@JsonSerialize的使用講解
解決前端顯示和后臺存儲數據單位不一致的問題。
在返回對象時，進行自定義數據格式轉換。
1.寫一個類繼承JsonSerializer 抽象類
實現其serialize()方法，然后在方法中寫入轉換規則即可
舉例是把Date時間戳從 毫秒 轉換成 秒 為單位
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.SerializerProvider;
import java.io.IOException;
import java.util.Date;
/**
* @program: sell
* @description: 時間轉換Json序列化工具
* @author: Liang Shan
* @create: 2019-08-06 16:58
**/
public class Date2LongSerializer extends JsonSerializer<Date> {
@Override
public void serialize(Date date, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException {
jsonGenerator.writeNumber(date.getTime() / 1000);
}
}
2.然后在傳輸的實體類中的屬性上
打上@JsonSerialize注解即可
import com.fasterxml.jackson.databind.annotation.JsonSerialize;
import com.ls.sell.enums.OrderStatusEnum;
import com.ls.sell.enums.PayStatusEnum;
import com.ls.sell.util.serializer.Date2LongSerializer;
import lombok.Data;
import org.hibernate.annotations.DynamicUpdate;
import javax.persistence.Entity;
import javax.persistence.Id;
import java.math.BigDecimal;
import java.util.Date;
/**
* @program: sell
* @description: 訂單主表
* @author: Liang Shan
* @create: 2019-07-24 09:44
**/
@Entity
@Data
@DynamicUpdate
public class OrderMaster {
@Id
private String orderId;
private String buyerName;
private String buyerPhone;
private String buyerAddress;
private String buyerOpenid;
private BigDecimal orderAmount;
/** 訂單狀態，默認為新下單. */
private Integer orderStatus = OrderStatusEnum.NEW.getCode();
/** 支付狀態，默認為0未支付. */
private Integer payStatus = PayStatusEnum.WAIT.getCode();
@JsonSerialize(using = Date2LongSerializer.class)
private Date createTime;
@JsonSerialize(using = Date2LongSerializer.class)
private Date updateTime;
}
3.附加：還有一個比較好用的注解
如果返回對象中變量存在null，可以使用@JsonInclude(JsonInclude.Include.NON_NULL)注解來忽略為null的變量，這樣前端比較好處理
package com.ls.sell.dto;
import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.databind.annotation.JsonSerialize;
import com.ls.sell.entity.OrderDetail;
import com.ls.sell.entity.OrderMaster;
import lombok.Data;
import java.util.List;
/**
* @program: sell
* @description: 數據傳輸對象，傳給前端時忽略值為null的屬性
* @author: Liang Shan
* @create: 2019-07-25 16:05
**/
@Data
@JsonInclude(JsonInclude.Include.NON_NULL)
public class OrderDTO extends OrderMaster {
private List<OrderDetail> orderDetailList;
}
使用注解之前的返回值：
使用注解之后：
還是比較好用的。
4.附加：之前附件3的注解，還是有個問題
如果一個一個實體類配置的話，未免太過麻煩，所以可以在配置文件中直接配置，yml配置文件如下：
@JsonSerialize 相關使用（jsonUtil）
基礎注解使用
1、實現JsonSerializer接口
例：
public class MySerializerUtils extends JsonSerializer<Integer> {
@Override
public void serialize(Integer status, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException, JsonProcessingException {
String statusStr = "";
switch (status) {
case 0:
statusStr = "新建狀態";
break;
}
jsonGenerator.writeString(statusStr);
}
}
2、添加注解
注:@JsonSerialize注解,主要應用于數據轉換,該注解作用在該屬性的getter()方法上。
①用在屬性上（自定義的例子）
@JsonSerialize(using = MySerializerUtils.class) private int status;
②用在屬性上（jackson自帶的用法）
@JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss")
@JsonDeserialize(using = LocalDateTimeDeserializer.class)
@JsonSerialize(using = LocalDateTimeSerializer.class)
private LocalDateTime sendTime;
③用在空對象上可以轉化
@JsonSerialize
public class XxxxxBody {
// 該對象暫無字段，直接new了返回
}
框架層面的使用
jsonUtil工具類
實現json轉換時所有的null轉為“”
1、實現JsonSerializer類
public class CustomizeNullJsonSerializer {
public static class NullStringJsonSerializer extends JsonSerializer<Object> {
@Override
public void serialize(Object value, JsonGenerator jsonGenerator,
SerializerProvider serializerProvider) throws IOException {
jsonGenerator.writeString("");
}
}
}
2、實現BeanSerializerModifier類
public class CustomizeBeanSerializerModifier extends BeanSerializerModifier {
@Override
public List<BeanPropertyWriter> changeProperties(SerializationConfig config,
BeanDescription beanDesc,
List<BeanPropertyWriter> beanProperties) {
for (int i = 0; i < beanProperties.size(); i++) {
BeanPropertyWriter writer = beanProperties.get(i);
if (isStringType(writer)) {
writer.assignNullSerializer(new CustomizeNullJsonSerializer.NullStringJsonSerializer());
}
}
return beanProperties;
}
/**
* 是否是String
*/
private boolean isStringType(BeanPropertyWriter writer) {
Class<?> clazz = writer.getType().getRawClass();
return CharSequence.class.isAssignableFrom(clazz) || Character.class.isAssignableFrom(clazz);
}
}
3、工具類調用
public class JsonUtil {
//序列化時String 為null時變成""
private static ObjectMapper mapperContainEmpty = new ObjectMapper();
static {
mapperContainEmpty.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);
mapperContainEmpty.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
mapperContainEmpty.setSerializerFactory(mapperContainEmpty.getSerializerFactory()
.withSerializerModifier(new CustomizeBeanSerializerModifier()));
}
/**
* 將對象轉換為Json串,針對String 類型 null 轉成""
*/
public static String toJsonContainEmpty(Object o) {
try {
return mapperContainEmpty.writeValueAsString(o);
} catch (IOException e) {
logger.error("render object to json error: {}", e.getMessage(), e);
throw new RuntimeException("render object to json error!", e);
}
}
}
附：jsonUtil完整代碼
/**
* json串和對象之間相互轉換工具類
*/
public class JsonUtil {
private static Logger logger = LoggerFactory.getLogger(JsonUtil.class);
private static ObjectMapper mapper = new ObjectMapper();
//序列化時String 為null時變成""
private static ObjectMapper mapperContainEmpty = new ObjectMapper();
static {
mapper.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);
mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
mapper.setSerializationInclusion(Include.NON_NULL);
mapperContainEmpty.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);
mapperContainEmpty.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
mapperContainEmpty.setSerializerFactory(mapperContainEmpty.getSerializerFactory()
.withSerializerModifier(new CustomizeBeanSerializerModifier()));
}
/**
* 將對象轉換為Json串
*/
public static String toJson(Object o) {
try {
return mapper.writeValueAsString(o);
} catch (IOException e) {
logger.error("render object to json error: {}", e.getMessage(), e);
throw new RuntimeException("render object to json error!", e);
}
}
/**
* 將對象轉換為Json串,針對String 類型 null 轉成""
*/
public static String toJsonContainEmpty(Object o) {
try {
return mapperContainEmpty.writeValueAsString(o);
} catch (IOException e) {
logger.error("render object to json error: {}", e.getMessage(), e);
throw new RuntimeException("render object to json error!", e);
}
}
/**
* 將Json串轉換為對象
*/
public static <T> T toObject(String json, Class<T> clazz) {
try {
return mapper.readValue(json, clazz);
} catch (IOException e) {
logger.error("render json to object error: {}", e.getMessage(), e);
throw new RuntimeException("render json to object error!", e);
}
}
/**
* 將Json串轉換為List
*/
public static <T> List<T> toList(String json, Class<T> clazz) {
try {
JavaType javaType = mapper.getTypeFactory().constructParametricType(List.class, clazz);
return mapper.readValue(json, javaType);
} catch (IOException e) {
logger.error("render json to List<T> error: {}", e.getMessage(), e);
throw new RuntimeException("render json to List<T> error!", e);
}
}
/**
* 將Json串轉換為Map
*/
public static <K, V> Map<K, V> toMap(String json, Class<K> clazzKey, Class<V> clazzValue) {
try {
JavaType javaType = mapper.getTypeFactory().constructParametricType(Map.class, clazzKey, clazzValue);
return mapper.readValue(json, javaType);
} catch (IOException e) {
logger.error("render json to Map<K, V> error: {}", e.getMessage(), e);
throw new RuntimeException("render json to Map<K, V> error!", e);
}
}
}
以上為個人經驗，希望能給大家一個參考，也希望大家多多支持服務器之家。
原文鏈接：https://blog.csdn.net/qq_28021299/article/details/98635201
