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Package org.apache.commons.lang3

Provides highly reusable static utility methods, chiefly concerned with adding value to the java.lang classes.

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Package org.apache.commons.lang3 Description

Provides highly reusable static utility methods, chiefly concerned with adding value to the java.lang classes. Most of these classes are immutable and thus thread-safe. However CharSet is not currently guaranteed thread-safe under all circumstances.

The top level package contains various Utils classes, whilst there are various subpackages including org.apache.commons.lang3.math, org.apache.commons.lang3.concurrent and org.apache.commons.lang3.builder. Using the Utils classes is generally simplicity itself. They are the equivalent of global functions in another language, a collection of stand-alone, thread-safe, static methods. In contrast, subpackages may contain interfaces which may have to be implemented or classes which may need to be extended to get the full functionality from the code. They may, however, contain more global-like functions.

Lang 3.0 requires JDK 1.5+, since Lang 3.2 it requires JDK 6+; The legacy release 2.6 requires JDK 1.2+. In both cases you can find features of later JDKs being maintained by us and likely to be removed or modified in favour of the JDK in the next major version. Note that Lang 3.0 uses a different package than its predecessors, allowing it to be used at the same time as an earlier version.

You will find deprecated methods as you stroll through the Lang documentation. These are removed in the next major version.

All util classes contain empty public constructors with warnings not to use. This may seem an odd thing to do, but it allows tools like Velocity to access the class as if it were a bean. In other words, yes we know about private constructors and have chosen not to use them.

String manipulation - StringUtils, StringEscapeUtils, RandomStringUtils

Lang has a series of String utilities. The first is StringUtils, oodles and oodles of functions which tweak, transform, squeeze and cuddle java.lang.Strings. In addition to StringUtils, there are a series of other String manipulating classes; RandomStringUtils and StringEscapeUtils. RandomStringUtils speaks for itself. It's provides ways in which to generate pieces of text, such as might be used for default passwords. StringEscapeUtils contains methods to escape and unescape Java, JavaScript, JSON, HTML and XML.

These are ideal classes to start using if you're looking to get into Lang. StringUtils' StringUtils.capitalize(String), StringUtils.substringBetween(String, String)/Before/After, StringUtils.split(String) and StringUtils.join(Object[]) are good methods to begin with.

Character handling - CharSetUtils, CharSet, CharRange, CharUtils

In addition to dealing with Strings, it's also important to deal with chars and Characters. CharUtils exists for this purpose, while CharSetUtils exists for set-manipulation of Strings. Be careful, although CharSetUtils takes an argument of type String, it is only as a set of characters. For example, CharSetUtils.delete("testtest", "tr") will remove all t's and all r's from the String, not just the String "tr".

CharRange and CharSet are both used internally by CharSetUtils, and will probably rarely be used.

JVM interaction - SystemUtils, CharEncoding

SystemUtils is a simple little class which makes it easy to find out information about which platform you are on. For some, this is a necessary evil. It was never something I expected to use myself until I was trying to ensure that Commons Lang itself compiled under JDK 1.2. Having pushed out a few JDK 1.3 bits that had slipped in (Collections.EMPTY_MAP is a classic offender), I then found that one of the Unit Tests was dying mysteriously under JDK 1.2, but ran fine under JDK 1.3. There was no obvious solution and I needed to move onwards, so the simple solution was to wrap that particular test in a if (SystemUtils.isJavaVersionAtLeast(1.3f)) {, make a note and move on.

The CharEncoding class is also used to interact with the Java environment and may be used to see which character encodings are supported in a particular environment.

Serialization - SerializationUtils, SerializationException

Serialization doesn't have to be that hard! A simple util class can take away the pain, plus it provides a method to clone an object by unserializing and reserializing, an old Java trick.

Assorted functions - ObjectUtils, ClassUtils, ArrayUtils, BooleanUtils

Would you believe it, ObjectUtils contains handy functions for Objects, mainly null-safe implementations of the methods on Object.

ClassUtils is largely a set of helper methods for reflection. Of special note are the comparators hidden away in ClassUtils, useful for sorting Class and Package objects by name; however they merely sort alphabetically and don't understand the common habit of sorting java and javax first.

Next up, ArrayUtils. This is a big one with many methods and many overloads of these methods so it is probably worth an in depth look here. Before we begin, assume that every method mentioned is overloaded for all the primitives and for Object. Also, the short-hand 'xxx' implies a generic primitive type, but usually also includes Object.

Lastly, ArrayUtils.toMap(Object[]) is worthy of special note. It is not a heavily overloaded method for working with arrays, but a simple way to create Maps from literals.

Using toMap

 Map colorMap = ArrayUtils.toMap(new String[][] {{
   {"RED", "#FF0000"},
   {"GREEN", "#00FF00"},
   {"BLUE", "#0000FF"}

Our final util class is BooleanUtils. It contains various Boolean acting methods, probably of most interest is the BooleanUtils.toBoolean(String) method which turns various positive/negative Strings into a Boolean object, and not just true/false as with Boolean.valueOf.

Flotsam - BitField, Validate

On reaching the end of our package, we are left with a couple of classes that haven't fit any of the topics so far.

The BitField class provides a wrapper class around the classic bitmask integer, whilst the Validate class may be used for assertions (remember, we support Java 1.2).

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