基于这个链接，你的代码很好。
你必须检查环境变量和权限：apache无权执行。要么java-jar在目录中启动运行，那么无法通过java找到打印机找不到的pdf文件。

Based on this link, your code is good. You have to check the environment variables and permissions: either apache has no right to execute., either the java-jar starts an runs in a directory, where has no access to your pdf file either printer not found, by java.