Extending Enum for UT using Reflection

gistfile1.java

/////// Based on idea from http://stackoverflow.com/questions/25355936/aspectj-is-is-possible-to-extend-an-enums-value
/////// new imports
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;
import antlr.CommonHiddenStreamToken;
import com.puppycrawl.tools.checkstyle.api.DetailAST;
import com.puppycrawl.tools.checkstyle.api.TokenTypes;

/////// test itself
    @Test
    public void testVisitTokenSwitchReflection() throws Exception {
        DynamicEnumExtender.addEnum(ImportOrderOption.class, "NEW_OPTION_FOR_UT");
        ImportOrderCheck check = new ImportOrderCheck ();
        check.setOption("NEW_OPTION_FOR_UT");
        
        DetailAST astImport = mockAST(TokenTypes.IMPORT, "import", "mockfile", 0, 0);
        DetailAST astIdent = mockAST(TokenTypes.IDENT, "myTestImport", "mockfile", 0, 0);
        astImport.addChild(astIdent);
        DetailAST astSemi = mockAST(TokenTypes.SEMI, ";", "mockfile", 0, 0);
        astIdent.addNextSibling(astSemi);

        check.visitToken(astImport);
    }

/////// mocking method from test
    /**
     * Creates MOCK lexical token and returns AST node for this token
     * @param tokenType type of token
     * @param tokenText text of token
     * @param tokenFileName file name of token
     * @param tokenRow token position in a file (row)
     * @param tokenColumn token position in a file (column)
     * @return AST node for the token
     */
    private static DetailAST mockAST(final int tokenType, final String tokenText,
            final String tokenFileName, final int tokenRow, final int tokenColumn)
    {
        CommonHiddenStreamToken tokenImportSemi = new CommonHiddenStreamToken();
        tokenImportSemi.setType(tokenType);
        tokenImportSemi.setText(tokenText);
        tokenImportSemi.setLine(tokenRow);
        tokenImportSemi.setColumn(tokenColumn);
        tokenImportSemi.setFilename(tokenFileName);
        DetailAST astSemi = new DetailAST();
        astSemi.initialize(tokenImportSemi);
        return astSemi;
    }


/////// Reflection class
class DynamicEnumExtender {

    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) {
        // 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,                         // 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);
        }
    }
}