/*
* SingletonLoader.java a dynamic class instantiation algorithm
* with singleton instantiation support.
*
* Copyright (C) Achim Westermann, created on 20.07.2004, 11:14:49
*
* ***** BEGIN LICENSE BLOCK *****
* Version: MPL 1.1/GPL 2.0/LGPL 2.1
*
* The contents of this collection are subject to the Mozilla Public License Version
* 1.1 (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
* http://www.mozilla.org/MPL/
*
* Software distributed under the License is distributed on an "AS IS" basis,
* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
* for the specific language governing rights and limitations under the
* License.
*
* The Original Code is the cpDetector code in [sub] packages info.monitorenter and
* cpdetector.
*
* The Initial Developer of the Original Code is
* Achim Westermann <achim.westermann@gmx.de>.
*
* Portions created by the Initial Developer are Copyright (c) 2007
* the Initial Developer. All Rights Reserved.
*
* Contributor(s):
*
* Alternatively, the contents of this file may be used under the terms of
* either the GNU General Public License Version 2 or later (the "GPL"), or
* the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
* in which case the provisions of the GPL or the LGPL are applicable instead
* of those above. If you wish to allow use of your version of this file only
* under the terms of either the GPL or the LGPL, and not to allow others to
* use your version of this file under the terms of the MPL, indicate your
* decision by deleting the provisions above and replace them with the notice
* and other provisions required by the GPL or the LGPL. If you do not delete
* the provisions above, a recipient may use your version of this file under
* the terms of any one of the MPL, the GPL or the LGPL.
*
* ***** END LICENSE BLOCK ***** *
*
* If you modify or optimize the code in a useful way please let me know.
* Achim.Westermann@gmx.de
*/
package info.monitorenter.cpdetector.reflect;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
/**
* <p>
* A stateless helper that performs dynamic class loading and instantiation with support for invoking
* Singleton-retrieval methods of classes if detected.
* </p>
* <p>
* Before invoking <code>someClass.newInstance()</code> the loaded class is inspected for methods, that are public,
* static, parameterless, contain the substring "intance" in their name (case-insensitive) and return an instance of the
* same type.
* </p>
* <p>
* If such a method is found, it is considered to be a singleton retrieval method and will be invoked instead of trying
* to use the default constructor triggered by <code>newInstance()</code> (which then should be private if it is
* really a singleton.
* </p>
* <p>
* This class is in turn a singleton as it only contains procedural code. For possible desireable future configuration
* requirements, the single public method is not declared static but bound to the singleton instance.
* </p>
*
* @author <a href="mailto:Achim.Westermann@gmx.de">Achim Westermann</a>
*
*/
public final class SingletonLoader {
private static SingletonLoader instance = null;
private Object[] dummyParameters = new Object[0];
/**
* Singleton retrieval
*/
private SingletonLoader() {
super();
}
public static SingletonLoader getInstance() {
if (instance == null) {
instance = new SingletonLoader();
}
return instance;
}
/**
* High-level method for instantiation of a new instance of the class specified by the given fully qualified class
* name with singleton retrieval support. Delegates to {@link #newInstance(Class)}.
*
*/
public Object newInstance(String fullyQualifiedClassName) throws InstantiationException,
IllegalAccessException, ClassNotFoundException {
Object ret = this.newInstance(Class.forName(fullyQualifiedClassName));
return ret;
}
/**
* Dynamic instantiation of the given type with singleton retrieval support as described in this class description.
*
*/
public Object newInstance(Class c) throws InstantiationException, IllegalAccessException {
Object ret = null;
Method[] methods = c.getDeclaredMethods();
Method m;
int modifiers;
// searching for static methods:
for (int i = 0; i < methods.length; i++) {
m = methods[i];
modifiers = m.getModifiers();
if ((modifiers & Modifier.STATIC) != 0) {
// searching for public access:
if ((modifiers & Modifier.PUBLIC) != 0) {
// searching for no parameters:
if (m.getParameterTypes().length == 0) {
// searching for return type:
if (m.getReturnType() == c) {
// searching for substring "instance" in method name:
if (m.getName().toLowerCase().indexOf("instance") != -1) {
try {
// Finally we found a singleton method:
// we are static and don't need an instance.
ret = m.invoke(null, dummyParameters);
} catch (IllegalArgumentException e) {
// This will not happen:
// we ensured that no arguments are needed.
e.printStackTrace();
} catch (IllegalAccessException e) {
// This will not happen (only in applet context perhaps or with some
// SecurityManager):
// we ensured public access.
e.printStackTrace();
} catch (InvocationTargetException e) {
e.printStackTrace();
}
}
}
}
}
}
}
// check, if we found a singleton:
if (ret == null) {
// try to invoke the default constructor:
Constructor[] constructors = c.getConstructors();
Constructor con = null;
// search for a parameterless constructor:
for (int i = 0; i < constructors.length; i++) {
con = constructors[i];
if (con.getParameterTypes().length == 0) {
// see, if public:
modifiers = con.getModifiers();
try {
if ((modifiers & Modifier.PUBLIC) == 0) {
// try to set accessible:
con.setAccessible(true);
}
// invokes the default constructor
ret = c.newInstance();
} catch (SecurityException se) {
// damn
}
}
}
}
if (ret == null) {
System.err.println("Unable to instantiate: " + c.getName()
+ ": no singleton method, no public default constructor.");
}
return ret;
}
}