apollo-client/src/main/java/com/ctrip/framework/apollo/model/ConfigFileChangeEvent.java/ConfigFileChangeEvent/toString
class ConfigFileChangeEvent:  @Override
  public String toString() {
    final StringBuilder sb = new StringBuilder("ConfigFileChangeEvent{");
    sb.append("namespace='").append(namespace).append('\'');
    sb.append(", oldValue='").append(oldValue).append('\'');
    sb.append(", newValue='").append(newValue).append('\'');
    sb.append(", changeType=").append(changeType);
    sb.append('}');
    return sb.toString();
  }