How hard have you looked?  This is pretty basic stuff.

String.substring() in a loop to break it into parts,
prepend each part with \u00, add them back together.

[ Voila.. ]

BTW - beginner questions are best handled on c.l.j.h.
<http://www.physci.org/codes/javafaq.jsp#cljh>

see http://mindprod.com/jgloss/hex.html

Do a search on google for "Base64.java".  You should find plenty of examples
including at least one public domain utility at sourceforge.net.  The Base64
scheme can encode/decode anything to ascii characters.  Its been around for
years.  Its pretty much the standard.

If for some reason that doesn't float your boat, use this as a starting
point.  It essentially produces 2 "hex" characters for every byte so its
extremely inefficient.  Base64 is much more efficient.  I had to remove some
company specific stuff so no gaurantees that this compiles/works.

public static String encodeHexString(String sourceText) {

 Byte[] rawData = sourceText.getBytes();
 StringBuffer hexText= new StringBuffer();
 String initialHex = null;
 int initHexLength=0;

 for(int i=0; i<rawData.length; i++) {
  int positiveValue = rawData[i] & 0x000000FF;
  initialHex = Integer.toHexString(positiveValue);
  initHexLength=initialHex.length();
  while(initHexLength++ < 2) {
   hexText.append("0");
  }
  hexText.append(initialHex);
 }
 return hexText.toString();
}
public static String decodeHexString(String hexText) {

 String decodedText=null;
 String chunk=null;

 if(hexText!=null && hexText.length()>0) {
  int numBytes = hexTextlength()/2;

  byte[] rawToByte = new byte[numBytes];
  int offset=0;
  int bCounter=0;
  for(int i =0; i <numBytes; i++) {
   chunk = hexText.substring(offset,offset+2);
   offset+=2;
   rawToByte[i] = (byte) (Integer.parseInt(chunk,16) & 0x000000FF);
  }
  decodedText= new String(rawToByte);
 }
 return decodedText;
}

You pluck out pairs, convert to int with radix 16, building up a char
array, then convert to string.

For details see http://mindprod.com/jgloss/conversion.html