Servlet hosting - JDBC and Connector/J 12 In the two-tier deployment
JDBC and Connector/J 12 In the two-tier deployment model, commonly called client/server, the client application communicates directly to the database through a JDBC driver. The JDBC API supports both two-tier and three-tier models for database access. The model supports the database being on the same machine as the client application or on a remote machine, with all communication being handled by JDBC. While the two-tier model is effective and has been in use for many years, there are problems with it, including a lack of security for updates occurring on the database, performance issues, and a lack of scalability. Modern systems use a three-tier deployment model, as shown in Figure 2.2. Business Servlet Other business app Client Java Applet Java Application Java JSP JDBC Server MySQL Database Figure 2.2 A three-tier deployment model. As shown in the three-tier model, the client doesn t have direct access to the database. Instead, the client sends all its requests to a middle, or business, tier. This tier is responsible for implementing all business rules relating to the application and the data that is received from both the client and the database. Using a third tier has many advantages, the least of which is the ability of the business tier to handle security issues with the client application. The business tier is able to determine what a client is allowed to request and to filter data as needed when it is returned from the database. Within the Java arena, three-tier models are commonly created using a JSP page communicated to the client via a Web browser. The JSP triggers a servlet on the business, or middle, tier, where rules and logic are applied to the client s request. The middle tier servlet contacts the database, or third, tier either directly or through EJBs.
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