dubbo-cluster/src/main/java/org/apache/dubbo/rpc/cluster/loadbalance/
ConsistentHashLoadBalance.java
![image](https://user-images.githubusercontent.com/30815149/55045041-740f4980-5077-11e9-8b6c-7a2b18b0d58e.png)
我看其他地方都是用Constants进行替换，这里是不是可以使用Constants类里的属性进行替换
* @see #CALLBACK_INSTANCES_LIMIT_KEY
     */
    public static final int DEFAULT_CALLBACK_INSTANCES = 1;
    public static final String CALLBACK_SERVICE_PROXY_KEY = "callback.service.proxy";
    public static final String IS_CALLBACK_SERVICE = "is_callback_service";
    /**
     * Invokers in channel's callback
     */
    public static final String CHANNEL_CALLBACK_KEY = "channel.callback.invokers.key";
    @Deprecated
    public static final String SHUTDOWN_WAIT_SECONDS_KEY = "dubbo.service.shutdown.wait.seconds";
    public static final String SHUTDOWN_WAIT_KEY = "dubbo.service.shutdown.wait";
    public static final String IS_SERVER_KEY = "isserver";
    /**
     * Default timeout value in milliseconds for server shutdown
     */
    public static final int DEFAULT_SERVER_SHUTDOWN_TIMEOUT = 10000;
    public static final String ON_CONNECT_KEY = "onconnect";
    public static final String ON_DISCONNECT_KEY = "ondisconnect";
    public static final String ON_INVOKE_METHOD_KEY = "oninvoke.method";
    public static final String ON_RETURN_METHOD_KEY = "onreturn.method";
    public static final String ON_THROW_METHOD_KEY = "onthrow.method";
    public static final String ON_INVOKE_INSTANCE_KEY = "oninvoke.instance";
    public static final String ON_RETURN_INSTANCE_KEY = "onreturn.instance";
    public static final String ON_THROW_INSTANCE_KEY = "onthrow.instance";
    public static final String OVERRIDE_PROTOCOL = "override";
    public static final String CONFIG_PROTOCOL = "config";
    public static final String PRIORITY_KEY = "priority";
    public static final String RULE_KEY = "rule";
    public static final String TYPE_KEY = "type";