java - What's the difference between InputStream and ByteArrayInputStream?

Question

The following code is extracted from the java web start chapter of the core java volume 1.

     ByteArrayOutputStream out = new ByteArrayOutputStream();
     PrintStream printOut = new PrintStream(out);
     printOut.print(panel.getText());
     //panel.getText() return a String
     InputStream data = new ByteArrayInputStream(out.toByteArray());
     FileSaveService service = (FileSaveService) ServiceManager
           .lookup("javax.jnlp.FileSaveService");
     service.saveFileDialog(".", new String[] { "txt" }, data, "calc.txt");

There are four objects created ,the stream is redirected three times. Is there any other methods to write data to a file by using jnlp api? what's the difference between InputStream and ByteArrayInputStream?

Answer 1

ByteArrayInputStream and ByteArrayOututStream are in-memory implementations for use when you want to temporarily store the data in memory in a stream-like fashion, then pump it out again somewhere else.

For example, let's assume you have a method that expects an input stream as a parameter, eg

public Document parseXml(InputStream in) // build an XML document from data read in

but you want to send the contents of say a String to it. Then you'd use a ByteArrayInputStream and fill it with the contents of your String and pass the ByteArrayInputStream to the method.

An example of an ByteArrayOutputStream usage might be if a method writes to an output stream, but you just want to capture the result and get it directly.