Recommended way to get hostname in Java

Question

Which of the following is the best and most portable way to get the hostname of the current computer in Java   Runtime getRuntime   exec  hostname     vs   InetAddress getLocalHost   getHostName

User · Answer

Strictly speaking - you have no choice but calling either hostname(1) or - on Unix gethostname(2). This is the name of your computer. Any attempt to determine the hostname by an IP address like this

InetAddress.getLocalHost().getHostName()

is bound to fail in some circumstances:

The IP address might not resolve into any name. Bad DNS setup, bad system setup or bad provider setup may be the reason for this.
A name in DNS can have many aliases called CNAMEs. These can only be resolved in one direction properly: name to address. The reverse direction is ambiguous. Which one is the "official" name?
A host can have many different IP addresses - and each address can have many different names. Two common cases are: One ethernet port has several "logical" IP addresses or the computer has several ethernet ports. It is configurable whether they share an IP or have different IPs. This is called "multihomed".
One Name in DNS can resolve to several IP Addresses. And not all of those addresses must be located on the same computer! (Usecase: A simple form of load-balancing)
Let's not even start talking about dynamic IP addresses.

Also don't confuse the name of an IP-address with the name of the host (hostname). A metaphor might make it clearer:

There is a large city (server) called "London". Inside the city walls much business happens. The city has several gates (IP addresses). Each gate has a name ("North Gate", "River Gate", "Southampton Gate"...) but the name of the gate is not the name of the city. Also you cannot deduce the name of the city by using the name of a gate - "North Gate" would catch half of the bigger cities and not just one city. However - a stranger (IP packet) walks along the river and asks a local: "I have a strange address: 'Rivergate, second left, third house'. Can you help me?" The local says: "Of course, you are on the right road, simply go ahead and you will arrive at your destination within half an hour."

This illustrates it pretty much I think.

The good news is: The real hostname is usually not necessary. In most cases any name which resolves into an IP address on this host will do. (The stranger might enter the city by Northgate, but helpful locals translate the "2nd left" part.)

In the remaining corner cases you must use the definitive source of this configuration setting - which is the C function gethostname(2). That function is also called by the program hostname.

User · Answer

InetAddress getLocalHost   getHostName   is better  as explained by Nick   but still not very good  One host can be known under many different hostnames  Usually you ll be looking for the hostname your host has in a specific context   For example  in a web application  you might be looking for the hostname used by whoever issued the request you re currently handling  How to best find that one depends on which framework you re using for your web application   In some kind of other internet-facing service  you ll want the hostname your service is available through from the  outside   Due to proxies  firewalls etc this might not even be a hostname on the machine your service is installed on - you might try to come up with a reasonable default  but you should definitely make this configurable for whoever installs this

User · Answer

As others have noted  getting the hostname based on DNS resolution is unreliable   Since this question is unfortunately still relevant in 2018  I d like to share with you my network-independent solution  with some test runs on different systems   The following code tries to do the following    On Windows   Read the COMPUTERNAME environment variable through System getenv    Execute hostname exe and read the response  On Linux   Read the HOSTNAME environment variable through System getenv   Execute hostname and read the response Read  etc hostname  to do this I m executing cat since the snippet already contains code to execute and read  Simply reading the file would be better  though      The code   public static void main String   args  throws IOException       String os   System getProperty  os name   toLowerCase         if  os contains  win              System out println  Windows computer name through env       System getenv  COMPUTERNAME                    System out println  Windows computer name through exec       execReadToString  hostname                  else if  os contains  nix      os contains  nux      os contains  mac os x              System out println  Unix-like computer name through env       System getenv  HOSTNAME                    System out println  Unix-like computer name through exec       execReadToString  hostname                    System out println  Unix-like computer name through  etc hostname       execReadToString  cat  etc hostname                     public static String execReadToString String execCommand  throws IOException       try  Scanner s   new Scanner Runtime getRuntime   exec execCommand  getInputStream    useDelimiter    A              return s hasNext     s next                   Results for different operating systems   macOS 10 13 2  Unix-like computer name through env  null  Unix-like computer name through exec  machinename   Unix-like computer name through  etc hostname      OpenSuse 13 1  Unix-like computer name through env  machinename  Unix-like computer name through exec  machinename   Unix-like computer name through  etc hostname      Ubuntu 14 04 LTS  This one is kinda strange since echo  HOSTNAME returns the correct hostname  but System getenv  HOSTNAME   does not   Unix-like computer name through env  null  Unix-like computer name through exec  machinename   Unix-like computer name through  etc hostname  machinename     EDIT  According to legolas108  System getenv  HOSTNAME   works on Ubuntu 14 04 if you run export HOSTNAME before executing the Java code   Windows 7  Windows computer name through env  MACHINENAME  Windows computer name through exec  machinename     Windows 10  Windows computer name through env  MACHINENAME  Windows computer name through exec  machinename     The machine names have been replaced but I kept the capitalization and structure  Note the extra newline when executing hostname  you might have to take it into account in some cases

User · Answer

Environment variables may also provide a useful means -- COMPUTERNAME on Windows  HOSTNAME on most modern Unix Linux shells   See   https   stackoverflow com a 17956000 768795  I m using these as  supplementary  methods to InetAddress getLocalHost   getHostName    since as several people point out  that function doesn t work in all environments   Runtime getRuntime   exec  hostname   is another possible supplement  At this stage  I haven t used it   import java net InetAddress  import java net UnknownHostException      try InetAddress LocalHost first          NOTE -- InetAddress getLocalHost   getHostName   will not work in certain environments  try       String result   InetAddress getLocalHost   getHostName        if  StringUtils isNotEmpty  result           return result    catch  UnknownHostException e           failed   try alternate means        try environment properties           String host   System getenv  COMPUTERNAME    if  host    null      return host  host   System getenv  HOSTNAME    if  host    null      return host      undetermined  return null

User · Answer

hostName    null  Enumeration lt NetworkInterface gt  interfaces   NetworkInterface getNetworkInterfaces          while  interfaces hasMoreElements              NetworkInterface nic   interfaces nextElement            Enumeration lt InetAddress gt  addresses   nic getInetAddresses            while  hostName    null  amp  amp  addresses hasMoreElements                  InetAddress address   addresses nextElement                if   address isLoopbackAddress                      hostName   address getHostName

User · Answer

InetAddress getLocalHost   getHostName   is the best way out of the two as this is the best abstraction at the developer level

User · Answer

InetAddress getLocalHost   getHostName   is the more portable way   exec  hostname   actually calls out to the operating system to execute the hostname command    Here are a couple other related answers on SO     Java current machine name and logged in user   Get DNS name of local machine as seen by a remote machine   EDIT  You should take a look at A H  s answer or Arnout Engelen s answer for details on why this might not work as expected  depending on your situation  As an answer for this person who specifically requested portable  I still think getHostName   is fine  but they bring up some good points that should be considered

User · Answer

Although this topic has already been answered there s more to say   First of all  Clearly we need some definitions here  The InetAddress getLocalHost   getHostName   gives you the name of the host as seen from a network perspective  The problems with this approach are well documented in the other answers   it often requires a DNS lookup  it s ambiguous if the host has multiple network interfaces and it just plain fails sometimes  see below    But on any OS there s another name as well  A name of the host that gets defined very early in the boot process  long before the network is initialized  Windows refers to this as computername  Linux calls it kernel hostname and Solaris uses the word nodename  I like best the word computername  so I ll use that word from now on   Finding the computername   On Linux Unix the computername is what you get from the C function gethostname    or hostname command from shell or HOSTNAME environment variable in Bash-like shells  On Windows the computername is what you get from environment variable COMPUTERNAME or Win32 GetComputerName function    Java has no way of obtaining what I ve defined as  computername   Sure  there are workarounds as described in other answers  like for Windows calling System getenv  COMPUTERNAME    but on Unix Linux there s no good workaround without resorting to JNI JNA or Runtime exec    If you don t mind a JNI JNA solution then there s gethostname4j which is dead simple and very easy to use   Let s move on with two examples  one from Linux and one from Solaris  which demonstrate how you can easily get into a situation where you cannot obtain the computername using standard Java methods   Linux example  On a newly created system  where the host during installation has been named as  chicago   we now change the so-called kernel hostname     hostnamectl --static set-hostname dallas   Now the kernel hostname is  dallas   as evident from the hostname command     hostname dallas   But we still have    cat  etc hosts 127 0 0 1   localhost 127 0 0 1   chicago   There s no misconfiguration in this  It just means the host s networked name  or rather the name of the loopback interface  is different from the host s computername   Now  try executing InetAddress getLocalHost   getHostName    and it will throw java net UnknownHostException  You are basically stuck  There s no way to retrieve neither the value  dallas  nor the value  chicago    Solaris example  The example below is based on Solaris 11 3   The host has deliberately been configured so that the loopback name  lt   nodename   In other words we have     svccfg -s system identity node listprop config         config loopback             astring        chicago config nodename             astring        dallas   and the contents of  etc hosts     1 chicago localhost 127 0 0 1 chicago localhost loghost   and the result of the hostname command would be     hostname dallas   Just like in the Linux example a call to InetAddress getLocalHost   getHostName   will fail with   java net UnknownHostException  dallas   dallas  node name or service name not known   Just like the Linux example you are now stuck  There s no way to retrieve neither the value  dallas  nor the value  chicago    When will you really struggle with this   Very often you ll find that InetAddress getLocalHost   getHostName   will indeed return a value which is equal to the computername  So there s no problem  except for the added overhead of name resolution    The problem arises typically within PaaS environments where there s a difference between computername and the name of the loopback interface  For example people report problems in Amazon EC2   Bug RFE reports  A bit of searching reveals this RFE report   link1  link2  However  judging from the comments on that report the issue seems to have been largely misunderstood by the JDK team  so it is unlikely it will be addressed   I like the comparison in the RFE to other programming languages

User · Answer

Just one-liner     cross platform  Windows-Linux-Unix-Mac Unix    Always works  No DNS required    String hostname   new BufferedReader      new InputStreamReader Runtime getRuntime   exec  hostname   getInputStream         readLine      You re done

User · Answer

If you re not against using an external dependency from maven central  I wrote gethostname4j to solve this problem for myself  It just uses JNA to call libc s gethostname function  or gets the ComputerName on Windows  and returns it to you as a string   https   github com mattsheppard gethostname4j

User · Answer

The most portable way to get the hostname of the current computer in Java is as follows   import java net InetAddress  import java net UnknownHostException   public class getHostName        public static void main String   args  throws UnknownHostException           InetAddress iAddress   InetAddress getLocalHost            String hostName   iAddress getHostName              To get  the Canonical host name         String canonicalHostName   iAddress getCanonicalHostName             System out println  HostName     hostName           System out println  Canonical Host Name     canonicalHostName

[java] Recommended way to get hostname in Java

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