DataInputStream who close stream if IOException

Question

In all examples everybody can find code like this:

DataInputStream inputStream = null;
try {
    inputStream = new DataInputStream( new FileInputStream("file.data"));
    int i = inputStream.readInt();
    inputStream.close();
} catch (FileNotFoundException e) { 
    //print message File not found
} catch (IOException e) { e.printStackTrace() }

When this code met FileNotFound exception, inputStream was not open, so it doesn't need to be closed.

But why when IOException mets in that catch block I don't see inputStream.close(). This operation did's automatically when input data exception throws? Because if programm has problem with input this means that stream already open.

score 2 · Answer 1 · answered Jan 16 '13 at 20:11

DataInputStream inputStream = null;
try {
    inputStream = new DataInputStream( new FileInputStream("file.data"));
    int i = inputStream.readInt();
} catch (FileNotFoundException e) { 
  //print message File not found
} catch (IOException e) { 
  e.printStackTrace();
} finally{
  if(null!=inputStream)
    inputStream.close();
}

Andremoniy · Accepted Answer · 2013-01-16T20:19:29.280

2

No, close operation doesn't invoke automatically. For this purposes use try-with-resources introduced in Java 7:

try (DataInputStream inputStream = new DataInputStream( new FileInputStream("file.data"))) {
    int i = inputStream.readInt();
} catch (Exception e) { e.printStackTrace() }

UPD: Explanation: DataInputStream implements AutoCloseable interface. That means, that in construction try-with-resources Java automatically will call close() method of inputStream in hidden finally block.

edited Jan 16 '13 at 20:19

answered Jan 16 '13 at 20:12

Andremoniy

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what do you mean "try-catch-with-resources" introduced in Java7? in your code part I don't see inputStream.close() operator. you mean to let closing for Java? – Lesya Makhova Jan 16 '13 at 20:17
2

@LesyaMakhova I suggest you to read about this construction here: http://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html – Andremoniy Jan 16 '13 at 20:18

score 2 · Answer 3 · answered Jan 16 '13 at 20:14

Even if the file not found exception occurs the steam is open, you would simply need to close it again as well.

You should always add a finally block in your try catch and close the stream. Finally will always execute if there is an exception

 finally {
            if(reader != null){
                try {
                    reader.close();
                } catch (IOException e) {
                    //do something clever with the exception
                }
            }
            System.out.println("--- File End ---");
        }

DataInputStream who close stream if IOException

3 Answers3