Spring Boot中如何获取Spring自身使用的自动配置ObjectMapper实例？

在Spring Boot应用中，我通过如下方式自定义Jackson ObjectMapper：

@Configuration
public class JacksonConfig {
    
    @Value("${app.dateFormat}")
    private String dateFormat;
    
    @Value("${app.dateFormat} ${app.timeFormat}")
    private String dateTimeFormat;
    
    
    @Bean
    public Jackson2ObjectMapperBuilderCustomizer jsonCustomizer() {
        return builder -> {
            builder.serializationInclusion(Include.NON_NULL);
            builder.simpleDateFormat("yyyy-MM-dd'T'HH:mm:ss'Z'");
            builder.serializers(new LocalDateSerializer(DateTimeFormatter.ISO_OFFSET_DATE));
            builder.serializers(new LocalDateTimeSerializer(DateTimeFormatter.ISO_OFFSET_DATE_TIME));
        };
    }
}

另有一个使用ObjectMapper的Bean：

@Autowired
private ApplicationContext springContext;

@Bean
public ISEAClient createPubClient() {
    OkHttpClient client = new OkHttpClient();   
    return new HttpRestSEAClient("http://localhost:8081/sea/", client, springContext.getBean(ObjectMapper.class));
}

但ISEAClient Bean在JSON序列化时仍会包含null属性，似乎ObjectMapper Bean并未受到Jackson2ObjectMapperBuilderCustomizer的影响。请问如何获取Spring自身使用的同一个ObjectMapper实例？

1. 直接注入ObjectMapper而非从ApplicationContext获取 #

把createPubClient Bean改成直接注入ObjectMapper，Spring会自动注入已经被Jackson2ObjectMapperBuilderCustomizer定制好的实例：

@Autowired
private ObjectMapper objectMapper;

@Bean
public ISEAClient createPubClient() {
    OkHttpClient client = new OkHttpClient();   
    return new HttpRestSEAClient("http://localhost:8081/sea/", client, objectMapper);
}

或者更推荐构造注入（符合Spring最佳实践）：

private final ObjectMapper objectMapper;

public YourConfigClass(ObjectMapper objectMapper) {
    this.objectMapper = objectMapper;
}

@Bean
public ISEAClient createPubClient() {
    OkHttpClient client = new OkHttpClient();   
    return new HttpRestSEAClient("http://localhost:8081/sea/", client, objectMapper);
}

2. 检查是否存在多个ObjectMapper Bean #

如果应用中存在其他自定义的ObjectMapper Bean，Spring可能会注入未被定制的实例。可以通过两种方式确认：

• 启动应用时查看日志，搜索ObjectMapper相关的Bean注册信息
• 在代码中调用springContext.getBeansOfType(ObjectMapper.class)，打印所有ObjectMapper实例，排查哪个是Spring默认的

3. 直接定制默认ObjectMapper Bean #

如果上述方法无效，可以直接定义自己的ObjectMapper Bean，替代Spring默认实例：

@Configuration
public class JacksonConfig {
    
    @Value("${app.dateFormat}")
    private String dateFormat;
    
    @Value("${app.dateFormat} ${app.timeFormat}")
    private String dateTimeFormat;
    
    @Bean
    public ObjectMapper objectMapper() {
        ObjectMapper objectMapper = new ObjectMapper();
        objectMapper.setSerializationInclusion(Include.NON_NULL);
        objectMapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss'Z'"));
        JavaTimeModule timeModule = new JavaTimeModule();
        timeModule.addSerializer(LocalDate.class, new LocalDateSerializer(DateTimeFormatter.ISO_OFFSET_DATE));
        timeModule.addSerializer(LocalDateTime.class, new LocalDateTimeSerializer(DateTimeFormatter.ISO_OFFSET_DATE_TIME));
        objectMapper.registerModule(timeModule);
        return objectMapper;
    }
}

这种方式会让Spring直接使用你定义的ObjectMapper，确保所有依赖它的Bean都能拿到定制后的实例。

内容的提问来源于stack exchange，提问作者WestFarmer