Java: send string to input stream

Question

I try to send string to my InputStream:

String _source = "123";
InputStream in = new ByteArrayInputStream(_source.getBytes("UTF-8"));
tempLab2.readR(in);
            
String _source2 = "321";
in.read(_source2.getBytes());
_myClass.readR(in);

When I create new ByteArrayInputStream and set _source as an argument, then everything works well. My method readR does not wait any \n or EOF charapters and reads 123.

Please enter R:

R: 123

readR method:

public void readR(InputStream inpSteram) {
    Scanner tScanner = new Scanner(inpSteram);
    System.out.println("Please enter R:");
    _R = tScanner.nextDouble();
    System.out.println("R: " + _R);
}

But if I send _source2 with in.read(_source2.getBytes()) so my Scanner is waiting and I see only

Please enter R:

Any ideas?

Wouter · Accepted Answer · 2013-10-26 12:31:51Z

5

The line

in.read(_source2.getBytes());

does not add new info to the inputstream, instead it empties it, if there would have been more data. So the inputstream is exhausted.

You just need to create a new inputstream before the next call to readR. So:

String _source2 = "321";
in = new ByteArrayInputStream(_source2.getBytes("UTF-8"));
_myClass.readR(in);

answered Oct 26, 2013 at 12:31

Wouter

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2 Comments

Leo Over a year ago

Is there any way without creating a new ByteArrayInputStream?

Wouter Over a year ago

No. Once you create a ByteArrayInputStream you cannot feed it with new bytes. You could change readR to accept a String and create the inputstream inside the method.

JB Nizet · Accepted Answer · 2013-10-26 12:30:58Z

2

Your code doesn't make sense:

String _source2 = "321";
in.read(_source2.getBytes());

in.read() reads bytes from in, and stores what it has read in the byte array passed as argument. So basically, the above code creates a three bytes-long array, fills it with 3 bytes, and then tries to read bytes from the input stream and fills the 3-bytes-long byte array with the result.

answered Oct 26, 2013 at 12:30

JB Nizet

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1 Comment

Leo Over a year ago

Okey, but you did not answer how to fix it.

jtahlborn · Accepted Answer · 2013-10-26 12:31:11Z

0

Don't use an InputStream for working with characters, use a Reader.

Also, in your second example, you are not doing what you think you are doing. you are not adding the _source2 bytes to the input stream. you are instead attempting to re-use the original bytes from the original InputStream, which is now empty.

answered Oct 26, 2013 at 12:31

jtahlborn

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Comments

Shaun Wild · Accepted Answer · 2013-10-26 12:47:12Z

0

It's not entirely obvious what you're after here, but when using the Scanner class, you can simply send a string straight to it like so:

Scanner scanner = new Scanner(System.in);
String s = scanner.nextLine();

And so on.. This is assuming, of course, that you're taking input from the console.

answered Oct 26, 2013 at 12:47

Shaun Wild

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