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package org.glassfish.pfl.basic.reflection;

import java.lang.reflect.Field;
import java.security.AccessController;
import java.security.PrivilegedAction;

public class FieldValueHelper {
    private static final Bridge bridge = Bridge.get();

    /**
     * Returns the value of a field in an object.
     * @param obj the object holding the field
     * @param field the field whose value is to be returned.
     * @throws IllegalAccessException if the field cannot directly be accessed.
     */
    public static Object getFieldValue(Object obj, final Field field) throws IllegalAccessException {
        if (field.isAccessible())
            return field.get(obj);
        else
            return getPrivateFieldValue(obj, field);
    }

    private static Object getPrivateFieldValue(Object obj, final Field field) throws IllegalAccessException {
        try {
            makeFieldAccessible(field);
            return field.get(obj);
        } catch(Throwable t) {
            return getInacessibleFieldValue(obj, field);
        }
    }

    private static void makeFieldAccessible(final Field field) {
        AccessController.doPrivileged(new PrivilegedAction() {
            public Object run() {
                field.setAccessible(true);
                return null;
            }
        });
    }

    private static Object getInacessibleFieldValue(Object obj, Field field) {
        long offset = bridge.objectFieldOffset(field);

        if (!field.getType().isPrimitive())
            return bridge.getObject(obj, offset);
        else if (field.getType() == Integer.TYPE)
            return bridge.getInt(obj, offset);
        else if (field.getType() == Byte.TYPE)
            return bridge.getByte(obj, offset);
        else if (field.getType() == Long.TYPE)
            return bridge.getLong(obj, offset);
        else if (field.getType() == Float.TYPE)
            return bridge.getFloat(obj, offset);
        else if (field.getType() == Double.TYPE)
            return bridge.getDouble(obj, offset);
        else if (field.getType() == Short.TYPE)
            return bridge.getShort(obj, offset);
        else if (field.getType() == Character.TYPE)
            return bridge.getChar(obj, offset);
        else if (field.getType() == Boolean.TYPE)
            return bridge.getBoolean(obj, offset);
        else
            return null;
    }
}