如何在单个ObjectMapper实例中为指定包配置Jackson集合序列化规则？

可以实现，无需多个ObjectMapper实例，下面提供两种可行方案：

方案一：自定义AnnotationIntrospector #

通过扩展Jackson的JacksonAnnotationIntrospector，根据字段所属类的包路径，动态设置集合/Map类型字段的序列化包含规则。

实现步骤 #

1. 定义自定义Introspector类：

public class PackageSpecificIncludeIntrospector extends JacksonAnnotationIntrospector {
    private static final String TARGET_PACKAGE_PREFIX = "com.mycompany.";
    private static final String GENERATED_PACKAGE_MARKER = ".generated.";
    private final JsonInclude.Value NON_EMPTY_NON_NULL = JsonInclude.Value.construct(
            JsonInclude.Include.NON_EMPTY,
            JsonInclude.Include.NON_NULL
    );

    @Override
    public JsonInclude.Value findPropertyInclusion(AnnotatedMember member) {
        Class<?> declaringClass = member.getDeclaringClass();
        String className = declaringClass.getName();
        // 校验类是否属于目标包范围
        if (className.startsWith(TARGET_PACKAGE_PREFIX) && className.contains(GENERATED_PACKAGE_MARKER)) {
            Class<?> propertyType = member.getRawType();
            // 仅对集合/Map类型字段应用规则
            if (Collection.class.isAssignableFrom(propertyType) || Map.class.isAssignableFrom(propertyType)) {
                return NON_EMPTY_NON_NULL;
            }
        }
        // 其他情况沿用默认规则
        return super.findPropertyInclusion(member);
    }
}

2. 将自定义Introspector注册到ObjectMapper：

ObjectMapper objectMapper = new ObjectMapper();
objectMapper.setAnnotationIntrospector(new PackageSpecificIncludeIntrospector());

方案二：使用BeanSerializerModifier #

通过自定义BeanSerializerModifier，在序列化前修改目标包类中集合/Map字段的序列化规则。

实现步骤 #

1. 定义自定义SerializerModifier类：

public class PackageSpecificSerializerModifier extends BeanSerializerModifier {
    private static final String TARGET_PACKAGE_PREFIX = "com.mycompany.";
    private static final String GENERATED_PACKAGE_MARKER = ".generated.";
    private final JsonInclude.Value NON_EMPTY_NON_NULL = JsonInclude.Value.construct(
            JsonInclude.Include.NON_EMPTY,
            JsonInclude.Include.NON_NULL
    );

    @Override
    public List<BeanPropertyWriter> changeProperties(SerializationConfig config, BeanDescription beanDesc, List<BeanPropertyWriter> beanProperties) {
        Class<?> beanClass = beanDesc.getBeanClass();
        String className = beanClass.getName();
        if (className.startsWith(TARGET_PACKAGE_PREFIX) && className.contains(GENERATED_PACKAGE_MARKER)) {
            for (BeanPropertyWriter writer : beanProperties) {
                Class<?> propType = writer.getType().getRawClass();
                if (Collection.class.isAssignableFrom(propType) || Map.class.isAssignableFrom(propType)) {
                    // 为目标字段设置空值不序列化规则
                    writer.setInclusion(NON_EMPTY_NON_NULL);
                }
            }
        }
        return super.changeProperties(config, beanDesc, beanProperties);
    }
}

2. 注册到ObjectMapper：

ObjectMapper objectMapper = new ObjectMapper();
SimpleModule customModule = new SimpleModule();
customModule.setSerializerModifier(new PackageSpecificSerializerModifier());
objectMapper.registerModule(customModule);

注意事项 #

• 请移除原来全局的configOverride配置，避免与自定义规则冲突。
• 两种方案均通过动态判断类的包路径来选择性应用规则，完全基于单个ObjectMapper实例实现。

内容的提问来源于stack exchange，提问作者bilak