package java.lang;

public class Integer {

    public void print(){
        System.out.println("this is Integer.");
    }

    public static void main(String[] args) {
        new Integer().print();
    }
}

protected Class<?> findClass(String name) throws ClassNotFoundException {
        throw new ClassNotFoundException(name);
    }

package com.aliencat.javabase.classloader;

public class MyClassLoader extends ClassLoader{

    protected Class<?> findClass(String name) throws ClassNotFoundException {
        switch (name){
            case "java.lang.Integer":return Double.class;
            case "com.aliencat.javabase.classloader.LoaderDemo" :  return loadClassFromDisk(name);
        }
        throw new ClassNotFoundException(name);
    }

    //從calsspath下加載類(lèi)的字節(jié)碼文件
    public byte[] loadClassFromDisk(String name) {
        String classPathRoot = Thread.currentThread().getContextClassLoader().getResource("").getPath();
        classPathRoot = classPathRoot.substring(1);
        String filePath = classPathRoot + name.replace(".","/") + ".class";
        try(InputStream in = new FileInputStream(filePath) ;
            ByteOutputStream stream = new ByteOutputStream()) {
            byte[] buff = new byte[1024];
            for(int num = 0; (num=in.read(buff)) != -1;){
                stream.write(buff,0,num);
            }
            return stream.toByteArray();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }


    public static void main(String[] args) throws ClassNotFoundException {
        Class clzz = new MyClassLoader().loadClass("com.aliencat.javabase.classloader.LoaderDemo");
        System.out.println(clzz);
        clzz = new MyClassLoader().loadClass("java.lang.Integer");
        System.out.println(clzz);
        clzz = new MyClassLoader().loadClass("java.lang.String");
        System.out.println(clzz);
        clzz = new MyClassLoader().loadClass("java.lang.xxxxx");
        System.out.println(clzz);
    }
}

  protected Class<?> loadClass(String name, boolean resolve)
            throws ClassNotFoundException
    {
        synchronized (getClassLoadingLock(name)) {
            // 首先，在當(dāng)前加載器加載過(guò)的類(lèi)中檢查這個(gè)類(lèi)有沒(méi)有被加載過(guò)
            Class<?> c = findLoadedClass(name);
            if (c == null) {
                long t0 = System.nanoTime();
                try {
                    if (parent != null) {
                        //存在上層類(lèi)加載器，則讓上層取執(zhí)行l(wèi)oadClass方法
                        c = parent.loadClass(name, false);
                    } else {
                        //讓BootstrapClass類(lèi)加載器去查找該類(lèi)
                        c = findBootstrapClassOrNull(name);
                    }
                } catch (ClassNotFoundException e) {
                    // 上層類(lèi)加載器拋出了ClassNotFoundException 則不進(jìn)行處理

                }

                if (c == null) {

                    long t1 = System.nanoTime();
                    // 如果上層類(lèi)加載器都沒(méi)有找到
                    // 那么這個(gè)類(lèi)加載器自己去找
                    // 如果找到了，則將resolve置為true
                    c = findClass(name);

                    // 這是定義類(lèi)加載器；記錄統(tǒng)計(jì)數(shù)據(jù)
                    sun.misc.PerfCounter.getParentDelegationTime().addTime(t1 - t0);
                    sun.misc.PerfCounter.getFindClassTime().addElapsedTimeFrom(t1);
                    sun.misc.PerfCounter.getFindClasses().increment();
                }
            }
            if (resolve) {
                //解析此類(lèi)的信息
                resolveClass(c);
            }
            return c;
        }
    }

public class MyClassLoader extends ClassLoader {

    public static void main(String[] args) throws ClassNotFoundException {
        Class clzz = new MyClassLoader().loadClass("com.aliencat.javabase.classloader.ClassTest");
        System.out.println(clzz);
        clzz = new MyClassLoader().loadClass("java.lang.Double");
        System.out.println(clzz);
        clzz = new MyClassLoader().loadClass("java.lang.String");
        System.out.println(clzz);
    }

    protected Class<?> findClass(String name) throws ClassNotFoundException {
        switch (name) {
            case "java.lang.Double":
                return Integer.class;
            case "java.lang.Object":  //如果去掉此項(xiàng)，則破壞雙親委任的情況下會(huì)報(bào)找不到Object的NoClassDefFoundError異常
                return Object.class;
            case "com.aliencat.javabase.classloader.ClassTest":
                byte[] bytes = loadClassFromDisk(name);
                if(bytes != null){
                    return defineClass(name,bytes,0,bytes.length);
                }else {
                    return null;
                }
        }
        throw new ClassNotFoundException(name);
    }

    //從calsspath下加載類(lèi)的字節(jié)碼文件
    public byte[] loadClassFromDisk(String name) {
        String classPathRoot = Thread.currentThread().getContextClassLoader().getResource("").getPath();
        classPathRoot = classPathRoot.substring(1);
        String filePath = classPathRoot + name.replace(".","/") + ".class";
        try(InputStream in = new FileInputStream(filePath) ;
            ByteOutputStream stream = new ByteOutputStream()) {
            byte[] buff = new byte[1024];
            for(int num = 0; (num=in.read(buff)) != -1;){
                stream.write(buff,0,num);
            }
            return stream.toByteArray();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }

    protected Class<?> loadClass(String name, boolean resolve)
            throws ClassNotFoundException {
        synchronized (LoaderDemo.class) {
            // 首先，在當(dāng)前加載器加載過(guò)的類(lèi)中檢查這個(gè)類(lèi)有沒(méi)有被加載過(guò)
            Class<?> c = findLoadedClass(name);
            if (c == null) {
                //沒(méi)加載過(guò)的話(huà)就去磁盤(pán)對(duì)應(yīng)路徑下去找
                c = findClass(name);
            }
            return c;
        }
    }

}

class ClassTest{

}