jvm添加自定义dns实现过程示例

// mapping from host name to Addresses - either NameServiceAddresses (while
    // still being looked-up by NameService(s)) or CachedAddresses when cached
    private static final ConcurrentMap<String, Addresses> cache =
        new ConcurrentHashMap<>();
    // CachedAddresses that have to expire are kept ordered in this NavigableSet
    // which is scanned on each access
    private static final NavigableSet<CachedAddresses> expirySet =
        new ConcurrentSkipListSet<>();

// remove expired addresses from cache - expirySet keeps them ordered
        // by expiry time so we only need to iterate the prefix of the NavigableSet...
        long now = System.nanoTime();
        for (CachedAddresses caddrs : expirySet) {
            // compare difference of time instants rather than
            // time instants directly, to avoid possible overflow.
            // (see System.nanoTime() recommendations...)
            if ((caddrs.expiryTime - now) < 0L) {
                // ConcurrentSkipListSet uses weakly consistent iterator,
                // so removing while iterating is OK...
                if (expirySet.remove(caddrs)) {
                    // ... remove from cache
                    cache.remove(caddrs.host, caddrs);
                }
            } else {
                // we encountered 1st element that expires in future
                break;
            }
        }

Class<?> cachedAddresses_Class = Class.forName("java.net.InetAddress$CachedAddresses");
        Constructor<?> constructor = cachedAddresses_Class.getDeclaredConstructors()[0];
        constructor.setAccessible(true);
        Object o = constructor.newInstance(host, toInetAddressArray(host, ip), Long.MAX_VALUE);
        Field cacheField = InetAddress.class.getDeclaredField("cache");
        cacheField.setAccessible(true);
        ConcurrentMap<String, Object> cm = (ConcurrentMap<String, Object>) cacheField.get(null);
        cm.put(host, o);
        Field expirySetField = InetAddress.class.getDeclaredField("expirySet");
        expirySetField.setAccessible(true);
        ConcurrentSkipListSet<Object> cs = (ConcurrentSkipListSet<Object>) expirySetField.get(null);
        cs.add(o);