JVM 修改类加载器启动类加载器

1、类加载器加载路径

public class MyTest18 {

    public static void main(String[] args) {

        //系统类加载器加载路径

        System.out.println(System.getProperty("sun.boot.class.path"));

        System.out.println();

        //扩展类加载器加载路径

        System.out.println(System.getProperty("java.ext.dirs"));

        System.out.println();

        //应用类加载器加载路径

        System.out.println(System.getProperty("java.class.path"));

    }

}

　　

返回结果

C:\Program Files\Java\jdk1.8.0_131\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\rt.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\sunrsasign.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_131\jre\classes

C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext;C:\Windows\Sun\Java\lib\ext

C:\Program Files\Java\jdk1.8.0_131\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_131\jre\lib\rt.jar;D:\workspace\study\ jvm_demo\build\classes\java\main;D:\Program Files\JetBrains\IntelliJ IDEA 2017.1.4\lib\idea_rt.jar

　　将打印结果变成多行数据

C:\Program Files\Java\jdk1.8.0_131\jre\lib\resources.jar;

C:\Program Files\Java\jdk1.8.0_131\jre\lib\rt.jar;

C:\Program Files\Java\jdk1.8.0_131\jre\lib\sunrsasign.jar;

C:\Program Files\Java\jdk1.8.0_131\jre\lib\jsse.jar;

C:\Program Files\Java\jdk1.8.0_131\jre\lib\jce.jar;

C:\Program Files\Java\jdk1.8.0_131\jre\lib\charsets.jar;

C:\Program Files\Java\jdk1.8.0_131\jre\lib\jfr.jar;

C:\Program Files\Java\jdk1.8.0_131\jre\classes

C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext;C:\Windows\Sun\Java\lib\ext

C:\Program Files\Java\jdk1.8.0_131\jre\lib\charsets.jar;

C:\Program Files\Java\jdk1.8.0_131\jre\lib\deploy.jar;

C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\access-bridge-64.jar;

C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\cldrdata.jar;

C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\dnsns.jar;

C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\jaccess.jar;

C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\jfxrt.jar;

C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\localedata.jar;

C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\nashorn.jar;

C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\sunec.jar;

C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\sunjce_provider.jar;

C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\sunmscapi.jar;

C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\sunpkcs11.jar;

C:\Program Files\Java\jdk1.8.0_131\jre\lib\ext\zipfs.jar;

C:\Program Files\Java\jdk1.8.0_131\jre\lib\javaws.jar;

C:\Program Files\Java\jdk1.8.0_131\jre\lib\jce.jar;

C:\Program Files\Java\jdk1.8.0_131\jre\lib\jfr.jar;

C:\Program Files\Java\jdk1.8.0_131\jre\lib\jfxswt.jar;

C:\Program Files\Java\jdk1.8.0_131\jre\lib\jsse.jar;

C:\Program Files\Java\jdk1.8.0_131\jre\lib\management-agent.jar;

C:\Program Files\Java\jdk1.8.0_131\jre\lib\plugin.jar;

C:\Program Files\Java\jdk1.8.0_131\jre\lib\resources.jar;

C:\Program Files\Java\jdk1.8.0_131\jre\lib\rt.jar;

D:\workspace\study\ jvm_demo\build\classes\java\main;

D:\Program Files\JetBrains\IntelliJ IDEA 2017.1.4\lib\idea_rt.jar

　　

2、修改类加载器启动类加载器

现在想把自己生成的类交给启动类加载器，那要怎么做呢？

主需要把生成的class文件放到根加载器的加载路径下 C:\Program Files\Java\jdk1.8.0_131\jre\classes

创建测试类

public class MyTest18_1 {

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

        MyTest16 loader1 = new MyTest16("loader1");

        loader1.setPath("D:/temp/");

        Class<?> clazz = loader1.loadClass("com.example.jvm.classloader.MyTest1");

        System.out.println("class: " +clazz.hashCode());

        System.out.println("class loader: " + clazz.getClassLoader());

    }

}

　　

运行结果如下：

class: 356573597

class loader: null

　　说明是启动加载器加载的MyTest1