由于开发的需要,需要根据配置动态加载类,所以简单测试了一下JAVA动态加载类
定义接口
package loader;
public interface HelloIface {
public String hello();
public String sayHi(String name);
}
实现接口
在其他插件类实现此接口,并导出为jar,如D:/tmp/test.jar
package loader;
public class HelloImpl implements HelloIface{
@Override
public String hello() {
return "hello,JAVA世界";
}
@Override
public String sayHi() {
return "Hi,JAVA World " + name;
}
}
动态加载类
import java.lang.reflect.Method;
import java.net.URL;
import java.net.URLClassLoader;
public class LoadJar {
public static void main(String[] args) {
String classPath = "loader.HelloImpl";// Jar中的所需要加载的类的类名
String jarPath = "file:///D:/tmp/test.jar";// jar所在的文件的URL
loadJar1(classPath, jarPath);
loadClass(classPath);
loadJar2(classPath, jarPath);
loadClass(classPath);
}
public static void loadJar1(String classPath, String jarPath) {
ClassLoader cl;
try {
// 从Jar文件得到一个Class加载器
cl = new URLClassLoader(new URL[] { new URL(jarPath) });
// 从加载器中加载Class
Class<?> c = cl.loadClass(classPath);
// 从Class中实例出一个对象
HelloIface impl = (HelloIface) c.newInstance();
// 调用Jar中的类方法
System.out.println(impl.hello());
System.out.println(impl.sayHi("zhangsan"));
try {
HelloIface impl2 = (HelloIface) Class.forName(classPath)
.newInstance();
System.out.println(impl2.hello());
} catch (ClassNotFoundException e) {
System.out.println("非系统加载器加载的JAR,不能通过Class.forName使用");
}
} catch (Exception e) {
e.printStackTrace();
}
}
public static void loadJar2(String classPath, String jarPath) {
URLClassLoader urlLoader = (URLClassLoader) ClassLoader.getSystemClassLoader();
Class<URLClassLoader> sysClass = URLClassLoader.class;
try {
//改变方法的可见性(即通过反映访问本来不可以访问的方法)
Method method = sysClass.getDeclaredMethod("addURL", new Class[] { URL.class });
method.setAccessible(true);
method.invoke(urlLoader, new URL(jarPath));
Class<?> objClass = urlLoader.loadClass(classPath);
Object instance = objClass.newInstance();
Method method2 = objClass.getDeclaredMethod("sayHi", new Class[]{ String.class});
System.out.println(method2.invoke(instance, "zhangsan"));
HelloIface impl2 = (HelloIface) Class.forName(classPath).newInstance();
System.out.println(impl2.hello());
} catch (Exception e) {
e.printStackTrace();
}
}
public static void loadClass(String classPath){
try {
HelloIface impl2 = (HelloIface) Class.forName(classPath)
.newInstance();
System.out.println(impl2.hello());
} catch (Exception e) {
System.out.println("非系统加载器加载的JAR,不能通过Class.forName使用");
}
}
}