1, 共5个必备线程,和1个用户线程Thread[Thread-0,5,main] //[name,priority,group.name]
main group: 5-main; 5-Thread-0
system group: 10-Reference Handler, 9-Signal Dispatcher, 8-Finalizer, 5-Attach Listener
2,共2个ClassLoader:
Bootstrap classloader是C写的,故==null, 加载10-Reference Handler, 8-Finalizer
AppClassLoader,
/** * output : * Thread[Thread-0,5,main]====sun.misc.Launcher$AppClassLoader@5984cf08 * Thread[main,5,main]====sun.misc.Launcher$AppClassLoader@5984cf08 * Thread[Finalizer,8,system]====null [Bootstrap classloader] * Thread[Thread-0,5,main]====sun.misc.Launcher$AppClassLoader@5984cf08 * Thread[Reference Handler,10,system]====null [Bootstrap classloader] * Thread[Signal Dispatcher,9,system]====sun.misc.Launcher$AppClassLoader@5984cf08 * Thread[Attach Listener,5,system]====sun.misc.Launcher$AppClassLoader@5984cf08 * @author naijiang.wang * @date 2013-08-05 9:37:22 AM */ public class T { public static void main( String[] args ) throws Exception { new Thread(new Runnable() { @Override public void run() { Thread t0 = Thread.currentThread(); System.out.println(t0+"===="+t0.getContextClassLoader()); try { Thread.sleep( 1000 ); } catch ( InterruptedException e ) { e.printStackTrace(); } } }).start(); for(Thread t : Thread.getAllStackTraces().keySet()){ System.out.println(t+"===="+t.getContextClassLoader()); } } }
2,自定义java.lang package,会导致jvm错误:
关键:可以看出加载类顺序
package java.lang; /** * output: * Exception in thread "main" java.lang.SecurityException: Prohibited package name: java.lang at java.lang.ClassLoader.preDefineClass(ClassLoader.java:649) at java.lang.ClassLoader.defineClass(ClassLoader.java:785) at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142) at java.net.URLClassLoader.defineClass(URLClassLoader.java:449) at java.net.URLClassLoader.access$100(URLClassLoader.java:71) at java.net.URLClassLoader$1.run(URLClassLoader.java:361) at java.net.URLClassLoader$1.run(URLClassLoader.java:355) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:354) at java.lang.ClassLoader.loadClass(ClassLoader.java:423) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308) at java.lang.ClassLoader.loadClass(ClassLoader.java:356) at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:476) * @author rivertime.wang * @date 2014-3-8 15:06:38 */ public class TestClassLoader { public static void main(String[] args) { System.out.println("user define 'java.lang' package"); } }
3,bootstrap, sun.misc.Launcher$AppClassLoader, ExtClassLoader
public class Test { public static void main( String[] args ) throws IOException { System.out.println( System.getProperty( "java.class.path" ) ); // null,bootstrap classloader(不是ClassLoader实例) System.out.println( System.class.getClassLoader() ); // sun.misc.Launcher$AppClassLoader@4089f3e5 System.out.println( ClassLoader.getSystemClassLoader() ); System.out.println( Test.class.getClassLoader() ); // sun.misc.Launcher$ExtClassLoader@20eb607d System.out.println( ClassLoader.getSystemClassLoader().getParent() ); System.out.println( Test.class.getClassLoader().getParent() ); } }