在此记载Java动态重新加载Class的点点滴滴,实现之前也在网上看了很多文章,但发现不是很清晰,后来发现总结,看源码实现还是最靠谱。
直接上代码:
package com.lkb.autoCode.util; import com.lkb.autoCode.constant.AutoCodeConstant; import java.io.File;
import java.io.FileInputStream;
import java.io.InputStream; /**
* DynamicClassLoader 动态类加载器
*
* @author Lilin
* @date 2016/5/23
*/
public class DynamicClassLoader extends ClassLoader { private String classPath; public DynamicClassLoader(String classPath, ClassLoader parent) {
super(parent);
this.classPath = classPath;
} @Override
public Class<?> loadClass(String name) throws ClassNotFoundException {
// 判断当前加载的类是否是需要动态重新加载的类,
// 假如是通过重写的findClass在自定义的ClassLoader里面加载,
// 假如不是就调用父ClassLoader默认加载
if (name != null && name.equals(classPath)) {
return findClass(name);
}
return super.loadClass(name, false);
} /**
* 根据类名查找class
*
* @param fullClassPath 类全路径(包)
* @return
* @throws ClassNotFoundException
*/
@Override
protected Class<?> findClass(String fullClassPath)
throws ClassNotFoundException {
byte[] raw = readClassBytes(fullClassPath);
// definClass方法参数说明:name:类包的全路径如com.lkb.sb.client.shanghaiC.ShangHaiLoginClient
// b:读取的class文件的byte数组
// off:从byte数组中读取的索引
// len:从byte数组中读取的长度
// 注:假如此类中有引入别的class类,如com.lkb.sb.client.BaseClient,循环执行findClass方法
Class<?> clazz = defineClass(fullClassPath, raw, 0, raw.length);
// 连接class
resolveClass(clazz);
return clazz;
} /**
* 读取class
*
* @param fullClassPath
* @return
*/
private byte[] readClassBytes(String fullClassPath) {
byte[] raw = null;
InputStream stream = null;
try {
File file = new File(AutoCodeConstant.BASE_PATH + fullClassPath.replaceAll("\\.", "/") + AutoCodeConstant.CLASS_SUFFIX);
stream = new FileInputStream(file);
raw = new byte[(int) file.length()];
stream.read(raw);
} catch (Exception e) { } finally {
try {
stream.close();
} catch (Exception e) {
}
}
return raw;
} }
注:调用方式:
// 通过自定义类加载器来加载
// 获取类的完成路径
String fullClassPath = getFullClassPath(AutoCodeConstant.CLIENT_PACKAGE, provinceCode, cityCode, AutoCodeConstant.LOGIN_CLIENT);
// 父ClassLoader设为当前线程的ClassLoader,试过使用ClassLoader.getSystemClassLoader(),发现获取的是系统级的,懒加载的类找不到
dynamicClassLoader = new DynamicClassLoader(fullClassPath, Thread.currentThread().getContextClassLoader());
loginInterface = (LoginInterface) dynamicClassLoader.loadClass(fullClassPath).getConstructor(new Class[]{CommonLoginSb.class, SbDefultModel.class}).newInstance(new Object[]{commonLoginSb, sbDefultModel});
// 执行start方法
resOutput = loginInterface.start(commonLoginSb.getMethod());