java - 将 ObjectMapper 声明为 bean 有什么好处？

Question

假设我只想要一个 ObjectMapper 对象的普通实例。将其声明为 bean 有什么好处吗？

@Bean
public ObjectMapper objectMapper() {
    return new ObjectMapper();
}

为什么不每次需要时都通过 new ObjectMapper() 创建一个新的 ObjectMapper 呢？

或者将其声明为静态对象？

private static final ObjectMapper mapper = new ObjectMapper();

Answer 1

这里是关于 ObjectMapper 的 API 说明

Mapper instances are fully thread-safe provided that ALL configuration of the instance occurs before ANY read or write calls. If configuration of a mapper is modified after first usage, changes may or may not take effect, and configuration calls themselves may fail.

这是 improve jackson performance 的指南:

Reuse heavy-weight objects: ObjectMapper (data-binding) and JsonFactory (streaming API) To a lesser degree, you may also want to reuse ObjectReader and ObjectWriter instances -- this is just some icing on the cake, but they are fully thread-safe and reusable

总结一下:

• ObjectMapper 是线程安全的，只要您没有动态更改配置

• ObjectMapper初始化是一项繁重的操作

因此，将您的 ObjectMapper 声明为 @Bean 将:

• 提高解析性能(解析时不需要重新初始化实例)

• 减少内存使用(创建更少的对象)

• 从 @Bean 方法返回的 ObjectMapper 已完全配置。它是线程安全的。 (但显然，不要修改 @Autowired 实例 XD)

• 为您的应用程序提供通用配置(例如时区、空故障转移配置...)