类加载器测试与理解

package classLoader;
 
import java.io.File;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.net.MalformedURLException;
import java.net.URL;
 
import org.apache.log4j.Logger;
 
 
/**
 * @author eblly
 */
public class ClassLoaderTs {
 
	public static void main(String[] args) throws MalformedURLException, ClassNotFoundException, InstantiationException, IllegalAccessException, NoSuchMethodException, SecurityException, IllegalArgumentException, InvocationTargetException{
		
		IsolatedClassLoader loaderA = null;
		IsolatedClassLoader loaderB = null;
 
		File file = new File("F:/WIN_git/java_learning/target/classes");
		URL[] urls = new URL[] { file.toURL()};
		loaderA = new IsolatedClassLoader(urls);
		loaderB = new IsolatedClassLoader(urls);
		
		Class aClass = loaderA.findClass2("classLoader.CannotCastBean"); 
		Object obj = aClass.newInstance();
		
		Class bClass = loaderB.findClass2("classLoader.CannotCastBean"); 
		Object obj2 = bClass.newInstance(); 
		
		System.out.println(" obj class loader : " + obj.getClass().getClassLoader());
		System.out.println(" obj2 class loader : " + obj2.getClass().getClassLoader());
		
		/**
		 * ERROR A: java.lang.IllegalArgumentException: object is not an instance of declaring class
		 * obj2不是loaderA的实例。
		 */
//		Method method = aClass.getMethod("test", null);
//		method.invoke(obj2, null);		
		
		
		/**
		 * ERROR B: classLoader.CannotCastBean cannot be cast to classLoader.CannotCastBean
		 * ccb的ClassLoader是AppClassLoader,obj的ClassLoader是loaderA
		 * 不同类加载器实例的实体不可相互转换。
		 */
//		System.out.println("CannotCastBean ClassLoader:" + CannotCastBean.class.getClassLoader());
//		CannotCastBean ccb = (CannotCastBean)obj;
		
		/**
		 * ERROR C: java.lang.NoSuchMethodException: classLoader.CannotCastBean.test(classLoader.CannotCastBean)
		 * 此处的CannotCastBean的类加载器是AppClassLoader,
		 * CannotCastBean中的test方法的CannotCastBean类加载器是loaderA(IsolatedClassLoader).
		 * 因此找不到对应的方法。
		 * 如果将CannotCastBean换成String,则正常运行，因为此处和CannotCastBean的String的加载器都为Bootstrap loader。
		 */
		Method method = aClass.getMethod("test", CannotCastBean.class);
		method.invoke(obj,new CannotCastBean());	
	}
}

/**
 * @author eblly
 */
public class CannotCastBean {
 
	public void test(){
		System.out.println(" test cannot cast!!!");
		System.out.println(" this class loader : " + this.getClass().getClassLoader());
	}
	
	public void test(CannotCastBean ccb){
		System.out.println(" test cannot cast!!!");
		
		System.out.println(" this class loader : " + this.getClass().getClassLoader());
		System.out.println(" ccb class loader : " + ccb.getClass().getClassLoader());
		
		CannotCastBean2 ccb2 = new CannotCastBean2();
		System.out.println(ccb.getClass().getClassLoader());
		System.out.println(ccb2.getClass().getClassLoader());
		
	}
	
	public void test(String ccb){
		System.out.println(" test cannot cast!!!");
		
		System.out.println(" ccb class loader : " + ccb.getClass().getClassLoader());//ccb class loader : null
		
		CannotCastBean2 ccb2 = new CannotCastBean2();
		System.out.println("this:" + this.getClass().getClassLoader());//this:classLoader.IsolatedClassLoader@2e81d81e
		System.out.println("ccb2:" + ccb2.getClass().getClassLoader());//ccb2:classLoader.IsolatedClassLoader@2e81d81e
		
		Abean a = new Abean();
		System.out.println("a:" + a.getClass().getClassLoader());//a:classLoader.IsolatedClassLoader@2e81d81e
		
		HashMap map = new HashMap();
		System.out.println("map:" + map.getClass().getClassLoader());//map:null
 
		
	}
}