动态防止某些字段被 Jackson 的 PropertyFilter 序列化

Question

我需要能够防止对象的某些字段被序列化，主要是基于它们的类型。例如，考虑以下对象：

class MyPojo {
    private int myInt;
    private boolean myBoolean;

    // getters, setters, etc.
}

我希望能够在序列化时不序列化布尔字段（如果它为 false）。或者如果它为零则不序列化 int。基本上，不要根据类型或特定值的任何属性序列化任何特定字段。

我知道 JsonSerializers，我用它来部分解决我的问题，但它是 impossible to choose not to serialize a field in a JsonSerializer。

我最接近的是实现我自己的 PropertyFilter，并通过 @JsonFilter:

将其应用于我的对象

public class XmlPropertyFilter implements PropertyFilter {
    @Override
    public void serializeAsField(Object pojo, JsonGenerator gen, SerializerProvider prov, PropertyWriter writer) throws Exception {
        JavaType type = writer.getType();

        if (writer instanceof BeanPropertyWriter) {
            BeanPropertyWriter bWriter = (BeanPropertyWriter) writer;

            String fieldName = bWriter.getSerializedName().getValue();
            Field f = pojo.getClass().getDeclaredField(fieldName);
            f.setAccessible(true);
            Object value = f.get(pojo);

            if (!type.isTypeOrSubTypeOf(int.class) && value != null) {
                // Serialize everything that isn't an int and doesn't have a null value
                prov.defaultSerializeField(fieldName, value, gen);
            } else if (type.isTypeOrSubTypeOf(int.class)) {
                // Only serialize ints if the value isn't 0
                if (value != 0) prov.defaultSerializeField(fieldName, value, gen);
            }
        }

    }

    // ...
}

这正是我想要的，除了它有破坏包装的令人讨厌的副作用（例如序列化列表）。根据 @JsonFilter 文档，将过滤器应用于字段而不是整个 class 是有效的，这会很棒，但我已经尝试过了，但我似乎无法理解上班。

Answer 1

我找到了解决方案，这正是我要找的。秘诀就是方法BeanPropertyWriter#serializeAsOmittedField(Object, JsonGenerator, SerializerProvider)。这正是在 JsonSerializer 内部不可能做的事情——它从输出中完全删除了该字段。

这是此 DynamicPropertyFilter 的示例：

public class DynamicPropertyFilter implements PropertyFilter {
    public void serializeAsField(Object pojo, JsonGenerator jgen, SerializerProvider prov, PropertyWriter writer) throws Exception {
        if (writer instanceof BeanPropertyWriter) {
            BeanPropertyWriter bWriter = (BeanPropertyWriter) writer;

            String fieldName = bWriter.getFullName().getSimpleName();
            Field field = pojo.getClass().getDeclaredField(fieldName);
            field.setAccessible(true);
            Object object = field.get(pojo);

            if (Double.class.isInstance(object) && (double) object == 0.0) {
                // Remove all double fields that are equal to 0.0
                bWriter.serializeAsOmittedField(pojo, jgen, prov);
                return;
            } else if (Boolean.class.isInstance(object)) {
                // Change all boolean fields to 1 and 0 instead of true and false
                prov.defaultSerializeField(fieldName, (boolean) object ? 1 : 0, jgen);
                return;
            }
        }

        // Serialize field as normal if property is not filtered
        writer.serializeAsField(pojo, jgen, prov);
    }

    public void serializeAsElement(Object elementValue, JsonGenerator jgen, SerializerProvider prov, PropertyWriter writer) throws Exception {
        writer.serializeAsField(elementValue, jgen, prov);
    }

    public void depositSchemaProperty(PropertyWriter writer, JsonObjectFormatVisitor objectVisitor, SerializerProvider provider) throws JsonMappingException {
        writer.depositSchemaProperty(objectVisitor, provider);
    }

    @Deprecated
    public void depositSchemaProperty(PropertyWriter writer, ObjectNode propertiesNode, SerializerProvider provider) throws JsonMappingException {
        writer.depositSchemaProperty(propertiesNode, provider);
    }
}

我不仅可以过滤字段，这主要是我想要的，而且我还可以更改它们（如布尔示例所示）。这消除了对 PropertyFilter 和 JsonSerializer 的需要。

动态防止某些字段被 Jackson 的 PropertyFilter 序列化

Dynamically prevent certain fields from being serialized with Jackson's PropertyFilter

java

serialization

jackson

jackson-dataformat-xml