Java借助Runtime调用外部程序阻塞的代码
有时候在java代码中会调用一些外部程序,比如SwfTools来转换swf、ffmpeg来转换视频等。如果你的代码这样写:Runtime.getRuntime().exec(command),会发现程序一下就执行完毕,而在命令行里要执行一会,是因为java没有等待外部程序的执行完毕,此时就需要使用阻塞,来等待外部程序执行结果:
InputStream stderr = process.getInputStream(); InputStreamReader isr = new InputStreamReader(stderr, "GBK"); BufferedReader br = new BufferedReader(isr); String line = null; while ((line = br.readLine()) != null) System.out.println(line); int exitValue = process.waitFor();
对于一般的外部程序使用上面的阻塞代码就可以,至少pdf2swf.exe是没有问题的。
但我发现对于ffmpeg来说,以上代码会让程序卡住不动,需要使用另一种方式,封装成了一个方法,如下:
@SuppressWarnings("static-access") public static int doWaitFor(Process process) { InputStream in = null; InputStream err = null; int exitValue = -1; // returned to caller when p is finished try { in = process.getInputStream(); err = process.getErrorStream(); boolean finished = false; // Set to true when p is finished while (!finished) { try { while (in.available() > 0) { // Print the output of our system call Character c = new Character((char) in.read()); System.out.print(c); } while (err.available() > 0) { // Print the output of our system call Character c = new Character((char) err.read()); System.out.print(c); } // Ask the process for its exitValue. If the process // is not finished, an IllegalThreadStateException // is thrown. If it is finished, we fall through and // the variable finished is set to true. exitValue = process.exitValue(); finished = true; } catch (IllegalThreadStateException e) { // Process is not finished yet; // Sleep a little to save on CPU cycles Thread.currentThread().sleep(500); } } } catch (Exception e) { e.printStackTrace(); } finally { try { if (in != null) { in.close(); } } catch (IOException e) { e.printStackTrace(); } if (err != null) { try { err.close(); } catch (IOException e) { e.printStackTrace(); } } } return exitValue; }