大家给看看啊

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class SysteminReaderTest {
public static void main(String[] args) {

InputStreamReader isr = new InputStreamReader(System.in);
BufferedReader br = new BufferedReader(isr);
String s = null;
StringBuilder sb = new StringBuilder();
try {
while ((s = br.readLine()) != null) {
sb.append(s);
}
} catch (IOException e) {
e.printStackTrace();
}

System.out.println(sb.toString());

try {
isr.close();
} catch (IOException e) {
e.printStackTrace();
}

try {
br.close();
} catch (IOException e) {
e.printStackTrace();
}

}

}

怎么没有输出结果啊！？哪里出错了呢？！请赐教！