使用 Jackson 对 Scala 案例类进行(反)序列化 [英] Using Jackson to (De)-serialize a Scala Case Class

问题描述

我使用 Jackson 测试了 Scala 案例类的序列化.

I tested out the serialization of a Scala case class using Jackson.

DeserializeTest.java

    public static void main(String[] args) throws Exception { // being lazy to catch-all

        final ObjectMapper mapper          = new ObjectMapper();
        final ByteArrayOutputStream stream = new ByteArrayOutputStream();

        mapper.writeValue(stream, p.Foo.personInstance());

        System.out.println("result:" +  stream.toString());
    }
}

Foo.scala

object Foo {
  case class Person(name: String, age: Int, hobbies: Option[String])
  val personInstance = Person("foo", 555, Some("things"))
  val PERSON_JSON = """ { "name": "Foo", "age": 555 } """
}

当我运行上述Java类的main时，抛出了一个异常:

When I ran the above main of the Java class, an exception was thrown:

[error] Exception in thread "main" org.codehaus.jackson.map.JsonMappingException: 
 No serializer found for class p.Foo$Person and no properties discovered 
 to create BeanSerializer (to avoid exception, 
 disable SerializationConfig.Feature.FAIL_ON_EMPTY_BEANS) )

我如何(反)序列化 Scala 案例类?

How can I (de)-serialize Scala case classes?

推荐答案

Jackson 希望您的类是 JavaBean，这意味着它希望该类的每个属性都具有 getX() 和/或 setX().

Jackson is expecting your class to be a JavaBean, which means its expects the class to have a getX() and/or setX() for every property.

选项 1

您可以使用注释 在 Scala 中创建 JavaBean 类BeanProperty.

示例

case class Person(
   @BeanProperty val name: String, 
   @BeanProperty val age: Int, 
   @BeanProperty val hobbies: Option[String]
)

在这种情况下，val 意味着只定义了一个 getter.如果你想要反序列化的 setter，你可以将属性定义为 var.

In this case a val will mean only a getter is defined. If you want setters for deserialization you defined the properties as var.

选项 2

虽然选项 1 可以工作，但如果您真的想使用 Jackson，则有一些包装器允许它处理 Scala 类，例如 FasterXML 的 scala 模块 这可能是更好的方法.我没有使用它，因为我只是使用内置的 Json 库来播放.

While option 1 will work, if you really want to use Jackson there are wrappers that allow it to deal with Scala classes like FasterXML's scala module which might be a better approach. I haven't used it as I've just been using the Json library built in to play.

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