encoding/character 设置 Java 默认使用什么 BufferedReader？

Question

当我们创建新的 BufferedReader 对象而不显式提供编码时，Java 默认使用什么 encoding/character 设置？

例如：

try (final BufferedReader reader = new BufferedReader(new FileReader("my_file.txt"))) {
  reader.readLine(); // What encoding is used to read the file?
}

Answer 1

FileReader 是一个 InputStreamReader，它使用 FileInputStream 作为输入，而 InputStreamReader 在没有指定字符集的情况下构造时使用默认字符集。

源码jdk10中，使用Charset.defaultCharset():

public static StreamDecoder forInputStreamReader(InputStream in,
                                                 Object lock,
                                                 String charsetName)
    throws UnsupportedEncodingException
{
    String csn = charsetName;
    if (csn == null)
        csn = Charset.defaultCharset().name(); // get default charset
    try {
        if (Charset.isSupported(csn))
            return new StreamDecoder(in, lock, Charset.forName(csn));
    } catch (IllegalCharsetNameException x) { }
    throw new UnsupportedEncodingException (csn);
}

哪个

Returns the default charset of this Java virtual machine.

The default charset is determined during virtual-machine startup and typically depends upon the locale and charset of the underlying operating system.

可以打印：

public static void main(String[] args) {
    System.out.println(Charset.defaultCharset());
}

Answer 2

BufferedReader 不做任何解码。它是另一个 Reader 的包装器......可能会也可能不会解码。

FileReader decodes using the JVM's default character encoding, as returned by Charset.defaultCharset()

javadoc 指出：

Convenience class for reading character files. The constructors of this class assume that the default character encoding and the default byte-buffer size are appropriate. To specify these values yourself, construct an InputStreamReader on a FileInputStream.

encoding/character 设置 Java 默认使用什么 BufferedReader？

What encoding/character set does Java use per default for BufferedReader?

java

encoding

bufferedreader