获得path变量

import java.io.*;

public class Exec {
 public static void main(String[] args) throws IOException {
  Runtime r = Runtime.getRuntime();
  Process p = r.exec("cmd");
  PrintWriter writer = new PrintWriter(new OutputStreamWriter(p
    .getOutputStream()));
  BufferedReader reader = new BufferedReader(new InputStreamReader(p
    .getInputStream()));
  writer.println("set path");
  writer.println("exit");
  writer.flush();
  String path = "";
  final String prefix = "Path=";
  for (String line = null; (line = reader.readLine()) != null;) {
   if (line.startsWith("Path=")) {
    path = line.substring(prefix.length());
   }
  }
  System.out.println(path);
  writer.close();
  reader.close();
 }