I check-in java doc and it says the file position is updated with the
number of bytes actually read. You can see below
* Reads a sequence of bytes from this channel into the given buffer.
*
* <p> Bytes are read starting at this channel's current file position, and
* then the file position is updated with the number of bytes actually
* read. Otherwise this method behaves exactly as specified in the {@link
* ReadableByteChannel} interface. </p>
*/
public abstract int read(ByteBuffer dst) throws IOException;
you can also see it in
https://docs.oracle.com/javase/8/docs/api/java/nio/channels/FileChannel.html#read-java.nio.ByteBuffer-
best,
Boris zhu
On Tue, Sep 10, 2019 at 12:00 AM Yuan Tian <[email protected]> wrote:
> Hi, Boris
>
> If the position is not specified, I think the position should be modified.
> There are two methods in TsFileInput interface that don’t have position
> parameter in their function signature.
>
> 1.
> int read(ByteBuffer dst) throws IOException;
> 2.
> int read() throws IOException;
>
> Actually, in the corresponding methods in the FileChannel, they really
> don’t modify the position which you can verify by reading the java doc of
> that class. Perhaps, the reason for that is when you use the method without
> position parameter, you just want to read from it by order like using a
> input stream.
>
>
>
> Best,
> --------------
> Yuan Tian
> School of Software, Tsinghua University
>
> 田原
> 清华大学 软件学院
>
> > 在 2019年9月9日，下午11:46，Boris Zhu <[email protected]> 写道：
> >
> > I agree with you that shouldn’t modify the position of TsFileInput when
> > having already specified the position. Sorry for the misunderstanding.
> But
> > if not specified, should it be changed for hdfs or local?
> >
> > Best,
> > Boris zhu
> >
> > On Mon, Sep 9, 2019 at 11:35 PM Yuan Tian <[email protected]>
> wrote:
> >
> >> In fact, I am working on the hadoop-connector, so I should create a
> >> HDFSInput that implements TsFileInput interface for reading tsfile from
> >> HDFS.
> >>
> >> And actually, in DefaultTsFileInput, this method is unsupported which
> you
> >> can see in the following.
> >>
> >> @Override
> >> public int read(byte[] b, int off, int len) throws IOException {
> >> throw new UnsupportedOperationException();
> >> }
> >>
> >> Not all read methods in DefaultTsFileInput modify the position, such as
> >> 'int read(ByteBuffer dst, long position)’.
> >>
> >> So it seems that if you specify the position where you want to start in
> >> the method signature, the method shouldn’t modify the position of
> >> TsFileInput which is consistent with FileChannel’s interface.
> >>
> >>
> >> Best,
> >> --------------
> >> Yuan Tian
> >> School of Software, Tsinghua University
> >>
> >> 田原
> >> 清华大学 软件学院
> >>
> >>> 在 2019年9月9日，下午11:19，Boris Zhu <[email protected]> 写道：
> >>>
> >>> Hi, tian
> >>> DefaultTsFileInput is a class to implement TsFileInput
> >>> interface. DefaultTsFileInput's method read actually change the
> position
> >> of
> >>> itself because it uses java.io.FileChannel, and we can use a "position"
> >>> method to change its position back. But I'm also confusing that why
> can't
> >>> change the position of TsFileInput or modify this TsFileInput.
> >>>
> >>> Best,
> >>> Boris zhu
> >>>
> >>> On Mon, Sep 9, 2019 at 10:55 PM Yuan Tian <[email protected]>
> >> wrote:
> >>>
> >>>> Hi,
> >>>>
> >>>> While implementing one read method(shown in the following) in
> >> TsFileInput
> >>>> interface, I don’t know whether to modify the position of TsFileInput.
> >>>>
> >>>> /**
> >>>> * read an array of byte from the Input.
> >>>> *
> >>>> * @param b -array of byte
> >>>> * @param off -offset of the Input
> >>>> * @param len -length
> >>>> */
> >>>> int read(byte[] b, int off, int len) throws IOException;
> >>>>
> >>>>
> >>>> I think this method should not modify this TsFileInput and it should
> be
> >>>> specified in the comments.
> >>>>
> >>>> Best,
> >>>> --------------
> >>>> Yuan Tian
> >>>> School of Software, Tsinghua University
> >>>>
> >>>> 田原
> >>>> 清华大学 软件学院
> >>>>
> >>>>
> >>
> >>
>
>
