11. Servlet Collaboration | Java Servlet Programming (Java Series)

Java Servlet Programming, 2nd Edition > 11. Servlet Collaboration

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Chapter 11. Servlet Collaboration

Servlets running together in the same server have several ways to communicate with one another. There are two main styles of servlet collaboration:

Sharing information: This involves two or more servlets sharing state or resources. For example, a set of servlets managing an online store could share the store's product inventory count or share a database connection. Session tracking (see Chapter 7) is a special case of sharing information.
Sharing control: This involves two or more servlets sharing control of the request. For example, one servlet could receive the request but let another servlet handle some or all of the request-handling responsibilities.

In the past (before Servlet API 2.1) we would have listed another style of collaboration: direct manipulation . With this style of collaboration, a servlet could obtain a direct reference to another through the getServlet( ) method and invoke methods on the other servlet. This style of collaboration is no longer supported; the getServlet( ) method has been deprecated and defined to return null for API 2.1 and later. The reason: a servlet may be destroyed by the web server at any time, so nothing but the server should hold a direct reference to a servlet. Everything that could be done with getServlet( ) can be accomplished better and safer using the alternatives we'll learn about in this chapter.

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