java - 无法在 Spring Boot 中将 ProblemHandler 设置为 ObjectMapper

Question

我尝试使用 Jackson2ObjectMapperBuilderCustomizer 将自定义问题处理程序添加到对象映射器:

@Bean
public Jackson2ObjectMapperBuilderCustomizer customizer() {
    return new Jackson2ObjectMapperBuilderCustomizer() {
        @Override
        public void customize(Jackson2ObjectMapperBuilder builder) {
            ObjectMapper m = builder.build();
            m.addHandler(
                    new DeserializationProblemHandler() {
                        @Override
                        public boolean handleUnknownProperty(DeserializationContext ctxt, JsonParser p, JsonDeserializer<?> deserializer, Object beanOrClass, String propertyName) throws IOException {
                            System.out.println("ahahahaa");
                            return super.handleUnknownProperty(ctxt, p, deserializer, beanOrClass, propertyName);
                        }
                    }
            );
        }
    };
}

但是当我 Autowiring ObjectMapper bean 时，_problemHandlers 属性为空。

我还尝试使用以下方法自定义现有的 ObjectMapper:

@Autowired
public customize(ObjectMapper mapper) {
...
}

但结果是一样的。我不知道谁可以删除这个属性。我根本不在另一个地方初始化对象映射器的另一个构建器/工厂/等。我做错了什么？

Answer 1

不可能通过 Jackson2ObjectMapperBuilder 或 Jackson2ObjectMapperBuilderCustomizer 直接将 DeserializationProblemHandler 添加到 ObjectMapper。在构建器上调用 build() 是不行的，因为生成的 ObjectMapper 是方法本地的:Spring 本身将调用 build() 稍后，创建另一个 ObjectMapper 实例。

但是，可以通过注册 Jackson 模块来实现:

• 构建器有一个 modules() 方法
• 该模块可以通过 setupModule() 访问 SetupContext 实例，该实例具有 addDeserializationProblemHandler() 方法

这应该可以工作

@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 MyDeserializationProblemHandler());
    } 
}

private static class MyDeserializationProblemHandler extends DeserializationProblemHandler {
    @Override
    public boolean handleUnknownProperty(DeserializationContext ctxt,
                                         JsonParser p,
                                         JsonDeserializer<?> deserializer,
                                         Object beanOrClass,
                                         String propertyName)
            throws IOException {
        System.out.println("ahahahaa");
        return super.handleUnknownProperty(ctxt, p, deserializer, beanOrClass, propertyName);
    }
}

---

编辑 (2022-06-27)

正如 E-Riz 在评论中提到的，使用较新的 Spring Boot 版本，您只需将模块注册为 Spring Bean，它将与所有其他模块一起在 ObjectMapper 上进行配置模块。

// Or declare it as a @Bean in a @Configuration
@Component
public class MyModule extends SimpleModule {
    @Override
    public void setupModule(SetupContext context) {
        // Required, as documented in the Javadoc of SimpleModule
        super.setupModule(context);
        context.addDeserializationProblemHandler(new MyDeserializationProblemHandler());
    } 

    private static class MyDeserializationProblemHandler extends DeserializationProblemHandler {
        @Override
        public boolean handleUnknownProperty(DeserializationContext ctxt,
                                             JsonParser p,
                                             JsonDeserializer<?> deserializer,
                                             Object beanOrClass,
                                             String propertyName)
                throws IOException {
            System.out.println("ahahahaa");
            return super.handleUnknownProperty(ctxt, p, deserializer, beanOrClass, propertyName);
        }
    }
}