进度条用于指示上传或下载文件的进度。本文以ossClient.getObject方法为例，介绍如何使用进度条。

以下代码用于演示通过ossClient.getObject下载文件时使用进度条的方法。

static class GetObjectProgressListener implements ProgressListener {
        private long bytesRead = 0;
        private long totalBytes = -1;
        private boolean succeed = false;
        @Override
        public void progressChanged(ProgressEvent progressEvent) {
            long bytes = progressEvent.getBytes();
            ProgressEventType eventType = progressEvent.getEventType();
            switch (eventType) {
            case TRANSFER_STARTED_EVENT:
                System.out.println("Start to download......");
                break;
            case RESPONSE_CONTENT_LENGTH_EVENT:
                this.totalBytes = bytes;
                System.out.println(this.totalBytes + " bytes in total will be downloaded to a local file");
                break;
            case RESPONSE_BYTE_TRANSFER_EVENT:
                this.bytesRead += bytes;
                if (this.totalBytes != -1) {
                    int percent = (int)(this.bytesRead * 100.0 / this.totalBytes);
                    System.out.println(bytes + " bytes have been read at this time, download progress: " +
                            percent + "%(" + this.bytesRead + "/" + this.totalBytes + ")");
                } else {
                    System.out.println(bytes + " bytes have been read at this time, download ratio: unknown" +
                            "(" + this.bytesRead + "/...)");
                }
                break;
            case TRANSFER_COMPLETED_EVENT:
                this.succeed = true;
                System.out.println("Succeed to download, " + this.bytesRead + " bytes have been transferred in total");
                break;
            case TRANSFER_FAILED_EVENT:
                System.out.println("Failed to download, " + this.bytesRead + " bytes have been transferred");
                break;
            default:
                break;
            }
        }
        public boolean isSucceed() {
            return succeed;
        }
    }
public static void main(String[] args) { 
    // Endpoint以杭州为例，其它Region请按实际情况填写。
    String endpoint = "http://oss-cn-hangzhou.aliyuncs.com";
    // 阿里云主账号AccessKey拥有所有API的访问权限，风险很高。强烈建议您创建并使用RAM账号进行API访问或日常运维，请登录RAM控制台创建RAM账号。
    String accessKeyId = "<yourAccessKeyId>";
    String accessKeySecret = "<yourAccessKeySecret>";
    String bucketName = "<yourBucketName>";
    String objectName = "<yourObjectName>";
    OSS ossClient = new OSSClientBuilder().build(endpoint, accessKeyId, accessKeySecret);
    try {            
            // 下载文件的同时指定了进度条参数。
            ossClient.getObject(new GetObjectRequest(bucketName, objectName).
                    <GetObjectRequest>withProgressListener(new GetObjectProgressListener()),
                    new File("<yourLocalFile>"));
    } catch (Exception e) {
        e.printStackTrace();
    }
    // 关闭OSSClient。
    ossClient.shutdown();
}

ossClient.putObject、ossClient.getObject、ossClient.uploadPart、ossClient.uploadFile以及ossClient.downloadFile方法均支持进度条功能，使用方法与ossClient.getObject类似。

下载文件的进度条使用方法的完整代码请参见GitHub。