Android下执行Runtime.getRuntime().exec后返回状态

private String doExec(String cmd)返回输出值，private String doExec2(String cmd)返回错误列表。你如果有不明白的地方，可以给我留言。
private String doExec(String cmd) {
String s = "\n";  
       try {  
           Process p = Runtime.getRuntime().exec(cmd);  
           BufferedReader in = new BufferedReader(  
                               new InputStreamReader(p.getInputStream()));  
           String line = null;  
           while ((line = in.readLine()) != null) {  
               s += line + "\n";                 
           }  
       } catch (IOException e) {  
           // TODO Auto-generated catch block  
           e.printStackTrace();  
       }  
       return s;    
}


private String doExec2(String cmd) {
String s = "\n";
try{
Process ps=Runtime.getRuntime().exec(cmd);
DataInputStream ise = new DataInputStream(ps.getErrorStream());
String error = null;
while((error = ise.readLine()) != null) {
s += error + "\n";   
}
}
catch(IOException ex){
String temp = ex.getMessage();
Log.i("doInBackground", temp);
}
return s;

}