Developers often end up writing many utility methods and classes that extend in small but useful ways the core Java APIs. Manipulating Strings, working with Number and Dates, or dealing with exceptions are all areas where the core Java APIs are often enhanced in convenient ways.

The Apache Commons Lang project has been collecting some useful, reusable extensions to the core Java APIs in an open-source project:

The Commons Lang library provides much needed additions to the standard JDK's java.lang package... Very generic, very reusable components for everyday use.

The top level package contains various Utils classes, whilst there are various subpackages including enums, exception and builder. Using the Utils classes is ... the equivalent of global functions in another language, a collection of stand-alone, thread-safe, static methods... 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.

Now in release 2.3, Commons Lang offers utilities in the following areas:

• String manipulation: StringUtils, StringEscapeUtils, RandomStringUtils, Tokenizer, WordUtils
• Character handling: CharSetUtils, CharSet, CharRange, CharUtils
• JVM interaction: SystemUtils, CharEncoding
• Serialization: SerializationUtils, SerializationException
• Assorted functions: ObjectUtils, ClassUtils, ArrayUtils, BooleanUtils

What types of utility methods do you find yourself writing over and over in different projects?