Spring boot json序列化的配置

先贴配置

这段配置配置了Long类型和时间类型的序列化配置

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/**
 * 自定义json序列化
 */
@Bean
public Jackson2ObjectMapperBuilderCustomizer customizer() {
    return builder ->
            builder.simpleDateFormat("yyyy-MM-dd HH:mm:ss")
                    // long类型转string， 前端处理Long类型，数值过大会丢失精度
                    .serializerByType(Long.class, ToStringSerializer.instance)
                    .serializerByType(Long.TYPE, ToStringSerializer.instance)
                    .serializationInclusion(JsonInclude.Include.NON_NULL)
                    //指定反序列化类型，也可以使用@JsonFormat(pattern = "yyyy-MM-dd")替代。主要是mvc接收日期时使用
                    .deserializerByType(LocalTime.class, new LocalDateTimeDeserializer(DateTimeFormatter.ofPattern("HH:mm:ss")))
                    .deserializerByType(LocalDate.class, new LocalDateDeserializer(DateTimeFormatter.ofPattern("yyyy-MM-dd")))
                    .deserializerByType(LocalDateTime.class, new LocalDateTimeDeserializer(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss")))
                    // 日期序列化，主要返回数据时使用
                    .serializerByType(LocalTime.class, new LocalTimeSerializer(DateTimeFormatter.ofPattern("HH:mm:ss")))
                    .serializerByType(LocalDate.class, new LocalDateSerializer(DateTimeFormatter.ofPattern("yyyy-MM-dd")))
                    .serializerByType(LocalDateTime.class, new LocalDateTimeSerializer(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss")));
}

集成原理

Spring boot通过JacksonAutoConfiguration类来实现jackson的个性化的配置

在这个类中有如下代码：

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@Bean
@Primary
@ConditionalOnMissingBean
ObjectMapper jacksonObjectMapper(Jackson2ObjectMapperBuilder builder) {
    return builder.createXmlMapper(false).build();
}

这段代码注册了一个ObjectMapper的bean(ObjectMapper用于java对象的序列化和反序列化)，需要完成这个bean的创建，需要提供Jackson2ObjectMapperBuilderd的bean

在这个类中，还可以找到如下代码：

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@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);
        }
    }

}

此段代码会生成一个Jackson2ObjectMapperBuilder的bean，也就是我们上面生成ObjectMapper使用到的bean,而Jackson2ObjectMapperBuilder bean的生成又依赖了List

等于说spring boot会把容器里面的所有的Jackson2ObjectMapperBuilderCustomizer拿出来，统一对Jackson2ObjectMapperBuilder进行设置操作，也就间接的控制了ObjectMapper的生成，所以我们如果要对ObjectMapper做特殊的配置化操作的话，我们只需要实现Jackson2ObjectMapperBuilderCustomizer这个接口并注册这个实现的bean就可以了。可以看到Jackson2ObjectMapperBuilderCustomizer只有一个方法，void customize(Jackson2ObjectMapperBuilder jacksonObjectMapperBuilder);其实就是Jackson2ObjectMapperBuilder提供给用户的回调钩子方法，我们只需要使用Jackson2ObjectMapperBuilder进行配置就可以了。