import java.lang.reflect.AccessibleObject;
import java.lang.reflect.Array;
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List; import sun.reflect.ConstructorAccessor;
import sun.reflect.FieldAccessor;
import sun.reflect.ReflectionFactory; public class DynamicEnumUtil { private static ReflectionFactory reflectionFactory = ReflectionFactory.getReflectionFactory(); private static void setFailsafeFieldValue(Field field, Object target, Object value) throws NoSuchFieldException,
IllegalAccessException { // let's make the field accessible
field.setAccessible(true); // next we change the modifier in the Field instance to
// not be final anymore, thus tricking reflection into
// letting us modify the static final field
Field modifiersField = Field.class.getDeclaredField("modifiers");
modifiersField.setAccessible(true);
int modifiers = modifiersField.getInt(field); // blank out the final bit in the modifiers int
modifiers &= ~Modifier.FINAL;
modifiersField.setInt(field, modifiers); FieldAccessor fa = reflectionFactory.newFieldAccessor(field, false);
fa.set(target, value);
} private static void blankField(Class<?> enumClass, String fieldName) throws NoSuchFieldException,
IllegalAccessException {
for (Field field : Class.class.getDeclaredFields()) {
if (field.getName().contains(fieldName)) {
AccessibleObject.setAccessible(new Field[] { field }, true);
setFailsafeFieldValue(field, enumClass, null);
break;
}
}
} private static void cleanEnumCache(Class<?> enumClass) throws NoSuchFieldException, IllegalAccessException {
blankField(enumClass, "enumConstantDirectory"); // Sun (Oracle?!?) JDK 1.5/6
blankField(enumClass, "enumConstants"); // IBM JDK
} private static ConstructorAccessor getConstructorAccessor(Class<?> enumClass, Class<?>[] additionalParameterTypes)
throws NoSuchMethodException {
Class<?>[] parameterTypes = new Class[additionalParameterTypes.length + 2];
parameterTypes[0] = String.class;
parameterTypes[1] = int.class;
System.arraycopy(additionalParameterTypes, 0, parameterTypes, 2, additionalParameterTypes.length);
return reflectionFactory.newConstructorAccessor(enumClass.getDeclaredConstructor(parameterTypes));
} private static Object makeEnum(Class<?> enumClass, String value, int ordinal, Class<?>[] additionalTypes,
Object[] additionalValues) throws Exception {
Object[] parms = new Object[additionalValues.length + 2];
parms[0] = value;
parms[1] = Integer.valueOf(ordinal);
System.arraycopy(additionalValues, 0, parms, 2, additionalValues.length);
return enumClass.cast(getConstructorAccessor(enumClass, additionalTypes).newInstance(parms));
} /**
* Add an enum instance to the enum class given as argument
*
* @param <T> the type of the enum (implicit)
* @param enumType the class of the enum to be modified
* @param enumName the name of the new enum instance to be added to the class.
*/
@SuppressWarnings("unchecked")
public static <T extends Enum<?>> void addEnum(Class<T> enumType, String enumName, Class<?>[] additionalTypes, Object[] additionalValues) { // 0. Sanity checks
if (!Enum.class.isAssignableFrom(enumType)) {
throw new RuntimeException("class " + enumType + " is not an instance of Enum");
} // 1. Lookup "$VALUES" holder in enum class and get previous enum instances
Field valuesField = null;
Field[] fields = enumType.getDeclaredFields();
for (Field field : fields) {
if (field.getName().contains("$VALUES")) {
valuesField = field;
break;
}
}
AccessibleObject.setAccessible(new Field[] { valuesField }, true); try { // 2. Copy it
T[] previousValues = (T[]) valuesField.get(enumType);
List<T> values = new ArrayList<T>(Arrays.asList(previousValues)); // 3. build new enum
T newValue = (T) makeEnum(enumType, enumName, values.size(), additionalTypes, additionalValues); // 4. add new value
values.add(newValue); // 5. Set new values field
setFailsafeFieldValue(valuesField, null, values.toArray((T[]) Array.newInstance(enumType, 0))); // 6. Clean enum cache
cleanEnumCache(enumType); } catch (Exception e) {
e.printStackTrace();
throw new RuntimeException(e.getMessage(), e);
}
} }
测试类
import java.lang.reflect.Field;
public class MainTest {
private static enum TestEnum {
a(111,"AAA"),
b(222,"BBB"),
c(333,"CCC");
private int value;
private String text;
TestEnum(int value,String text){
this.value = value;
this.text = text;
}
public int getValue() {
return value;
}
public void setValue(int value) {
this.value = value;
}
public String getText() {
return text;
}
public void setText(String text) {
this.text = text;
}
@Override
public String toString() {
return "TestEnum{" +
"value=" + value +
", text='" + text + '\'' +
'}';
}
};
private static void addTestEnum(String enumName,int value,String text){
DynamicEnumUtil.addEnum(TestEnum.class,enumName,new Class<?>[] {int.class,String.class},new Object[] {value,text});
}
public static void main(String[] args) {
addTestEnum("d",444,"DDD");
addTestEnum("e",555,"EEE");
addTestEnum("f",666,"FFF");
addTestEnum("g",777,"GGG");
for (TestEnum testEnum:TestEnum.values()){
System.out.println(testEnum.toString());
}
Class<TestEnum> ccc = TestEnum.class;
Field[] fff = ccc.getDeclaredFields();
TestEnum testEnum = TestEnum.b;
switch (testEnum){
case a:{
System.out.println("22222reefwsfsds");
break;
}
case b:
System.out.println("bbb");
break;
}
}
}