The *Tools* library is an important part of gvSIG. It provides a number of utilities and services which support the other modules in gvSIG. The main functionality provided by this library relates to:

- Registration of extension points
- Initialisation of libraries
- Utilities for the separation of the API and implementation
  (Registration of APIs, registration of implementations for the APIs, registration of SPI service providers or localisation of an API implementation)
- Monitoring of Tasks

Although these are the most important services the library provides, it also provides other tools that can be considered structural to the application. These include:

- Disposables
- Interfaces for managing Observers-observables
- Interfaces for managing visitors
- Definition of data types
- Base interfaces for evaluators
- Object Persistence

.. tip::
    
    You can find more detailed information on how the
    library mechanism works in gvSIG at     org.gvsig.tools.library_, on the use of *locators* you can    consult
    org.gvsig.tools.locator_, and for
    *managers* you can find documentation at
    org.gvsig.tools.service_.


We will focus now on three basic concepts that are repeated throughout the code that we see, and that are linked to utilities that enable a strict separation of the API from the implementation:

- **Libraries**. These are pieces of code normally associated with a *jar* that provides a functionality. Each of these libraries must be a class that implements the *Library* interface, usually extending the *AbstractLibrary* class. They have methods for initialising the library that are invoked when it is loaded.

- **Managers**. These components provide functionality to the application, acting as an agent for the various services offered by the library and for their configuration. Acts as a *singleton*, since in the application there is usually only one instance of each of these components. Libraries will have one or more of these according to their logic.
  
- **Locators**. This is a utility that allows you to register implementations of *managers* for a given library, and to retrieve the *manager* implementation of a specific API.

These three components play a major role whenever we want to use or create new components, as they are the devices that allow us to access different parts of gvSIG

.. _`org.gvsig.tools.library` : https://gvsig.org/web/reference_catalog/lookupObject?uuid=603a7a0d9e4f0f0306401bd3c238a89d

.. _`org.gvsig.tools.service` : https://gvsig.org/web/reference_catalog/lookupObject?uuid=0aa6c6f67612c991f723fd8f4e069937

.. _`org.gvsig.tools.locator` : https://gvsig.org/web/reference_catalog/lookupObject?uuid=f628030a648208d04db33e339ba79176