Java dynamic replacement for DNS in inetaddress simple analysis 1

In the java.net package description, a brief description of some of the key interfaces. Which is responsible for networking identifiers is addresses. The concrete implementation class of this class is inetaddress, the bottom encapsulates the similarities and differences between inet4address and inet6address, can be regarded as a facade tool class.

1. A low Level API, which deals with the following abstractions:
2. Addresses, which is networking identifiers, like IP Addresses.
3. Sockets, which is basic bidirectional data communication mechanisms.
4. Interfaces, which describe network Interfaces.

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In OpenJDK's InetAddress source code section, the IP is parsed according to DNS or hostname:

2. private static inetaddress[] GETALLBYNAME0 (String host, InetAddress reqaddr, Boolean check)
4. Throws Unknownhostexception {
8. /* If It gets here it's presumed to be a hostname */
10. /* Cache.get can return:null, unknownaddress, or inetaddress[] */
14. /* Make sure the connection to the host is allowed, before we
16. * Give out a hostname
18. */
20. if (check) {
22. SecurityManager security = System.getsecuritymanager ();
24. if (Security! = null) {
26. Security.checkconnect (host,-1);
28. }
30. }
34. Inetaddress[] addresses = getcachedaddresses (host);
38. /* If No entry in cache, then do the host lookup */
40. if (addresses = = null) {
42. Addresses = Getaddressesfromnameservice (host, reqaddr);
44. }
48. if (addresses = = Unknown_array)
50. throw new Unknownhostexception (host);
54. return Addresses.clone ();
56. }

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The

Key two methods are:
Getcachedaddresses (host);
Getaddressesfromnameservice (host, reqaddr); The
parses the cached IP from Addresscache, or Negativecache according to Dns/hostname. The
then iterates through the nameservices, calls each Nameservice's LOOKUPALLHOSTADDR (host) to find the IP, and then caches the HOST:IP to the previous cache.
based on the above, there are two ways to dynamically resolve DNS:
1. Reflect Addresscache, or negativecache, and put Host:ip through the cache's put () method.
2. Reflect the nameservices and put the Nameservice instance of the agent into.
Two ways to do this:
1. Addresscache, or Negativecache, are java.net.InetAddress.Cache, and their internal cacheentry are affected by the two sets of JVM options:
Networkaddress.cache.ttl
Networkaddress.cache.negative.ttl
After the TTL, CacheEntry get () returns only null.
2. Nameservices is only a OPENJDK implementation. In other words, just the sun family. The other JDK does not use this property name.
Write the snippet code to see the properties inside the JRockit and IBM JVM inetaddress:

1. class<inetaddress> type = Inetaddress.class;
3. field[] fields = Type.getdeclaredfields ();
5. for (Field f:fields) {
6. System.out.println (F.getname () + ":" + F.gettype ());
7. }

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OpenJDK:

1. IPv4
2. IPv6
3. Preferipv6address
4. Holder
5. Nameservices
6. Canonicalhostname
7. Serialversionuid
8. Addresscache
9. Negativecache
10. Addresscacheinit
11. Unknown_array
12. Impl
13. LookupTable
14. Cachedlocalhost
15. CacheTime
16. Maxcachetime
17. Cachelock
18. Fields_offset
19. UNSAFE
20. Serialpersistentfields
21. $assertionsDisabled

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JRockit:

1. IPv4
2. IPv6
3. Preferipv6address
4. HostName
5. Address
6. Family
7. Nameservice
8. Canonicalhostname
9. Serialversionuid
10. Addresscache
11. Negativecache
12. Addresscacheinit
13. Unknown_array
14. Impl
15. LookupTable
16. $assertionsDisabled

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IBM JDK

1. Ipv4:int
2. Ipv6:int
3. Preferipv6address
4. Hostname:class java.lang.String
5. Address:int
6. Family:int
7. Nameservice:interface Sun.net.spi.nameservice.NameService
8. Canonicalhostname:class java.lang.String
9. Serialversionuid:long
10. Addresscache:class Java.net.inetaddress$cache
11. Negativecache:class Java.net.inetaddress$cache
12. Localhostname:class java.lang.String
13. Localhostnamelock:class Java.lang.Object
14. Cachelocalhost:boolean
15. Addresscacheinit:boolean
16. Unknown_array:class [Ljava.net.InetAddress;
17. Impl:interface Java.net.InetAddressImpl
18. Lookuptable:class Java.util.HashMap
19. $assertionsDisabled: Boolean

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See here, know the egg hurts. Three types of JDK,
OpenJDK is Nameservices is a list<nameservice>
JRockit and the IBM JVM are Nameservice, just a separate nameservice instance.
So with a 2nd approach, you should at least meet the needs of these three mainstream JDK types.
Simple implementation of two practices:
Procedure 1, dynamically replaces the Addresscache.
Procedure 2, dynamic proxy nameservice.
The source code is as follows

1. Length limit, source view Huitie.

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Temporarily test to this bar, interested students can be perfect together. Strive to meet OpenJDK, Jrockit, IBM JDK Three mainstream environment DNS dynamic resolution class.

Java dynamic replacement for DNS in inetaddress simple analysis 1