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