java - Gson:java.lang.StackOverflowError: null

Question

我有一个类Delete，我想使用Gson库将其转换为json，但是当我转换它时，它会抛出java.lang.StackOverflowError: null的异常这是我的课

import models.UserNotifications.MailMessages.DeleteReason._
import models.UserNotifications.MailMessages.DeleteStatus._

@SerialVersionUID(1)
class Delete extends Serializable {

  var deleteStatus : DeleteStatus = DELETED
  var deleteReason : DeleteReason = EXPIRED

  /*
   * Setters
   */

  def setDeleteStatus(deletestatus : String)= {
    deleteStatus = DeleteStatus.withName(deletestatus)
  } 
  def setDeleteReason ( deletereason : String) ={
    deleteReason = DeleteReason.withName(deletereason)
  }

  /*
   * Getter
   */

  def getDeleteStatus : DeleteStatus = {
    deleteStatus
  }
  def getDeleteReason : DeleteReason = {
    deleteReason
  }


}

这里是枚举类删除状态.scala

object DeleteStatus extends Enumeration {

  type DeleteStatus = Value
  val DELETED, ACTIVE = Value

}

删除原因.scala

object DeleteReason extends Enumeration{
  type DeleteReason = Value
  val EXPIRED , MANUALLY_DELETED = Value
}

这是我如何在 Json 中进行转换

var delete = new Delete

    val gson = new Gson();
    val g=gson.toJson(delete)

但它抛出以下异常

java.lang.StackOverflowError: null
    at com.google.gson.reflect.TypeToken.equals(TypeToken.java:284) ~[gson-2.3.1.jar:na]
    at java.util.HashMap.getNode(HashMap.java:571) ~[na:1.8.0_45]
    at java.util.HashMap.get(HashMap.java:556) ~[na:1.8.0_45]
    at java.util.Collections$SynchronizedMap.get(Collections.java:2584) ~[na:1.8.0_45]
    at com.google.gson.Gson.getAdapter(Gson.java:335) ~[gson-2.3.1.jar:na]
    at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:55) ~[gson-2.3.1.jar:na]
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.write(ReflectiveTypeAdapterFactory.java:99) ~[gson-2.3.1.jar:na]
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:219) ~[gson-2.3.1.jar:na]
    at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68) ~[gson-2.3.1.jar:na]
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.write(ReflectiveTypeAdapterFactory.java:99) ~[gson-2.3.1.jar:na]
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:219) ~[gson-2.3.1.jar:na]

请帮忙看看哪里出了问题

Answer 1

问题在于 Scala 枚举的字节码包含可能值的集合 - 每个值都是枚举的一个实例。

例如，如果我们在以下位置运行 javap CoinFaces:

object CoinFaces extends Enumeration {
  type CoinFaces = Value
  val Heads, Tails = Value
}

我们可以看到 Java 反汇编包含 Enumeration$Value 类型的静态字段 values:

public final class CoinFaces {
  public static scala.Enumeration$Value Tails();
  public static scala.Enumeration$Value Heads();
  public static scala.Enumeration$ValueSet$ ValueSet();
  public static scala.Enumeration$ValueOrdering$ ValueOrdering();
  public static scala.Enumeration$Value withName(java.lang.String);
  public static scala.Enumeration$Value apply(int);
  public static int maxId();
  public static scala.Enumeration$ValueSet values();
  public static java.lang.String toString();
}

这意味着从 Java 开始，所有 Scala 枚举都包含循环引用。最简单的解决方案是将此类字段注释为 @transient ( https://stackoverflow.com/a/14489534/323177 )。不幸的是，由于我们无法注释自定义 Scala Enumeration 生成的字节码，解决方案是创建一个自定义 GSON 序列化程序，手动将枚举值序列化为字符串。

import com.google.gson.JsonElement;
import com.google.gson.JsonPrimitive;
import com.google.gson.JsonSerializationContext;
import com.google.gson.JsonSerializer;
import scala.Enumeration;

import java.lang.reflect.Type;

// Scala enumerations are static Java classes with values of type `Enumeration.Value`
public class GsonScalaEnumerationSerializer implements JsonSerializer<Enumeration.Value> {
  @Override
  public JsonElement serialize(final Enumeration.Value enumValue,
                               final Type typeOfEnum,
                               final JsonSerializationContext context) {

    return new JsonPrimitive(enumValue.toString());
  }
}

然后在构建 Gson 对象期间将其注册为类型适配器，然后这将序列化枚举值。

Gson gson = new GsonBuilder()
    .registerTypeAdapter(Enumeration.Value.class, new GsonScalaEnumerationSerializer())
    .create();