概述
本文的编写初衷,是想了解一下Spring Boot2中,具体是怎么序列化和反序列化JSR 310日期时间体系的,Spring MVC应用场景有如下两个:
- 使用@RequestBody来获取JSON参数并封装成实体对象;
- 使用@ResponseBody来把返回给前端的数据转换成JSON数据。
对于一些Integer、String等基础类型的数据,Spring MVC可以通过一些内置转换器来解决,无需用户关心,但是日期时间类型(例如LocalDateTime),由于格式多变,没有内置转换器可用,就需要用户自己来配置和处理了。
阅读本文,假设读者初步了解了如何使用Jackson。
测试环境
本文使用Spring Boot2.6.6版本,锁定的Jackson版本如下:
<jackson-bom.version>2.13.2.20220328</jackson-bom.version>
Jackson处理JSR 310日期时间需要引入依赖:
<dependency>
<groupId>com.fasterxml.jackson.datatype</groupId>
<artifactId>jackson-datatype-jsr310</artifactId>
<version>2.13.2</version>
</dependency>
Spring Boot自动配置
在spring-boot-autoconfigure包中,自动配置了Jackson:
package org.springframework.boot.autoconfigure.jackson;
@Configuration(proxyBeanMethods = false)
@ConditionalOnClass(ObjectMapper.class)
public class JacksonAutoConfiguration {
// 详细代码略
}
其中有一段代码配置了ObjectMapper
@Bean
@Primary
@ConditionalOnMissingBean
ObjectMapper jacksonObjectMapper(Jackson2ObjectMapperBuilder builder) {
return builder.createXmlMapper(false).build();
}
可以看到ObjectMapper是由Jackson2ObjectMapperBuilder构建的。
再往下会看到如下代码:
@Configuration(proxyBeanMethods = false)
@ConditionalOnClass(Jackson2ObjectMapperBuilder.class)
static class JacksonObjectMapperBuilderConfiguration {
@Bean
@Scope("prototype")
@ConditionalOnMissingBean
Jackson2ObjectMapperBuilder jacksonObjectMapperBuilder(ApplicationContext applicationContext,
List<Jackson2ObjectMapperBuilderCustomizer> customizers) {
Jackson2ObjectMapperBuilder builder = new Jackson2ObjectMapperBuilder();
builder.applicationContext(applicationContext);
customize(builder, customizers);
return builder;
}
private void customize(Jackson2ObjectMapperBuilder builder,
List<Jackson2ObjectMapperBuilderCustomizer> customizers) {
for (Jackson2ObjectMapperBuilderCustomizer customizer : customizers) {
customizer.customize(builder);
}
}
}
发现在这里创建了Jackson2ObjectMapperBuilder,并且调用了customize(builder, customizers)方法,传入Lis<Jackson2ObjectMapperBuilderCustomizer> 进行定制ObjectMapper。
Jackson2ObjectMapperBuilderCustomizer是个接口,只有一个方法,源码如下:
@FunctionalInterface
public interface Jackson2ObjectMapperBuilderCustomizer {
/**
* Customize the JacksonObjectMapperBuilder.
* @param jacksonObjectMapperBuilder the JacksonObjectMapperBuilder to customize
*/
void customize(Jackson2ObjectMapperBuilder jacksonObjectMapperBuilder);
}
简单点说,Spring Boot会收集容器里面所有的Jackson2ObjectMapperBuilderCustomizer实现类,统一对Jackson2ObjectMapperBuilder进行设置,从而实现定制ObjectMapper。因此,如果我们想个性化定制ObjectMapper,只需要实现Jackson2ObjectMapperBuilderCustomizer接口并注册到容器就可以了。
自定义Jackson配置类
废话不多说,直接上代码:
@Component
public class JacksonConfig implements Jackson2ObjectMapperBuilderCustomizer, Ordered {
/** 默认日期时间格式 */
private final String dateTimeFormat = "yyyy-MM-dd HH:mm:ss";
/** 默认日期格式 */
private final String dateFormat = "yyyy-MM-dd";
/** 默认时间格式 */
private final String timeFormat = "HH:mm:ss";
@Override
public void customize(Jackson2ObjectMapperBuilder builder) {
// 设置java.util.Date时间类的序列化以及反序列化的格式
builder.simpleDateFo