ecological-engine/src/main/java/org/gcube/dataanalysis/ecoengine/utils/DynamicEnum.java

152 lines
5.6 KiB
Java

package org.gcube.dataanalysis.ecoengine.utils;
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 org.gcube.dataanalysis.ecoengine.utils.LMEEnum.LMEEnumType;
import sun.reflect.ConstructorAccessor;
import sun.reflect.FieldAccessor;
import sun.reflect.ReflectionFactory;
public class DynamicEnum {
private ReflectionFactory reflectionFactory = ReflectionFactory.getReflectionFactory();
private 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 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 void cleanEnumCache(Class<?> enumClass) throws NoSuchFieldException, IllegalAccessException {
blankField(enumClass, "enumConstantDirectory"); // Sun (Oracle?!?) JDK 1.5/6
blankField(enumClass, "enumConstants"); // IBM JDK
}
private 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 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 <T extends Enum<?>> void addEnum(Class<T> enumType, String enumName) {
// 0. Sanity checks
if (!Enum.class.isAssignableFrom(enumType)) {
throw new RuntimeException("class " + enumType + " is not an instance of Enum");
}
// 1. Lookup "$VALUES" holder in enum class and get previous enum instances
Field valuesField = null;
Field[] fields = getFields();
for (Field field : fields) {
if (field.getName().contains("$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, // The target enum class
enumName, // THE NEW ENUM INSTANCE TO BE DYNAMICALLY ADDED
values.size(),
new Class<?>[] {}, // could be used to pass values to the enum constuctor if needed
new Object[] {}); // could be used to pass values to the enum constuctor if needed
// 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);
}
}
public static enum DynamicEnumE {
};
public Field[] getFields(){
Field[] fields =DynamicEnumE.class.getDeclaredFields();
return fields;
}
public static void main(String[] args) {
DynamicEnum en = new DynamicEnum();
// Dynamically add 3 new enum instances d, e, f to TestEnum
en.addEnum(DynamicEnumE.class, "d");
en.addEnum(DynamicEnumE.class, "e");
en.addEnum(DynamicEnumE.class, "f");
// Run a few tests just to show it works OK.
System.out.println(Arrays.deepToString(DynamicEnumE.values()));
// Shows : [a, b, c, d, e, f]
}
}