如何将条目放入 dnsjava 缓存以覆盖 DNS 查找

Question

为了避免出于测试目的从公共 DNS 中查找主机名，我需要设置 /etc/hosts 文件，但我并不总是知道需要哪些主机名来覆盖 IP 地址，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。尽管也支持所有其他 DNS 条目类型，但很可能应该使用 A（对于 IPv4）或 AAAA（对于 IPv6）。您需要创建一个 Name 实例，并从中创建一个 ARecord，它将被插入到缓存中。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
}