Hi, Boris Yes, like what I said, the method without position signature acts like the inputStream that you can’t manually change the position where you want to read. Instead, you can only read by order. The position will automatically move forward while you read data from the stream.
Best, -------------- Yuan Tian School of Software, Tsinghua University 田原 清华大学 软件学院 > 在 2019年9月10日，上午12:09，Boris Zhu <[email protected]> 写道： > > 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 >>>>>> >>>>>> >>>> >>>> >> >>
