Java DataInputStream read operations throwing Exceptions

Question

I'm trying to familiarize myself with Java IO classes, so I wrote the code below:

public static void main(String[] args)throws IOException {
    FileOutputStream fos = new FileOutputStream("fileIO.txt");
    BufferedOutputStream bos = new BufferedOutputStream(fos);
    DataOutputStream dos = new DataOutputStream(bos);

    //fos.write(9999);
    //bos.write(9999);
    dos.writeInt(9999);
    dos.writeBytes("中文字(Chinese)\n");
    dos.writeChars("中文字(Chinese)\n");
    dos.flush();

    FileInputStream fis = new FileInputStream("fileIO.txt");
    BufferedInputStream bis = new BufferedInputStream(fis);
    DataInputStream dis = new DataInputStream(bis);

    System.out.println(dis.readInt());
    System.out.println(dis.readUTF());
}

Unfortunately, I get this:

9999
Exception in thread "main" java.io.EOFException
at java.io.DataInputStream.readFully(DataInputStream.java:180)
at java.io.DataInputStream.readUTF(DataInputStream.java:592)
at java.io.DataInputStream.readUTF(DataInputStream.java:547)
at IO.main(IO.java:34)

Could anyone point out why? Thanks.

bajafresh4life · Accepted Answer · 2011-03-30 17:44:59Z

4

Instead of

dos.writeBytes("中文字(Chinese)\n");
dos.writeChars("中文字(Chinese)\n");

you need

dos.writeUTF("中文字(Chinese)\n");

answered Mar 30, 2011 at 17:44

bajafresh4life

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1 Comment

Some Noob Student Over a year ago

I see, so you can throw in a lot of bytes and character with writeBytes & writeChars but only read one at a time with their repective read operations?

Carl Manaster · Accepted Answer · 2011-10-13 16:47:25Z

3

When you perform a readUTF, the first two byte are used for the length. This means if you have random bytes there (not from writeUTF) you will attempt to read very long string instead and as there is not enough data, you will get EOFException.

edited Oct 13, 2011 at 16:47

Carl Manaster

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answered Mar 30, 2011 at 18:11

Peter Lawrey

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1 Comment

Some Noob Student Over a year ago

I see! I suppose this also explains the suspicious blank space ' ' in between every English letter when using writeChar. ex: ( C h i n e s e )

user207421 · Accepted Answer · 2020-03-17 23:22:35Z

1

You can only use readUTF() to read items that were written with writeUTF().

This is true in general for readXXX() and writeXXX() for any XXX (unless you want to read the bytes of an int or some such and you know what you're doing).

edited Mar 17, 2020 at 23:22

answered Mar 30, 2011 at 23:14

user207421

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Comments

user207421 · Accepted Answer · 2020-03-17 23:25:17Z

1

I think this link will be helpful. The exception is thrown (from oracle docs) -

if this input stream reaches the end before reading all the bytes.

edited Mar 17, 2020 at 23:25

user207421

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answered Mar 30, 2011 at 17:44

MByD

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2 Comments

Some Noob Student Over a year ago

+1 for the diagram at the top. I find it to be of much greater importance. I wonder why they didn't copy & paste it to DataOutputStream, which I read, and missed out writeUTF.

user207421 Over a year ago

@SomeNoobStudent Because DataOutputStream() doesn't throw EOFExceptions?

lukastymo · Accepted Answer · 2011-03-30 17:44:32Z

0

You haven't UTF char after Integer number in your file. When you're trying read UTF there is End of File so you have the exception.

Try in debug mode stop before you read and check manually to your file, what do you have then?

answered Mar 30, 2011 at 17:44

lukastymo

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