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);
                        }
                    }
            );
        }
    };
}

但是当我自动装配ObjectMapper bean时,_problemHandlers属性为null.

我也试过用以下方法定制现有的ObjectMapper：

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

但结果是一样的.我不知道谁可以擦除这个属性.我根本没有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？

解决方法:

通过Jackson2ObjectMapperBuilder或Jackson2ObjectMapperBuilderCustomizer直接将DeserializationProblemHandler添加到ObjectMapper是不可能的.在构建器上调用build()是不行的,因为生成的ObjectMapper是方法的本地：Spring本身稍后将调用build(),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
>模块可以通过setupModule()访问SetupContext实例,该实例具有addDeserializationProblemHandler()方法

这应该工作

@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);
    }
}