package com.jysemel.java.basic.claasloader;

public class ClassLoaderDemo {

    public static void main(String[] args) {
        //父子关系 AppClassLoader-> ExtClassLoader-> BootStrapClassLoader
        ClassLoader demo  = ClassLoaderDemo.class.getClassLoader();
        System.out.println("demo " + demo);
        System.out.println("demo parent " + demo.getParent());

        //BootStrapClassLoader 引导类加载器，由C++ 实现，无法获取
        System.out.println("BootStrapClassLoader " + demo.getParent().getParent());

        //String,Integer 等基础均由 BootStrapClassLoader 加载
        ClassLoader c1 = String.class.getClassLoader();
        System.out.println("c1 " + c1);
        ClassLoader c2 = Integer.class.getClassLoader();
        System.out.println("c2 " + c2);
    }
}

package com.jysemel.java.basic.claasloader;

public class ClassLoaderDemo1 {

    public static void main(String[] args) {

        //BootStrapClassLoader
        System.out.println("BootStrapClassLoader " + System.getProperty("sun.boot.class.path"));
        //ExtClassLoader
        System.out.println("ExtClassLoader " + System.getProperty("java.ext.dirs"));
        //AppClassLoader
        System.out.println("AppClassLoader " + System.getProperty("java.class.path"));
    }
}

package com.jysemel.java.basic.claasloader;

import com.jysemel.java.basic.claasloader.spi.SpiService;

import java.util.ServiceLoader;

public class SpiDemo {

    public static void main(String[] args) {

        ServiceLoader<SpiService> serviceLoader = ServiceLoader.load(SpiService.class);

        System.out.println("加载到的 spiService 实现：");

        for (SpiService spiService : serviceLoader) {
            spiService.execute();
        }

    }
}

package com.jysemel.java.basic.claasloader.spi;

public interface SpiService {

    void execute();

}

package com.jysemel.java.basic.claasloader.spi;

public class SpiServiceImpl1 implements SpiService {
    
    @Override
    public void execute() {
        System.out.println("SpiServiceImpl1 执行，当前线程: " + Thread.currentThread().getName());
    }
}

package com.jysemel.java.basic.claasloader.spi;

public class SpiServiceImpl2 implements SpiService {

    @Override
    public void execute() {
        System.out.println("SpiServiceImpl2 执行，当前线程: " + Thread.currentThread().getName());
    }
}

package com.jysemel.java.basic.claasloader.loadclass;

import java.io.*;

public class MyClassLoader extends ClassLoader {

    @Override
    public Class<?> loadClass(String name) throws ClassNotFoundException {
        System.out.println("MyClassLoader 尝试加载类: " + name);
        // 1. 检查类是否已被加载
        Class<?> loadedClass = findLoadedClass(name);
        if (loadedClass != null) {
            System.out.println("类已加载，直接返回: " + name);
            return loadedClass;
        }
        // 2. 尝试使用父加载器加载（双亲委派）
        try {
            Class<?> parentLoaded = super.loadClass(name);
            System.out.println("父加载器成功加载: " + name);
            return parentLoaded;
        } catch (ClassNotFoundException e) {
            System.out.println("父加载器无法加载: " + name);
        }

        // 3. 如果父加载器失败，自己尝试加载（本例未实现，直接抛出异常）
        // 实际中可以在这里添加 findClass 逻辑
        throw new ClassNotFoundException("类 " + name + " 找不到");
    }
}

package com.jysemel.java.basic.claasloader.loadclass;

public class Test {
    public static void main(String[] args) throws Exception {
        // 创建自定义类加载器实例
        MyClassLoader loader = new MyClassLoader();

        // 使用自定义加载器加载一个存在的类（如 java.lang.String）
        Class<?> stringClass = loader.loadClass("java.lang.String");
        System.out.println("加载 String 的类加载器: " + stringClass.getClassLoader());

        System.out.println("----------------------------");

        // 加载一个不存在的类（触发异常）
        try {
            Class<?> unknownClass = loader.loadClass("com.example.Unknown");
        } catch (ClassNotFoundException e) {
            System.out.println("捕获异常: " + e.getMessage());
        }
    }
}