apollo-core/src/main/java/com/ctrip/framework/apollo/core/dto/ApolloConfig.java/ApolloConfig/toString
class ApolloConfig:  @Override
  public String toString() {
    final StringBuilder sb = new StringBuilder("ApolloConfig{");
    sb.append("appId='").append(appId).append('\'');
    sb.append(", cluster='").append(cluster).append('\'');
    sb.append(", namespaceName='").append(namespaceName).append('\'');
    sb.append(", configurations=").append(configurations);
    sb.append(", releaseKey='").append(releaseKey).append('\'');
    sb.append('}');
    return sb.toString();
  }