Jackson ObjectMapper 使用教程

本文主要是介绍Jackson ObjectMapper 使用教程，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

添加 依赖

gradle

    implementation("com.fasterxml.jackson.dataformat:jackson-dataformat-xml")

maven

    <dependency><groupId>com.fasterxml.jackson.dataformat</groupId><artifactId>jackson-dataformat-xml</artifactId><version>2.8.2</version></dependency>

配置 ObjectMapper

    /*** Jackson config* @return 自定义 {@link com.fasterxml.jackson.databind.ObjectMapper} 配置*/@Beanpublic Jackson2ObjectMapperBuilderCustomizer objectMapperBuilderCustomizer() {return builder -> {// 序列化时字段值为 null 时不输出builder.serializationInclusion(JsonInclude.Include.NON_NULL);// 序列化时按照字幕顺序输出(降低点性能,但是关键时刻方便进行字段对比)builder.featuresToEnable(MapperFeature.SORT_PROPERTIES_ALPHABETICALLY);// 有不匹配的字段是否抛出异常builder.featuresToDisable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);// 接受单个字符的值反序列化为数组。builder.featuresToEnable(DeserializationFeature.ACCEPT_SINGLE_VALUE_AS_ARRAY);// 配置 时间序列化builder.serializerByType(LocalDateTime.class, new LocalDateTimeSerializer(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss")));builder.serializerByType(LocalDate.class, new LocalDateSerializer(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss")));builder.serializerByType(LocalTime.class, new LocalTimeSerializer(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss")));builder.serializerByType(Date.class, new DateSerializer(false, new SimpleDateFormat("yyyy-MM-dd HH:mm:ss")));builder.deserializerByType(LocalDateTime.class, new LocalDateTimeDeserializer(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss")));builder.deserializerByType(LocalDate.class, new LocalDateDeserializer(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss")));builder.deserializerByType(LocalTime.class, new LocalTimeDeserializer(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss")));builder.deserializerByType(Date.class, new DateDeserializers.DateDeserializer(DateDeserializers.DateDeserializer.instance, new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"), "yyyy-MM-dd HH:mm:ss"));};}

Jackson 的注解使用

序列化生效 实体转为json
反序列化生效 json转为实体类

序列化生效@JsonProperty("名字key")
public String name;   //{"名字key":"张三"}@JsonFormat(shape = JsonFormat.Shape.STRING, pattern = "yyyy/MM/dd HH:mm:ss", locale = "zh", timezone = "GMT+8")
private Date profileCreateTime;  //{"profileCreateTime":"2018/12/7 12:30:00"}反序列化生效@JsonInclude(JsonInclude.Include.NON_EMPTY)
public static class aBean {}
// 放在类名上面 则对此类全部属性起作用 序列化或往页面传值时起作用
JsonInclude.Include.ALWAYS 默认不生效					序列化
JsonInclude.Include.NON_NULL 属性为NULL				不序列化
JsonInclude.Include.NON_ABSENT 属性为空字符串			不序列化
JsonInclude.Include.NON_EMPTY 属性为空字符串 或 NULL	不序列化
JsonInclude.Include.NON_DEFAULT 属性为默认值时			不序列化
JsonInclude.Include.CUSTOM 指定自定义筛选器			不序列化
JsonInclude.Include.USE_DEFAULTS 使用类或对象的默认值	序列化//自定义 序列化  处理 
@JsonSerialize(using = Data2LongSerizlizer.class )
public class Data2LongSerizlizer extends JsonSerializer<Date> {
@Override
/** 该类可以将日期13位时间戳转换成10位时间戳的long类型 */
}//反序列化期间接受的属性定义一个或多个替代名称, 序列化时候还是取 userName
@JsonAlias({"aName", "bName"})
private String userName;

ObjectMapper 的简单使用

@Resource
private ObjectMapper objectMapper;Person person = new Person();

entity 转 string json 如果有@JsonSerialize("") ,key 就取的是这个的值

```java
String personString =objectMapper.writeValueAsString(person));

string json [{“a”:2},{“a”:4}] 转 list

List<Person> plist = objectMapper.readValue(personString , new TypeReference<List<.Person>>(){});

string json {“a”:2} 转 entity

Person  p= objectMapper.readValue(personString , Person.class);

string json {“a”:2} 转 Map

TypeReference<HashMap<String, Object>> typeRef = new TypeReference<HashMap<String, Object>>() {};
HashMap<String, Object> o = objectMapper.readValue(value, typeRef);

更新对象的值 将personString 值 覆盖部分有的属性. entity

ObjectReader objectReader = objectMapper.readerForUpdating(person);
Person updatedPerson = objectReader.readValue(personString);

entity 转 jsonObject 如果有@JsonSerialize("") ,key 就取的是这个的值

objectMapper.convertValue(personString, JSONObject.class);

string json 转 person Node

JsonNode actualObj = objectMapper.readTree(personString);

@JsonRawValue 防止添加多余的内容\r\n 转换成原始对象

in
{ "name" : "Mark", "rollNo" : 1, "json" : {\"attr\":false} 
} @JsonRawValue  private String json;out
{ "name" : "Mark", "rollNo" : 1, "json" : {"attr":false} 
}

例子 ,数据库存的 jons 字符串 页面想返回 对象

//因为全局 配置 ,所以要先判断下是否为 字符串
public class StringSerializer extends JsonSerializer<String> {@Resourceprivate ObjectMapper objectMapper;@Overridepublic void serialize(String value, JsonGenerator gen, SerializerProvider serializers) throws IOException {boolean flag = false;if (StringUtils.isNotBlank(value)) {value = value.trim();if (value.startsWith("{") && value.endsWith("}")) {flag = true;}if (value.startsWith("[") && value.endsWith("]")) {flag = true;}if (value.startsWith("[{") && value.endsWith("}]")) {flag = true;}}if (flag) {try {objectMapper.readTree(value);flag = true;} catch (Exception e) {flag = false;}if (flag) {TypeReference<HashMap<String, Object>> typeRef = new TypeReference<HashMap<String, Object>>() {};HashMap<String, Object> o = objectMapper.readValue(value, typeRef);gen.writeObject(o);}}gen.writeString(value);}
}

全局配置

	@Beanpublic MappingJackson2HttpMessageConverter mappingJackson2HttpMessageConverter() {MappingJackson2HttpMessageConverter jsonConverter = new MappingJackson2HttpMessageConverter();objectMapper.configure(DeserializationFeature.USE_JAVA_ARRAY_FOR_JSON_ARRAY, true);objectMapper.configure(JsonParser.Feature.ALLOW_UNQUOTED_CONTROL_CHARS, true);objectMapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd"));SimpleModule simpleModule = new SimpleModule();
//		simpleModule.addDeserializer(String.class, new StringDeserializer());simpleModule.addSerializer(String.class, new StringSerializer());objectMapper.registerModule(simpleModule);jsonConverter.setObjectMapper(objectMapper);return jsonConverter;}

复杂对象json 转换 (泛型)

例子 jsonSting  to  ObjectEntityjson = "{"code": 0,"msg": null,"obj": {"current": 1,"hitCount": false,"optimizeCountSql": true,"orders": [],"pages": 1,"records": [{"address": "海南省三亚市海棠区","deviceId": "8880139","deviceName": "海南省三亚市海棠区微心测试","hospitalId": 12,"hospitalName": "测试专用医院","id": 896,"lat": 18.34801783549779,"lng": 109.71318002841308,"status": 1,"updateTime": 1602228247000},{"address": "北站","deviceId": "80801108","deviceName": "测试设备1","hospitalId": 12,"hospitalName": "测试专用医院","id": 895,"lat": 30.21715956845446,"lng": 115.01468563671428,"status": 1,"updateTime": 1601374004000}],"searchCount": true,"size": 500,"total": 11}}";JavaType javaType1 = objectMapper.getTypeFactory().constructParametricType(Page.class, DeviceEntity.class);JavaType javaTyp = objectMapper.getTypeFactory().constructParametricType(JsonResult.class,javaType1);TypeReference<JsonResult<Page<DeviceEntity>>> typeReference = new TypeReference<JsonResult<Page<DeviceEntity>>>() {};//通过 javaType 转换JsonResult<Page<DeviceEntity>> page1 = objectMapper.readValue(json,javaTyp);// 通过 TypeReference 来转换JsonResult<Page<DeviceEntity>> page2 = objectMapper.readValue(json,typeReference);public class JsonResult<T> implements Serializable {private static final long serialVersionUID = 7982365785632121536L;private int code;private T obj;private String msg;}public class Page<T> implements IPage<T> {private static final long serialVersionUID = 8545996863226528798L;/*** 查询数据列表*/private List<T> records = Collections.emptyList();/*** 总数*/private long total = 0;/*** 每页显示条数，默认 10*/private long size = 10;/*** 当前页*/private long current = 1;/*** 排序字段信息*/private List<OrderItem> orders = new ArrayList<>();/*** 自动优化 COUNT SQL*/private boolean optimizeCountSql = true;/*** 是否进行 count 查询*/private boolean isSearchCount = true;}@Datapublic class DeviceEntity implements Serializable {@ApiModelProperty(value = "ID")@JsonProperty("id")Integer id;@ApiModelProperty(value = "设备ID")@JsonProperty("deviceId")String deviceId;@ApiModelProperty(value = "设备名称")@JsonProperty("deviceName")String deviceName;@ApiModelProperty(value = "设备地址")@JsonProperty("address")String address;@ApiModelProperty(value = "设备管理员名称")@JsonProperty("manager")String manager;@ApiModelProperty(value = "设备管理员电话")@JsonProperty("phone")String phone;@ApiModelProperty(value = "所属医院Id")@JsonProperty("hospitalId")Integer hospitalId;@ApiModelProperty(value = "所属医院名称")@JsonProperty("hospitalName")String hospitalName;@ApiModelProperty(value = "是否有效")@JsonProperty("status")Integer status;@ApiModelProperty(value = "新增或更新时间")@JsonProperty("updateTime")Date updateTime;@ApiModelProperty(value = "纬度值")@JsonProperty("lat")Double lat;@ApiModelProperty(value = "经度值")@JsonProperty("lng")Double lng;}

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