Jackson：项目结构分析

目录

1、核心modules

2、datatype modules

3、JAX-RS（Java API for RESTful Web Services）支持

4、Data format modules

5、JVM系语言支持

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作为java体系下标准的json函数库，目前默认被应用在spring boot中。jackson是一套用于Java和JVM平台的数据处理工具，包括流式json解析器/生成器函数库、数据绑定函数库（POJO和JSON的互转），以及用以处理Avro,BSON,CBOR,CSV,Smile,(Java)Properties,Protobuf,XML,和YAML编码的数据格式化模块。还有很多的数据格式模块用以支持更广泛的数据类型，诸如Guava，Joda，PCollections中的更多其他的数据类型也是支持转换的。

1、核心modules

实际的核心组件属于他们自己的项目下-包括三个核心程序包（streaming【core】，databind，annotations），数据格式（dataformat）函数库，数据类型（datatype）库，JAX-RS（提供JSON、Smile【binary JSON】、CBOR【another kind of binary JSON】、XML、YAML的自动注册）

核心modules

1. Streaming(jackson-core)：定义了较低级别的流式API，并包含JSON的特定实现
2. Annotations(jackson-annotations)：包含jackson的标准注解
3. Databind(jackson-databind)：在Streaming包上实现了数据绑定和对象序列化，它依赖于以上两个包

2、datatype modules

支持第三方数据类型的modules

这些扩展作为jackson的module的插件（以ObjectMapper.registerModule()的方式），并通过添加序列化器和反序列化器来支持常用java库的数据类型，以便databind包（objectMapper，objectReader，objectWriter）能够对这些类型进行读写。

以下这些数据类型包是由jackson团队进行维护的：

• 标准的集合（ Collections ）数据类型modules:
  • jackson-datatype-eclipse-collections: support for Eclipse Collections (NEW in Jackson 2.10!)
  • jackson-datatype-guava: support for many of Guava datatypes
  • jackson-datatype-hppc: support for High-Performance Primitive Containers containers
  • jackson-datatype-pcollections: support for PCollections datatypes (since Jackson 2.7)
• Hibernate: support for Hibernate features (lazy-loading, proxies)
• Java 8 Modules: support or JDK 8 features and datatypes through 3 separate modules
  • jackson-module-parameter-names: Module that adds support for using a new JDK8 feature, ability to access names of constructor and method parameters, to allow omitting @JsonProperty.
  • jackson-datatype-jsr310: support for "Java 8 Dates" (ones added in JDK 8)
    • Also, for pre-Java8 users can use one of alternate pre-Java8 backports:
      • joschi/jackson-datatype-threetenbp
      • lldata/jackson-datatype-threetenbp
  • jackson-datatype-jdk8: support for JDK 8 data types other than date/time types, including Optional
• Joda datatypes:
  • jackson-datatype-joda: support for types of Joda-Time date/time library datatypes
  • jackson-datatype-joda-money: support types of Joda-Money datatypes (Money, CurrencyUnit)
• jackson-datatype-jsr353: support for JSON-P ("Java JSON API") types (specifically its tree model objects)
• jackson-datatype-json-org: support for org.json library types like JSONObject, JSONArray

此外，jackson团队并未直接维护的modules：

• jackson-datatype-bolts support for reading/writing types defined by Yandex Bolts collection types (Functional Programming inspired immutable collections)
• jackson-datatype-commons-lang3 for types of Apache Commons Lang v3
• jackson-datatype-money for "Java Money", see javax.money
• javaslang-jackson for Javaslang support (Feature-rich & self-contained functional programming in Java™ 8 and above)
• jackson-datatype-json-lib for supporting types defined by "net.sf.json" library (aka "json-lib")
• jackson-datatype-jts (JTS Geometry) for GeoJSON support
• jackson-lombok for better support of Lombok classes
• jackson-datatype-mongo for MongoDB types
  • NOTE: there are a few alternatives to handling MongoDB datatypes
• jackson-module-objectify for datatypes of Objectify
• jackson-datatype-protobuf for handling datatypes defined by the standard Java protobuf library, developed by HubSpot
  • NOTE! This is different from jackson-dataformat-protobuf which adds support for encoding/decoding protobuf content but which does NOT depend on standard Java protobuf library
• TinyTypes includes Jackson module (group id com.github.caligin.tinytypes, artifact tinytypes-jackson)
• jackson-datatype-vertx for reading/writing Vert.x org.vertx.java.core.json.JsonObject objects (repackaged org.json node types)

3、JAX-RS（Java API for RESTful Web Services）支持

Jackson JAX-RS Providers has handlers to add dataformat support for JAX-RS implementations (like Jersey, RESTeasy, CXF). Providers implement MessageBodyReader and MessageBodyWriter. Supported formats currently include JSON, Smile, XML, YAML and CBOR.

4、Data format modules

Data format modules 提供了除json外的其他格式支持。大部分都是简单继承了streaming的api，所以databinding组件可以使用。

• Avro: supports Avro data format, with streaming implementation plus additional databind-level support for Avro Schemas
• CBOR: supports CBOR data format (a binary JSON variant).
• CSV: supports Comma-separated values format -- streaming api, with optional convenience databind additions
• Ion (NEW with Jackson 2.9!): support for Amazon Ion binary data format (similar to CBOR, Smile, i.e. binary JSON - like)
• (Java) Properties (2.8): creating nested structure out of implied notation (dotted by default, configurable), flattening similarly on serialization
• Protobuf (2.6): supported similar to Avro
• Smile: supports Smile (binary JSON) -- 100% API/logical model compatible via streaming API, no changes for databind
• XML: supports XML; provides both streaming and databind implementations. Similar to JAXB' "code-first" mode (no support for "XML Schema first", but can use JAXB beans)
• YAML: supports YAML, which being similar to JSON is fully supported with simple streaming implementation

另外，还有一些由其他人员开发的data format 的modules：

• BEncode: support for reading/writing BEncode (BitTorrent format) encoded data
• bson4jackson: adds support for BSON data format (by Mongo project).
  • Implemented as full streaming implementation, which allows full access (streaming, data-binding, tree-model)
  • Also see [MongoJack] library below; while not a dataformat module, it allows access to BSON data as well.
• EXIficient supports Efficient XML Interchange
• jackson-dataformat-msgpack adds support MessagePack (aka MsgPack) format
  • Implemented as full streaming implementation, which allows full access (streaming, data-binding, tree-model)
• HOCON: experimental, partial implementation to support HOCON format -- work in progress
• Rison: Jackson backend to support Rison)

5、JVM系语言支持

• Kotlin to handle native types of Kotlin
• Scala to handle native Scala types (including but not limited to Scala collection/map types, case classes)
  • Currently (April 2020) Scala 2.10, 2.11, 2.12 and 2.13 are supported (2.9 was supported up to Jackson 2.3)