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18.9 Sharing Connection Pools

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18.9 Sharing Connection Pools

In the previous example, each servlet had its own connection pool. This

approach makes sense when different servlets perform substantially different

tasks and thus talk to different databases. However, it is also quite common

for some or all of the servlets on a server to talk to the same database and thus

to share a connection pool. There are two main approaches to sharing pools:

using the servlet context (a servlet specific technique) and using static meth 

ods or singleton classes (a general Java technique).

Using the Servlet Context to Share Connection 

Pools

You can call the servlet 

getServletContext

 method to get an object of type

ServletContext

 that is shared by all servlets on the server (or within a Web

application if your server supports Web applications). This 

ServletContext

object has a 

setAttribute

 method that takes a 

String

 and an 

Object

 and

stores the 

Object

 in a table with the 

String

 as a key. You can obtain the

Object

 at a later time by calling 

getAttribute

 with the 

String

 (this

method returns 

null

 if there is no value associated with the key).

So, for example, a group of servlets that all use the books database could

share pools by having each servlet perform the following steps:

ServletContext context = getServletContext();

ConnectionPool bookPool = 

(ConnectionPool)context.getAttribute("book pool");

if (bookPool == null) {

bookPool = new ConnectionPool(...);

context.setAttribute("book pool", bookPool);

}

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