简介

ObjectMapper类(com.fasterxml.jackson.databind.ObjectMapper)是Jackson的主要类,它可以帮助我们快速的进行各个类型和Json类型的相互转换。

使用

1、引入Jackson的依赖
<!-- 根据自己需要引入相关版本依赖。 --> <dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-core</artifactId> <version>2.9.10</version> </dependency>
<dependency> <groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId> <version>2.9.10</version>
</dependency> <dependency> <groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-annotations</artifactId> <version>2.9.10</version>
</dependency>
2、ObjectMapper的常用配置
private static final ObjectMapper mapper; public static ObjectMapper
getObjectMapper(){ return this.mapper; } static{ //创建ObjectMapper对象 mapper =
new ObjectMapper() //configure方法 配置一些需要的参数 // 转换为格式化的json 显示出来的格式美化
mapper.enable(SerializationFeature.INDENT_OUTPUT); //序列化的时候序列对象的那些属性
//JsonInclude.Include.NON_DEFAULT 属性为默认值不序列化 //JsonInclude.Include.ALWAYS 所有属性
//JsonInclude.Include.NON_EMPTY 属性为 空(“”) 或者为 NULL 都不序列化
//JsonInclude.Include.NON_NULL 属性为NULL 不序列化
mapper.setSerializationInclusion(JsonInclude.Include.ALWAYS);
//反序列化时,遇到未知属性会不会报错 //true - 遇到没有的属性就报错 false - 没有的属性不会管,不会报错
mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
//如果是空对象的时候,不抛异常 mapper.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS,
false); // 忽略 transient 修饰的属性
mapper.configure(MapperFeature.PROPAGATE_TRANSIENT_MARKER, true); //修改序列化后日期格式
mapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
mapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"));
//处理不同的时区偏移格式 mapper.disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS);
mapper.registerModule(new JavaTimeModule()); }
3、ObjectMapper的常用方法

a.json字符串转对象
ObjectMapper mapper = new ObjectMapper(); String jsonString =
"{\"name\":\"Hyl\", \"age\":20}"; //将字符串转换为对象 Student student =
mapper.readValue(jsonString, Student.class); System.out.println(student);
//将对象转换为json字符串 jsonString = mapper.writeValueAsString(student);
System.out.println(jsonString); 结果: Student [ name: Hyl, age: 20 ] { "name" :
"Hyl", "age" : 20 }
b. 数组和对象之间转换
//对象转为byte数组 byte[] byteArr = mapper.writeValueAsBytes(student);
System.out.println(byteArr); //byte数组转为对象 Student student=
mapper.readValue(byteArr, Student.class); System.out.println(student); 结果:
[B@3327bd23 Student [ name: Hyl, age: 20 ]
c. 集合和json字符串之间转换
List<Student> studentList= new ArrayList<>(); studentList.add(new
Student("hyl1" ,20 , new Date())); studentList.add(new Student("hyl2" ,21 , new
Date())); studentList.add(new Student("hyl3" ,22 , new Date()));
studentList.add(new Student("hyl4" ,23 , new Date())); String jsonStr =
mapper.writeValueAsString(studentList); System.out.println(jsonStr);
List<Student> studentList2 = mapper.readValue(jsonStr, List.class);
System.out.println("字符串转集合:" + studentList2 ); 结果: [ { "name" : "hyl1", "age" :
20, "sendTime" : 1525164212803 }, { "name" : "hyl2", "age" : 21, "sendTime" :
1525164212803 }, { "name" : "hyl3", "age" : 22, "sendTime" : 1525164212803 }, {
"name" : "hyl4", "age" : 23, "sendTime" : 1525164212803 } ] [{name=hyl1,
age=20, sendTime=1525164212803}, {name=hyl2, age=21, sendTime=1525164212803},
{name=hyl3, age=22, sendTime=1525164212803}, {name=hyl4, age=23,
sendTime=1525164212803}]
d. map和json字符串之间转换
Map<String, Object> testMap = new HashMap<>(); testMap.put("name", "22");
testMap.put("age", 20); testMap.put("date", new Date()); testMap.put("student",
new Student("hyl", 20, new Date())); String jsonStr =
mapper.writeValueAsString(testMap); System.out.println(jsonStr); Map<String,
Object> testMapDes = mapper.readValue(jsonStr, Map.class);
System.out.println(testMapDes); 结果: { "date" : 1525164212803, "name" : "22",
"student" : { "name" : "hyl", "age" : 20, "sendTime" : 1525164212803, "intList"
: null }, "age" : 20 } {date=1525164212803, name=22, student={name=hyl, age=20,
sendTime=1525164212803, intList=null}, age=20}
e. 日期转json字符串
// 修改时间格式 mapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"));
Student student = new Student ("hyl",21, new Date());
student.setIntList(Arrays.asList(1, 2, 3)); String jsonStr =
mapper.writeValueAsString(student); System.out.println(jsonStr); 结果: { "name" :
"hyl", "age" : 21, "sendTime" : "2020-07-23 13:14:36", "intList" : [ 1, 2, 3 ] }
js中将字符串转换为json对象
var data = "{\"name\":\"Hyl\", \"age\":20}"; var student = eval(data);
console.info(student.name); console.info(student.age); 结果: Hyl 20
 

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