Scala:ArrayBuffer/ArrayList的Json表示...如何避免在集合中打印出空信息?

问题描述

我的Scala类中有一个ArrayBuffer(如果使用Java，则有点像ArrayList).以下是我的代码:

I have an ArrayBuffer in my Scala class (somewhat like a ArrayList if using Java). The following is my code:

class MyClass {

  val names: ArrayBuffer[Name] = new ArrayBuffer[Name]
  var phone: String = null;

  def toJsonString(): String = {
    return (new GsonBuilder().serializeNulls().create()).toJson(this);
  }

  override def toString(): String = {
    return toJsonString();
  }
}

然后，当我尝试打印MyClass对象时:

Then when I try to print my MyClass object:

  var myObj = new MyClass

  val name = new Name()
  name.setFirstName("John")
  name.setLastName("Smith")

  myObj.names.append(name)

  println(myObj.toString())

---

然后我的输出如下:

---

Then my output looks like:

{"names":{"initialSize":16,"array":[{"firstName":"John","middleName":null,"lastName":"Smith"},null,null,null,null,null,n
ull,null,null,null,null,null,null,null,null,null],"size0":1},"phone":null}

有没有一种方法可以使输出JSON如下所示?也许使用除ArrayBuffer以外的其他集合?谢谢！

Is there a way I can make the output JSON like below? Perhaps using a different collection other than ArrayBuffer? Thanks!

{"names":[{"firstName":"John","middleName":null,"lastName":"Smith"}],"phone":null}

推荐答案

您有很多不错的选择(例如，使用另一个序列化库代替Gson，使用不可变集合等)，但这是使用最小代码的解决方案更改:

You have many good options (e.g. use another serialization library instead of Gson, use an immutable collection etc.), but here's a solution with minimal code changes:

为ArrayBuffer添加一个自定义序列化器，将其转换为不可变的Array，从而摆脱空单元格:

Add a custom serializer for ArrayBuffer that converts it to an immutable Array, thus getting rid of the empty cells:

import com.google.gson._
import scala.reflect.ClassTag
import java.lang.reflect.Type

class ArrayBufferSerializer[T : ClassTag] extends JsonSerializer[ArrayBuffer[T]] {
    override def serialize(src: ArrayBuffer[T], typeOfSrc: Type, context: JsonSerializationContext): JsonElement = {
        context.serialize(src.toArray)
    }
}

然后在MyClass.toJsonString的GsonBuilder中注册它:

Then register it in the GsonBuilder in MyClass.toJsonString:

def toJsonString(): String = {
  new GsonBuilder()
    .registerTypeAdapter(classOf[ArrayBuffer[Name]], new ArrayBufferSerializer[Name]())
    .serializeNulls()
    .create()
    .toJson(this)
}

这会产生您想要的结果:

This produces the result you're looking for:

{"names":[{"firstName":"John","middleName":null,"lastName":"Smith"}],"phone":null}

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