最近在用aws的s3做云存储，把文件上传上去，在数据库中记录对应的url，下面是示例代码：

    public static String uploadToS3(File tempFile, String remoteFileName) throws IOException {
        PropertiesUtil propertiesUtil = new PropertiesUtil("s3.properties");
        //首先创建一个s3的客户端操作对象（需要amazon提供的密钥）
        AmazonS3 s3 = new AmazonS3Client(
                new BasicAWSCredentials(propertiesUtil.getKeyValue(Consts.S3_ACCESS_KEY),
                        propertiesUtil.getKeyValue(Consts.S3_SCERET_KEY)));
        Region usWest2 = Region.getRegion(Regions.US_WEST_2);
        s3.setRegion(usWest2);
        //设置bucket,key
        String bucketName = Consts.S3_BUCKET_NAME;
        String key = UUID.randomUUID() + ".apk";
        try {
            //验证名称为bucketName的bucket是否存在，不存在则创建
            if (!checkBucketExists(s3, bucketName)) {
                s3.createBucket(bucketName);
            }
            //上传文件
            s3.putObject(new PutObjectRequest(bucketName, key, tempFile));
            S3Object object = s3.getObject(new GetObjectRequest(bucketName, key));
            //获取一个request
            GeneratePresignedUrlRequest urlRequest = new GeneratePresignedUrlRequest(
                    bucketName, key);
            Date expirationDate = null;
            try {
                expirationDate = new SimpleDateFormat("yyyy-MM-dd").parse("2020-12-31");
            } catch (Exception e) {
                e.printStackTrace();
            }
            //设置过期时间
            urlRequest.setExpiration(expirationDate);
            //生成公用的url
            URL url = s3.generatePresignedUrl(urlRequest);
            System.out.println("=========URL=================" + url + "============URL=============");
            if (url == null) {
                throw new OperateFailureException("can't get s3 file url!");
            }
            return url.toString();
        } catch (AmazonServiceException ase) {
            ase.printStackTrace();
            logger.info("====================================AWS S3 UPLOAD ERROR START======================================");
            logger.info("Caught an AmazonServiceException, which means your request made it "
                    + "to Amazon S3, but was rejected with an error response for some reason.");
            logger.info("Caught an AmazonServiceException, which means your request made it "
                    + "to Amazon S3, but was rejected with an error response for some reason.");
            logger.info("Error Message:    " + ase.getMessage());
            logger.info("HTTP Status Code: " + ase.getStatusCode());
            logger.info("AWS Error Code:   " + ase.getErrorCode());
            logger.info("Error Type:       " + ase.getErrorType());
            logger.info("Request ID:       " + ase.getRequestId());
            logger.info(ase.getMessage(), ase);
            logger.info("====================================AWS S3 UPLOAD ERROR END======================================");
            throw new OperateFailureException("error occurs during upload to s3!");
        } catch (AmazonClientException ace) {
            logger.info("====================================AWS S3 UPLOAD ERROR START======================================");
            logger.info("Caught an AmazonClientException, which means the client encountered "
                    + "a serious internal problem while trying to communicate with S3, "
                    + "such as not being able to access the network.");
            logger.info("Error Message: " + ace.getMessage());
            logger.info("====================================AWS S3 UPLOAD ERROR END======================================");
            throw new OperateFailureException("error occurs during upload to s3!");
        }
    }

    /**
     * 验证s3上是否存在名称为bucketName的Bucket
     * @param s3
     * @param bucketName
     * @return
     */
    public static boolean checkBucketExists (AmazonS3 s3, String bucketName) {
        List<Bucket> buckets = s3.listBuckets();
        for (Bucket bucket : buckets) {
            if (Objects.equals(bucket.getName(), bucketName)) {
                return true;
            }
        }
        return false;
    }

 上面的代码只是一部分，整个过程是在jsp页面吧文件上传到后台，后台创建一个临时文件，把临时文件上传到s3上，并获取一个可以下载文件的url；

这里是一个英文的参考：http://ceph.com/docs/master/radosgw/s3/java/