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Get an OutputStream into a String

Posted by: admin November 2, 2017 Leave a comment


What’s the best way to pipe the output from an java.io.OutputStream to a String in Java?

Say I have the method:

  writeToStream(Object o, OutputStream out)

Which writes certain data from the object to the given stream. However, I want to get this output into a String as easily as possible.

I’m considering writing a class like this (untested):

class StringOutputStream extends OutputStream {

  StringBuilder mBuf;

  public void write(int byte) throws IOException {
    mBuf.append((char) byte);

  public String getString() {
    return mBuf.toString();

But is there a better way? I only want to run a test!


I would use a ByteArrayOutputStream. And on finish you can call:

new String( baos.toByteArray(), codepage );

or better

baos.toString( codepage );

For the String constructor the codepage can be a String or an instance of java.nio.charset.Charset. A possible value is java.nio.charset.StandardCharsets.UTF_8.

The method toString accept only a String as codepage parameter (stand Java 8).


I like the Apache Commons IO library. Take a look at its version of ByteArrayOutputStream, which has a toString(String enc) method as well as toByteArray(). Using existing and trusted components like the Commons project lets your code be smaller and easier to extend and repurpose. Good luck.


this worked nicely

    OutputStream output = new OutputStream()
        private StringBuilder string = new StringBuilder();
        public void write(int b) throws IOException {
            this.string.append((char) b );

        //Netbeans IDE automatically overrides this toString()
        public String toString(){
            return this.string.toString();

method call =>> marshaller.marshal( (Object) toWrite , (OutputStream) output);

then to print the string or get it just reference the “output” stream itself
As an example, to print the string out to console =>> System.out.println(output);

FYI: my method call marshaller.marshal(Object,Outputstream) is for working with xml. It is irrelevant to this topic.

This is higly wasteful for productional use, there are way to many conversion and it is a bit loose. This was just coded to prove to you that it is totally possible to create a custom OuputStream and output a string. But just go Horcrux7 way and all is good with merely two method calls.

And the world lives on another day….


Here’s what I ended up doing:

Obj.writeToStream(toWrite, os);
try {
    String out = new String(os.toByteArray(), "UTF-8");
} catch (UnsupportedEncondingException e) {
    fail("Caught exception: " + e.getMessage());

Where os is a ByteArrayOutputStream.


Why don’t you use a ByteArrayOutputStream? That’s what you are supposed to use for this purpose.