Jackson 介绍

Jackson框架是基于Java平台的一套数据处理工具，被称为“最好的Java Json解析器”。

Jackson框架包含了3个核心库：streaming,databind,annotations.Jackson还包含了其它数据处理类库，此外不作说明。

Jackson版本： 1.x (目前版本从1.1~1.9)与2.x。1.x与2.x从包的命名上可以看出来，1.x的类库中，包命名以：org.codehaus.jackson.xxx开头，而2.x类库中包命令：com.fastxml.jackson.xxx开头

jackson核心类说明

JsonGenerator：定义了写JSON内容的公共api基类，实例使用工厂方法创建；

JsonFactory：jackson包最主要的工厂类，主要被用于配置和构建reader(JsonParser)和writer(JsonGenerator)；

ObjectMapper：ObjectMapper提供读写JSON、POJOs对象序列化成JSON和反序列化、JSON树模型；ObjectMapper是json序列化与反序列化的核心，可以在ObjectMapper配置许多属性。

ConfigFeature——配置类接口

MapperFeature——Enumeration that defines simple on/off features to set for {@link ObjectMapper}

DeserializationFeature——Enumeration that defines simple on/off features that affect the way Java objects are deserialized from JSON

SerializationFeature——Enumeration that defines simple on/off features that affect the way Java objects are serialized

maven引入jackson包

com.fasterxml.jackson.core

jackson-core

2.8.5

com.fasterxml.jackson.core

jackson-annotations

2.8.5

com.fasterxml.jackson.core

jackson-databind

2.8.5

POJOs序列化为JSON以及JSON反序列化成POJOs

POJOs (Plain Old Java Objects)

public static class MyClass {

private String name;

private String passwd;

private String address;

public String getName() {

return name;

}

public void setName(String name) {

this.name = name;

}

public String getPasswd() {

return passwd;

}

public void setPasswd(String passwd) {

this.passwd = passwd;

}

public String getAddress() {

return address;

}

public void setAddress(String address) {

this.address = address;

}

@Override

public String toString() {

return "MyClass{" +

"name='" + name + '\'' +

", passwd='" + passwd + '\'' +

", address='" + address + '\'' +

'}';

}

}

jackson序列化以及反序列化

@Test

public void test() throws IOException {

ObjectMapper mapper = new ObjectMapper();

MyClass myClass = new MyClass();

myClass.setName("daidai");

myClass.setPasswd("123456");

myClass.setAddress("beijing");

File newFile = new File("my-class.json");

System.out.println(mapper.canSerialize(Timestamp.class));

System.out.println(mapper.canDeserialize(JsonUtil.constructParametricType(List.class, MyClass.class)));

// json序列化

// 序列化到文件

mapper.writeValue(newFile, myClass);

// 序列化成字符串

String json = mapper.writeValueAsString(myClass);

System.out.println(json);

// json反序列化

// 从文件反序列化

MyClass older = mapper.readValue(new File("my-class.json"), MyClass.class);

System.out.println(older);

// 从json串反序列化

MyClass older2 = mapper.readValue(json, MyClass.class);

System.out.println(older2);

// json Tree解析

JsonNode root = mapper.readTree(newFile);

System.out.println(root.at("/passwd"));

System.out.println(root.at("/name"));

System.out.println(root.at("/address"));

}