I have code which Zip and Unzip Text. I'm facing weird behavior - only when I close the GZIPOutputStream
in certain place, the code works but when I try to place the GZIPOutputStream close
in the finally block, it breaks and does not work. If you place the : gzipoutputstream.close()
in the czip
function where comment is placed, it will work. However if you keep it only in finally
block, it will break. Why?
the ByteStreams.copy
function is from com.google.common.io guava
public class Main {
public static byte[] dzip(byte[] s) throws IOException {
ByteArrayInputStream sStream = null;
ByteArrayOutputStream oStream = null;
InputStream gzipoutputStream = null;
ByteBuffer arrReturn = null;
try {
sStream = new ByteArrayInputStream(s);
oStream = new ByteArrayOutputStream();
gzipoutputStream = new GZIPInputStream(sStream, 1024);
ByteStreams.copy(gzipoutputStream, oStream);
arrReturn = ByteBuffer.wrap(oStream.toByteArray());
}
catch (Exception e) {
return null;
} finally {
if (gzipoutputStream != null) {
gzipoutputStream.close();
}
if (oStream != null) {
oStream.close();
}
if (sStream != null) {
sStream.close();
}
}
return arrReturn.array();
}
public static byte[] czip(byte[] s) throws IOException {
ByteArrayInputStream sStream =null;
ByteArrayOutputStream oStream =null;
OutputStream gzipoutputstream = null;
byte[] returnValue = null;
try {
sStream = new ByteArrayInputStream(s);
oStream = new ByteArrayOutputStream(s.length / 2);
gzipoutputstream = new GZIPOutputStream(oStream, 1024);
ByteStreams.copy(sStream, gzipoutputstream);
//////////// ------------------------------------ \\\\\\\\\\\\
//gzipoutputstream.close(); // < --- Works only when placed here
//////////// ------------------------------------ \\\\\\\\\\\\
returnValue = oStream.toByteArray(); // Here the zip is 000
}catch(Exception e) {
return null;
} finally {
if (gzipoutputstream != null) {
gzipoutputstream.close();
}
if (oStream != null) {
oStream.close();
}
if (sStream != null) {
sStream.close();
}
}
return returnValue;
}
public static void main(String[] args) throws IOException {
String s = "12313dsfafafafaf";
byte[] source = (byte[]) s.getBytes();
byte[] returnZipByteArr = czip(source);
byte[] dd = dzip(returnZipByteArr);
String ss = new String(dd);
System.out.println(ss);
}
}
That's expected. The javadoc of close() says:
Writes remaining compressed data to the output stream and closes the underlying stream.
So if you try to access the bytes in the ByteArrayOutputStream() before close() has been called, the gzip compression hasn't been finished yet: the GZIP stream needs to know that nothing will never be written again to properly write the remaining data.
You could call finish()
to have the same effect but without closing the stream (and thus still close it in the finally block).