package jvm;



 import java.io.File;

 import java.io.FileInputStream;

 import java.lang.reflect.Method;



 public class LoaderSomeClass {

public static void main(String[] args) throws Exception {

ClassLoaderSub classLoaderSub = new ClassLoaderSub();

Class clazz = classLoaderSub.getClassByFile("C:/A.class");

System.out.println("类的名字：" + clazz.getName());

System.out.println("类的加载器：" + clazz.getClassLoader());

classLoaderSub.loadClass(A.class.getName());

Object obj = clazz.newInstance();

Method method = clazz.getMethod("doSome");

method.invoke(obj, null);

}

 }



 class ClassLoaderSub extends ClassLoader {

public Class defineClassByName(String name, byte[] b, int off, int len) {

// 由于defineClass是protected，所以需要继承后来调用

Class clazz = super.defineClass(name, b, off, len);

return clazz;

}



public Class getClassByFile(String fileName) throws Exception {

File classFile = new File(fileName);

// 一般的class文件通常都小于100k，如果现实情况超出这个范围可以放大长度

byte bytes[] = new byte[102400];

FileInputStream fis = null;

Class clazz = null;

try {

fis = new FileInputStream(classFile);

int j = 0;

while (true) {

int i = fis.read(bytes);

if (i == -1)

break;

j += i;

}

clazz = defineClassByName(null, bytes, 0, j);

} finally {

fis.close();

return clazz;

}

}
}


package jvm;


 public class A {
public static void doSome() {
System.out.println("!!!!!");
}
 }