Using the analyzer

To use this analyzer you can use it either directly in your Java based applications or use one of the User Defined Functions that are available for many of Apache bigdata tools (Pig, Hive, Flink, Beam, ...) as described here.

Using in Java applications

To use the library you must first add it as a dependency to your application. The library has been published to maven central so that should work in almost any environment.

If you use a maven based project simply add this dependency to your project.


and in your application you can use it as simple as this

UserAgentAnalyzer uaa = UserAgentAnalyzer

UserAgent agent = uaa.parse("Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv: Gecko/20071127 Firefox/");

for (String fieldName: agent.getAvailableFieldNamesSorted()) {
    System.out.println(fieldName + " = " + agent.getValue(fieldName));

Please instantiate a new UserAgentAnalyzer as few times as possible because the initialization step for a full UserAgentAnalyzer (i.e. all fields) usually takes something in the range of 2-5 seconds. If you need multiple instances of the UserAgentAnalyzer then you MUST create a new Builder instance for each of those.

Note that not all fields are available after every parse. So be prepared to receive a 'null' or "Unknown" if you extract a specific name.

Logging dependencies

The Yauaa engine uses Log4j2 as the primary logging framework; yet some of the transitive dependencies of this project use different logging frameworks.

To minimize the complexity of the dependency handling I have chosen to simply not include ANY logging framework and expect the consuming system to provide what ever fits best.

So in the end to use this you must provide either an implementation or a bridge for:

  • Apache Log4j2
  • Apache (Jakarta) Commons logging (like org.apache.commons.logging.LogFactory) aka JCL.
  • Simple Logging Facade for Java (SLF4J)

So it all depends on your exact context (i.e. which logging framework are you going to use) what the best solution is for you to make all of this logging work as intended.

In case you are using Apache Log4j2 you should have these dependencies in addition to Yauaa in your project

<!-- The default logging implementation for Yauaa -->



NOTE: Some of those logging frameworks are only used in specific analysis situations (like robots with a url). To avoid failing only when such an event occurs a fail fast construct has been added: At the moment of creating the UserAgentAnalyzer (i.e. during the .build()) a temporary instance all of these Logging frameworks are created. If one of them is not present it will immediately throw an InvalidLoggingDependencyException (=RuntimeException).


If your application needs to serialize the instance of the UserAgentAnalyzer then both the standard Java serialization and Kryo are supported. Note that with Kryo 5.x you need to register all classes and configure Kryo correctly.

To facilitate doing this correctly the static method configureKryo was created. So in general your code should look something like this:

    Kryo kryo = new Kryo();

Note that both the serializing and the deserializing instance of Kryo must be configured in the same way.

Avoid using it as a static member

If you make the UserAgentAnalyzer a static member of a class then cleaning it up after use may be a problem. One case where this happens is in the context of something like Tomcat where a webapp is loaded and then unloaded. If the analyzer is a static member of your servlet then this unloading may retain a lot of the memory used for the internal data structures.

Cache size setting

I recommend you leave the cache to a size that is roughly the unique number of useragents your site finds in a limited timespan. Something like 15/30/60 minutes usually gives you a fine cache size. On a very busy website I see ~50K-60K distinct useragents per day and ~10K per hour. So in my opinion a cache size of 5K-10K elements is a good choice.

Limiting to only certain fields

In some scenarios you only want a specific field and all others are unwanted. This can be achieved by creating the analyzer in Java like this:

UserAgentAnalyzer uaa;

uaa = UserAgentAnalyzer

One important effect is that this speeds up the system because it will kick any rules that do not help in getting the desired fields. The above example showed an approximate 40% speed increase (i.e. times dropped from ~1ms to ~0.6ms).

In the nl.basjes.parse.useragent.UserAgent many (not all!!) of the provided variables are provided as a constant String. You can choose to use these and avoid subtle typos in the requested attribute names.

Building your project with -Xlint:all

If you are trying to get rid of all possible problems in your application and set the compiler flag -Xlint:all you will see warnings relating to the Kryo serialization system.

[INFO] -------------------------------------------------------------
[WARNING] Cannot find annotation method 'value()' in type 'com.esotericsoftware.kryo.DefaultSerializer': class file for com.esotericsoftware.kryo.DefaultSerializer not found
[WARNING] Cannot find annotation method 'value()' in type 'com.esotericsoftware.kryo.DefaultSerializer'
[INFO] 2 warnings

The Yauaa analyzer has been prepared in such a way that it can be serialized using both the standard Java serialization and the Kryo serialization library. The Kryo library has been configured as a "provided" dependency because many do not need it, and (to avoid version conflicts) those who do need it have this dependency already.

If your project does not use Kryo and you have this warning then there are several ways to work around this:

  1. Disable the Xlint check that triggers this warning. Apparently this is the "classfile" so try to use -Xlint:all,-classfile instead.
  2. Add the otherwise needless Kryo library as a "provided" dependency to your project.


IMPORTANT: This library is single threaded !

Because the internal analyzer code is not reentrant the main method has been synchronized on the instance. So from the prespective of you the application developer this library is thread safe.

If you are in a multi threaded situation you should create a separate instance per thread or accept the speed limitation of the shared synchronized instance.

Note that you should really instantiate it only once per thread (and use a ThreadPool or something similar) because starting a new instance takes several seconds.

Eclipse users

Be aware of there is a bug in Eclipse which will show you errors in perfectly valid Java code: The errors you see are related to the inheritance model used by the Builders in this project and the fact that Eclipse does not interpret it correctly.

Scala usage

When using this library from a Scala application the way the Builders have been constructed turns out to be very unfriendly to use.

Starting with Yauaa version 5.14 the rewritten builders (contributed by Robert Stoll) will become available which will make it a lot easier for Scala users to use:

val uaa = UserAgentAnalyzer.newBuilder


Occasionally I publish a snapshot version. If you want to use such a version then the repository can be configured in your maven with something like this

    <name>Sonatype OSS Snapshots</name>

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