POJO instantiator Utility

Just a random post for everyone.

If you don't know what Plain Old Java Object (POJO) is, take a look at Wikipedia's explanation thereof.

I have written a simple POJO instantiator. This instantiator is not fully perfect but it does what it was designed thus far.

My criteria I have choose of what constitutes a POJO is simple:

A class must have a no constructor at all, or a public zero-argument constructor.
The instance variables must have a respective getter and setter method (of which, both must be public).

What this utility class doesn't do is the following:

It never instantiates a final instance or a static final instance.
serialVersionUID is ignored.
Array instance variables are not instantiated.
Any instance variable which has the same type as the class it is declared is not instantiated. The reason is that the utility class will go into an infinite recursive loop and a StackOverflowError is thrown.

OK, enough of the pleasantries, let's get to the code, shall we? And here it is.

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import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.util.ArrayList;
import java.util.List;
 
import org.apache.log4j.Logger;
 
/**
 * @author The Elite Gentleman
 * @since 17 August 2011
 * 
 */
public class PojoInstantiatorUtil {
     
    private static final Logger logger = Logger.getLogger(PojoInstantiatorUtil.class);
    private static List<String> ignoreFieldList = new ArrayList<String>();
     
    static {
        ignoreFieldList.add("serialVersionUID");
    }
 
    /**
     * Hidden, for a good cause.
     */
    private PojoInstantiatorUtil() {
        // TODO: NOOP
    }
     
    /**
     * Creates a class and instantiate all properties that needs instantiating.
     * Class must have a default/public zero-based constructor.
     * 
     * @param clazz
     * @return
     * @throws Exception
     */
    public static <T> T newInstance(Class<T> clazz) throws Exception {
         
        //Cannot instantiate interfaces and abstract classes.
        if (Modifier.isAbstract(clazz.getModifiers()) || clazz.isInterface()) {
            String message = "Cannot create a new instance of class '" + clazz.getName() +"'. Class is either abstract or interface.";
            logger.error(message);
            throw new Exception(message);
        }
         
        T object = clazz.newInstance();
        instantiateInstances(object);
        return object;
         
    }
 
    public static <T> void instantiateInstances(T object) throws Exception {
         //We use reflection to see if we can instantiate this.
         if (object == null) {
             throw new NullPointerException("object is null.");
         }
         
         Class<?> objectClass = object.getClass();
         logger.info("instantiateInstances(" + objectClass.getName() + ")");
                  
         while (Object.class != objectClass && !isClassTypeJavaImplemented(objectClass)) {
         
             Field[] fields = objectClass.getDeclaredFields();
             if (fields != null && fields.length > 0) {
                 for (Field field : fields) {
                     
                     if (ignoreFieldList.contains(field.getName())) {
                         //We can safely ignore it and move on...
                         logger.info(objectClass.getName() + ": Field name '" + field.getName() + "' is on our ignore list. Ignoring...");
                         continue;
                     }
                     
                     Class<?> fieldType = field.getType();
                     if (isTypesIdentical(objectClass, fieldType)) {
                         logger.warn("WARNING: This class '" + objectClass.getName() + "' and instance variable '" + field.getName() + "' of class '" + fieldType.getName() + "' are of the same class name. Redundancy will occur, therefore skipping instantiation.");
                         continue;
                     }
                     
                    //Final fields will be overlooked
                     if (Modifier.isFinal(fieldType.getModifiers()) || Modifier.isStatic(fieldType.getModifiers())) {
                         Object v = field.get(object);
                         if (v != null) {
                             logger.info(objectClass.getName() + ": Field '" + field.getName() + "' is a final. Overlooking...");
                         }
                     }
                     
                     if (isTypeInterface(fieldType)) {
                         logger.info(objectClass.getName() + ": Field '" + field.getName() + "' of type '" + fieldType.getName() + "' is an interface. Nulling it is safer.");
                         continue;
                     }
                     
                     //Get it's declared method.
                     String fieldName = field.getName();
                     Method declaredMethod = objectClass.getMethod("set" + Character.toUpperCase(fieldName.charAt(0)) + fieldName.substring(1), fieldType);
                     Object value = null;
                     
                     if (!fieldType.isArray()) {
                         if (String.class == fieldType) {
                             value = "";
                         } else if (isTypePrimitive(fieldType)){
                            value = defaultPrimitiveValue(fieldType);
                         } else if (isTypeBoxable(fieldType)) {
                             value = defaultBoxableValue(fieldType);
                         } else {
                             try {
                                 logger.info("Going to instantiate field '" + field.getName() + " of type '" + fieldType.getName() + "'.");
                                value = newInstance(fieldType);
                            } catch (Exception e) {
                                // TODO Auto-generated catch block
                                logger.info(objectClass.getName() + ": Field '" + field.getName() + "' of type '" + fieldType.getName() + "' threw the following exception. We're, therefore, nulling the field.", e);
                                value = null;
                            }
                         }
                     }
                     
                     if (value != null) {
                         declaredMethod.invoke(object, value);
                     }
                 }
             }
         
             //Instantiate our parents....
             objectClass = objectClass.getSuperclass();
         }    
    }
     
    private static boolean isClassTypeJavaImplemented(Class<?> clazz) {
        //Ignore Sun's implementations
        return (clazz.getName().startsWith("java.") || clazz.getName().startsWith("javax.") || clazz.getName().startsWith("sun."));
    }
     
    /**
     * Check if the provided class type (or component type, if array) is an interface.
     * 
     * @param type
     * @return
     */
    private static boolean isTypeInterface(Class<?> type) {
        Class<?> clazz = type;
        if (clazz.isArray()) {
            clazz = getArrayComponentType(type);
        }
         
        return clazz.isInterface();
    }
     
    /**
     * Determines whether parent class and any of its instance variable are of the same type (including arrays).
     * To prevent {@link StackOverflowError} from occurring.
     * 
     * @param parent
     * @param other
     * @return
     */
    private static boolean isTypesIdentical(Class<?> parent, Class<?> other) {
        if (parent == other) {
            return true;
        }
         
        if (other.isArray() && !parent.isArray()) {
            Class<?> componentType = getArrayComponentType(other);
            return (parent == componentType);
        }
         
        if (parent.isArray() && !other.isArray()) {
            Class<?> componentType = getArrayComponentType(parent);
            return (other == componentType);
        }
         
        return false;
    }
 
    /**
     * Determines whether the type specified is a primitive type.
     * 
     * @param type
     * @return true, if it is, false otherwise.
     */
    private static boolean isTypePrimitive(Class<?> type) {
        return (char.class == type || byte.class == type || int.class == type || short.class == type
                || long.class == type || float.class == type
                || double.class == type || boolean.class == type);
    }
 
    /**
     * Determine whether the type is boxable (using autoboxing/unboxing).
     * 
     * @param type
     * @return
     */
    private static boolean isTypeBoxable(Class<?> type) {
        return (Character.class == type
                || Byte.class == type || Integer.class == type || Short.class == type
                || Long.class == type || Float.class == type
                || Double.class == type || Boolean.class == type);
    }
     
    /**
     * Returns a default value based on it's boxable type;
     * @param type
     * @return
     */
    private static Object defaultBoxableValue(Class<?> type) {
        if (Byte.class == type) {
            return Byte.valueOf((byte)0);
        }
         
        if (Character.class == type) {
            return Character.valueOf((char) 0);
        }
         
        if (Integer.class == type) {
            return Integer.valueOf(0);
        }
         
        if (Short.class == type) {
            return Short.valueOf((short)0);
        }
         
        if (Long.class == type) {
            return Long.valueOf(0);
        }
         
        if (Float.class == type) {
            return Float.valueOf(0f);
        }
         
        if (Double.class == type) {
            return Double.valueOf(0d);
        }
         
        if (Boolean.class == type) {
            return Boolean.FALSE;
        }
         
        return null;
    }
     
    /**
     * Returns a default value based on it's boxable type;
     * @param type
     * @return
     */
    private static Object defaultPrimitiveValue(Class<?> type) {
        if (byte.class == type) {
            return (byte)0;
        }
         
        if (char.class == type) {
            return (char) 0;
        }
         
        if (short.class == type) {
            return (short)0;
        }
         
        if (long.class == type) {
            return (long)0;
        }
         
        if (float.class == type) {
            return 0f;
        }
         
        if (double.class == type) {
            return 0d;
        }
         
        if (boolean.class == type) {
            return false;
        }
         
        //We assume it's an int
        return 0;
    }
     
    /**
     * <b>For arrays only:</b>: This method returns the dimension length of an array.
     * @param arrayClass
     * @return
     */
    private static int getArrayDimensionLength(Class<?> arrayClass) {
        if (!arrayClass.isArray()) {
            throw new IllegalArgumentException("Class '" + arrayClass.getName() + "' is not an array.");
        }
         
        int count = 0;
        Class<?> componentType = arrayClass;
        while (componentType.isArray()) {
            componentType = arrayClass.getComponentType();
            count++;
        }
         
        return count;
    }
     
    /**
     * <b>For arrays only:</b> This method returns the component type of the array.
     * @param arrayClass
     * @return
     */
    private static Class<?> getArrayComponentType(Class<?> arrayClass) {
        if (!arrayClass.isArray()) {
            throw new IllegalArgumentException("Class '" + arrayClass.getName() + "' is not an array.");
        }
         
        Class<?> componentType = arrayClass;
        while (arrayClass.isArray()) {
            componentType = arrayClass.getComponentType();
        }
         
        return componentType;
    }
}

If you have found any issues or have further things to see from this utility, please feel free to comment below or give a shout out! :-)

Happy coding! :-)

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POJO instantiator Utility

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