简单的从文件系统中加载类

chzhh383

package com.hong.classLoader;import java.io.File;import java.io.FileInputStream;import java.io.IOException;public class FileClassLoader extends ClassLoader {private static int byteLength;public Class myLoadClass(String name) throws IOException {byte[] date = getBytesFromFile(name);// 参数name要包含包名,否则找不到return defineClass(this.getClass().getPackage().getName() + "." + name,date, 0, byteLength);}public byte[] getBytesFromFile(String name) throws IOException {FileInputStream fis = new FileInputStream(new File("D:\\eclipse\\workspace\\MyProject\\bin\\com\\hong\\classLoader\\"+ name + ".class"));byte[] data = new byte[2048];int ch;while ((ch = fis.read(data)) != -1) {byteLength = ch;}return data;}} 继承ClassLoader,从文件系统中读取类的class文件，转换成byte流，调用defineClass 返回Class对象
 
main调用：
package com.hong.classLoader;import java.io.IOException;public class AppMain {public static void main(String[] args) throws IOException, Exception{FileClassLoader fileClassLoader = new FileClassLoader();Class fileClass=fileClassLoader.myLoadClass( "FileClassLoader");System.out.println(fileClass.newInstance().toString());}}