Using the analyzer

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 (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.


To actually use it in your application you need to create an instance of the UserAgentAnalyzer.

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 and uses a few hundred MiB of memory to store all the analysis datastructures.

This analyzer can only do a single analysis at a time and to ensure correct working the main method is synchronized. If you have a high load you should simply create multiple instances and spread the load over those instances. When running in a framework (like Apache Flink or Apache Beam) this is usually automatically managed by these frameworks. In other systems may choose something like a threadpool to do that.

Note that if you need multiple instances of the UserAgentAnalyzer then you MUST create a new Builder instance for each of those (or serialize an instance and deserialize it multiple times).

UserAgentAnalyzer uaa = UserAgentAnalyzer

Then for each useragent (or set of request headers) you call the parse method to give you the desired result:

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));

Note that not all fields are available after every parse. So be prepared to receive a null, Unknown or another field specific default.

Custom caching implementation

Since version 6.7 you can specify a custom implementation for the cache by providing an instance of the factory interface CacheInstantiator.

Do note that Yauaa assumes the caching implementation to be threadsafe. If you use a non-threadsafe implementation in a multithreaded context it will break.

The default caching implementation uses Caffeine (since version 6.8).

return Caffeine.newBuilder().maximumSize(cacheSize).<String, ImmutableUserAgent>build().asMap();

A custom implementation can be specified via the Builder using the withCacheInstantiator(...) method:

UserAgentAnalyzer uaa = UserAgentAnalyzer
        new CacheInstantiator() {
            public Map<String, ImmutableUserAgent> instantiateCache(int cacheSize) {
                return new MyMuchBetterCacheImplementation(cacheSize);
        (ClientHintsCacheInstantiator<?>) size ->
            Collections.synchronizedMap(new LRUMap<>(size)))

Running on Java 8

Normal use

Yauaa 7.x still allows running on Java 8, yet the default caching library needs Java 11.

Since version 7.19.0 the selection of the caching implementation is automatically based upon the Java version used to run it. Running in Java 8 - Java 10 the LRUMap (caching implementation that is part of the Apache commons-collections library) is used, Java 11 and newer Caffeine is used.

If needed (and also for backwards compatibility and testing) you can still force it to use the LRUMap regardless of the Java version by doing something like this:

UserAgentAnalyzer uaa = UserAgentAnalyzer

Really ONLY Java 8

If you have a very strict requirement that no classes are in the project that are above JDK 8 then you should do 2 things:

  1. Exclude the caffeine dependency

Maven pom.xml snippet


Gradle snippet

implementation('nl.basjes.parse.useragent:yauaa:7.26.1') {
    exclude group: 'com.github.ben-manes.caffeine', module: 'caffeine'
  1. Make sure the used caching library is always the Java 8 compatible one.
  • Either by only running on Java 8
  • Or by forcing the caching to always use the Java 8 with something like this:
UserAgentAnalyzer uaa = UserAgentAnalyzer

Logging dependencies

The Yauaa engine uses Log4j2 API as the logging framework.

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. Even the required log4j-api 2.x dependency is configured as provided to avoid any needless version conflicts.

To use Yauaa you must provide the desired version of log4j-api and either an implementation or a bridge for Apache Log4j2 to route the logging to where you want it.

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 -->

Regarding the Log4J2 issues

The Yauaa analyzer uses the Log4J2 API to do the logging.


  • The core of Yauaa is safe as it does not include any logging dependencies and expects the application to provide everything.
  • In normal operations user input is not logged.
  • The Snowflake UDF is affected by these problems (due to shading the dependencies in).

NO batteries included

By design the Yauaa library expects the application in which it is used to provide the actual logging dependencies and configuration. If you do not provide the needed logging classes it will simply fail at startup.

So by design the Yauaa library expects all of these frameworks to be provided (and configured) and does not include any of them or any configuration for them.

This is true for most of the released artifacts (including the base library) except for the Snowflake UDF which does include almost all dependencies. So the Snowflake UDF IS affected by this issue and all users are recommended to update.

Minimal logging

Note that Yauaa does not log any user input and/or analysis results from user input during normal operation. Only during development and during unit tests the Useragents are logged.

This is because it was designed to run in very large scale batch and streaming situations (very large as in “Let’s analyze these 10^10 records”).

Bring your own batteries

To assist in running Yauaa without the logj4-core jar an example was created that only uses SLF4J 1.x and and example that only uses SLF4J 2.x.


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.

Reducing the memory footprint

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 = 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).

Do note that some fields need other fields as input (i.e. intermediate result). For example the DeviceBrand also needs the AgentInformationEmail and AgentInformationUrl because in some cases the actual brand is derived from for example the domainname that usually is present in those. So if you only ask for the DomainBrand you will get those fields also.

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.

UserAgentAnalyzer uaa = UserAgentAnalyzer

Sharing the config between instances (new in 7.24.0)

In some situations you may want to have multiple instances to handle the load within in a single JVM. In those cases you’ll also want the configuration of all instances to be identical.

If you are in exactly that scenario you can create a duplicate instance with the exact same configuration and save a few MiB of memory. The currently estimated savings is at about 20-30MiB for each extra instance (depending on the configuration).

UserAgentAnalyzer extraUaa = uaa.cloneWithSharedAnalyzerConfig(false, true);

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 perspective 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>