Java supports and encourages socket communication using UTF-8. To this end two methods are provided:
readUTF() [http://java.sun.com/j2se/1.4.2/docs/api/java/io/DataInputStream.html#readUTF()] and writeUTF() [http://java.sun.com/j2se/1.4.2/docs/api/java/io/DataOutputStream.html#writeUTF(java.lang.String)]. Socket communication between a Java process that uses these methods and Tcl is easy. First, you will have to put your socket in binary mode, through a command such as the following:

 fconfigure $socket -translation binary

Specifying the translation is a shortcut for not having any conversion, for not having CRLF at the end of your lines, etc.

The rest of the code on this page issues from a discussion between [DKF] and [EF] on the chatroom. Both functions should help you reading and writing data to a socket coupled to a Java process using the methods above for its communication with the external world. Error handling is minimal.

 proc writeJavaUtf {stream string} {
     set data [encoding convertto utf-8 $string]
     if {[string length $data] > 0xffff} {
 	error "string to long after encoding"
     }
     set len [binary format S [string length $data]]
     puts -nonewline $stream $len$data
     flush $stream
 }

 proc readJavaUtf {stream} {
     set len [read $stream 2]
     binary scan $len S length
     set data [read $stream [expr {$length & 0xffff}]]
     return [encoding convertfrom utf-8 $data]
 }