Develop Reference

Get name of computer from ipaddress

I am trying to get the name of computer from its local IP. This is what I've done so far, but nothing works it just returns the IP address as hostname
InetAddress addr = null;
String hostIP = "192.168.100.10";
try {
addr = InetAddress.getByName(hostIP);
} catch (UnknownHostException e) {
System.out.println("Host " + hostIP + " not found!");
}
String host = addr.getHostAddress();
String hostname= addr.getHostName();
String hostname2 = addr.getCanonicalHostName();
I am expecting to get DESKTOP-DWASDFW as hostname but instead i get 192.168.100.10
UPDATE:
I managed to "fix" it by adding my computer and its ip address manually into the router configuration
but this isn't what im looking for as it requires manually entering every name and IP address. I want something like this app WakeOnLan, it can scan the whole network and get IP address, MAC address and hostname. This app uses arp requests, i researched a lot about how to accomplish something like that in android but found nothing that worked for me (I'm using android 4.2.2)

How to implement ping like functionality using pcap4j library

I want to implement basic network check functionality to test if the provided url is responding or not (eg. ping www.google.com).It must provide operational information indicating, for example, that a requested service is not available or that a host could not be reached. I am able to achive it using icmp4j library. But i want to achieve the same using pcap4j library. I want to put the url in text box and click on connect button which will call pcap4j api to check whether the host is responding or not.

You can create ICMPv4 Echo (ping) on Ethernet packets using the Builders of IcmpV4EchoPacket, IcmpV4CommonPacket, IpV4Packet, and EthernetPacket and send them by PcapHandle.sendPacket(). Please refer to org.pcap4j.sample.SendFragmentedEcho in pcap4j-sample project.
You will need to implement ARP to resolve IP addresses to MAC addresses like org.pcap4j.sample.SendArpRequest in pcap4j-sample project.
And you will also need to implement a feature to find the next hop (default gateway or so) from the given IP address somehow. Pcap4J doesn't provide API to support this implementation. (Java doesn't provide API to get routing table...)
You'd maybe better use java.net.InetAddress#isReachable() instead.

It took me more than a year to figure this out, as I wanted to make a traceroute with pcap4j, so here is what I did:
Get your IPv4 Address and Mac Address, this can be easily achieved by querying the PcapNetworkInterface
Get target IP Address, if you have a DNS Name you need to resolve it beforehand.
Get target Mac Address.
Target is in the same subnet: send an ARP Request to resolve the mac (alternatively, a mac broadcast will likely work fine too).
Target is in different subnet: you need to get the mac of your gateway server then, this is not as easy. Assuming you have other network traffic going on, you could listen for incoming packets and get the source mac, where the source IP address is from a different subnet, this is likely the mac address of your gateway server.
Create IcmpV4EchoPacket and sent it
Listen for incoming ICMP traffic, you will get one of these three:
A IcmpV4EchoReplyPacket which is likely to be an answer to your request (check identifier and sequence number to be sure)
A IcmpV4TimeExceededPacket if the target could not be reached with the time-to-live you specified
Nothing, routers and pinged targets are free to ignore and not answer your request
Variables that need to be filled:
short IDENTIFIER; // identifer may be any 16 bit interger
short SEQUENCE; // sequence may be any 16 bit integer
byte TTL; // time to live (1-255)
Inet4Address IP_TARGET; // ip address of your ping target
Inet4Address IP_ORIGIN; // your own ip address
MacAddress MAC_TARGET; // target or gateway mac address
MacAddress MAC_SOURCE; // your own mac address
PcapNetworkInterface PCAP4J_NETWORK_INTERFACE; // network interface used to execute the ping
How to make a ICMP Echo Request Packet (as payload of IcmpV4CommonPacket of IpV4Packet of EthernetPacket):
public Packet buildPacket() {
IcmpV4EchoPacket.Builder icmpV4Echo = new IcmpV4EchoPacket.Builder()
.identifier(IDENTIFIER) // optional, default zero
.sequenceNumber(SEQUENCE); // optional, default zero
IcmpV4CommonPacket.Builder icmpV4Common = new IcmpV4CommonPacket.Builder()
.type(IcmpV4Type.ECHO) // type is echo
.code(IcmpV4Code.NO_CODE) // echo request doesn't need this
.payloadBuilder(icmpV4Echo)
.correctChecksumAtBuild(true);
IpV4Packet.Builder ipv4Builder = new IpV4Packet.Builder()
.correctChecksumAtBuild(true)
.correctLengthAtBuild(true)
.dstAddr(IP_TARGET) // IPv4 Address where tp send the request
.payloadBuilder(icmpV4Common)
.protocol(IpNumber.ICMPV4) // payload is ICMPV4
.srcAddr(IP_ORIGIN) // Your own IPv4 Address
.tos(IpV4Rfc1349Tos.newInstance((byte) 0))
.ttl(TTL) // time to live (1-255)
.version(IpVersion.IPV4); // IP Version is IPv4
EthernetPacket.Builder etherBuilder = new EthernetPacket.Builder()
.dstAddr(MAC_TARGET) // the targets mac address
.srcAddr(MAC_SOURCE) // your own mac address
.type(EtherType.IPV4) // payload protocl is IPv4
.payloadBuilder(ipv4Builder)
.paddingAtBuild(true);
return etherBuilder.build(); // build your packet
}
Listener for ICMP Echo Answers or timeouts:
public PacketListener buildListener() {
return new PacketListener() {
#Override
public void gotPacket(Packet packet) {
if (!(packet instanceof EthernetPacket))
return;
EthernetPacket ethernetPacket = (EthernetPacket) packet;
packet = ethernetPacket.getPayload();
if (!(packet instanceof IpV4Packet))
return;
IpV4Packet ipV4Packet = (IpV4Packet) packet;
IpV4Header ipV4Header = ipV4Packet.getHeader();
packet = ipV4Packet.getPayload();
if (!(packet instanceof IcmpV4CommonPacket))
return;
IcmpV4CommonPacket icmpPacket = (IcmpV4CommonPacket) packet;
packet = icmpPacket.getPayload();
// successful reply just measure time and done
if (packet instanceof IcmpV4EchoReplyPacket) {
IcmpV4EchoReplyPacket icmpV4EchoReplyPacket = (IcmpV4EchoReplyPacket) packet;
IcmpV4EchoReplyHeader icmpV4EchoReplyHeader = icmpV4EchoReplyPacket.getHeader();
if (icmpV4EchoReplyHeader.getIdentifier() != identifier)
return;
if (icmpV4EchoReplyHeader.getSequenceNumber() != sequence)
return;
// here you got an echo reply
System.out.println(packet);
return;
}
// try handle time to live exceeded messages
if (packet instanceof IcmpV4TimeExceededPacket) {
packet = packet.getPayload(); // original IPv4
if (!(packet instanceof IpV4Packet))
return;
packet = packet.getPayload(); // original ICMP common
if (!(packet instanceof IcmpV4CommonPacket))
return;
packet = packet.getPayload(); // original ICMP echo
if (!(packet instanceof IcmpV4EchoPacket))
return;
IcmpV4EchoHeader icmpV4EchoHeader = ((IcmpV4EchoPacket)packet).getHeader();
if (icmpV4EchoHeader.getIdentifier() != IDENTIFIER)
return;
if(icmpV4EchoHeader.getSequenceNumber() != SEQUENCE)
return;
// HERE you got an answer, that the time to live has been used up
System.out.println(packet);
return;
}
};
}
Combining it togther:
public static void main(String[] args) throws IOException, PcapNativeException, NotOpenException, InterruptedException {
try (PcapHandle handle = PCAP4J_NETWORK_INTERFACE.openLive(1024, PromiscuousMode.PROMISCUOUS, 1000)) {
// set filter to only get incoming ICMP traffic
handle.setFilter("icmp and dst host " + Pcaps.toBpfString(IP_ORIGIN), BpfCompileMode.OPTIMIZE);
// send ARP request
Packet p = buildPacket();
handle.sendPacket(p);
// wait (forever) for ARP answer
PacketListener listener = buildListener();
handle.loop(-1, listener);
}
}

How to learn system (Windows) non-proxy hosts in Java

I'm writting a Java (1.7) application to be running on Windows. The application is accessing additional services running on the same host and other ones running in the Internet. The application can be run in two environments where in one, proxy settings must be specified (there is proxy when accessing the Internet); while in the other environment, the proxy settings must not be specified (there is no proxy).
I want the application to be simple and don't want its users bother with specification of the proxy settings on cmd-line (-Dhttp.proxyHost, etc.) - the application should learn the proxy settings from Windows system settings (IE / Tools / Internet Properties / Connections / LAN Settings).
I have written a piece of code that is supposed to learn that settings, see below. The trouble is that this piece of code does not identify localhost, 127.0.0.1 and my-computer-name (where my-computer-name is the name of my computer) as URLs where proxy should be by-passed when being accessed (yes, I do have 'Bypass proxy server for local addresses' checked). As a result, the application tries to access local services through the proxy which is wrong.
So far I've found out that one way to teach JVM not to use proxy for 'local addresses' is to list the strings (localhost, 127.0.0.1, my-computer-name) in Proxy Settings / Exceptions (Do not use proxy server for addresses beginning with). Obviously, this is not a good solution as usually no one is listing these strings there (the first check-box is enough for non-Java applications).
Second (trivial) solution would be just to count with these strings in my piece of code and do not use proxy settings for them even when JVM thinks otherwise. I don't think this is a good solution and if this is the only solution, IMHO, there is a defect in JVM.
I've found many resources in the Internet how to learn System proxy settings. But how to learn the non-proxy settings?
Thanks,
PP
public static final String HTTP_PROXY_HOST_KEY = "http.proxyHost";
public static final String HTTPS_PROXY_HOST_KEY = "https.proxyHost";
public static final String HTTP_PROXY_PORT_KEY = "http.proxyPort";
public static final String HTTPS_PROXY_PORT_KEY = "https.proxyPort";
public static final String NO_PROXY_HOSTS_KEY = "http.nonProxyHosts";
// provide list of urls which are to be accessed by this application and return proxy and non-proxy settings
private Properties getSystemProxyConfiguration(String[] urls) {
log.debug("Getting system proxy");
Properties properties = new Properties();
SortedSet<String> nonProxyHosts = new TreeSet<>();
for (String url : urls) {
URI uri;
try {
uri = new URI(url);
} catch (URISyntaxException e) {
throw new IllegalStateException(e);
}
InetSocketAddress address = getSystemProxy(uri);
if (address != null) {
if (url.toLowerCase().startsWith("https")) {
properties.put(HTTPS_PROXY_HOST_KEY, address.getHostString());
properties.put(HTTPS_PROXY_PORT_KEY, ""+address.getPort());
//todo verify that all previous URLs in this array are using the same proxy
log.debug("HTTPS proxy: " + address.getHostString() + ":" + address.getPort());
} else {
properties.put(HTTP_PROXY_HOST_KEY, address.getHostString());
properties.put(HTTP_PROXY_PORT_KEY, ""+address.getPort());
//todo verify that all previous URLs in this array are using the same proxy
log.debug("HTTP proxy: " + address.getHostString() + ":" + address.getPort());
}
} else { //todo DEFECT -> this does not find the non-proxy hosts (even though specified in IE Internet settings)
nonProxyHosts.add(uri.getHost());
}
}
if (nonProxyHosts.size() > 0) {
String nonProxyHostsString = nonProxyHosts.first();
nonProxyHosts.remove(nonProxyHostsString);
for (String nonProxyHost : nonProxyHosts) {
nonProxyHostsString = nonProxyHostsString + "|" + nonProxyHost;
}
properties.put(NO_PROXY_HOSTS_KEY, nonProxyHostsString);
log.debug("Non HTTP(S) proxy hosts: "+nonProxyHostsString);
} else {
log.debug("No non HTTP(S) proxy hosts set");
}
return properties;
}
private InetSocketAddress getSystemProxy(URI uri) {
List<Proxy> proxyList;
proxyList = ProxySelector.getDefault().select(uri);
if (proxyList != null && proxyList.size() > 0) { //todo DEFECT - this never returns DIRECT proxy for localhost, 127.0.0.1, my-computer-name strings
Proxy proxy = proxyList.get(0);
if (proxyList.size() > 1) {
log.warn("There is more " + proxy.type() + " proxies available. Use "+PROXY_PROPERTIES_FILE_NAME+" to set the right one.");
}
InetSocketAddress address = (InetSocketAddress) proxy.address();
return address;
}
return null;
}

Suggestion about detecting Private Ip Address with an applet

I'm having some troubles to detect client's private ip that conect to a web application I built.
Take a look at my tests results(In machines that runs windows):
1-In some machines(from different location ,countries..) the applet give me the correct ip but
2-In others I've obtained ip=127.0.0.1 :
What have I tried to solve this?
A- for example: I've stopped the avast program protection(web shield) and the applet start to give me the correct private ip.
B- In others machines I tried "point A" but It didn't work
C- I also edit host file but I didn't work as well
What I need from you is to help me to understand what is happening? where to look in order to resolve this...
Please don't answer saying "Why do you need the private ip? It could change..." ... I know all the machines that are going to connect to my web application so I can configure them.
Part of the source code that my applet use:
private String PrivateIP(boolean flag)
{
String s1 = "unknown";
String s2 = getDocumentBase().getHost();
int i = 80;
if(getDocumentBase().getPort() != -1)
i = getDocumentBase().getPort();
try
{
String s = (new Socket(s2, i)).getLocalAddress().getHostAddress();
if(!s.equals("255.255.255.255"))
s1 = s;
}
catch(SecurityException _ex)
{
s1 = "FORBIDDEN";
}
catch(Exception _ex)
{
s1 = "ERROR";
}
if(flag)
try
{
s1 = (new Socket(s2, i)).getLocalAddress().getHostName();
}
catch(Exception _ex)
{
Stat = "Cannot Lookup this IP";
}
return s1;
}
I'll let you more information:
I've traid this http://www.auditmypc.com/digital-footprint.asp in order to obtain the ip from probably other method but the same result, I've also run http://www.auditmypc.com/firewall-test.asp and obtained in the machines that I couldn't obtained the correct ip a message like "Congratulations you don't have any port to be open" xD...
Thanks in advance!

First of all, there can be more than one IP address available on the client, if there is more than one network interface. Which one is returned by your method depends on which is used for new Socket() to open.
Now, you do not have to open sockets to get the client's IP. What you can do instead is to enumerate them like this:
String host = InetAddress.getLocalHost().getHostName();
InetAddress[] addressArray = InetAddress.getAllByName(host);
String[] ipArray = new String[addressArray.length];
for (int i = 0; i < addressArray.length; i++) {
InetAddress addr = addressArray[i];
ipArray[i] = addr.getHostAddress();
}
return ipArray;
Now the ipArray will hold a list of available IP adresses on client's workstation.

Get Application Server name or ip and port in Java

We would like to identify and display the server and port that a Java application is running on that is behind a proxy web server. This means that getServerName() and getServerPort() return the server name of the proxy and its port (80).
We have two application server instances running on a single physical box and therefore have two active ports per box i.e. 9080, 9081. What I'd like to have is <Application Server Name>:<Application Server Port> displayed.
Any ideas? I'm a complete Java noob, sorry if this is a basic question.

The server hostname is part of the request, as it depends on what URL the client used to reach your host. The value you get in this way is defined on the client and does not have to be what you expect.
If you are interested in the local hostname, you can try:
String hostname = InetAddress.getLocalHost().getHostName();

You can use ServletRequest#getLocalXXX() methods for this.
ServletRequest#getLocalName() returns local hostname.
ServletRequest#getLocalAddr() returns local IP.
ServletRequest#getLocalPort() returns local port.

Crunchify provides a nice example for this.
import java.net.InetAddress;
import java.net.UnknownHostException;
public class CrunchifyGetIPHostname {
public static void main(String[] args) {
InetAddress ip;
String hostname;
try {
ip = InetAddress.getLocalHost();
hostname = ip.getHostName();
System.out.println("Your current IP address : " + ip);
System.out.println("Your current Hostname : " + hostname);
} catch (UnknownHostException e) {
e.printStackTrace();
}
}
}