Examples of org.apache.derby.impl.jdbc.PositionedStoreStream

org.apache.derby.impl.jdbc.PositionedStoreStream
A wrapper-stream able to reposition the underlying store stream.
Where a user expects the underlying stream to be at a given position, {@link #reposition} must be called with the expected position first. A usecase for this scenario is the LOB objects, where you can request a stream and at the same time (this does not mean concurrently) query the LOB about its length or ask to get a part of the LOB returned. Such multiplexed operations must result in consistent and valid data, and to achieve this the underlying store stream must be able to reposition itself. Synchronization: Access to instances of this class must be externally synchronized on the connection synchronization object. There are two reasons for this:
- Access to store must be single threaded.
- This class is not thread safe, and calling the various methods from different threads concurrently can result in inconsistent position values. To avoid redundant internal synchronization, this class assumes and requires external synchronization (also called client-side locking).
@see EmbedConnection#getConnectionSynchronization

     * read.
     */
    public void testReadEverythingInOneGo()
            throws IOException, StandardException {
        InputStream in = new LoopingAlphabetStream(127);
        PositionedStoreStream pss = new PositionedStoreStream(in);
        byte[] b = new byte[256];
        for (int i=0; i < 3; i++) {
            Arrays.fill(b, (byte)-1);
            assertEquals(127, pss.read(b, 0, 256));
            assertEquals(-1, pss.read(b, 127, 10));
            assertEquals(-1, b[127]);
            assertTrue( -1 != b[126]);
            assertEquals('a', b[0]);
            pss.reposition(0);
        }
    }

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    public void testRepositionForwards()
            throws IOException, StandardException {
        final long length = 20L;
        InputStream in = new LoopingAlphabetStream(length);
        PositionedStoreStream pss = new PositionedStoreStream(in);
        assertEquals(0, pss.getPosition());
        //  Position forwards one by one.
        for (int i=0; i < length; i++) {
            InputStream inComp = new LoopingAlphabetStream(length);
            pss.reposition(i);
            inComp.skip(i);
            assertEquals(inComp.read(), pss.read());
        }
        // Position forwards two by two.
        for (int i=1; i < length; i += 2) {
            InputStream inComp = new LoopingAlphabetStream(length);
            pss.reposition(i);
            inComp.skip(i);
            assertEquals(inComp.read(), pss.read());
        }
    }

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    public void testRepositionBackwards()
            throws IOException, StandardException {
        final long length = 20L;
        InputStream in = new LoopingAlphabetStream(length);
        PositionedStoreStream pss = new PositionedStoreStream(in);
        assertEquals(0, pss.getPosition());
        // Position backwards one by one.
        for (int i=(int)length; i >= 0; i--) {
            InputStream inComp = new LoopingAlphabetStream(length);
            pss.reposition(i);
            inComp.skip(i);
            assertEquals(inComp.read(), pss.read());
        }
        // Position backwards two by two.
        for (int i=(int)length -1; i >= 0; i -= 2) {
            InputStream inComp = new LoopingAlphabetStream(length);
            pss.reposition(i);
            inComp.skip(i);
            assertEquals(inComp.read(), pss.read());
        }
    }

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     * alphabet, which involves some repositioning.
     */
    public void testSimpleReadSequence()
            throws IOException, StandardException {
        InputStream in = new LoopingAlphabetStream(26);
        PositionedStoreStream pss = new PositionedStoreStream(in);
        assertEquals('a', pss.read());
        pss.reposition(9);
        assertEquals('j', pss.read());
        pss.reposition(10);
        assertEquals('k', pss.read());
        pss.reposition(9);
        assertEquals('j', pss.read());
        pss.reposition(25);
        assertEquals('z', pss.read());
        assertEquals(-1, pss.read());
        pss.reposition(1);
        assertEquals('b', pss.read());
        pss.reposition(1);
        assertEquals('b', pss.read());
    }

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     * be thrown in {@code skipFully}.
     */
    public void testDerby3735()
            throws IOException, StandardException {
        InputStream in = new LoopingAlphabetStream(2);
        PositionedStoreStream pss = new PositionedStoreStream(in);
        byte[] b = new byte[2];
        for (int i=0; i < 10; i++) {
            // After the first iteration, the position will be decreased and
            // eventually become negative.
            pss.read(b);
            println("Position at iteration " + i + ": " + pss.getPosition());
        }
        // This failed, because we tried skipping more bytes than there are in
        // the stream to get to position 0.
        pss.reposition(0);
    }

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     */
    public void testDerby3781()
            throws IOException, StandardException {
        final long size = 10;
        InputStream in = new LoopingAlphabetStream(size);
        PositionedStoreStream pss = new PositionedStoreStream(in);
        assertEquals("Invalid initial position", 0L, pss.getPosition());
        pss.reposition(size -1); // Goto end.
        assertEquals(size -1, pss.getPosition());
        assertEquals('j', pss.read());
        assertEquals(size, pss.getPosition());
        assertEquals(-1, pss.read());
        // This step is crucial, position must be different than zero when the
        // first exception below is thrown.
        pss.reposition(size / 2); // Goto middle.
        assertEquals(size / 2, pss.getPosition());
        try {
            pss.reposition(size *2); // Try to go past end.
            fail("Should have failed with EOFException");
        } catch (EOFException eofe) {
            // Ignore this exception
        }
        // Failed here before, because internal state was inconsistent.
        // Assumed: pos = 5, underlying stream at pos 5, skipped (size -1 - pos)
        // Actual: pos = 5, underlying stream at pos (size -1)
        pss.reposition(size -1); // Goto end.
        assertEquals(size -1, pss.getPosition());
        assertEquals('j', pss.read());
    }

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