Question

I am trying to read data from a binary stream, portions of which should be parsed as UTF-8.

Using the InputStream directly for the binary data and an InputStreamReader on top of it for the UTF-8 text does not work as the reader will read ahead and mess up the subsequent binary data even if it is told to read a maximum of n characters.

I recognize this question is very similar to Read from InputStream in multiple formats, but the solution proposed there is specific to HTTP streams, which does not help me.

I thought of just reading everything as binary data and converting the relevant pieces to text afterwards. But I only have the length information of the character data in characters, not in bytes. Thus, I need the thing which reads characters from the stream to be aware of the encoding.

Is there a way to tell InputStreamReader not to read ahead further than is needed for reading the given number of characters? Or is there a reader that supports both binary data and text with an encoding and can be switched between these modes on the fly?

Answer 1

You need to read the binary portions first. Where you recognise a portion of bytes which need UTF-8 decoding you need to extract those bytes and decode it.

DataInputStream dis = 
// read a binary type.
int num = dis.readInt();
int len = dis.readUnsignedShort();
// read a UTF-8 portion.
byte[] bytes = new byte[len];
dis.readFully(bytes);
String text = new String(bytes, "UTF-8");
// read some binary
double d = dis.readDouble();