package org.ovirt.engine.core.utils;
import java.lang.annotation.Annotation;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
/**
* General utilities for using Java's reflection mechanism.
*
*/
public class ReflectionUtils {
/**
* Find the first constructor of the given type which matches the expected parameters, which is the one which has
* parameters that can be assigned from the expected parameters.<br>
* <b>Note:</b> In case the type is a non-static inner class, then all it's constructors have the outer class as the
* first parameter.<br>
* <b>Warning:</b> The returned constructor may not be normally visible to the calling class, so use it with care.<br>
* <br>
* For example, suppose we have a class A and a class B which extends it:
* <ul>
* <li>If the class has 2 constructors accepting A and B (respectfully), and we look for one accepting A, then the A
* constructor is returned.</li>
* <li>If the class has 2 constructors accepting A and B (respectfully), and we look for one accepting B, then the
* first matching constructor is returned (not guaranteed to be the same each time).</li>
* <li>If the class has only a constructor accepting B, and we look for one accepting B, then the B constructor is
* returned.</li>
* <li>If the class has only a constructor accepting B, and we look for one accepting A, then <code>null</code> is
* returned.</li>
* <li>If the class has a default constructor and we don't expect any arguments, then it is returned.</li>
* </ul>
*
* @param type
* The type to look up the constructor for.
* @param expectedParams
* The expected parameters for the constructor.
*
* @return The right constructor, or <code>null</code> in none found.
*/
public static <T> Constructor<T> findConstructor(Class<T> type,
Class<?>... expectedParams) {
@SuppressWarnings("unchecked")
Constructor<T>[] constructors = (Constructor<T>[]) type.getDeclaredConstructors();
for (Constructor<T> constructor : constructors) {
if (isCompatible(expectedParams, constructor.getParameterTypes())) {
return constructor;
}
}
return null;
}
/**
* Check if the actual parameters are compatible with (assignable from) the expected parameters.
*
* @param expected
* The expected parameters.
* @param actual
* The actual parameters.
*
* @return <code>true</code> iff the actual parameters are the same length and are assignable from the expected
* ones.
*/
private static boolean isCompatible(Class<?>[] expected, Class<?>[] actual) {
if (expected.length != actual.length) {
return false;
}
for (int i = 0; i < expected.length; i++) {
if (!actual[i].isAssignableFrom(expected[i])) {
return false;
}
}
return true;
}
/**
* @param className
* The class to load.
* @return The class corresponding to the given classname.
*/
public static Class<?> getClassFor(String className) {
try {
return Class.forName(className);
} catch (ClassNotFoundException e) {
throw new IllegalStateException(e);
}
}
/**
*
* @param c the class
* @return the Table annotation of the class if exists, otherwise null.
*/
public static Annotation getTableAnnotation(Class c) {
Annotation[] annotations = (Annotation[]) c.getAnnotations();
for(Annotation annotation : annotations){
if(annotation instanceof javax.persistence.Table){
return annotation;
}
}
return null;
}
/**
* Get a Field Column annotation
* @param f the field in the class
* @return the Column annotation of the given Field
*/
public static Annotation getColumnAnnotation(Field f) {
Annotation[] annotations = (Annotation[]) f.getAnnotations();
for(Annotation annotation : annotations){
if(annotation instanceof javax.persistence.Column){
return annotation;
}
}
return null;
}
/**
* Get a Field Size annotation
* @param f
* @return
*/
public static Annotation getSizeAnnotation(Field f) {
Annotation[] annotations = (Annotation[]) f.getAnnotations();
for(Annotation annotation : annotations){
if(annotation instanceof javax.validation.constraints.Size){
return annotation;
}
}
return null;
}
}