无法使用Gson将对象(使用Room DB)序列化为json字符串

Question

我有一个类Item(见下文),其中我使用了一些Room db注释.它还有一个名为ItemInfo的嵌套类.这两个类都有一个空构造函数.

问题是,当我尝试序列化Item类的对象时,应用程序崩溃时出现以下错误:

E/AndroidRuntime: FATAL EXCEPTION: main
              Process: com.android.carrymates, PID: 18526
              java.lang.SecurityException: Can not make a java.lang.reflect.Method constructor accessible
                  at java.lang.reflect.AccessibleObject.setAccessible0(AccessibleObject.java:133)
                  at java.lang.reflect.AccessibleObject.setAccessible(AccessibleObject.java:119)
                  at com.google.gson.internal.reflect.PreJava9ReflectionAccessor.makeAccessible(PreJava9ReflectionAccessor.java:31)
                  at com.google.gson.internal.ConstructorConstructor.newDefaultConstructor(ConstructorConstructor.java:103)
                  at com.google.gson.internal.ConstructorConstructor.get(ConstructorConstructor.java:85)
                  at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.create(ReflectiveTypeAdapterFactory.java:101)
                  at com.google.gson.Gson.getAdapter(Gson.java:458)
                  at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.createBoundField(ReflectiveTypeAdapterFactory.java:117)
                  at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.getBoundFields(ReflectiveTypeAdapterFactory.java:166)
                  at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.create(ReflectiveTypeAdapterFactory.java:102)
                  at com.google.gson.Gson.getAdapter(Gson.java:458)
                  at com.google.gson.internal.bind.ArrayTypeAdapter$1.create(ArrayTypeAdapter.java:48)
                  at com.google.gson.Gson.getAdapter(Gson.java:458)
                  at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.createBoundField(ReflectiveTypeAdapterFactory.java:117)
                  at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.getBoundFields(ReflectiveTypeAdapterFactory.java:166)
                  at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.create(ReflectiveTypeAdapterFactory.java:102)
                  at com.google.gson.Gson.getAdapter(Gson.java:458)
                  at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.createBoundField(ReflectiveTypeAdapterFactory.java:117)
                  at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.getBoundFields(ReflectiveTypeAdapterFactory.java:166)
                  at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.create(ReflectiveTypeAdapterFactory.java:102)
                  at com.google.gson.Gson.getAdapter(Gson.java:458)
                  at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.createBoundField(ReflectiveTypeAdapterFactory.java:117)
                  at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.getBoundFields(ReflectiveTypeAdapterFactory.java:166)
                  at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.create(ReflectiveTypeAdapterFactory.java:102)
                  at com.google.gson.Gson.getAdapter(Gson.java:458)
                  at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.createBoundField(ReflectiveTypeAdapterFactory.java:117)
                  at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.getBoundFields(ReflectiveTypeAdapterFactory.java:166)
                  at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory.create(ReflectiveTypeAdapterFactory.java:102)
                  at com.google.gson.Gson.getAdapter(Gson.java:458)
                  at com.google.gson.Gson.toJson(Gson.java:696)
                  at com.google.gson.Gson.toJson(Gson.java:683)
                  at com.google.gson.Gson.toJson(Gson.java:638)
                  at com.google.gson.Gson.toJson(Gson.java:618)
                  ... more log (irrelevant to question asked)

Item.java

@Entity(tableName = "items", indices = {@Index(value = {"id"}, unique = true), @Index(value = {"owner", "type"})})
public class Item {

    @PrimaryKey
    @NonNull
    String id="";

   //...rest fields are int, boolean and String only

    @Embedded
    ItemInfo itemInfo; // see ItemInfo


    public Item() {

   }


    // ...getters and setters

    @IgnoreExtraProperties
    public static class ItemInfo {

        //...fields are int, boolean and String only

        public ItemInfo() {

        }

        //...getters and setters
    }
}

我的猜测是Room DB注释添加了至少一个java.lang.reflect.MethodGson无法序列化的类型对象.

下面是我用来将Item对象序列化为json字符串的代码,其中item是Item类的对象,其中包含类型String和字段的非null值ItemInfo.

Gson gson = new Gson();
String result = gson.toJson(item); // crash begins from here

我该如何解决这个问题？我希望至少有一个解决方案.

Answer 1

通常当我尝试这个时我会得到输出，

public class Car { 

    public String brand = null;

    public int    doors = 0;

}


Car car = new Car();

car.brand = "Rover";

car.doors = 5;

Gson gson = new Gson();

String json = gson.toJson(car);

签出这个： http: //tutorials.jenkov.com/java-json/gson.html