关闭输出流“行为异常”？

Question

In the following code:

    for(int i = 5; i  <= 100; i+=5)
    {
        linearSurprise(i); // Function calling 'System.out.print()'

        System.setOut(outStream); // Reassigns the "standard" output stream.

        System.out.println("Value of i: " + i); // Outputting the value to the .txt file.

        outStream.close(); // 'outStrem' is closed so that when I recall my function, output will 
                           // will be sent to the console and not file.

      // After debugging, I notice that nothing is being displayed to either the console or file, 
      // but everything else is still working fine. 
    }

I am calling a function 'linearSurprise' and in that function I output some information to the console. Once the function call is over, I redirect the value of 'i' to a text file. This works for the first iteration of the loop, but as soon as I call 'outStream.close()' no output whatsoever is displayed in the next iteration(console or file). Does anyone know why this is happening? Also what would be a workaround to this problem?

Answer 1

You're closing the OutputStream inside your loop, and System.out is now closed; you have to reassign an open OutputStream to it to be able to write any more output.

For this purpose, you really ought to be writing directly to the FileOutputStream instead; there's no value in redirecting System.out to it, and it leads to problems like this one.

PrintStream outStream = new PrintStream(File outputFile);
for(int i = 5; i <= 100; i += 5)
{
    linearSurprise(i);
    outStream.println("Value of i: " + i);
}
outStream.close();

Answer 2

This assumption is invalid:

'outStrem' is closed so that when I recall my function, output will be sent to the console and not file.

Why would it magically go back to the console? It will just be written to a closed stream instead, which will cause an exception which is swallowed by PrintStream .

If you want to set it back to the original console stream, you need to do that explicitly:

PrintStream originalOutput = System.out;

// Do stuff...

System.setOut(originalOutput); // Now we can write back to the console again

Answer 3

循环后关闭文件

outStream.close();

Answer 4

System.setOut(outStream); // Reassigns the "standard" output stream.
for(int i = 5; i  <= 100; i+=5)
    {
        linearSurprise(i); // Function call


        System.out.println("Value of i: " + i); // Outputting the value to the .txt file.

will 
                           // will be sent to the console and not file.

      // After debugging, I notice that nothing is being displayed to either the console or file, 
      // but everything else is still working fine. 
    }
    outStream.close(); // 'outStrem' is closed so that when I recall my function, output 

If you close the outStream after you are finished writing to it instead of after one iteration it should work.

Answer 5

You can try outStream.flush() instead of outStream.close() inside loop. It may work. As outStream.close(); will close your file. it is better to close after loop completion.

Answer 6

由于您调用CLose（），因此流已被处置，因此不再存在

Answer 7

Print to File as follow:

outStream.println("What ever you want");

And close the stream after the loop.

Dont't setOut(outStream);