[十万火急]高分求救。java调用linux命令问题。

问题说明：
      1.程序（web）需要实现一个客户端来备份服务器数据库的功能。
      2.数据库是postgresql，备份命令在linux下为：/usr/local/pgsql/bin/pg_dump dbname -U dbuser >要保存的路径文件(如：./aaa.dmp);
      3.现通过Runtime.getRuntime().exec()命令来执行。

代码如下：
Java code:

backupCmd = "/usr/local/pgsql/bin/pg_dump books2 -n books_"
+ sch_id + " -U postgres -c >" + address + "books_" + sch_id + "_" + num + ".dmp";

process = Runtime.getRuntime().exec(backupCmd);

System.out.print(Utils.loadStream(process.getInputStream()));
System.err.print(Utils.loadStream(process.getErrorStream()));


Utils.loadStream(）的代码：
Java code:

public static String loadStream(InputStream in) throws IOException {

int ptr = 0;
try {
in = new BufferedInputStream(in);
StringBuffer buffer = new StringBuffer();
while ((ptr = in.read()) != -1) {
buffer.append((char)ptr);
}

return b