only unpack data string if we're successful (java callbacks)
only unpack data string if we're successful (java callbacks)

songling88/zookeeper,rickypai/zookeeper,rickypai/zookeeper,zk-ruby/zookeeper,songling88/zookeeper,rickypai/zookeeper,zk-ruby/zookeeper,songling88/zookeeper,songling88/zookeeper,zk-ruby/zookeeper,rickypai/zookeeper