列化器/反序列化器作为内部类的类上使用它，如以下示例所示：

```
@JsonComponent
public class MyJsonComponent {
​
    public static class Serializer extends JsonSerializer<MyObject> {
​
        @Override
        public void serialize(MyObject value, JsonGenerator jgen, SerializerProvider serializers) throws IOException {
            jgen.writeStartObject();
            jgen.writeStringField("name", value.getName());
            jgen.writeNumberField("age", value.getAge());
            jgen.writeEndObject();
        }
​
    }
​
    public static class Deserializer extends JsonDeserializer<MyObject> {
​
        @Override
        public MyObject deserialize(JsonParser jsonParser, DeserializationContext ctxt) throws IOException {
            ObjectCodec codec = jsonParser.getCodec();
            JsonNode tree = codec.readTree(jsonParser);
            String name = tree.get("name").textValue();
            int age = tree.get("age").intValue();
            return new MyObject(name, age);
        }
​
    }
​
}
```

`ApplicationContext`中的所有`@JsonComponent`bean 都会自动向 Jackson 注册。因为`@JsonComponent`是用元注解的`@Component`，所以通常的组件扫描规则适用。

Spring Boot 还提供了[`JsonObjectSerializer`](https://github.com/spring-projects/spring-boot/tree/v2.7.3/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/jackson/JsonObjectSerializer.java)和[`JsonObjectDeserializer`](https://github.com/spring-projects/spring-boot/tree/v2.7.3/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/jackson/JsonObjectDeserializer.java)基类，它们在序列化对象时提供了标准 Jackson 版本的有用替代方案。有关详细信息，请参阅[`JsonObjectSerializer`](https://docs.spring.io/spring-boot/docs/2.7.3/api/org/springframework/boot/jackson/JsonObjectSerializer.html)和[`JsonObjectDeserializer`](https://docs.spring.io/spring-boot/docs/2.7.3/api/org/springframework/boot/jackson/JsonObjectDeserializer.html)的Javadoc。

上面的例子可以重写为使用`JsonObjectSerializer`/`JsonObjectDeserializer`如下：

```
@JsonComponent
public class MyJsonComponent {
​
    public static class Serializer extends JsonObjectSerializer<MyObject> {
​
        @Override
        protected void serializeObject(MyObject value, JsonGenerator jgen, SerializerProvider provider)
                throws IOException {
            jgen.writeStringField("name", value.getName());
            jgen.writeNumberField("age", value.getAge());
        }
​
    }
​
    public static class Deserializer extends JsonObjectDeserializer<MyObject> {
​
        @Override
        protected MyObject deserializeObject(JsonParser jsonParser, DeserializationContext context, ObjectCodec codec,
                JsonNode tree) throws IOException {
            String name = nullSafeValue(tree.get("name"), String.class);
            int age = nullSafeValue(tree.get("age"), Integer.class);
            return new MyObject(name, age);
        }
​
    }
​
}
```

7.7.**1.2. 混合**

Jackson 支持 mixins，可用于将其他注解混合到已在目标类上声明的注释中。Spring Boot 的 Jackson 自动配置将扫描您应用程序的包以查找带有`@JsonMixin`注解的类，并将它们注册到自动配置的`ObjectMapper`中。通过 Spring Boot 的`JsonMixinModule`注册.

#### 7.7.2. gson

提供了 Gson 的自动配置。当 Gson 在类路径上时，会自动配置一个`Gson` bean。提供了几个`spring.gson.*`配置属性用于自定义配置。要进行更多控制，可以使用一个或多个`GsonBuilderCustomizer` bean。

#### 7.7.3. JSON-B

提供了 JSON-B 的自动配置。当 JSON-B API 和实现在类路径上时，将自动配置一个`Jsonb` bean。首选的 JSON-B 实现是为其提供依赖管理的 Apache Johnzon。


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