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();
}