Java Examples in a Nutshell, 3rd Edition

Advanced Byte-to-Character Conversion

In Example 6-4 we saw a basic loop for copying bytes from one channel to another. Another commonly seen loop in programs that use the New I/O API is one that combines reading or writing bytes with decoding bytes to characters, or encoding characters to bytes. In Example 6-3 we saw the Charset.decode( ) method for decoding a buffer of bytes into a buffer of characters. This is actually a high-level convenience method, and we’ll see similar convenience methods elsewhere in this chapter. For better streaming performance, however, you can use the lower-level CharsetDecoder and CharsetEncoder classes, as is done in Example 6-5. This example is the ChannelToWriter class, which defines a single static copy( ) method. This method reads bytes from a specified channel, decodes them to characters using the specified Charset, and then writes them to the specified Writer. (Note that this is not the same function performed by Channels.newReader( ), Channels.newWriter( ), or Channels.newChannel( ). The factory methods of the Channels class allow you to wrap a channel around a stream or a stream around a channel, but do not perform a copy.)

The read/decode/write loop shown in this example is a common one in java.nio code, but is more complex than you might expect. One reason for the complexity is that in many character encodings, there is not a one-to-one correspondence between bytes and characters. This means that there is no guarantee that all bytes in a ...