src/org/nutz/lang/stream/QueueInputStream.java
public int peek(int index) throws IOException{
        while(cache.size() <= index){
            cache.add(is.read());
        }
        return cache.get(index);
    }
public int peek(int index) throws IOException{
        while(cache.size() <= index){
            cache.add(is.read());
        }
        return cache.get(index);
    }
访问头部开始第几个字节, 不删除
@param index
@return 头部的第N个字节
@throws IOException