- [x] I have searched the [issues](https://github.com/apache/incubator-dubbo/issues) of this repository and believe that this is not a duplicate.
- [x] I have checked the [FAQ](https://github.com/apache/incubator-dubbo/blob/master/FAQ.md) of this repository and believe that this is not a duplicate.

### Environment

* Dubbo version: 2.6.5
* Operating System version: Windows 7
* Java version: 1.8.0_31

### Steps to reproduce this issue
1. API的方式配置两个registry地址，例如：        registryConfig.setAddress("127.0.0.1:2181|127.0.0.1:2182")。

2. API的方式配置ReferenceConfig按照文档配置stub，例如：       referenceConfig.setStub("com.liupeng.dubbo.api.MyStub")。

  3.API的方式启动consumer。

Pls. provide [GitHub address] to reproduce this issue.

### Expected Result

What do you expected from the above steps？

### Actual Result

What actually happens?

If there is an exception, please attach the exception trace:

```
Just put your stack trace here!
```

import org.apache.dubbo.rpc.RpcException;
import org.apache.dubbo.rpc.cluster.Directory;
import org.apache.dubbo.rpc.cluster.Router;
import org.apache.dubbo.rpc.cluster.RouterFactory;
import org.apache.dubbo.rpc.cluster.router.MockInvokersSelector;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
/**
 * Abstract implementation of Directory: Invoker list returned from this Directory's list method have been filtered by Routers
 *
 */
public abstract class AbstractDirectory<T> implements Directory<T> {
    
    private static final Logger logger = LoggerFactory.getLogger(AbstractDirectory.class);
    private final URL url;
    private volatile boolean destroyed = false;
    private volatile URL consumerUrl;
    private volatile List<Router> routers;
    public AbstractDirectory(URL url) {
        this(url, null);
    }
    public AbstractDirectory(URL url, List<Router> routers) {
        this(url, url, routers);
    }
    public AbstractDirectory(URL url, URL consumerUrl, List<Router> routers) {
        if (url == null) {
            throw new IllegalArgumentException("url == null");
        }
        this.url = url;