Convert OutputStream to ByteArrayOutputStream

问题:

I am trying to convert an OutputStream to a ByteArrayOutput Stream. I was unable to find any clear simple answers on how to do this. This question was asked in the title of the question on StackOverflow, but the body of the question aske how to change a ByteArrayStream to OuputStream. I have an OutputStream that is already created and this example given in the answer will not compile!

That Question is Here

I have an OutputStream that is already constructed and has a length of 44 bytes called waveHeader. I want to convert that to a ByteArrayOutputStream because I want to be able to change that into a byte[] with waveHeader.ToByteArray() for simplicity in later processes;

Is there a simple type of casting or something that will allow this?

If not then:

• Is there a way to construct a pointer to the data in the original OutputStream if it is not possible to convert it?

• How would someone go about accessing the data that is contained in the OutputStream?

I am new to JAVA. This is just a hobby for me. Streams In VisualBasic .net where much easier!

回答1:

There are multiple possible scenarios:

a) You have a ByteArrayOutputStream, but it was declared as OutputStream. Then you can do a cast like this:

void doSomething(OutputStream os)
{
    // fails with ClassCastException if it is not a BOS
    ByteArrayOutputStream bos = (ByteArrayOutputStream)os;
...

b) if you have any other type of output stream, it does not really make sense to convert it to a BOS. (You typically want to cast it, because you want to access the result array). So in this case you simple set up a new stream and use it.

void doSomething(OutputStream os)
{
    ByteArrayOutputStream bos = new ByteArrayOutputStream();
    bos.write(something);
    bos.close();
    byte[] arr = bos.toByteArray();
    // what do you want to do?
    os.write(arr); // or: bos.writeTo(os);
...

c) If you have written something to any kind of OutputStream (which you do not know what it is, for example because you get it from a servlet), there is no way to get that information back. You must not write something you need later. A solution is the answer b) where you write it in your own stream, and then you can use the array for your own purpose as well as writing it to the actual output stream.

Keep in mind ByteArrayOutputStreams keep all Data in Memory.

回答2:

You could use the writeTo method of ByteArrayOutputStream.

ByteArrayOutputStream bos = new ByteArrayOutputStream();
byte[] bytes = new bytes[8];
bos.write(bytes);
bos.writeTo(oos);

You can create an instance of ByteArrayOutputStream. You then need to write the data to this ByteOutputStream instance and then using the writeTo method, which accepts an OutputStream, you can enable the ByteArrayOutputStream to write the output, to the instance of OutputStream which you passed as the argument.

回答3:

You can use toByteArray function on the output stream you have.That's is let say you have outputStream buffer So you can do buffer.toByteArray .

For more you can look at the answer of Convert InputStream to byte array in Java .