Java底层：JVM(三）

版权声明：本文为博主原创文章，遵循 CC 4.0 BY-SA 版权协议，转载请附上原文出处链接和本声明。

本文链接： https://blog.csdn.net/hukehukehukehuke/article/details/102770854

谈谈ClassLoader

ClassLoader的种类

(1)BootStraoClassLoader:C++编写，加载核心库java.
(2)ExtClassLoader:Java编写，加载扩展库javax.
(3)AppClassLoader:java编写，加载程序所在目录
(4)用户自定义ClassLoader:java编写，定制化加载**

先自定义编译好一个java文件假如定义好了一个Wali.java的文件

具体代码实现

    public static void main(String[] args) throws Exception {
        MyClassLoader mc = new MyClassLoader("xxx","xxx");
        Class c = mc.loadClass("Wali");
        System.out.println(c.getClassLoader());
        c.newInstance();
    }
}



public class MyClassLoader extends ClassLoader {
    private String path;
    private String classLoaderName;
    public MyClassLoader(String path,String classLoaderName){
        this.path = path;
        this.classLoaderName = classLoaderName;
    }
    //用于寻找类文件
    public Class findClass(String name){
        byte[] b = loadClassDate(name);
        return defineClass(name,b,0,b.length);
    }
    //用于加载类文件
    private byte[] loadClassDate(String name) {
        name = path + name + ".class";
        InputStream in = null;
        ByteArrayOutputStream out = null;
        try {
            in = new FileInputStream(new File(name));
            out = new ByteArrayOutputStream();
            int i = 0;
            while ((i = in.read()) != -1) {
                out.write(i);
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                out.close();
                in.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return out.toByteArray();
    }
}