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# dnsjava Examples
All of these examples are code fragments. Code using these fragments should
check exceptions when appropriate, and should:
```java
import org.xbill.DNS.*;
```
## Get the IP address associated with a name
```java
InetAddress addr = Address.getByName("www.dnsjava.org");
```
## Get the MX target and preference of a name (modern)
```java
LookupSession s = LookupSession.defaultBuilder().build();
Name mxLookup = Name.fromString("gmail.com.");
s.lookupAsync(mxLookup, Type.MX)
.whenComplete(
(answers, ex) -> {
if (ex == null) {
if (answers.getRecords().isEmpty()) {
System.out.println(mxLookup + " has no MX");
} else {
for (Record rec : answers.getRecords()) {
MXRecord mx = ((MXRecord) rec);
System.out.println(
"Host " + mx.getTarget() + " has preference " + mx.getPriority());
}
}
} else {
ex.printStackTrace();
}
})
.toCompletableFuture()
.get();
```
## Get the MX target and preference of a name (legacy)
```java
Record[] records = new Lookup("gmail.com", Type.MX).run();
for (int i = 0; i < records.length; i++) {
MXRecord mx = (MXRecord) records[i];
System.out.println("Host " + mx.getTarget() + " has preference " + mx.getPriority());
}
```
## Simple lookup with a Resolver
```java
Record queryRecord = Record.newRecord(Name.fromString("dnsjava.org."), Type.A, DClass.IN);
Message queryMessage = Message.newQuery(queryRecord);
Resolver r = new SimpleResolver("8.8.8.8");
r.sendAsync(queryMessage)
.whenComplete(
(answer, ex) -> {
if (ex == null) {
System.out.println(answer);
} else {
ex.printStackTrace();
}
})
.toCompletableFuture()
.get();
```
## Query a remote name server for its version
```java
Lookup l = new Lookup("version.bind.", Type.TXT, DClass.CH);
l.setResolver(new SimpleResolver(args[0]));
l.run();
if (l.getResult() == Lookup.SUCCESSFUL) {
System.out.println(l.getAnswers()[0].rdataToString());
}
```
## Transfer a zone from a server and print it
```java
ZoneTransferIn xfr = ZoneTransferIn.newAXFR(Name.root, "192.5.5.241", null);
xfr.run();
for (Record r : xfr.getAXFR()) {
System.out.println(r);
}
```
## Use DNS dynamic update to set the address of a host to a value specified on the command line
```java
Name zone = Name.fromString("dyn.test.example.");
Name host = Name.fromString("host", zone);
Update update = new Update(zone);
update.replace(host, Type.A, 3600, args[0]);
Resolver res = new SimpleResolver("10.0.0.1");
res.setTSIGKey(new TSIG(host, base64.fromString("1234")));
res.setTCP(true);
Message response = res.send(update);
```
## Manipulate domain names
```java
Name n = Name.fromString("www.dnsjava.org");
Name o = Name.fromString("dnsjava.org");
System.out.println(n.subdomain(o)); // True
System.out.println(n.compareTo(o)); // > 0
Name rel = n.relativize(o); // the relative name 'www'
Name n2 = Name.concatenate(rel, o);
System.out.println(n2.equals(n)); // True
// www
// dnsjava
// org
for (int i = 0; i < n.labels(); i++) {
System.out.println(n.getLabelString(i));
}
```
## DNSSEC Resolver
```java
import java.io.*;
import java.nio.charset.StandardCharsets;
import org.xbill.DNS.*;
public class ResolveExample {
// Root anchors, see https://data.iana.org/root-anchors/root-anchors.xml
static String ROOT =
". IN DS 20326 8 2 E06D44B80B8F1D39A95C0B0D7C65D08458E880409BBC683457104237C7F8EC8D\n" +
". IN DS 38696 8 2 683D2D0ACB8C9B712A1948B27F741219298D0A450D612C483AF444A4C0FB2B16";
public static void main(String[] args) throws Exception {
// Send two sample queries using a standard resolver
SimpleResolver sr = new SimpleResolver("4.2.2.1");
System.out.println("Standard resolver:");
sendAndPrint(sr, "www.dnssec-failed.org.");
sendAndPrint(sr, "nic.ch.");
// Send the same queries using the validating resolver with the
// trust anchor of the root zone
// https://data.iana.org/root-anchors/root-anchors.xml
ValidatingResolver vr = new ValidatingResolver(sr);
vr.loadTrustAnchors(new ByteArrayInputStream(ROOT.getBytes(StandardCharsets.US_ASCII)));
System.out.println("\n\nValidating resolver:");
sendAndPrint(vr, "www.dnssec-failed.org.");
sendAndPrint(vr, "nic.ch.");
}
private static void sendAndPrint(Resolver vr, String name) throws IOException {
System.out.println("\n---" + name);
Record qr = Record.newRecord(Name.fromConstantString(name), Type.A, DClass.IN);
Message response = vr.send(Message.newQuery(qr));
System.out.println("AD-Flag: " + response.getHeader().getFlag(Flags.AD));
System.out.println("RCode: " + Rcode.string(response.getRcode()));
for (RRset set : response.getSectionRRsets(Section.ADDITIONAL)) {
if (set.getName().equals(Name.root) && set.getType() == Type.TXT
&& set.getDClass() == ValidatingResolver.VALIDATION_REASON_QCLASS) {
System.out.println("Reason: " + ((TXTRecord) set.first()).getStrings().get(0));
}
}
}
}
```
This should result in an output like
```
Standard resolver:
---www.dnssec-failed.org.
AD-Flag: false
RCode: NOERROR
---nic.ch.
AD-Flag: false
RCode: NOERROR
Validating resolver:
---www.dnssec-failed.org.
AD-Flag: false
RCode: SERVFAIL
Reason: Could not establish a chain of trust to keys for [dnssec-failed.org.]. Reason: No keys for dnssec-failed.org. have a DS for alg RSASHA1
---nic.ch.
AD-Flag: true
RCode: NOERROR
```
|
