/**
* Obtains streams from the Clob and makes sure we can always read the last char in the Clob.
*
* <p>See DERBY-4060.
*
* @param id id of the Clob to use
* @param length the length of the Clob
* @param alphabet the alphabet used to create the content
* @throws IOException if reading from a stream fails
* @throws SQLException if something goes wrong
*/
private void getCharacterStreamLongLastChar(int id, int length, CharAlphabet alphabet)
throws IOException, SQLException {
// Get last char from the source stream.
Reader cmpReader = new LoopingAlphabetReader(length, alphabet);
cmpReader.skip(length - 1);
char srcLastChar = (char) cmpReader.read();
assertTrue(cmpReader.read() == -1);
PreparedStatement ps = prepareStatement("select CLOBDATA from BLOBCLOB where ID=?");
ps.setInt(1, id);
// Read everything first.
int charsToRead = length;
ResultSet rs = ps.executeQuery();
rs.next();
Reader reader = rs.getClob(1).getCharacterStream(length - charsToRead + 1, charsToRead);
// Drain the stream, and make sure we are able to read the last char.
char lastCharRead = getLastCharInStream(reader, charsToRead);
assertEquals(srcLastChar, lastCharRead);
reader.close();
rs.close();
// Read a portion of the stream.
charsToRead = length / 4;
rs = ps.executeQuery();
rs.next();
reader = rs.getClob(1).getCharacterStream(length - charsToRead + 1, charsToRead);
lastCharRead = getLastCharInStream(reader, charsToRead);
assertEquals(srcLastChar, lastCharRead);
reader.close();
rs.close();
// Read a very small portion of the stream.
charsToRead = 1;
rs = ps.executeQuery();
rs.next();
reader = rs.getClob(1).getCharacterStream(length - charsToRead + 1, charsToRead);
lastCharRead = getLastCharInStream(reader, charsToRead);
assertEquals(srcLastChar, lastCharRead);
reader.close();
rs.close();
}
public void testReader() throws Exception {
Encoding encoding = Encoding.getDatabaseEncoding("SQL_ASCII");
InputStream stream = new ByteArrayInputStream(new byte[] {97, 98});
Reader reader = encoding.getDecodingReader(stream);
assertEquals(97, reader.read());
assertEquals(98, reader.read());
assertEquals(-1, reader.read());
}
/**
* Drains the stream and returns the last char read from the stream.
*
* @param reader stream to drain
* @param expectedCount expected number of chars (remaining) in the stream
* @return The last char read.
* @throws AssertionError if there are too many/few chars in the stream
* @throws IOException if reading from the stream fails
*/
public static char getLastCharInStream(Reader reader, int expectedCount) throws IOException {
int read = 0;
final char[] buf = new char[256];
assertTrue(buf.length > 0); // Do not allow an infinite loop here.
while (true) {
int readThisTime = reader.read(buf, 0, buf.length);
// -1 is expected, but catch all cases with a negative return value.
if (readThisTime < 0) {
assertEquals("Invalid return value from stream", -1, readThisTime);
fail("Reached EOF prematurely, expected " + expectedCount + ", got " + read);
} else if (readThisTime == 0) {
// Another special case that should not happen.
fail("Stream breaks contract, read zero chars: " + reader);
}
read += readThisTime;
if (read == expectedCount) {
return buf[readThisTime - 1];
} else if (read > expectedCount) {
fail(
"Too many chars in stream, expected "
+ expectedCount
+ "have "
+ read
+ "(EOF not reached/confirmed)");
}
}
}
