Java ObjectMapper使用详解
作者：西飘客
ObjectMapper类是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,本文给大家介绍Java ObjectMapper的相关知识,感兴趣的朋友跟随小编一起看看吧
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
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