如何将条目放入dnsjava缓存以覆盖DNS查找

Question

为了避免为了测试目的从公共DNS中查找主机名，我需要设置/etc/host文件，但我并不总是知道需要覆盖IP地址的主机名，所以我尝试使用dnsjava，因为默认的Java DNS解析不允许直接插入缓存。

Answer 1

基本上，您需要为dnsjava (A、AAAA等)获取正确的DNS类型缓存。很可能您应该使用A(用于IPv4)或AAAA (用于IPv6)，尽管也支持所有其他的DNS条目类型。您将需要创建一个名称实例，并从该实例中插入到缓存中的ARecord。例子如下：

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
}