Question

我需要以编程方式从Blobstore中获取blob，而不需要事先知道大小。有谁知道怎么做？

我尝试过使用

BlobstoreService blobStoreService = BlobstoreServiceFactory.getBlobstoreService();
byte[] picture = blobStoreService.fetchData(blobKey, 0, Integer.MAX_VALUE);

但我收到错误，因为（至少看似）Integer.MAX_VALUE太大了。

java.lang.IllegalArgumentException: Blob fetch size 2147483648 it larger than maximum size 1015808 bytes.
at com.google.appengine.api.blobstore.BlobstoreServiceImpl.fetchData(BlobstoreServiceImpl.java:250)

那么有谁知道如何正确地做到这一点？另外如果你可以顺便告诉我，将相同的图像作为“jpeg”或“png”更好地进入blobstore吗？

Answer 1

希望这会有所帮助，这是我一直在做的方式：

        BlobstoreService blobstoreService = BlobstoreServiceFactory.getBlobstoreService();
        BlobKey blobKey = new BlobKey(KEY);

        // Start reading
        ByteArrayOutputStream out = new ByteArrayOutputStream();

        long inxStart = 0;
        long inxEnd = 1024;
        boolean flag = false;

        do {
            try {
                byte[] b = blobstoreService.fetchData(blobKey,inxStart,inxEnd);
                out.write(b);

                if (b.length < 1024)
                    flag = true;

                inxStart = inxEnd + 1;
                inxEnd += 1025;

            } catch (Exception e) {
                flag = true;
            }

        } while (!flag);

        byte[] filebytes = out.toByteArray();

我以前用过：

BlobInfo blobInfo = blobInfoFactory.loadBlobInfo(blobKey);
filesize = blobInfo.getSize();

获取大小，但由于某种原因，有时此信息为空。

也许所有这些都可以给你一个想法。

Answer 2

def blob_fetch(blob_key):
  blob_info = blobstore.get(blob_key)
  total_size = blob_info.size
  unit_size = blobstore.MAX_BLOB_FETCH_SIZE
  pos = 0
  buf = cStringIO.StringIO()
  try:
    while pos < total_size:
      buf.write(blobstore.fetch_data(blob_key, pos, min(pos + unit_size - 1, total_size)))
      pos += unit_size
    return buf.getvalue()
  finally:
    buf.close()

MAX_BLOB_FETCH_SIZE在文档中并不明显。

Answer 3

在Python中：

from google.appengine.ext.blobstore import BlobInfo
from google.appengine.api import blobstore
import cStringIO as StringIO

blobinfo = BlobInfo.get(KEY)

offset = 0
accumulated_content = StringIO.StringIO()
while True:
  fetched_content = blobstore.fetch_data(
      blobinfo.key(),
      offset,
      offset + blobstore.MAX_BLOB_FETCH_SIZE - 1)
  accumulated_content.write(fetched_content)
  if len(fetched_content) < blobstore.MAX_BLOB_FETCH_SIZE:
    break
  offset += blobstore.MAX_BLOB_FETCH_SIZE

从Google Blobstore获取blob而不知道手头的大小

3 个答案: