GAE：以编程方式访问Blobstore内容？

Question

My Usecase: I don't use the blobstore for uploading and downloading files. I use the blobstore to store very large strings my program is creating. With persisting the path where the blob is stored, I can later load the string again (see documentation )

My Question: Is there an easier way to access the blob content without the need to store the path? BlobstoreService only allows me to directly serve to the HttpServletReponse.

Answer 1

You only need to store a BlobKey - there is never a need to store a path (files or not).

To access contents of a blob:

BlobstoreService blobStoreService = BlobstoreServiceFactory.getBlobstoreService();
String myString =
   new String(blobStoreService.fetchData(blobKey, 0, BlobstoreService.MAX_BLOB_FETCH_SIZE-1);

EDIT: If you have a very long string, you can use any standard way of reading a byte array into a string by fetching data from a blob in a loop.

Answer 2

I guess when you said "persisting the path where the blob is stored", you mean BlobKey ?

FileService allows you to directly access blob data:

// Get a file service
FileService fileService = FileServiceFactory.getFileService();

// Get a file backed by blob
AppEngineFile file = fileService.getBlobFile(blobKey)

// get a read channel
FileReadChannel readChannel = fileService.openReadChannel(file, false);

// Since you store a String, I guess you want to read it a such
BufferedReader reader = new BufferedReader(Channels.newReader(readChannel, "UTF8"));
// Do this in loop unitil all data is read
String line = reader.readLine();