apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/entity/vo/NamespaceIdentifier.java/NamespaceIdentifier/toString
class NamespaceIdentifier:  @Override
  public String toString() {
    return "NamespaceIdentifer{" +
        "appId='" + appId + '\'' +
        ", env='" + env + '\'' +
        ", clusterName='" + clusterName + '\'' +
        ", namespaceName='" + namespaceName + '\'' +
        '}';
  }