1.Jackson介绍
Jackson 是一个流行的 Java 库，用于处理 JSON 数据。它提供了高效的序列化和反序列化功能，能够将 Java 对象转换为 JSON 格式，反之亦然。
它由 FasterXML 开发和维护。Jackson 的设计目标是提供高效、灵活且易于使用的 JSON 处理功能。它广泛应用于各种 Java 项目和框架中，成为处理 JSON 的事实标准之一。
序列化是将 Java 对象转换为 JSON 字符串的过程。在 Jackson 中，这个过程通常由 ObjectMapper 类来完成。ObjectMapper 是 Jackson 的核心类，提供了许多方法来进行序列化操作。反序列化是将 JSON 字符串转换为 Java 对象的过程。在 Jackson 中，这个过程同样由 ObjectMapper 类来完成。
本文主要介绍Jaskson的序列化（writeValueAsString），涉及时间格式的自定义序列化
2.案例
尝试
Bean类，设置不同的数据类型。
java">import lombok.Data; // get/set方法
import java.time.LocalDateTime;
import java.util.Date;@Data
public class UserBean {private String name;private Integer age;private Date birthday;private LocalDateTime createTime;private Boolean isDelete;
}
测试类：测试Jackson的序列化功能，即将Java对象转为Json字符串
java">public class TestJackson {public static UserBean getBean(){UserBean userBean = new UserBean();userBean.setName("zhi");userBean.setAge(18);userBean.setBirthday(new Date());userBean.setCreateTime(LocalDateTime.now());userBean.setIsDelete(false);return userBean;}public static void main(String[] args) {UserBean user = getBean();ObjectMapper objectMapper = new ObjectMapper();try {String userJsonStr = objectMapper.writeValueAsString(user);System.out.println(userJsonStr);} catch (JsonProcessingException e) {throw new RuntimeException(e);}}
}
输出：
{"name":"zhi","age":18,"birthday":1735125463752,"createTime":{"dayOfWeek":"WEDNESDAY","dayOfYear":360,"year":2024,"month":"DECEMBER","nano":784000000,"monthValue":12,"dayOfMonth":25,"hour":19,"minute":17,"second":43,"chronology":{"calendarType":"iso8601","id":"ISO"}},"isDelete":false}
发现时间格式可读性差，想转换为2024-12-25 19:04:19类型。
修改：在实体类中添加注解
@JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss", timezone = "GMT+8")
java">@Data
public class UserBean {private String name;private Integer age;@JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss", timezone = "GMT+8")private Date birthday;@JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss", timezone = "GMT+8")private LocalDateTime createTime;private Boolean isDelete;
}
再次运行并输出
{"name":"zhi","age":18,"birthday":"2024-12-25 19:22:12","createTime":{"dayOfWeek":"WEDNESDAY","dayOfYear":360,"year":2024,"month":"DECEMBER","nano":851000000,"monthValue":12,"dayOfMonth":25,"hour":19,"minute":22,"second":12,"chronology":{"calendarType":"iso8601","id":"ISO"}},"isDelete":false}
发现birthday对了，但createTime不行。
继续修改
创建自定义LocalDateTime的序列化器：
java">import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.SerializerProvider;
import java.io.IOException;
import java.time.LocalDateTime;
import java.time.ZoneId;
import java.time.ZonedDateTime;
import java.time.format.DateTimeFormatter;
/*** 自定义LocalDateTime的序列化器* 该序列化器用于将LocalDateTime对象转换为符合特定格式的JSON字符串*/
public class LocalDateTimeSerializer extends JsonSerializer<LocalDateTime> {// 定义日期时间格式器，用于将LocalDateTime格式化为字符串// 格式为：年-月-日 时:分:秒 时区，时区为GMT+8private static final DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss").withZone(ZoneId.of("GMT+8"));/*** 序列化LocalDateTime对象** @param localDateTime 待序列化的LocalDateTime对象* @param jsonGenerator 用于生成JSON数据的工具* @param serializerProvider 提供序列化器的工具，通常未使用* @throws IOException 当JSON生成过程中发生错误时抛出*/@Overridepublic void serialize(LocalDateTime localDateTime, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException {// 将LocalDateTime转换为带有GMT+8时区的ZonedDateTime对象ZonedDateTime zonedDateTime = localDateTime.atZone(ZoneId.of("GMT+8"));// 使用定义好的格式器将ZonedDateTime格式化为字符串，并写入JSONjsonGenerator.writeString(zonedDateTime.format(formatter));}
}
在实体类中添加注解@JsonSerialize(using = XXX.class)
java">@Data
public class UserBean {private String name;private Integer age;@JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss", timezone = "GMT+8")private Date birthday;@JsonSerialize(using = LocalDateTimeSerializer.class)private LocalDateTime createTime;private Boolean isDelete;
}
在此运行测试方法
{"name":"zhi","age":18,"birthday":"2024-12-25 19:31:20","createTime":"2024-12-25 19:31:20","isDelete":false}
成功！
不用注解的实现
两个序列化器
java">public class DateSerializer extends JsonSerializer<Date> {private static final DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss").withZone(ZoneId.of("GMT+8"));@Overridepublic void serialize(Date date, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException {// 将Date对象转换为ZonedDateTime对象ZonedDateTime zonedDateTime = date.toInstant().atZone(ZoneId.of("GMT+8"));// 将ZonedDateTime对象格式化为字符串String formattedDate = formatter.format(zonedDateTime);// 将格式化后的日期时间字符串写入JSON生成器jsonGenerator.writeString(formattedDate);}
}public class LocalDateTimeSerializer extends JsonSerializer<LocalDateTime> {// 定义日期时间格式器，用于将LocalDateTime格式化为字符串// 格式为：年-月-日 时:分:秒 时区，时区为GMT+8private static final DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss").withZone(ZoneId.of("GMT+8"));@Overridepublic void serialize(LocalDateTime localDateTime, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException {// 将LocalDateTime转换为带有GMT+8时区的ZonedDateTime对象ZonedDateTime zonedDateTime = localDateTime.atZone(ZoneId.of("GMT+8"));// 使用定义好的格式器将ZonedDateTime格式化为字符串，并写入JSONjsonGenerator.writeString(zonedDateTime.format(formatter));}
}
实体类
java"> */
@Data
public class UserBean {private String name;private Integer age;private Date birthday;private LocalDateTime createTime;private Boolean isDelete;
}
测试方法
java">public class TestJackson {public static UserBean getBean(){UserBean userBean = new UserBean();userBean.setName("zhi");userBean.setAge(18);userBean.setBirthday(new Date());userBean.setCreateTime(LocalDateTime.now());userBean.setIsDelete(false);return userBean;}public static void main(String[] args) {UserBean user = getBean();ObjectMapper objectMapper = new ObjectMapper();// 配置ObjectMapper以处理LocalDateTime、Date类型的序列化JavaTimeModule javaTimeModule = new JavaTimeModule();javaTimeModule.addSerializer(LocalDateTime.class, new LocalDateTimeSerializer());javaTimeModule.addSerializer(Date.class, new DateSerializer());objectMapper.registerModule(javaTimeModule);try {String userJsonStr = objectMapper.writeValueAsString(user);System.out.println(userJsonStr);} catch (JsonProcessingException e) {throw new RuntimeException(e);}}
}
输出：
成功！
