There are few libraries out there:

•Transmorph: Transmorph is a free java library used to convert a Java object of one type into an object of another type (with another signature, possibly parameterized).

•EZMorph: EZMorph is simple java library for transforming an Object to another Object. It supports transformations for primitives and Objects, for multidimensional arrays and transformations with DynaBeans

•Commons-BeanUtils: ConvertUtils -> Utility methods for converting String scalar values to objects of the specified Class, String arrays to arrays of the specified Class.

•Commons-Lang: ArrayUtils -> Operations on arrays, primitive arrays (like int[]) and primitive wrapper arrays (like Integer[]).

•Commons-Convert: Commons-Convert aims to provide a single library dedicated to the task of converting an object of one type to another. The first stage will focus on Object to String and String to Object conversions.

•Morph: Morph is a Java framework that eases the internal interoperability of an application. As information flows through an application, it undergoes multiple transformations. Morph provides a standard way to implement these transformations.

•Lorentz: Lorentz is a generic object-to-object conversion framework. It provides a simple API to convert a Java objects of one type into an object of another type. (seems dead)

•Spring framework: Spring has an excellent support for PropertyEditors, that can also be used to transform Objects to/from Strings.

•Dozer: Dozer is a powerful, yet simple Java Bean to Java Bean mapper that recursively copies data from one object to another. Typically, these Java Beans will be of different complex types.

•OTOM: With OTOM, you can copy any data from any object to any other object. The possibilities are endless. Welcome to "Autumn".

•Smooks: The Smooks JavaBean Cartridge allows you to create and populate Java objects from your message data (i.e. bind data to) (suggested by superfilin in comments).

Transmorph (pretty recent), EZMorph, Dozer, OTOM are all serious candidates. Dozer seems to be the most active project though (and maybe the most advanced). I personally used Dozer and happy with it. (list from Pascal Thivent)