![image](https://user-images.githubusercontent.com/14085645/35564102-fa158f28-05f3-11e8-92b4-6e552c96476d.png)
这里，如果invokers为空的话，创建loadbalancer也没有用吧？是否可以去掉？
import com.alibaba.dubbo.rpc.RpcException;
import com.alibaba.dubbo.rpc.cluster.Directory;
import com.alibaba.dubbo.rpc.cluster.LoadBalance;
import com.alibaba.dubbo.rpc.support.RpcUtils;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.atomic.AtomicBoolean;
/**
 * AbstractClusterInvoker
 *
 */
public abstract class AbstractClusterInvoker<T> implements Invoker<T> {
    private static final Logger logger = LoggerFactory
            .getLogger(AbstractClusterInvoker.class);
    protected final Directory<T> directory;
    protected final boolean availablecheck;
    private AtomicBoolean destroyed = new AtomicBoolean(false);
    private volatile Invoker<T> stickyInvoker = null;
    public AbstractClusterInvoker(Directory<T> directory) {
        this(directory, directory.getUrl());
    }
    public AbstractClusterInvoker(Directory<T> directory, URL url) {
        if (directory == null)
            throw new IllegalArgumentException("service directory == null");
        this.directory = directory;
        
        this.availablecheck = url.getParameter(Constants.CLUSTER_AVAILABLE_CHECK_KEY, Constants.DEFAULT_CLUSTER_AVAILABLE_CHECK);
    }
    public Class<T> getInterface() {
        return directory.getInterface();