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;

	}