来自的流文件
来自的流文件
提问于 2017-07-11 14:32:48
下面是从下载文件的代码：
@Override
public void write(OutputStream outputStream) throws IOException {
try {
LOG.info(path);
InputStream stream = new ByteArrayInputStream(GoogleJsonKey.JSON_KEY.getBytes(StandardCharsets.UTF_8));
StorageOptions options = StorageOptions.newBuilder()
.setProjectId(PROJECT_ID)
.setCredentials(GoogleCredentials.fromStream(stream)).build();
Storage storage = options.getService();
final CountingOutputStream countingOutputStream = new CountingOutputStream(outputStream);
byte[] read = storage.readAllBytes(BlobId.of(BUCKET, path));
countingOutputStream.write(read);
} catch (Exception e) {
e.printStackTrace();
} finally {
outputStream.close();
}
}这是可行的，但这里的问题是，它必须先缓冲所有字节，然后才能流回该方法的客户端。这会导致大量的延迟，特别是当GCS中存储的文件很大时。
是否有一种方法可以从GCS和流直接获取文件到OutputStream，这里的OutputStream是用于Servlet的。
回答 5
Stack Overflow用户
回答已采纳
发布于 2017-07-11 16:11:13
澄清一下，你需要OutputStream还是InputStream？查看这一点的一种方法是，存储在对象中的数据作为文件存储，并且您有一个InputStream来读取该文件。如果这有效，继续读下去。
存储API中没有提供InputStream或OutputStream的现有方法。但是有云存储客户端库中的2个API，它公开了一个ReadChannel对象，该对象是从ReadableByteChannel (来自java )扩展而来的。
ReadChannel reader(String bucket, String blob, BlobSourceOption... options);
ReadChannel reader(BlobId blob, BlobSourceOption... options);使用此方法的一个简单示例(取自StorageSnippets.java)：
/**
* Example of reading a blob's content through a reader.
*/
// [TARGET reader(String, String, BlobSourceOption...)]
// [VARIABLE "my_unique_bucket"]
// [VARIABLE "my_blob_name"]
public void readerFromStrings(String bucketName, String blobName) throws IOException {
// [START readerFromStrings]
try (ReadChannel reader = storage.reader(bucketName, blobName)) {
ByteBuffer bytes = ByteBuffer.allocate(64 * 1024);
while (reader.read(bytes) > 0) {
bytes.flip();
// do something with bytes
bytes.clear();
}
}
// [END readerFromStrings]
}还可以使用newInputStream()方法将InputStream包装在ReadableByteChannel上。
public static InputStream newInputStream(ReadableByteChannel ch)
即使您需要一个OutputStream，您也应该能够将数据从InputStream或更好地从ReadChannel对象复制到OutputStream中。
完整示例
以以下方式运行此示例：PROGRAM_NAME <BUCKET_NAME> <BLOB_PATH>
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.Channels;
import java.nio.channels.WritableByteChannel;
import com.google.cloud.ReadChannel;
import com.google.cloud.storage.Bucket;
import com.google.cloud.storage.BucketInfo;
import com.google.cloud.storage.Storage;
import com.google.cloud.storage.StorageOptions;
/**
* An example which reads the contents of the specified object/blob from GCS
* and prints the contents to STDOUT.
*
* Run it as PROGRAM_NAME <BUCKET_NAME> <BLOB_PATH>
*/
public class ReadObjectSample {
private static final int BUFFER_SIZE = 64 * 1024;
public static void main(String[] args) throws IOException {
// Instantiates a Storage client
Storage storage = StorageOptions.getDefaultInstance().getService();
// The name for the GCS bucket
String bucketName = args[0];
// The path of the blob (i.e. GCS object) within the GCS bucket.
String blobPath = args[1];
printBlob(storage, bucketName, blobPath);
}
// Reads from the specified blob present in the GCS bucket and prints the contents to STDOUT.
private static void printBlob(Storage storage, String bucketName, String blobPath) throws IOException {
try (ReadChannel reader = storage.reader(bucketName, blobPath)) {
WritableByteChannel outChannel = Channels.newChannel(System.out);
ByteBuffer bytes = ByteBuffer.allocate(BUFFER_SIZE);
while (reader.read(bytes) > 0) {
bytes.flip();
outChannel.write(bytes);
bytes.clear();
}
}
}
}Stack Overflow用户
发布于 2018-06-23 07:41:35
目前，我能找到的最干净的选项如下：
Blob blob = bucket.get("some-file");
ReadChannel reader = blob.reader();
InputStream inputStream = Channels.newInputStream(reader);频道来自java.nio。此外，您还可以使用commons轻松地将InputStream读入OutputStream：
IOUtils.copy(inputStream, outputStream);Stack Overflow用户
发布于 2018-08-19 23:30:47
代码，基于@Tuxdude的答案
@Nullable
public byte[] getFileBytes(String gcsUri) throws IOException {
Blob blob = getBlob(gcsUri);
ReadChannel reader;
byte[] result = null;
if (blob != null) {
reader = blob.reader();
InputStream inputStream = Channels.newInputStream(reader);
result = IOUtils.toByteArray(inputStream);
}
return result;
}或
//this will work only with files 64 * 1024 bytes on smaller
@Nullable
public byte[] getFileBytes(String gcsUri) throws IOException {
Blob blob = getBlob(gcsUri);
ReadChannel reader;
byte[] result = null;
if (blob != null) {
reader = blob.reader();
ByteBuffer bytes = ByteBuffer.allocate(64 * 1024);
while (reader.read(bytes) > 0) {
bytes.flip();
result = bytes.array();
bytes.clear();
}
}
return result;
}助手代码：
@Nullable
Blob getBlob(String gcsUri) {
//gcsUri is "gs://" + blob.getBucket() + "/" + blob.getName(),
//example "gs://myapp.appspot.com/ocr_request_images/000c121b-357d-4ac0-a3f2-24e0f6d5cea185dffb40eee-850fab211438.jpg"
String bucketName = parseGcsUriForBucketName(gcsUri);
String fileName = parseGcsUriForFilename(gcsUri);
if (bucketName != null && fileName != null) {
return storage.get(BlobId.of(bucketName, fileName));
} else {
return null;
}
}
@Nullable
String parseGcsUriForFilename(String gcsUri) {
String fileName = null;
String prefix = "gs://";
if (gcsUri.startsWith(prefix)) {
int startIndexForBucket = gcsUri.indexOf(prefix) + prefix.length() + 1;
int startIndex = gcsUri.indexOf("/", startIndexForBucket) + 1;
fileName = gcsUri.substring(startIndex);
}
return fileName;
}
@Nullable
String parseGcsUriForBucketName(String gcsUri) {
String bucketName = null;
String prefix = "gs://";
if (gcsUri.startsWith(prefix)) {
int startIndex = gcsUri.indexOf(prefix) + prefix.length();
int endIndex = gcsUri.indexOf("/", startIndex);
bucketName = gcsUri.substring(startIndex, endIndex);
}
return bucketName;
}页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/45037540
复制相关文章
相似问题
腾讯云开发者
