Java 动态加载jar和class文件实例解析

package com.demo.test;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLClassLoader;
public class DynamicLoadDemo {
	enum FileType {
		JAR, CLASS, OTHER
	}
	static class MyClassLoader extends ClassLoader {
		public synchronized Class<?> loadClass(String name, File file) throws FileNotFoundException {
			Class<?> cls = findLoadedClass(name);
			if(cls != null) {
				return cls;
			}
			FileInputStream fis = new FileInputStream(file);
			ByteArrayOutputStream baos = new ByteArrayOutputStream();
			byte[] buffer = new byte[1024];
			int len;
			try {
				while (true) {
					len = fis.read(buffer);
					if (len == -1) {
						break;
					}
					baos.write(buffer, 0, len);
				}
				//FileInputStream的flush是空操作，因为flush的作用是把缓存中的东西写入实体(硬盘或网络流)中，这里没有这种必要所以为空
				//baos.flush();
				byte[] data = baos.toByteArray();
				return defineClass(null, data, 0, data.length);
			}
			catch (IOException e) {
				e.printStackTrace();
			}
			finally {
				try {
					baos.close();
				}
				catch (IOException e) {
					e.printStackTrace();
				}
				try {
					fis.close();
				}
				catch (IOException e) {
					e.printStackTrace();
				}
			}
			return null;
		}
	}
	public static void main(String[] args) {
		String className = "com.demo.test.HelloWorld";
		String paths[] = { "HelloWorld.jar", "HelloWorld.class" };
		for (String path : paths) {
			String lowerPath = path.toLowerCase();
			FileType fileType = FileType.OTHER;
			if (lowerPath.endsWith(".jar") || lowerPath.endsWith(".zip")) {
				fileType = FileType.JAR;
			} else if (lowerPath.endsWith(".class")) {
				fileType = FileType.CLASS;
			}
			if (fileType == FileType.OTHER) {
				return;
			}
			File file = new File(path);
			if (!file.exists()) {
				return;
			}
			try {
				URL url = file.toURI().toURL();
				System.out.println(url.toString());
				Class<?> cls = null;
				switch (fileType) {
					case JAR:
					          URLClassLoader classLoader = new URLClassLoader(new URL[] { url }, Thread.currentThread().getContextClassLoader());
					cls = classLoader.loadClass(className);
					break;
					case CLASS:
					          MyClassLoader myClassLoader = new MyClassLoader();
					cls = myClassLoader.loadClass(className, file);
					break;
					default:
					          break;
				}
				if (cls == null) {
					return;
				}
				// 实例变量
				Field field = cls.getDeclaredField("hello");
				if (!field.isAccessible()) {
					field.setAccessible(true);
				}
				System.out.println(field.get(cls.newInstance()));
				// 调用静态不带参数方法
				Method staticMethod = cls.getDeclaredMethod("sayStaticHello", null);
				if (!staticMethod.isAccessible()) {
					staticMethod.setAccessible(true);
				}
				// 如果函数的返回值是void，就会返回null
				staticMethod.invoke(cls, null);
				// 实例带参数方法方法
				Method method = cls.getDeclaredMethod("say", String.class);
				if (!method.isAccessible()) {
					method.setAccessible(true);
				}
				Object ret = method.invoke(cls.newInstance(), "hello world");
				System.out.println(ret);
			}
			catch (MalformedURLException e) {
				e.printStackTrace();
			}
			catch (ClassNotFoundException e) {
				e.printStackTrace();
			}
			catch (NoSuchMethodException e) {
				e.printStackTrace();
			}
			catch (SecurityException e) {
				e.printStackTrace();
			}
			catch (IllegalAccessException e) {
				e.printStackTrace();
			}
			catch (IllegalArgumentException e) {
				e.printStackTrace();
			}
			catch (InvocationTargetException e) {
				e.printStackTrace();
			}
			catch (InstantiationException e) {
				e.printStackTrace();
			}
			catch (NoSuchFieldException e) {
				e.printStackTrace();
			}
			catch (FileNotFoundException e) {
				e.printStackTrace();
			}
		}
	}
}