Java calls an external program blocking solution based on Runtime

This article illustrates an example of how Java can block calls to external programs based on Runtime. Share with you for your reference. Specific analysis is as follows:

Sometimes external programs are called in Java code, such as SwfTools to convert SWF, ffmpeg to convert video, and so on. If your code reads: Runtime. GetRuntime (). Exec (command), you will find that the program will execute in one go, and in the command line will execute for a while.

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();

For general external programs using the above blocking code can be, at least pdf2swf.exe is no problem.

But then I found out that for ffmpeg, the above code would make the program stuck, so I needed to use another way to encapsulate a method, as follows:

@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;
}

I hope this article will be helpful to your Java programming study.