RFC: System.console().encoding()

[Aleksey Shipilev]

On 09/15/2016 09:06 AM, Xueming Shen wrote:
> Console is supposed to be a "char/String" based class, "encoding"
> really should have no business here in its api. Simply for some
> implementation convenience is really not a good reason to add such a
> public method.

Let's look at it this way: there is a problem with console encoding that
Console class solves, nicely abstracting the subtleties away. In doing
so, it polls GetConsoleCP, the WinAPI call:

JNIEXPORT jstring JNICALL
Java_java_io_Console_encoding(JNIEnv *env, jclass cls)
{
    char buf[64];
    int cp = GetConsoleCP();
    if (cp >= 874 && cp <= 950)
        sprintf(buf, "ms%d", cp);
    else
        sprintf(buf, "cp%d", cp);
    return JNU_NewStringPlatform(env, buf);
}

If by "convenience" you mean avoiding doing the JNI call that polls that
OS-specific bit of data, then yes, APIs provide lots of those conveniences.

> That said, I would be fine to have such informative info in the
> system properties, together with its siblings, file,encoding and
> another "supposed to be private" property sun.jnu.encoding.

Actually, if you look into the launcher, it does:

static char* getConsoleEncoding()
{
    char* buf = malloc(16);
    int cp;
    if (buf == NULL) {
        return NULL;
    }
    cp = GetConsoleCP();
    if (cp >= 874 && cp <= 950)
        sprintf(buf, "ms%d", cp);
    else
        sprintf(buf, "cp%d", cp);
    return buf;
}

...
  sprops.sun_stdout_encoding = getConsoleEncoding();

...which opens a way to poll this without a Reflection hack. Extended
the JMH hack with it, but it still fragile:
 http://hg.openjdk.java.net/code-tools/jmh/rev/8c20adb08b2d

Thanks,
-Aleksey