System.setProperty无法在Java中用于file.encoding

Question

I have this simple program where Im trying to create a txt file with UTF-8 format. However, I see that the file is not encoded with UTF-8 but shows the encoding is set to ANSI. Below is the output. Can you please help.

public class fileCreate {
   public static void main(String[] args) {
      try {
             System.out.println("Before encoding: "+System.getProperty("file.encoding"));
             System.setProperty("file.encoding","UTF-8");
             System.out.println("After encoding: "+System.getProperty("file.encoding")); 

             File file = new File("C:/tmp/myfile_UTF-8.txt");

             if(file.createNewFile())System.out.println("Success!");
               else System.out.println ("Error, file already exists.");
          }
          catch(IOException ioe) {
          ioe.printStackTrace();
          }
      }
   }

Output:

Before encoding: Cp1252

After encoding: UTF-8

Success!

Answer 1

When you create a new file, it is initially empty. "Encoding" is not a property of the file, it is how you interpret its content bytes. That is also why you have to specify the encoding before reading and writing, because it is not stored anywhere.

Without content, the encoding is kind of undefined. Your editor probably picks its first guess, which might be ASCII. But empty content can probably be decoded with any encoding.

If you write some text to the file in your code, it will be encoded in UTF-8. Your editor will then show its encoding as such too (provided it is a good one and can detect it correctly).

Answer 2

您可以使用以下代码创建UTF-8文件

PrintWriter out1 = new PrintWriter(new File("C:/tmp/myfile_UTF-8.txt"), "UTF-8");