Default character encoding for java console output

Question

How does Java determine the encoding used for System.out?

Given the following class:

import java.io.File;
import java.io.PrintWriter;

p         


        

Answer 1

I'm assuming that your console still runs under cmd.exe. I doubt your console is really expecting UTF-8 - I expect it is really an OEM DOS encoding (e.g. 850 or 437.)

Java will encode bytes using the default encoding set during JVM initialization.

Reproducing on my PC:

java Foo

Java encodes as windows-1252; console decodes as IBM850. Result: Mojibake

java -Dfile.encoding=UTF-8 Foo

Java encodes as UTF-8; console decodes as IBM850. Result: Mojibake

cat test.txt

cat decodes file as UTF-8; cat encodes as IBM850; console decodes as IBM850.

java Foo | cat

Java encodes as windows-1252; cat decodes as windows-1252; cat encodes as IBM850; console decodes as IBM850

java -Dfile.encoding=UTF-8 Foo | cat

Java encodes as UTF-8; cat decodes as UTF-8; cat encodes as IBM850; console decodes as IBM850

This implementation of cat must use heuristics to determine if the character data is UTF-8 or not, then transcodes the data from either UTF-8 or ANSI (e.g. windows-1252) to the console encoding (e.g. IBM850.)

This can be confirmed with the following commands:

$ java HexDump utf8.txt
78 78 c3 a4 c3 b1 78 78

$ cat utf8.txt
xxäñxx

$ java HexDump ansi.txt
78 78 e4 f1 78 78

$ cat ansi.txt
xxäñxx

The cat command can make this determination because e4 f1 is not a valid UTF-8 sequence.

You can correct the Java output by:

• Setting the console encoding to the system ANSI value
• Using the Console type
• Using some shiv layer as you are doing with cat

HexDump is a trivial Java application:

import java.io.*;
class HexDump {
  public static void main(String[] args) throws IOException {
    try (InputStream in = new FileInputStream(args[0])) {
      int r;
      while((r = in.read()) != -1) {
        System.out.format("%02x ", 0xFF & r);
      }
      System.out.println();
    }
  }
}