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;
	}