Scala example source code file (EncodingHeuristics.scala)

This example Scala source code file (EncodingHeuristics.scala) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Scala tags/keywords

encodingheuristics, encodingnames, inputstream, io, iso-8859-1, string, string, ucs-4, ucs-4, utf-16be, utf-8, xml, xml, xxx, xxx

The Scala EncodingHeuristics.scala source code

/*                     __                                               *\
**     ________ ___   / /  ___     Scala API                            **
**    / __/ __// _ | / /  / _ |    (c) 2002-2011, LAMP/EPFL             **
**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
** /____/\___/_/ |_/____/_/ | |                                         **
**                          |/                                          **
\*                                                                      */


package scala.xml
package include.sax
import scala.xml.include._

import java.io.InputStream
import scala.util.matching.Regex

/** `EncodingHeuristics` reads from a stream
 * (which should be buffered) and attempts to guess
 * what the encoding of the text in the stream is.
 * If it fails to determine the type of the encoding,
 * it returns the default UTF-8. 
 *
 * @author Burak Emir
 * @author Paul Phillips
 */
object EncodingHeuristics
{
  object EncodingNames {
    // UCS-4 isn't yet implemented in java releases anyway...
    val bigUCS4       = "UCS-4"
    val littleUCS4    = "UCS-4"
    val unusualUCS4   = "UCS-4"
    val bigUTF16      = "UTF-16BE"
    val littleUTF16   = "UTF-16LE"
    val utf8          = "UTF-8"
    val default       = utf8
  }
  import EncodingNames._

  /** This utility method attempts to determine the XML character encoding
    * by examining the input stream, as specified at
    * [[http://www.w3.org/TR/xml/#sec-guessing w3]].
    *
    * @param    in   `InputStream` to read from. 
    * @throws IOException if the stream cannot be reset
    * @return         the name of the encoding.
    */    
  def readEncodingFromStream(in: InputStream): String = {
    var ret: String = null    
    val bytesToRead = 1024 // enough to read most XML encoding declarations
    def resetAndRet = { in.reset ; ret }
    
    // This may fail if there are a lot of space characters before the end
    // of the encoding declaration
    in mark bytesToRead
    val bytes = (in.read, in.read, in.read, in.read)
    
    // first look for byte order mark
    ret = bytes match {
      case (0x00, 0x00, 0xFE, 0xFF) => bigUCS4
      case (0xFF, 0xFE, 0x00, 0x00) => littleUCS4
      case (0x00, 0x00, 0xFF, 0xFE) => unusualUCS4
      case (0xFE, 0xFF, 0x00, 0x00) => unusualUCS4
      case (0xFE, 0xFF, _   , _   ) => bigUTF16
      case (0xFF, 0xFE, _   , _   ) => littleUTF16
      case (0xEF, 0xBB, 0xBF, _   ) => utf8
      case _                        => null
    }
    if (ret != null)
      return resetAndRet
    
    def readASCIIEncoding: String = {
      val data = new Array[Byte](bytesToRead - 4)
      val length = in.read(data, 0, bytesToRead - 4)

      // Use Latin-1 (ISO-8859-1) because all byte sequences are legal.
      val declaration = new String(data, 0, length, "ISO-8859-1")
      val regexp = """(?m).*?encoding\s*=\s*["'](.+?)['"]""".r
      (regexp findFirstMatchIn declaration) match {
        case None     => default
        case Some(md) => md.subgroups(0)
      }
    }
          
    // no byte order mark present; first character must be '<' or whitespace        
    ret = bytes match {    
      case (0x00, 0x00, 0x00, '<' ) => bigUCS4
      case ('<' , 0x00, 0x00, 0x00) => littleUCS4
      case (0x00, 0x00, '<' , 0x00) => unusualUCS4
      case (0x00, '<' , 0x00, 0x00) => unusualUCS4
      case (0x00, '<' , 0x00, '?' ) => bigUTF16     // XXX must read encoding
      case ('<' , 0x00, '?' , 0x00) => littleUTF16  // XXX must read encoding
      case ('<' , '?' , 'x' , 'm' ) => readASCIIEncoding
      case (0x4C, 0x6F, 0xA7, 0x94) => utf8         // XXX EBCDIC
      case _                        => utf8         // no XML or text declaration present
    }
    resetAndRet
  }
}