Encode data

Question

I want to encode the US-ASCII data into UTF-8.
For that what is the procedure.
I have to use
1.InputStreamReader and OutPutStreamReader
2.Charset/CharsetEncoder/CharsetDecoder
What is the difference between the two processes?
Process 1:
FileInputStream fis = new FileInputStream(inputFile);
InputStreamReader isr = new InputStreamReader(fis,"UTF-8");
FileOutputStream fos = new FileOutputStream(outputFile);
OutputStreamWriter osw = new OutputStreamWriter(fos, "UTF-8");
Process 2:
Charset charset = Charset.forName(encode);
CharsetDecoder decoder = charset.newDecoder();
CharsetEncoder encoder = charset.newEncoder();

Answer 1

InputStreamReader is for converting non unicode
charecter bytes to unicode.
outpuStreamWriter is for converting unicode charecter
to non unicode byte stream.is it correct?Yep, that's correct...Are you sure? Maybe it's just badly worded, but it doesn't sound correct to me. A CharsetDecoder converts a ByteBuffer to a CharBuffer, while an InputStreamReader converts a stream of bytes to a stream of characters. You couldn't replace one with the other--in fact, an InputStreamReader may use a CharsetDecoder under the hood, depending on how you construct it.
I think it's a mistake to talk about converting "to (or from) Unicode", especially in this case. Sure, Java uses one of the Unicode-standard encodings internally, but which one it uses is an implementation detail that you don't need to know. All you need to know is which encoding was used to create the byte stream you're trying to read at the moment.
@ssa_sbobba, if I understand you correctly, you want to read a file that you believe to be in the US-ASCII encoding, and write the text back out using the UTF-8 encoding. That's simple enough:   FileInputStream fis = new FileInputStream(inputFile);
  InputStreamReader isr = new InputStreamReader(fis,"US-ASCII");
  FileOutputStream fos = new FileOutputStream(outputFile);
  OutputStreamWriter osw = new OutputStreamWriter(fos, "UTF-8"); If that's all you're doing, though, it's pointless; as Jos pointed out, US-ASCII is a subset of UTF-8, so the new file will be identical to the old one.