Запрос:
function doAjaxPost() {
    console.log('start');
    $.ajax({
        type: 'POST',
        url: "genkeys"
        success: console.log('success')
    });
    console.log('stop');
}

Сервлет spring:
@RequestMapping(value = "genkeys", method = RequestMethod.POST)
public void genKeys() {
    System.out.println("PRIVATE KEY1111:" + Base64.getEncoder().encodeToString(keyPair.getPrivate().getEncoded()));
}