Java common lang api

Commons Lang

The standard Java libraries fail to provide enough methods for manipulation of its core classes. Apache Commons Lang provides these extra methods.

Apache Commons Lang provides a host of helper utilities for the java.lang API, notably String manipulation methods, basic numerical methods, object reflection, concurrency, creation and serialization and System properties. Additionally it contains basic enhancements to java.util.Date and a series of utilities dedicated to help with building methods, such as hashCode, toString and equals.

Note that Commons Lang 3.0 (and subsequent versions) use a different package (org.apache.commons.lang3) than the previous versions (org.apache.commons.lang), allowing Commons Lang 3 to be used at the same time as Commons Lang 2.

Documentation

The package descriptions in the Javadoc give an overview of the available features and various project reports are provided.

The Javadoc API documents are available online:

The git repository can be browsed, or you can browse/contribute via GitHub.

Release Information

The latest stable release of Lang is 3.12.0:

Pull it using a build tool like Maven using a dependency management reference.
Download the latest release from a mirror.
Read the release notes.
Examine the 2.x to 3.0 upgrade notes.
Compare major versions via the Lang2 to Lang3 Clirr report.

For information on previous releases see the Release History, and to download previous releases see the Commons Lang Archive.

Getting Involved

The commons developer mailing list is the main channel of communication for contributors. Please remember that the lists are shared between all commons components, so prefix your email by [lang].

You can also visit the #apache-commons IRC channel on irc.freenode.net or peruse JIRA. Specific links of interest for JIRA are:

Alternatively you can go through the Needs Work tags in the TagList report.

If you’d like to offer up pull requests via GitHub rather than applying patches to JIRA, we have a GitHub mirror.

Support

The commons mailing lists act as the main support forum. The user list is suitable for most library usage queries. The dev list is intended for the development discussion. Please remember that the lists are shared between all commons components, so prefix your email by [lang].

Bug reports and enhancements are also welcomed via the JIRA issue tracker. Please read the instructions carefully.

Apache Commons, Apache Commons Lang, Apache, the Apache feather logo, and the Apache Commons project logos are trademarks of The Apache Software Foundation. All other marks mentioned may be trademarks or registered trademarks of their respective owners.

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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.

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.

ArrayUtils provides singleton empty arrays for all the basic types. These will largely be of use in the Collections API with its toArray methods, but also will be of use with methods which want to return an empty array on error.
add(xxx[], xxx) will add a primitive type to an array, resizing the array as you’d expect. Object is also supported.
clone(xxx[]) clones a primitive or Object array.
contains(xxx[], xxx) searches for a primitive or Object in a primitive or Object array.
getLength(Object) returns the length of any array or an IllegalArgumentException if the parameter is not an array. hashCode(Object) , equals(Object, Object) , toString(Object)
indexOf(xxx[], xxx) and indexOf(xxx[], xxx, int) are copies of the classic String methods, but this time for primitive/Object arrays. In addition, a lastIndexOf set of methods exists.
isEmpty(xxx[]) lets you know if an array is zero-sized or null.
isSameLength(xxx[], xxx[]) returns true if the arrays are the same length.
Along side the add methods, there are also remove methods of two types. The first type remove the value at an index, remove(xxx[], int) , while the second type remove the first value from the array, remove(xxx[], xxx) .
Nearing the end now. The reverse(xxx[]) method turns an array around.
The subarray(xxx[], int, int) method splices an array out of a larger array.
Primitive to primitive wrapper conversion is handled by the toObject(xxx[]) and toPrimitive(Xxx[]) methods.

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[][] , , >);

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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