org.unix4j.util.Java7Util Maven / Gradle / Ivy
package org.unix4j.util;
/**
* Utility class with static methods to help loading a Java 7 version of a class
* if it is available, and the java 6 version otherwise.
*/
public class Java7Util {
/**
* The suffix used for Java 7 classes, the string "7".
*/
public static final String JAVA7_CLASS_NAME_SUFFIX = "7";
/**
* Returns a new instance of the Java 7 version of the given class if it
* exists and can be instantiated. Otherwise, the given
* {@code defaultInstance} is returned.
*
* The Java 7 version of the class must be a subtype of {@code baseClass}
* and its fully qualified name must be identical to that of
* {@code baseClass} with a suffix "7". For instance, if the Java 6 base
* class is called "org.unix4j.MyClass", the Java 7 version must be called
* "org.unix4j.MyClass7". Furthermore, the class must have a default
* constructor with no arguments.
*
* If the Java 7 version of the class is not found (usually because unix4j
* was compiled with a Java 6 compiler) or if the Java 7 class cannot be
* instantiated (usually because unix4j is run in a Java 6 JVM), the given
* {@code defaultInstance} is returned.
*
* @param
* the generic return type
* @param baseClass
* the base class and superclass of the Java 7 class
* @return a new instance of the Java 7 subtype if possible and
* {@code defaultInstance} otherwise
*/
public static T newInstance(Class baseClass, T defaultInstance) {
final Class clazz = loadClass(baseClass);
try {
return clazz.newInstance();
} catch (Exception e) {
return defaultInstance;
}
}
/**
* Returns the Java 7 version of the given class if it exists and can be
* loaded, and the given {@code baseClass} otherwise.
*
* The Java 7 version of the class must be a subtype of {@code baseClass}
* and its fully qualified name must be identical to that of
* {@code baseClass} with a suffix "7". For instance, if the Java 6 base
* class is called "org.unix4j.MyClass", the Java 7 version must be called
* "org.unix4j.MyClass7".
*
* If the Java 7 version of the class is not found (usually because unix4j
* was compiled with a Java 6 compiler), the given {@code defaultInstance}
* is returned. If the class is found but it is not a subtype of the given
* {@code baseClass}, an exception is thrown.
*
* @param
* the generic type of the base class
* @param baseClass
* the base class and superclass of the Java 7 class
* @return the Java 7 subclass if possible and {@code baseClass} otherwise
* @throws NullPointerException
* if {@code baseClass} is null
* @throws IllegalArgumentException
* if the Java 7 class is found but it is not a subclass of
* {@code baseClass}
*/
public static Class loadClass(Class baseClass) {
if (baseClass == null) {
throw new NullPointerException("baseClass cannot be null");
}
final Class java7Class;
try {
java7Class = Class.forName(baseClass.getName() + JAVA7_CLASS_NAME_SUFFIX);
} catch (ClassNotFoundException e) {
return baseClass;
}
if (baseClass.isAssignableFrom(java7Class)) {
return java7Class.asSubclass(baseClass);
}
throw new IllegalArgumentException("class " + java7Class.getName() + " is not a subclass of " + baseClass.getName());
}
}