1、类加载器的层次结构
在双亲委托机制中，各个加载器按照父子关系形成了树形结构（逻辑意义），除了根加载器之外，其余的类加载器都有且只有一个父加载器。
public class MyTest13 {
public static void main(String[] args) {
ClassLoader classLoader = ClassLoader.getSystemClassLoader();
System.out.println(classLoader);
while (null != classLoader){
classLoader = classLoader.getParent();
System.out.println(classLoader);
}
}
}
打印结果
sun.misc.Launcher$AppClassLoader@18b4aac2 sun.misc.Launcher$ExtClassLoader@1540e19d null
null说明classLoader是启动类加载器
2、类加载器的双亲委托机制
3、返回String类的ClassLoader
public class MyTest7 {
public static void main(String[] args) throws Exception{
Class<?> clazz = Class.forName("java.lang.String");
ClassLoader classLoader = clazz.getClassLoader();
System.out.println(classLoader);
}
}
返回结果
null
null说明classLoader是启动类加载器
4、返回自定义类的ClassLoader
public class MyTest7 {
public static void main(String[] args) throws Exception{
Class<?> clazz2 = Class.forName("com.example.jvm.classloader.C");
ClassLoader classLoader2 = clazz2.getClassLoader();
System.out.println(classLoader2);
}
}
class C{
}
返回结果
sun.misc.Launcher$AppClassLoader@18b4aac2
5、获得class文件的路径
public class MyTest14 {
public static void main(String[] args) throws IOException{
ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
System.out.println(classLoader);
String resourceName = "com/example/jvm/classloader/MyTest13.class";
Enumeration<URL> urls = classLoader.getResources(resourceName);
while (urls.hasMoreElements()){
URL url = urls.nextElement();
System.out.println(url);
}
}
}
打印结果：
sun.misc.Launcher$AppClassLoader@18b4aac2 file:/D:/workspace/study/%20jvm_demo/build/classes/java/main/com/example/jvm/classloader/MyTest13.class
6、获得ClassLoader的途径
获得当前类的ClassLoader
clazz.getClassLoader();
获得当前线程的上下文ClassLoader
Thread.currentThread().getContextClassLoader()
获得系统的ClassLoader
ClassLoader.getSystemClassLoader();
获得调用者的ClassLoader
DriverManager.getCallerClassLoader()