是的。
Gson 非常模块化，允许您将自己的TypeAdapterFactory 用于枚举案例。您的自定义适配器将返回您自己的 EnumTypeAdapter 并管理所需的案例。让代码说话。
package stackoverflow.questions.q16715117;
import java.io.IOException;
import java.util.*;
import com.google.gson.*;
import com.google.gson.annotations.SerializedName;
import com.google.gson.reflect.TypeToken;
import com.google.gson.stream.*;
public class Q16715117 {
public static void main(String[] args) {
GsonBuilder gb = new GsonBuilder();
gb.registerTypeAdapterFactory(CUSTOM_ENUM_FACTORY);
Container c1 = new Container();
Gson g = gb.create();
String s1 = "{\"colour\":\"RED\",\"number\":42}";
c1 = g.fromJson(s1, Container.class);
System.out.println("Result: "+ c1.toString());
}
public static final TypeAdapterFactory CUSTOM_ENUM_FACTORY = newEnumTypeHierarchyFactory();
public static TypeAdapterFactory newEnumTypeHierarchyFactory() {
return new TypeAdapterFactory() {
@SuppressWarnings({"rawtypes", "unchecked"})
public <T> TypeAdapter<T> create(Gson gson, TypeToken<T> typeToken) {
Class<? super T> rawType = typeToken.getRawType();
if (!Enum.class.isAssignableFrom(rawType) || rawType == Enum.class) {
return null;
}
if (!rawType.isEnum()) {
rawType = rawType.getSuperclass(); // handle anonymous subclasses
}
return (TypeAdapter<T>) new CustomEnumTypeAdapter(rawType);
}
};
}
private static final class CustomEnumTypeAdapter<T extends Enum<T>> extends TypeAdapter<T> {
private final Map<String, T> nameToConstant = new HashMap<String, T>();
private final Map<T, String> constantToName = new HashMap<T, String>();
private Class<T> classOfT;
public CustomEnumTypeAdapter(Class<T> classOfT) {
this.classOfT = classOfT;
try {
for (T constant : classOfT.getEnumConstants()) {
String name = constant.name();
SerializedName annotation = classOfT.getField(name).getAnnotation(SerializedName.class);
if (annotation != null) {
name = annotation.value();
}
nameToConstant.put(name, constant);
constantToName.put(constant, name);
}
} catch (NoSuchFieldException e) {
throw new AssertionError();
}
}
public T read(JsonReader in) throws IOException {
if (in.peek() == JsonToken.NULL) {
in.nextNull();
return null;
}
String nextString = in.nextString();
T enumValue = nameToConstant.get(nextString);
if (enumValue == null)
throw new GsonEnumParsinException(nextString, classOfT.getName());
return enumValue;
}
public void write(JsonWriter out, T value) throws IOException {
out.value(value == null ? null : constantToName.get(value));
}
}
}
另外我声明了一个自定义运行时异常：
public class GsonEnumParsinException extends RuntimeException {
String notFoundEnumValue;
String enumName;
String fieldName;
public GsonEnumParsinException(String notFoundEnumValue, String enumName) {
this.notFoundEnumValue = notFoundEnumValue;
this.enumName = enumName;
}
@Override
public String toString() {
return "GsonEnumParsinException [notFoundEnumValue="
+ notFoundEnumValue + ", enumName=" + enumName + "]";
}
public String getNotFoundEnumValue() {
return notFoundEnumValue;
}
@Override
public String getMessage() {
return "Cannot found " + notFoundEnumValue + " for enum " + enumName;
}
}
这些是我在示例中使用的类：
public enum Colour {
WHITE, YELLOW, BLACK;
}
public class Container {
private Colour colour;
private int number;
public Colour getColour() {
return colour;
}
public void setColour(Colour colour) {
this.colour = colour;
}
public int getNumber() {
return number;
}
public void setNumber(int number) {
this.number = number;
}
@Override
public String toString() {
return "Container [colour=" + colour + ", number=" + number + "]";
}
}
这给出了这个堆栈跟踪：
Exception in thread "main" GsonEnumParsinException [notFoundEnumValue=RED, enumName=stackoverflow.questions.q16715117.Colour]
at stackoverflow.questions.q16715117.Q16715117$CustomEnumTypeAdapter.read(Q16715117.java:77)
at stackoverflow.questions.q16715117.Q16715117$CustomEnumTypeAdapter.read(Q16715117.java:1)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.read(ReflectiveTypeAdapterFactory.java:93)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:172)
at com.google.gson.Gson.fromJson(Gson.java:803)
at com.google.gson.Gson.fromJson(Gson.java:768)
at com.google.gson.Gson.fromJson(Gson.java:717)
at com.google.gson.Gson.fromJson(Gson.java:689)
at stackoverflow.questions.q16715117.Q16715117.main(Q16715117.java:22)
不幸的是，EnumTypeAdapter 对它所调用的上下文一无所知，因此该解决方案不足以捕获字段名称。
编辑
所以你还必须使用另一个TypeAdapter，我称之为CustomReflectiveTypeAdapterFactory，几乎是CustomReflectiveTypeAdapterFactory的副本，我改变了一点例外，所以：
public final class CustomReflectiveTypeAdapterFactory implements TypeAdapterFactory {
private final ConstructorConstructor constructorConstructor;
private final FieldNamingStrategy fieldNamingPolicy;
private final Excluder excluder;
public CustomReflectiveTypeAdapterFactory(ConstructorConstructor constructorConstructor,
FieldNamingStrategy fieldNamingPolicy, Excluder excluder) {
this.constructorConstructor = constructorConstructor;
this.fieldNamingPolicy = fieldNamingPolicy;
this.excluder = excluder;
}
public boolean excludeField(Field f, boolean serialize) {
return !excluder.excludeClass(f.getType(), serialize) && !excluder.excludeField(f, serialize);
}
private String getFieldName(Field f) {
SerializedName serializedName = f.getAnnotation(SerializedName.class);
return serializedName == null ? fieldNamingPolicy.translateName(f) : serializedName.value();
}
public <T> TypeAdapter<T> create(Gson gson, final TypeToken<T> type) {
Class<? super T> raw = type.getRawType();
if (!Object.class.isAssignableFrom(raw)) {
return null; // it's a primitive!
}
ObjectConstructor<T> constructor = constructorConstructor.get(type);
return new Adapter<T>(constructor, getBoundFields(gson, type, raw));
}
private CustomReflectiveTypeAdapterFactory.BoundField createBoundField(
final Gson context, final Field field, final String name,
final TypeToken<?> fieldType, boolean serialize, boolean deserialize) {
final boolean isPrimitive = Primitives.isPrimitive(fieldType.getRawType());
// special casing primitives here saves ~5% on Android...
return new CustomReflectiveTypeAdapterFactory.BoundField(name, serialize, deserialize) {
final TypeAdapter<?> typeAdapter = context.getAdapter(fieldType);
@SuppressWarnings({"unchecked", "rawtypes"}) // the type adapter and field type always agree
@Override void write(JsonWriter writer, Object value)
throws IOException, IllegalAccessException {
Object fieldValue = field.get(value);
TypeAdapter t =
new CustomTypeAdapterRuntimeTypeWrapper(context, this.typeAdapter, fieldType.getType());
t.write(writer, fieldValue);
}
@Override void read(JsonReader reader, Object value)
throws IOException, IllegalAccessException {
Object fieldValue = null;
try {
fieldValue = typeAdapter.read(reader);
} catch (GsonEnumParsinException e){
e.setFieldName(field.getName());
throw e;
}
if (fieldValue != null || !isPrimitive) {
field.set(value, fieldValue);
}
}
};
}
// more copy&paste code follows
最重要的部分是read 方法，我在其中捕获异常并添加字段名称并再次抛出异常。请注意，类CustomTypeAdapterRuntimeTypeWrapper 只是库内部中TypeAdapterRuntimeTypeWrapper 的重命名副本，因为类是私有的。
所以，main方法变化如下：
Map<Type, InstanceCreator<?>> instanceCreators
= new HashMap<Type, InstanceCreator<?>>();
Excluder excluder = Excluder.DEFAULT;
FieldNamingStrategy fieldNamingPolicy = FieldNamingPolicy.IDENTITY;
GsonBuilder gb = new GsonBuilder();
gb.registerTypeAdapterFactory(new CustomReflectiveTypeAdapterFactory(new ConstructorConstructor(instanceCreators), fieldNamingPolicy, excluder));
gb.registerTypeAdapterFactory(CUSTOM_ENUM_FACTORY);
Gson g = gb.create();
现在你有了这个堆栈跟踪（对异常的更改非常简单，我省略了它们）：
Exception in thread "main" GsonEnumParsinException [notFoundEnumValue=RED, enumName=stackoverflow.questions.q16715117.Colour, fieldName=colour]
at stackoverflow.questions.q16715117.Q16715117$CustomEnumTypeAdapter.read(Q16715117.java:90)
at stackoverflow.questions.q16715117.Q16715117$CustomEnumTypeAdapter.read(Q16715117.java:1)
at stackoverflow.questions.q16715117.CustomReflectiveTypeAdapterFactory$1.read(CustomReflectiveTypeAdapterFactory.java:79)
at stackoverflow.questions.q16715117.CustomReflectiveTypeAdapterFactory$Adapter.read(CustomReflectiveTypeAdapterFactory.java:162)
at com.google.gson.Gson.fromJson(Gson.java:803)
at com.google.gson.Gson.fromJson(Gson.java:768)
at com.google.gson.Gson.fromJson(Gson.java:717)
at com.google.gson.Gson.fromJson(Gson.java:689)
at stackoverflow.questions.q16715117.Q16715117.main(Q16715117.java:35)
当然，这个解决方案需要付出一些代价。
- 首先，您必须复制一些私有/最终类并进行更改。如果库更新，您必须再次检查您的代码（源代码的一个分支是相同的，但至少您不必复制所有代码）。
- 如果您自定义字段排除策略、构造函数或字段命名策略，则必须将它们复制到
CustomReflectiveTypeAdapterFactory 中，因为我找不到从构建器传递它们的任何可能性。