循环Map，key值用Set<String>接收，最后把循环Set<String>后的StringBuffer 拼接

Map<String,Double> excepMap = item.getException();
		StringBuffer permission = new StringBuffer();
		for(int i =0;i<excepMap.size();i++){
			Set<String> exceptionS = excepMap.keySet();
			String[] st = new String[exceptionS.size()];
			int j = 0 ;
			for(String exceptionL : exceptionS){
				st[i++] = exceptionL;
				permission.append(exceptionL+"@");
			}
		}
		System.out.print("看看几个异常："+permission.toString());

最后的StringBUffer对象拼接后会多出一个“@”符号，下边代码是去掉最后的符号：

String permissionStr = permission.toString();
permissionStr = permissionStr.substring(0,permissionStr.length()-1);//去除多余符号

 StringBuilder与 StringBuffer 哪个好点？