有時候在java代碼中會調(diào)用一些外部程序，比如SwfTools來轉(zhuǎn)換swf、ffmpeg來轉(zhuǎn)換視頻等。如果你的代碼這樣寫：Runtime.getRuntime().exec(command)，會發(fā)現(xiàn)程序一下就執(zhí)行完畢，而在命令行里要執(zhí)行一會，是因為java沒有等待外部程序的執(zhí)行完畢，此時就需要使用阻塞，來等待外部程序執(zhí)行結(jié)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();

對于一般的外部程序使用上面的阻塞代碼就可以，至少pdf2swf.exe是沒有問題的。

但我發(fā)現(xiàn)對于ffmpeg來說，以上代碼會讓程序卡住不動，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 finishedtry {in = process.getInputStream();err = process.getErrorStream();boolean finished = false; // Set to true when p is finishedwhile (!finished) {try {while (in.available() > 0) {// Print the output of our system callCharacter c = new Character((char) in.read());System.out.print(c);}while (err.available() > 0) {// Print the output of our system callCharacter 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 cyclesThread.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;}