How to pass UTF-8 strings to and from Java in SWIG

txt

// inefficient, but correct
//
// See also: https://docs.rs/cesu8

namespace std {
  %typemap(jni) string "jbyteArray"
  %typemap(in) string {
    jsize length = jenv->GetArrayLength($input);
    char* buf = (char *) jenv->GetPrimitiveArrayCritical($input, NULL);
    // TODO: null/error check
    $1 = std::string(buf, length);
    jenv->ReleasePrimitiveArrayCritical($input, buf, 0);
  }
  %typemap(jtype) string "byte[]"
  %typemap(jstype) string "String"
  %typemap(out) string {
    const size_t len = $1.size();
    $result = jenv->NewByteArray(len);
    // TODO: check that this succeeded
    jenv->SetByteArrayRegion($result, 0, len, (const jbyte*)$1.data());
  }
  %typemap(javaout) string {
    return java.nio.charset.StandardCharsets.UTF_8.decode(java.nio.ByteBuffer.wrap($jnicall)).toString();
  }
  %typemap(javain,
    pre= "byte[] temp$javainput = $javainput.getBytes(java.nio.charset.StandardCharsets.UTF_8);"
  ) string 
    "temp$javainput"
}