如何把在进入dnsjava缓存覆盖DNS查找

Question

在试图避免主机名从公共DNS用于测试目的抬起头来，我需要基本设置/ etc/hosts文件，但我并不总是知道我需要重写IP地址的主机名，所以我试图使用dnsjava，因为默认的Java DNS解析不允许直接插入缓存。

Answer 1

基本上，你需要抢dnsjava正确的DNS缓存类型（A，AAAA，等等）。 A（对于IPv4）或AAAA（对于IPv6）很可能是您应该使用的，尽管也支持所有其他DNS条目类型。您需要创建一个Name实例，并从中创建一个将被插入到Cache中的ARecord。示例如下：

public void addHostToCacheAs(String hostname, String ipAddress) throws UnknownHostException, TextParseException { 
    //add an ending period assuming the hostname is truly an absolute hostname 
    Name host = new Name(hostname + "."); 
    //putting in a good long TTL, and using an A record, but AAAA might be desired as well for IPv6 
    Record aRec = new ARecord(host, Type.A, 9999999, getInetAddressFromString(ipAddress)); 
    Lookup.getDefaultCache(Type.A).addRecord(aRec, Credibility.NORMAL,this); 
} 


public InetAddress getInetAddressFromString(String ip) throws UnknownHostException { 
    //Assume we are using IPv4 
    byte[] bytes = new byte[4]; 
    String[] ipParts = ip.split("\\."); 
    InetAddress addr = null; 
    //if we only have one part, it must actually be a hostname, rather than a real IP 
    if (ipParts.length <= 1) { 
     addr = InetAddress.getByName(ip); 
    } else { 
     for (int i = 0; i < ipParts.length; i++) { 
      bytes[i] = Byte.parseByte(ipParts[i]); 
     } 
     addr = InetAddress.getByAddress(bytes); 
    } 
    return addr 
}