Чтение BlobstoreInputStream> = 1 МБ

Question

Чтение более 1 МБ данных из BlobstoreInputStream вызовет IOException «Размер выборки BLOB-объекта слишком велик».

Вы можете использовать класс ChainedBlobstoreInputStream в ответе ниже для решения этой проблемы.

Answer 1

Я создал простой класс-обертку, который решает эту проблему.Вы должны иметь возможность напрямую поменять ChainedBlobstoreInputStream на BlobstoreInputStream.Я не тестировал методы mark (), markSupported () или reset ().

Вы можете использовать этот код по своему усмотрению.

package net.magicscroll.server.blobstore;

import com.google.appengine.api.blobstore.BlobInfo;
import com.google.appengine.api.blobstore.BlobInfoFactory;
import com.google.appengine.api.blobstore.BlobKey;
import com.google.appengine.api.blobstore.BlobstoreInputStream;

import java.io.IOException;
import java.io.InputStream;

/**
 * ChainedBlobstoreInputStream works exactly like BlobstoreInputStream but does
 * not throw an error if more than 1mb is read.
 * 
 * @author Richard Wallis
 */
public class ChainedBlobstoreInputStream extends InputStream {
    /**
     * The maximum number of bytes that can be read by a single request.
     */
    private static final int MAX_READSIZE = 1015800;

    /**
     * The BlobKey of the blobstore item.
     */
    private BlobKey blobKey;
    /**
     * The current byte position of the reader.
     */
    private long offset;

    /**
     * The Total Size of the blob.
     */
    private long totalSize;
    /**
     * The current Input Stream being read.
     */
    private BlobstoreInputStream currentStream;
    /**
     * The next point at which a new InputStream will need to be initialized.
     */
    private long nextReadBreak;
    /**
     * The currentStream at the time of the last mark.
     */
    private BlobstoreInputStream markedStream;

    /**
     * Creates a new ChainedBlobstoreInputStream. This stream should behave
     * exactly the same as a BlobstoreInputStream and it should be possible to
     * interchange them.
     * 
     * @param theBlobKey
     *            - The blobkey of the object to be read.
     * @throws IOException
     *             - Thrown if there is an error reading the current stream.
     */
    public ChainedBlobstoreInputStream(final BlobKey theBlobKey)
            throws IOException {
        this(theBlobKey, 0);
    }

    /**
     * Creates a new ChainedBlobstoreInputStream. This stream should behave
     * exactly the same as a BlobstoreInputStream and it should be possible to
     * interchange them.
     * 
     * @param theBlobKey
     *            - The blobkey of the object to be read.
     * @param newOffset
     *            - The offset in the blob from where to read.
     * @throws IOException
     *             - Thrown if there is an error reading the current stream.
     */
    public ChainedBlobstoreInputStream(final BlobKey theBlobKey,
            final long newOffset) throws IOException {
        this.offset = newOffset;
        this.blobKey = theBlobKey;
        final BlobInfo blobInfo = 
            new BlobInfoFactory().loadBlobInfo(this.blobKey);
        this.totalSize = blobInfo.getSize();
        this.currentStream = 
            new BlobstoreInputStream(this.blobKey, this.offset);
        this.nextReadBreak = 
            this.offset + ChainedBlobstoreInputStream.MAX_READSIZE;
    }

    /*
     * (non-Javadoc)
     * @see java.io.InputStream#read()
     */
    @Override
    public final int read() throws IOException {
        if (this.offset < this.totalSize) {
            if (this.offset == this.nextReadBreak) {
                this.currentStream.close();
                this.currentStream = 
                    new BlobstoreInputStream(this.blobKey, this.offset);
                this.nextReadBreak = this.offset 
                + ChainedBlobstoreInputStream.MAX_READSIZE;
            }
            this.offset += 1;
            return this.currentStream.read();
        } else {
            this.currentStream.close();
            return -1;
        }
    }

    /*
     * (non-Javadoc)
     * @see java.io.InputStream#close()
     */
    @Override
    public final void close() throws IOException {
        this.currentStream.close();
        super.close();
    }

    /*
     * (non-Javadoc)
     * @see java.io.InputStream#mark(int)
     */
    @Override
    public final void mark(final int readlimit) {
        this.currentStream.mark(readlimit);
        this.markedStream = this.currentStream;
    }

    /*
     * (non-Javadoc)
     * @see java.io.InputStream#markSupported()
     */
    @Override
    public final boolean markSupported() {
        return this.currentStream.markSupported();
    }

    /*
     * (non-Javadoc)
     * @see java.io.InputStream#reset()
     */
    @Override
    public final void reset() throws IOException {
        this.currentStream = this.markedStream;
        this.currentStream.reset();
    }

}

Answer 2

while ((size = zis.read(buffer)) > 0)
  contents.write(buffer, 0, size);

Но вся концепция чтения целых файлов в память имеет ручки. Найдите способ обработать его во время чтения.

или я получаю ошибку.

Какая ошибка?