PDFBox：“你没有在打印后立即关闭PDFDocument”

Question

我使用以下Java代码打印PDF文档：

PrinterJob job = PrinterJob.getPrinterJob();
job.setPrintService(printer);
File file = new File(fileName);
PDDocument doc = PDDocument.load(file);
PDFPageable pageable = new PDFPageable(doc);
job.setPageable(pageable);
System.out.println("-- before printing --");
job.print();
System.out.println("-- after printing --");
doc.close();

控制台上的输出是：

-- before printing --
Aug 03, 2018 12:05:09 PM org.apache.pdfbox.cos.COSDocument finalize
WARNUNG: Warning: You did not close a PDF Document
-- after printing --

为什么我会收到这个警告？

Answer 1

您正在加载PDI文档，但没有关闭它。我想你需要做：

String yourText;
PDDocument yourDocument = PDDocument.load("yourDocument");
try {
    yourText = pdfs.getText(yourDocument);
} finally {
    yourDocument.close();
}

当pdf文档完成且尚未关闭时，会发出此警告。

有关警告信息，请参阅此处：

/**
 * Warn the user in the finalizer if he didn't close the PDF document. The method also
 * closes the document just in case, to avoid abandoned temporary files. It's still a good
 * idea for the user to close the PDF document at the earliest possible to conserve resources.
 * @throws IOException if an error occurs while closing the temporary files
 */
protected void finalize() throws IOException
{
    if (!closed) {
        if (warnMissingClose) {
            log.warn( "Warning: You did not close a PDF Document" );
        }
        close();
    }
}

Answer 2

正如在评论中所讨论的，通过更新到最新的jdk版本，问题得以解决：从jdk 1.8.0_131到1.8.0_181。我只能怀疑旧的jdk有一个bug，即对象被过早地标记为“未使用”，因此被最终确定。