# Converting Non-Unicode Text

Domains:

In the Java programming language char values represent Unicode characters. Unicode is a 16-bit character encoding that supports the world's major languages. You can learn more about the Unicode standard at the Unicode Consortium Web site .

Few text editors currently support Unicode text entry. The text editor we used to write this section's code examples supports only ASCII characters, which are limited to 7 bits. To indicate Unicode characters that cannot be represented in ASCII, such as ö, we used the \uXXXX escape sequence. Each X in the escape sequence is a hexadecimal digit. The following example shows how to indicate the ö character with an escape sequence:

	String str = "\u00F6";
char c = '\u00F6';
Character letter = new Character('\u00F6');


A variety of character encodings are used by systems around the world. Currently few of these encodings conform to Unicode. Because your program expects characters in Unicode, the text data it gets from the system must be converted into Unicode, and vice versa. Data in text files is automatically converted to Unicode when its encoding matches the default file encoding of the Java Virtual Machine. You can identify the default file encoding by creating an OutputStreamWriter using it and asking for its canonical name:

	OutputStreamWriter out = new OutputStreamWriter(new ByteArrayOutputStream());
System.out.println(out.getEncoding());


If the default file encoding differs from the encoding of the text data you want to process, then you must perform the conversion yourself. You might need to do this when processing text from another country or computing platform.

This section discusses the APIs you use to translate non-Unicode text into Unicode. Before using these APIs, you should verify that the character encoding you wish to convert into Unicode is supported. The list of supported character encodings is not part of the Java programming language specification. Therefore the character encodings supported by the APIs may vary with platform. To see which encodings the Java Development Kit supports, see the Supported Encodings document

The material that follows describes two techniques for converting non-Unicode text to Unicode. You can convert non-Unicode byte arrays into String objects, and vice versa. Or you can translate between streams of Unicode characters and byte streams of non-Unicode text.

## Byte Encodings and Strings

If a byte array contains non-Unicode text, you can convert the text to Unicode with one of the String constructor methods. Conversely, you can convert a String object into a byte array of non-Unicode characters with the String.getBytes method. When invoking either of these methods, you specify the encoding identifier as one of the parameters.

The example that follows converts characters between UTF-8 and Unicode. UTF-8 is a transmission format for Unicode that is safe for UNIX file systems. The full source code for the example is in the file StringConverter.java.

The StringConverter program starts by creating a String containing Unicode characters:

		String original = new String("A" + "\u00ea" + "\u00f1" + "\u00fc" + "C");


When printed, the String named original appears as:

		AêñüC


To convert the String object to UTF-8, invoke the getBytes method and specify the appropriate encoding identifier as a parameter. The getBytes method returns an array of bytes in UTF-8 format. To create a String object from an array of non-Unicode bytes, invoke the String constructor with the encoding parameter. The code that makes these calls is enclosed in a try block, in case the specified encoding is unsupported:

		try {
byte[] utf8Bytes = original.getBytes("UTF8");
byte[] defaultBytes = original.getBytes();

String roundTrip = new String(utf8Bytes, "UTF8");
System.out.println("roundTrip = " + roundTrip);
System.out.println();
printBytes(utf8Bytes, "utf8Bytes");
System.out.println();
printBytes(defaultBytes, "defaultBytes");
}
catch (UnsupportedEncodingException e) {
e.printStackTrace();
}


The StringConverter program prints out the values in the utf8Bytes and defaultBytes arrays to demonstrate an important point: The length of the converted text might not be the same as the length of the source text. Some Unicode characters translate into single bytes, others into pairs or triplets of bytes.

The printBytes method displays the byte arrays by invoking the byteToHex method, which is defined in the source file, UnicodeFormatter.java. Here is the printBytesmethod:

		public static void printBytes(byte[] array, String name) {
for (int k = 0; k < array.length; k++) {
System.out.println(name + "[" + k + "] = " + "0x" +
UnicodeFormatter.byteToHex(array[k]));
}
}


The output of the printBytes method follows. Note that only the first and last bytes, the A and C characters, are the same in both arrays:

		utf8Bytes[0] = 0x41
utf8Bytes[1] = 0xc3
utf8Bytes[2] = 0xaa
utf8Bytes[3] = 0xc3
utf8Bytes[4] = 0xb1
utf8Bytes[5] = 0xc3
utf8Bytes[6] = 0xbc
utf8Bytes[7] = 0x43
defaultBytes[0] = 0x41
defaultBytes[1] = 0xea
defaultBytes[2] = 0xf1
defaultBytes[3] = 0xfc
defaultBytes[4] = 0x43

## Character and Byte Streams

The java.io package provides classes that allow you to convert between Unicode character streams and byte streams of non-Unicode text. With the InputStreamReader class, you can convert byte streams to character streams. You use the OutputStreamWriter class to translate character streams into byte streams. The following figure illustrates the conversion process:

When you create InputStreamReader and OutputStreamWriter objects, you specify the byte encoding that you want to convert. For example, to translate a text file in the UTF-8 encoding into Unicode, you create an InputStreamReader as follows:

		FileInputStream fis = new FileInputStream("test.txt");


If you omit the encoding identifier, InputStreamReader and OutputStreamWriter rely on the default encoding. You can determine which encoding an InputStreamReader or OutputStreamWriter uses by invoking the getEncoding method, as follows:

		InputStreamReader defaultReader = new InputStreamReader(fis);


The example that follows shows you how to perform character-set conversions with the InputStreamReader and OutputStreamWriter classes. The full source code for this example is in StreamConverter.java. This program displays Japanese characters. Before trying it out, verify that the appropriate fonts have been installed on your system. If you are using the JDK software that is compatible with version 1.1, make a copy of the font.properties file and then replace it with the font.properties.ja file.

The StreamConverter program converts a sequence of Unicode characters from a String object into a FileOutputStream of bytes encoded in UTF-8. The method that performs the conversion is called writeOutput:

		static void writeOutput(String str) {
try {
FileOutputStream fos = new FileOutputStream("test.txt");
Writer out = new OutputStreamWriter(fos, "UTF8");
out.write(str);
out.close();
}
catch (IOException e) {
e.printStackTrace();
}
}


The readInput method reads the bytes encoded in UTF-8 from the file created by the writeOutput method. An InputStreamReader object converts the bytes from UTF-8 into Unicode and returns the result in a String. The readInput method is as follows:

		static String readInput() {
StringBuffer buffer = new StringBuffer();
try {
FileInputStream fis = new FileInputStream("test.txt");
int ch;
while ((ch = in.read()) > -1) {
buffer.append((char)ch);
}
in.close();
return buffer.toString();
}
catch (IOException e) {
e.printStackTrace();
return null;
}
}


The main method of the StreamConverter program invokes the writeOutput method to create a file of bytes encoded in UTF-8. The readInput method reads the same file, converting the bytes back into Unicode. Here is the source code for the main method:

		public static void main(String[] args) {
String jaString = new String("\u65e5\u672c\u8a9e\u6587\u5b57\u5217");
writeOutput(jaString);
String displayString = jaString + " " + inputString;
new ShowString(displayString, "Conversion Demo");
}


The original string (jaString) should be identical to the newly created string (inputString). To show that the two strings are the same, the program concatenates them and displays them with a ShowString object. The ShowString class displays a string with the Graphics.drawString method. The source code for this class is in ShowString.java. When the StreamConverter program instantiates ShowString, the following window appears. The repetition of the characters displayed verifies that the two strings are identical:

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