String str = DecimalFormat.getNumberInstance().format(1245600000);

        String currecy = NumberFormat.getCurrencyInstance().format(1245600000);

        System.out.println("转换成Currency格式："+currecy);

        System.out.println("转换成带千分位的格式："+str); 
         输出结果：    
          转换成Currency格式：￥1,245,600,000.00
          转换成带千分位的格式：1,245,600,000
       也可以用js实现类似的功能:
      function convert(num)   
     {               var str = num+"";            
        var reg = /(-?/d+)(/d{3})/;    
        while(reg.test(str))       {
        str = str.replace(reg,"$1,$2");     
       }   
       return str;