1.       用startProcessByReader()执行javac命令没有问题，而执行java命令就会阻塞，不知道怎么回事。startProcess（）函数就不会产生这样的问题。难道本地命令执行时返回的不能用Reader？
  2.       需研究jdk的源码。不知道这里的Runtime.getRuntime().exec()函数是怎么实现的，看看。
  3.       InputStream出来的是byte，在进行char转型后得到的字符是ASCII编码，须用GBK再转换一次
import java.io.*;
import java.util.*;

public class ExecNatComm {

    /**
     * Starts a native process
     *
     * @param command
     *            the command to start the process
     * @param dir
     *            the dir in which the process starts
     */
    public String startProcess(String command, String dir) throws IOException {
        StringBuffer ret = new StringBuffer();
        String[] comm = new String[3];
        comm[0] = "cmd";
        comm[1] = "/C";
        comm[2] = command;
        long start = System.currentTimeMillis();
        try {
            Process ls_proc = Runtime.getRuntime().exec(comm, null, new File(dir));
            // Get input and error streams
            BufferedInputStream ls_in = new BufferedInputStream(ls_proc.getInputStream());
            BufferedInputStream ls_err = new BufferedInputStream(ls_proc.getErrorStream());
            boolean end = false;
            while (!end) {
                int c = 0;
                while ((ls_err.available() > 0) && (++c <= 1000)) {
                    ret.append((char)(ls_err.read()));
                }
                c = 0;
                while ((ls_in.available() > 0) && (++c <= 1000)) {
                    ret.append((char)(ls_in.read()));
                }
                try {
                    ls_proc.exitValue();
                    while (ls_err.available() > 0)
                        ret.append((char)(ls_err.read()));
                    while (ls_in.available() > 0)
                        ret.append((char)(ls_in.read()));
                    end = true;
                } catch (IllegalThreadStateException ex) {
                    // Process is running
                }
                // The process is not allowed to run longer than given time.
                if (System.currentTimeMillis() - start > 20000) {
                    ls_proc.destroy();
                    end = true;
                    ret.append("!!!! Process has timed out, destroyed !!!!!");
                }
                try {
                    Thread.sleep(50);
                } catch (InterruptedException ie) {

                }
            }
        } catch (IOException e) {
            ret.append("Error: " + e);
        }
        String gbkRet =ret.toString();
        gbkRet= new String(gbkRet.getBytes("ISO8859-1"), "gbk");
        return gbkRet;
    }

    public String startProcessByReader(String command, String dir) throws IOException {
        StringBuffer ret = new StringBuffer();
        String[] comm = new String[3];
        comm[0] = "cmd";
        comm[1] = "/C";
        comm[2] = command;
        long start = System.currentTimeMillis();
        try {
            Process ls_proc = Runtime.getRuntime().exec(comm, null, new File(dir));
            // Get input and error streams
            InputStreamReader ls_in_reader = new InputStreamReader(ls_proc.getInputStream());
            InputStreamReader ls_err_reader = new InputStreamReader(ls_proc.getErrorStream());
            BufferedReader in_br = new BufferedReader(ls_in_reader);
            BufferedReader err_br = new BufferedReader(ls_err_reader);

            boolean end = false;
            String line = null;
            while (!end) {
                // Process is running
                while((line=err_br.readLine())!=null) ret.append(line).append("\r\n");
                while((line=in_br.readLine())!=null) ret.append(line).append("\r\n");
                try {
                    ls_proc.exitValue();
                    while((line=err_br.readLine())!=null) ret.append(line).append("\r\n");
                    while((line=in_br.readLine())!=null) ret.append(line).append("\r\n");
                    end = true;
                } catch (IllegalThreadStateException ex) {
                    // Process is running
                }
                // The process is not allowed to run longer than given time.
                if (System.currentTimeMillis() - start > 20000) {
                    ls_proc.destroy();
                    end = true;
                    ret.append("!!!! Process has timed out, destroyed !!!!!");
                }
                try {
                    Thread.sleep(50);
                } catch (InterruptedException ie) {
                }
            }
        } catch (IOException e) {
            ret.append("Error: " + e);
        }
        return (ret.toString());
    }

    /**
     * @param args
     * @throws IOException
     */
    public static void main(String[] args) throws IOException {
        // TODO Auto-generated method stub
        ExecNatComm exe = new ExecNatComm();
        String ret = exe.startProcess("javadd", "d:");
        System.out.println(ret);
        ret = exe.startProcessByReader("javac","d:");
        System.out.println(ret);
    }
}
呵呵，这个可以用在jsp中，远程执行命令。
有对上面的问题了解的看客请解我的疑惑。