Process.execにて、スレッド使わずに外部コマンド実行する

ProcessRun.java

import java.io.*;

public class ProcessRun {
    public static void main(String[] args) throws IOException, InterruptedException {
        Process p = Runtime.getRuntime().exec("locate javac");
        InputStream stdout = p.getInputStream();
        InputStream stderr = p.getErrorStream();
        int val = 0;
        while (true) {
            String so = readString(stdout);
            if (so != null) System.out.println(so);
            String se = readString(stderr);
            if (se != null) System.err.println(se);
            if (so != null || se != null) continue;
            // 両方空だったら、終了かも知れない
            try {
                val = p.exitValue();
                break;
            } catch (IllegalThreadStateException e) {
                // do nothing
            }
            Thread.sleep(50);
        }
        p.destroy();
        System.out.println("Exit: "+val);
    }

    private static byte[] buf = new byte[1024];

    private static String readString(InputStream in) throws IOException {
        int num = in.available();
        if (num > 0) {
            if (num > buf.length) buf = new byte[num];
            int ret = in.read(buf,0,Math.min(num, buf.length));
            if (ret < 0) return null;
            return new String(buf,0,ret);
            // ※厳密な文字コード変換は省略。
            // OutputStreamWriterとか使ってバイナリの切れ目をJavaに判断させる
        }
        return null;
    }
}