本文實例講述了Java基於Runtime呼叫外部程式出現阻塞的解決方法， 是一個很實用的技巧。分享給大家供大家參考。具體分析如下：
有時候在java程式碼中會呼叫一些外部程序，例如SwfTools來轉換swf、ffmpeg來轉換影片等。如果你的程式碼這樣寫：Runtime.getRuntime().exec(command)，會發現程式一下就執行完畢，而在命令列裡要執行一會，是因為java沒有等待外部程式的執行完畢，此時就需要使用阻塞，來等待外部程式執行結果：
InputStream stderr = process.getInputStream();InputStreamReader isr = new InputStreamReader(stderr, "GBK");BufferedReader br = new BufferedReader(isr);String line = null;while ((line = br.readLine()) ! ) System.out.println(line);int exitValue = process.waitFor();
對於一般的外部程式使用上面的阻塞程式碼就可以，至少pdf2swf.exe是沒有問題的。
但緊接著又發現對於ffmpeg來說，以上程式碼會讓程式卡住不動，需要使用另一種方式，封裝成了一個方法，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 { inStream process.Input (); 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(5000). } } } 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;}希望本文所述對大家Java程式設計的學習有幫助。