补全以下职责链模式的代码：抽象处理者：public abstract class Handler {//维持对下家的引用protected _____(1)______ successor;public void setSuccessor(Handler successor) {_____________(2)_________________;}public abstract void handleRequest(String request);}客户端：……Handler handler1, handler2, handler3;handler1 = new ConcreteHandlerA();handler2 = new ConcreteHandlerB();handler3 = new ConcreteHandlerC();//创建职责链handler1.________(3)__________;handler2.________(4)__________;//发送请求，请求对象通常为自定义类型_______(5)________.handleRequest("请求对象");……