java利用oss实现下载功能

<dependency>
  <groupId>com.aliyun.oss</groupId>
  <artifactId>aliyun-sdk-oss</artifactId>
  <version>3.6.0</version>
 </dependency>

public class OssParams {
 
 public static final String endpoint = "oss-cn-hangzhou.aliyuncs.com"; 
 public static final String accessKeyId = "";
 public static final String accessKeySecret = ""; 
 public static final String bucketName = "";
 
 public static final String rootName = "";//根目录
}

import com.aliyun.oss.ClientException;
import com.aliyun.oss.OSS;
import com.aliyun.oss.OSSClientBuilder;
import com.aliyun.oss.OSSException;
import com.aliyun.oss.model.AppendObjectRequest;
import com.aliyun.oss.model.ObjectMetadata;
import org.joda.time.DateTime;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
 
import java.io.ByteArrayInputStream;
import java.net.URL;
import java.util.Date;
import java.util.concurrent.atomic.AtomicLong;
 
import static OssParams.bucketName;
 
/**
 * 先做单例对象调用，防止多线程并发bug
 * 后期加入线程锁控制后，做成公共utils
 */
public class WriteLeadsOssUtils {
 private static Logger LOG = LoggerFactory.getLogger(WriteLeadsOssUtils.class.getName());
 
 private static final String fileSub = ".csv";
 
 private AtomicLong atomicLong = new AtomicLong(0L);
 
 private WriteLeadsOssUtils() {
 }
 
 private static class BuildWriteOSS {
  private static final WriteLeadsOssUtils instance = new WriteLeadsOssUtils();
 }
 
 public static WriteLeadsOssUtils getInstance() {
  return BuildWriteOSS.instance;
 }
 
 private OSS getOssClient() {
  return new OSSClientBuilder().build(OssParams.endpoint, OssParams.accessKeyId, OssParams.accessKeySecret);
 }
 
 public URL writeJSONObjectFile(String content,String fileName) {
  // 创建OSSClient实例。
  OSS ossClient = getOssClient();
  try {
   DateTime currentTime = new DateTime(System.currentTimeMillis());
//   String objectName = OssParams.rootName + currentTime.toString("yyyy-MM-dd-HH") + fileSub;
   String objectName = OssParams.rootName + fileName;
//   AppendObjectRequest appendObjectRequest = null;
   String data = content;
 
   ossClient.putObject(bucketName, objectName, new ByteArrayInputStream(content.getBytes()));
 
   Date expiration = new Date(System.currentTimeMillis() + 3600L * 1000 * 24 * 180);
   URL url = ossClient.generatePresignedUrl(bucketName, objectName, expiration);
 
   LOG.info("{} saved to OSS, url={}", objectName,url.toString());
//   for (IngestLeadingRequest param : params) {
//    String jsonStr = JSONObject.toJSONString(param);
//    JSONObject object = JSONObject.parseObject(jsonStr);
//    data += object.toJSONString() + "\n";
//   }
   //文件不存在
//   if (!ossClient.doesObjectExist(OssParams.bucketName, objectName)) {
//    atomicLong.set(0L);
//    appendObjectRequest = getAppendObjectRequest(data, true, objectName);
//    appendObjectRequest.setPosition(0L);
//   } else {
//    appendObjectRequest = getAppendObjectRequest(data, false, objectName);
//   }
//   AppendObjectResult appendObjectResult = ossClient.appendObject(appendObjectRequest);
//   atomicLong.set(appendObjectResult.getNextPosition());
//   System.gc();
   return url;
  } catch (OSSException e) {
   e.printStackTrace();
   return null;
  } catch (ClientException e) {
   e.printStackTrace();
   return null;
  } finally {
   ossClient.shutdown();
  }
 }
 
 
 /**
  * flag标志位，true为新文件，false为追加文件
  *
  * @param data
  * @param flag
  * @param objectName
  * @return
  */
 private AppendObjectRequest getAppendObjectRequest(String data, Boolean flag, String objectName) {
  ObjectMetadata meta = new ObjectMetadata();
  // 指定上传的内容类型。
  meta.setContentType("text/plain;charset=utf-8");
  if (flag == true) {
   return new AppendObjectRequest(bucketName, objectName,
     new ByteArrayInputStream(data.getBytes()), meta);
  } else {
   return new AppendObjectRequest(bucketName, objectName,
     new ByteArrayInputStream(data.getBytes()), meta).withPosition(atomicLong.get());
  }
 }
}

WriteLeadsOssUtils.getInstance().writeJSONObjectFile("hello");
//将hello作为内容存入oss，并获得可以下载的url