java jackson maven,jackson中objectMapper的使用

Jackson可以轻松的将Java对象转换成json对象和xml文档，同样也可以将json、xml转换成Java对象

ObjectMapper类是Jackson库的主要类。它称为ObjectMapper的原因是因为它将JSON映射到Java对象(反序列化)，或将Java对象映射到JSON(序列化)。它使用JsonParser和JsonGenerator的实例实现JSON实际的读/写。

maven 安装

com.fasterxml.jackson.core

jackson-core

2.9.6

com.fasterxml.jackson.core

jackson-annotations

2.9.6

com.fasterxml.jackson.core

jackson-databind

2.9.6

Jackson ObjectMapper如何将JSON字段与Java字段匹配

三种方式

1.Jackson通过将JSON字段的名称与Java对象中的getter和setter方法相匹配，将JSON对象的字段映射到Java对象中的字段。Jackson删除了getter和setter方法名称的“get”和“set”部分，并将剩余名称的第一个字符转换为小写。

2.Jackson还可以通过java反射进行匹配

3.通过注解或者其它方式进行自定义的序列化和反序列化程序。

转Java对象

Read Object From JSON String

ObjectMapper objectMapper = new ObjectMapper();

String carJson = "{ \"brand\" : \"Mercedes\", \"doors\" : 5 }";

Car car = objectMapper.readValue(carJson, Car.class);

2.Read Object From JSON Reader

ObjectMapper objectMapper = new ObjectMapper();

String carJson = "{ \"brand\" : \"Mercedes\", \"doors\" : 4 }";

Reader reader = new StringReader(carJson);

Car car = objectMapper.readValue(reader, Car.class);

3.Read Object From JSON File

ObjectMapper objectMapper = new ObjectMapper();

File file = new File("data/car.json");

Car car = objectMapper.readValue(file, Car.class);

Read Object From JSON via URL

ObjectMapper objectMapper = new ObjectMapper();

URL url = new URL("file:data/car.json");

Car car = objectMapper.readValue(url, Car.class);

本例使用的是文件URL，也可使用一个HTTP URL(如：http://jenkov.com/some-data.json ).

Read Object From JSON InputStream

ObjectMapper objectMapper = new ObjectMapper();

InputStream input = new FileInputStream("data/car.json");

Car car = objectMapper.readValue(input, Car.class);

6.Read Object From JSON Byte Array