Java: PrintStream to String?

Question

I have a function that takes an object of a certain type, and a PrintStream to which to print, and outputs a representation of that object. How can I capture this function's output in a String? Specifically, I want to use it as in a toString method.

Cageling

Answer 1

Use a ByteArrayOutputStream as a buffer:

import java.io.ByteArrayOutputStream;
import java.io.PrintStream;
import java.nio.charset.StandardCharsets;

    final ByteArrayOutputStream baos = new ByteArrayOutputStream();
    final String utf8 = StandardCharsets.UTF_8.name();
    try (PrintStream ps = new PrintStream(baos, true, utf8)) {
        yourFunction(object, ps);
    }
    String data = baos.toString(utf8);

Trigg

Don't forget to close the PrintStream to free all resources. – Cardoon

Use new String(baos.toByteArray(), java.nio.charset.StandardCharsets.UTF_8); available since 1.7, it doesn't throw – Binkley

@Cardoon certainly a good rule of thumb, but ByteArrayOutputStream.close() "has no effect", as there are no resources to free besides the backing array which will be dealt with by the garbage collector. – Historiography

ByteArrayOutputStream has toString(String charsetName), but only accept String argument. Also note that ByteArrayOutputStream is synchronized, which probably is not desirable – Preter

Both the PrintStream constructor and the baos.toString method now support the Charset objects directly, so there is no more need to convert UTF_8 to UTF_8.name() first... I recommend adding import static java.nio.charset.StandardCharsets.UTF_8; so you can use UTF_8 directly as a value. – Triune

Answer 2

You can construct a PrintStream with a ByteArrayOutputStream passed into the constructor which you can later use to grab the text written to the PrintStream.

ByteArrayOutputStream os = new ByteArrayOutputStream();
PrintStream ps = new PrintStream(os);
...
String output = os.toString("UTF8");

Prosperous

Note that toString("UTF8") should be toString("UTF-8") – Fustic

Answer 3

Why don't you use a StringWriter with a PrintWriter?

StringWriter writer = new StringWriter();
PrintWriter out = new PrintWriter(writer);
out.println("Hello World!");
String output = writer.toString();

Caprine

Apart from top rated answer this one doesn't bother you with charsetName. – Mcilroy

This won't work. You cannot pass the PrintWriter into a function which only takes a PrintStream as argument, which was what the question was about. – Tuneberg

I gave it as a suggestion on replacing the PrintStream. It's usually a good choice. If you must use a PrintStream then this i definitely not a choice. (I'm not sure why someone would vote -1 on this.. it still technically a viable option in most cases :) ) – Caprine

Answer 4

A unification of previous answers, this answer works with Java 1.7 and after. Also, I added code to close the Streams.

final Charset charset = StandardCharsets.UTF_8;
ByteArrayOutputStream baos = new ByteArrayOutputStream();
PrintStream ps = new PrintStream(baos, true, charset.name());
yourFunction(object, ps);
String content = new String(baos.toByteArray(), charset);
ps.close();
baos.close();

Longoria

Answer 5

Maybe this question might help you: Get an OutputStream into a String

Subclass OutputStream and wrap it in PrintStream

Venesection

Answer 6

Define and initialize a Scanner variable named inSS that creates an input string stream using the String variable myStrLine.

Ans: Scanner inSS = new Scanner(myStrLine);

Sousaphone