java 判断输入的字符串是否为正整数

//test.java

import java.io.*;

class test
{
public static void main(String[] args)
{
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
boolean b = true;

try
{
while (b)
{
System.out.print("请输入一个正整数：");
String s = (String) br.readLine();
for (int j = 0; j < s.length(); j++)
{
if (!(s.charAt(j) >= 48 && s.charAt(j) <= 57))
{
System.out.println("您输入的不是正整数!请重新输入.");
b = true;
break;
}
else
{
b = false;
}
}
if (!b)
{
int i = Integer.parseInt(s);
if(i==0)
{
System.out.println("您输入的不是正整数!请重新输入.");
break;
}

System.out.println("您输入的是:" + i);
}
}
}

catch (Exception e)
{
e.printStackTrace();
}

}
}