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动态防止某些字段被Jackson的PropertyFilter序列化

jackson-dataformat-xml jackson serialization java

Matthew Olsson · 技术社区 · 6 年前

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,如果布尔字段为false,则不序列化它。或者如果int为零,则不序列化它。基本上,不基于任何类型或特定值的属性序列化任何特定字段。

我知道JSONSerializer,我用它部分解决了我的问题,但它确实是 impossible to choose not to serialize a field in a JsonSerializer .

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

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,只是它有破坏包装的副作用(例如,序列化列表)。根据 @JsonFilter 在文档中,对一个字段而不是整个类应用过滤器是有效的,这将是非常棒的,但我已经尝试过了,我似乎无法让它工作。

1 回复 | 直到 6 年前

Matthew Olsson 6 年前

我找到了解决办法,这正是我想要的。秘密在于方法 BeanPropertyWriter#serializeAsOmittedField(Object, JsonGenerator, SerializerProvider) .这正是JsonSerializer内部不可能做到的事情——它完全删除了输出中的字段。

下面是此DynamicPropertyFilter的一个示例:

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),还可以更改它们(如布尔示例所示)。这样就不需要PropertyFilter和JsonSerializer。