大小虾们帮我看看我这段程序在linux下运行怎么有时可以执行，有时不能执行，谢谢大家！

File zip_path=new File("/usr/local/tomcat4/webapps/ROOT/report/");
String cmd = "zip 1111.zip 1111/*";
Process proc=Runtime.getRuntime().exec(cmd,null,zip_path);
BufferedReader procin=new BufferedReader(new InputStreamReader(proc.getInputStream()));
String outstr;
while((outstr=procin.readLine())!=null){
}
procin.close();
proc.destroy();