反射机制进行动态调用的两种创建方法实例与hama中的反射机制

package combine.invokeTest;

public class InvokeTest {

public static BaseClass getClass(String className) throws ClassNotFoundException {
return (BaseClass) ClassFactory.newInstance1(className);
//		return (BaseClass) ClassFactory.newInstance2(className);
}

public static void main(String[] args) throws InstantiationException,
IllegalAccessException, SecurityException {
try {
String className = "combine.invokeTest.SubClass" ;
BaseClass bClass = getClass(className) ;
bClass.f() ;
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (IllegalArgumentException e) {
e.printStackTrace();
}
}
}

class BaseClass {

BaseClass() {
System.out.println("BaseClass Construct!");
}

public void f() {
System.out.println("BaseClass! ");
}
}

class SubClass extends BaseClass {
SubClass() {
System.out.println("SubClass Construct!");
}

public void f() {
System.out.println("SubClass!");
}
}

package combine.invokeTest;

import java.lang.reflect.Constructor;

import org.apache.hadoop.conf.Configuration;

public class ClassFactory {
private static final Class<?>[] EMPTY_ARRAY = new Class[]{};

public static <T> T newInstance1(String classPath) {
T result;
try {
Class<?> policy = Class.forName(classPath);
result = (T) policy.newInstance();  //采用Class对象的newInstance
} catch (Exception e) {
throw new RuntimeException(e);
}
return result;
}

public static <T> T newInstance2( String classPath) {
T result;
try {
Class<?>  theClass = Class.forName(classPath);
Constructor<T> meth = (Constructor<T>)theClass.getDeclaredConstructor(EMPTY_ARRAY);
meth.setAccessible(true);
result = meth.newInstance();       //采用Constructor对象的newInstance
} catch (Exception e) {
throw new RuntimeException(e);
}
return result;
}
}

public class MessageManagerFactory {
public static final String MESSAGE_MANAGER_CLASS = "hama.messenger.class";

/**
* Returns a messenger via reflection based on what was configured.
*
* @param conf
* @return a messenger that was configured.
*/
@SuppressWarnings("unchecked")
public static <M extends Writable> MessageManager<M> getMessageManager(
Configuration conf) throws ClassNotFoundException {
return (MessageManager<M>) ReflectionUtils.newInstance(conf
.getClassByName(conf.get(MESSAGE_MANAGER_CLASS,
org.apache.hama.bsp.message.HamaMessageManagerImpl.class
.getCanonicalName())), conf);
}

}

public static <T> T newInstance(Class<T> theClass, Configuration conf) {
T result;
try {
Constructor<T> meth = (Constructor<T>) CONSTRUCTOR_CACHE.get(theClass);
if (meth == null) {
meth = theClass.getDeclaredConstructor(EMPTY_ARRAY);
meth.setAccessible(true);
CONSTRUCTOR_CACHE.put(theClass, meth);
}
result = meth.newInstance(); //使用java.lang.reflect.Constructor<T>创建的constructor创建实例
} catch (Exception e) {
throw new RuntimeException(e);
}
setConf(result, conf);
return result;
}