网站学什么,版面设计的概念,小程序app软件定制开发,搭建一个网站教程java类的动态加载
java动态加载的机制#xff1a; ClassLoader-SecureClassloader–URLClassLoader–AppClassLoader loadClass–findClass(重写方法)–defineClass(从字节码加载类)
初始化的时候会加载静态代码块 实例化的时候会加载构造代码块、无参构…java类的动态加载
java动态加载的机制 ClassLoader-SecureClassloader–URLClassLoader–AppClassLoader loadClass–findClass(重写方法)–defineClass(从字节码加载类)
初始化的时候会加载静态代码块 实例化的时候会加载构造代码块、无参构造函数
1、URLClassLoader动态加载任意类
测试静态类
package loadClass;import java.io.IOException;public class test {static {try {Runtime.getRuntime().exec(calc);} catch (IOException e) {e.printStackTrace();}}
}
测试动态加载
package loadClass;import com.sun.jndi.toolkit.url.UrlUtil;
import serializes.Person;import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLClassLoader;public class loadclass_test {public static void main(String[] args) throws ClassNotFoundException, IllegalAccessException, InstantiationException, MalformedURLException {//file协议加载//URLClassLoader urlClassLoader new URLClassLoader(new URL[] {new URL(file:///C:\\temp\\)}); //文件所在目录//http协议加载//URLClassLoader urlClassLoader new URLClassLoader(new URL[] {new URL(http://127.0.0.1:888/)});//jar协议URLClassLoader urlClassLoader new URLClassLoader(new URL[] {new URL(jar:file:///C:\\temp\\test.jar!/)});Class? loadClass urlClassLoader.loadClass(loadClass.test); //全名包名类名loadClass.newInstance();}
}执行完成截图
2、defineClass 动态加载任意类 ClassLoader systemClassLoader ClassLoader.getSystemClassLoader(); //获取系统的类加载器classloaderMethod defineClass ClassLoader.class.getDeclaredMethod(defineClass, String.class, byte[].class, int.class, int.class);defineClass.setAccessible(true);byte[] path Files.readAllBytes(Paths.get(C:\\temp\\test.class));Class test (Class)defineClass.invoke(systemClassLoader, loadClass.test, path, 0, path.length);test.newInstance();3、Unsave动态加载任意类: ClassLoader systemClassLoader ClassLoader.getSystemClassLoader();Class c Unsafe.class;Field theUnsafe c.getDeclaredField(theUnsafe);theUnsafe.setAccessible(true);Unsafe unsafe (Unsafe)theUnsafe.get(null);byte[] path Files.readAllBytes(Paths.get(C:\\temp\\test.class));Class? test1 unsafe.defineClass(loadClass.test, path, 0, path.length, systemClassLoader, null);test1.newInstance();编译方法
javac test.java————test.class test.class——test.jar 打包成jar包jar cvf 要生成的jar文件名 类名
