java - 为什么PrinterState始终为null？

我需要对打印机有更多控制，然后尝试获取打印机的PrinterState，然后使用PrintStareReasons。我的代码如下:

public void checkPrinterStatus(){

    try {
        logger.info("Check -------------- ");

        Thread.sleep(2000);
    } catch (InterruptedException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

    PrintService printer = configParamPrintService.getPrintService();
    logger.info("State " + printer.isAttributeCategorySupported(PrinterState.class));
    Set<Attribute> attributes = getAttributes(printer);
    for(Attribute attr : attributes){
        logger.info(attr.getName());
    }



}

public static Set<Attribute> getAttributes(PrintService printer) {
    Set<Attribute> set = new LinkedHashSet<Attribute>();

    //get the supported docflavors, categories and attributes
    Class<? extends Attribute>[] categories = (Class<? extends Attribute>[]) printer.getSupportedAttributeCategories();
    DocFlavor[] flavors = printer.getSupportedDocFlavors();
    AttributeSet attributes = printer.getAttributes();

    //get all the avaliable attributes
    for (Class<? extends Attribute> category : categories) {
        for (DocFlavor flavor : flavors) {
            //get the value
            Object value = printer.getSupportedAttributeValues(category, flavor, attributes);

            //check if it's something
            if (value != null) {
                //if it's a SINGLE attribute...
                if (value instanceof Attribute)
                    set.add((Attribute) value); //...then add it

                //if it's a SET of attributes...
                else if (value instanceof Attribute[])
                    set.addAll(Arrays.asList((Attribute[]) value)); //...then add its childs
            }
        }
    }

    return set;
}

谷歌搜索我还写了getAttributes()来获取所有属性，但是PrinterState不存在。

这是所有属性的列表:

21.12.2015 16:48:56 INFO  PrintWorker:142 - Check --------------
21.12.2015 16:48:58 INFO  PrintWorker:151 - State false
21.12.2015 16:48:58 INFO  PrintWorker:154 - copies-supported
21.12.2015 16:48:58 INFO  PrintWorker:154 - finishings
21.12.2015 16:48:58 INFO  PrintWorker:154 - job-sheets
21.12.2015 16:48:58 INFO  PrintWorker:154 - job-sheets
21.12.2015 16:48:58 INFO  PrintWorker:154 - number-up
21.12.2015 16:48:58 INFO  PrintWorker:154 - number-up
21.12.2015 16:48:58 INFO  PrintWorker:154 - number-up
21.12.2015 16:48:58 INFO  PrintWorker:154 - number-up
21.12.2015 16:48:58 INFO  PrintWorker:154 - number-up
21.12.2015 16:48:58 INFO  PrintWorker:154 - number-up
21.12.2015 16:48:58 INFO  PrintWorker:154 - orientation-requested
21.12.2015 16:48:58 INFO  PrintWorker:154 - orientation-requested
21.12.2015 16:48:58 INFO  PrintWorker:154 - orientation-requested
21.12.2015 16:48:58 INFO  PrintWorker:154 - orientation-requested
21.12.2015 16:48:58 INFO  PrintWorker:154 - page-ranges
21.12.2015 16:48:58 INFO  PrintWorker:154 - media
21.12.2015 16:48:58 INFO  PrintWorker:154 - spool-data-destination

尽管

logger.info("State " + printer.isAttributeCategorySupported(PrinterState.class));

总是返回:

21.12.2015 16:48:58 INFO  PrintWorker:151 - State false

我已经在Linux和Windows(7)上测试了以下代码，但是没有一个返回实际状态。可能是什么问题呢？打印机，驱动程序还是我的代码？

最佳答案

如果“打印请求”中的打印服务isAttributeCategorySupported()否则返回false，则true返回supports specifying a doc-level or job-level attribute in category。

看看the official oracle documentation将使我的观点更加清楚