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javastringhttp-redirectconsolestdout

Redirect console output to string in Java

I have one method whose return type is void and it prints directly on console.

However I need that output in a String so that I can work on it.

As I can't make any changes to the method with return type void I have to redirect that output to a String.

How can I redirect it in Java?

Solution

  • If the function is printing to System.out, you can capture that output by using the System.setOut method to change System.out to go to a PrintStream provided by you. If you create a PrintStream connected to a ByteArrayOutputStream, then you can capture the output as a String.

    Example:

    // Create a stream to hold the output
ByteArrayOutputStream baos = new ByteArrayOutputStream();
PrintStream ps = new PrintStream(baos);
// IMPORTANT: Save the old System.out!
PrintStream old = System.out;
// Tell Java to use your special stream
System.setOut(ps);
// Print some output: goes to your special stream
System.out.println("Foofoofoo!");
// Put things back
System.out.flush();
System.setOut(old);
// Show what happened
System.out.println("Here: " + baos.toString());

    This program prints just one line: 

    Here: Foofoofoo!