The Java Tutorials have been written for JDK 8. Examples and practices described in this page don't take advantage of improvements introduced in later releases and might use technology no longer available.
See Java Language Changes for a summary of updated language features in Java SE 9 and subsequent releases.
See JDK Release Notes for information about new features, enhancements, and removed or deprecated options for all JDK releases.
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"); InputStreamReader isr = new InputStreamReader(fis, "UTF8");
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); String defaultEncoding = defaultReader.getEncoding();
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"); InputStreamReader isr = new InputStreamReader(fis, "UTF8"); Reader in = new BufferedReader(isr); 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 inputString = readInput(); 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: