在Spring环境中配置Jackson的DeserializationProblemHandler [英] Configure a Jackson's DeserializationProblemHandler in Spring environment

问题描述

据我了解，Spring已经为杰克逊ObjectMapper提供了bean.因此，我正在尝试自定义此bean，而不是创建一个新bean.

As I understood, Spring is already providing a bean for Jackson ObjectMapper. Therefore, instead of creating a new bean, I'm trying to customize this bean.

此博客文章，然后再 Github项目我使用Jackson2ObjectMapperBuilder bean实现了这种自定义.

From this blog post, and then this Github project I used Jackson2ObjectMapperBuilder bean to achieve this customization.

@Bean
public Jackson2ObjectMapperBuilder jackson2ObjectMapperBuilder(ApplicationContext context) {
    Jackson2ObjectMapperBuilder builder = new Jackson2ObjectMapperBuilder();
    builder.findModulesViaServiceLoader(true);
    return builder;
}

然后，我尝试自定义反序列化器以使其宽大:如果反序列化属性时引发异常，则我希望结果对象的属性为null并让反序列化继续进行(默认是失败不能反序列化的第一个属性上.

Then, I was trying to customize the deserializer in order to make it lenient: if an exception is raised when deserializing a property, I want the result object's property to be null and let the deserialization continue (default is to fail on first property that cannot be deserialized).

我已经能够通过扩展DeserializationProblemHandler的类NullableFieldsDeserializationProblemHandler实现这一点(我认为代码不相关，但是如果需要，我可以共享它).

I've been able to achieve that with a class NullableFieldsDeserializationProblemHandler that extends DeserializationProblemHandler (I do not think the code is relevant but if needed, I can share it).

注册此处理程序的最简单方法是使用ObjectMapper的.addHandler()方法.但是，当然，要这样做，每次注入并使用ObjectMapper时都需要进行设置.我希望能够配置处理程序，以便每次自动连接ObjectMapper时，该处理程序就已经存在.

The simplest way to register this handler is to use the .addHandler() method of ObjectMapper. But of course, doing like this, I would need to set that every time I inject and use the ObjectMapper. I'd like to be able to configure handler so that every time the ObjectMapper is auto-wired, the handler is already present.

到目前为止，我想到的最好的解决方案是仅使用@PostConstruct批注来注册问题处理程序.

The best solution I came up with so far is to use a @PostConstruct annotation only to register the problem handler.

@Configuration
public class JacksonConfiguration implements InitializingBean {

  @Autowired private ObjectMapper objectMapper;

  @Bean
  public Jackson2ObjectMapperBuilder jackson2ObjectMapperBuilder(ApplicationContext context) {
    Jackson2ObjectMapperBuilder builder = new Jackson2ObjectMapperBuilder();
    builder.findModulesViaServiceLoader(true);
    return builder;
  }

  @Override
  public void afterPropertiesSet() {
    objectMapper.addHandler(new NullableFieldsDeserializationProblemHandler());
  }
}

但是此解决方案的问题是，看来我仍然可以访问尚未注册问题处理程序的自动连接的ObjectMapper(我可以在调试模式下需要它时看到它的发生).

But the problem of this solution is that it seems I can still access an autowired ObjectMapper that doesn't have yet registered the problem handler (I can see it happening after when I need it in debug mode).

有什么主意我应该如何注册这个处理程序?我注意到Jackson2ObjectMapperBuilder有一个.handlerInstantiator()，但我不知道如何使用它.

Any idea how I should register this handler? I've noticed Jackson2ObjectMapperBuilder has a .handlerInstantiator() but I couldn't figure out how to use it.

注意，我还尝试了

Note I've also tried with Jackson2ObjectMapperBuilderCustomizer since I'm using Spring Boot but had no better results.

推荐答案

不可能通过Jackson2ObjectMapperBuilder或Jackson2ObjectMapperBuilderCustomizer将DeserializationProblemHandler直接添加到ObjectMapper. handlerInstanciator()方法用于其他用途.

It's not possible to directly add a DeserializationProblemHandler to the ObjectMapper via a Jackson2ObjectMapperBuilder or Jackson2ObjectMapperBuilderCustomizer. The handlerInstanciator() method is for something else.

但是，可以通过注册Jackson模块来做到这一点:

However, it's possible to do so by registering a Jackson module:

• 构建器具有modules()方法
• 该模块可以通过setupModule()访问具有addDeserializationProblemHandler()方法的SetupContext实例

• the builder has a modules() method
• the module has access via setupModule() to a SetupContext instance, which has a addDeserializationProblemHandler() method

这有效:

@Bean
public Jackson2ObjectMapperBuilderCustomizer customizer() {
    return new Jackson2ObjectMapperBuilderCustomizer() {
        @Override
        public void customize(Jackson2ObjectMapperBuilder builder) {
            builder.modules(new MyModule());
        }
    };
}

private static class MyModule extends SimpleModule {
    @Override
    public void setupModule(SetupContext context) {
        // Required, as documented in the Javadoc of SimpleModule
        super.setupModule(context);
        context.addDeserializationProblemHandler(new NullableFieldsDeserializationProblemHandler());
    } 
}

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