J2EE Website Architecture

This architecture is for a relatively simple website that uses a J2EE-compliant application server. The diagram shows one new database in the Middle Tier of a website and no existing databases or systems in the EIS Tier. There are four ways that a database could be used in this architecture: 

  1. The first way is with a transparent interface such as Java Data Objects (JDO) coupled with an object database. In this case, there is no need for a mapping layer because the Java object model is the same model used by the object database. See transparent persistence in object databases. The lack of a mapping layer is show in this diagram.

    J2EE Website Architecture JDO middle tier
  2. The second way is with a transparent interface such as Java Data Objects (JDO) coupled with a relational database. In this case, there is a need for a mapping layer because the Java object model may not match the model used by the relational database. Nevertheless, the mapping can be moved to one location as described in JDO Data Conversion. Also see transparent persistence in object-relational mapping.
  3. The third way is with a call-level interface such as JDBC coupled with a relational database. In this case, there is a need for a mapping layer because the Java object model may not match the model used by the relational database. The mapping would need to be done at the application level as described in JDBC Data Conversion. Be sure to take a look at transparent persistence vs. JDBC call-level interface. This outlines some disadvantages of using JDBC that you should consider when designing persistence for J2EE.
  4. The fourth way is with SQLJ and a relational database. Having a new database would make it possible to minimize the mapping described in SQLJ Data Conversion. Also see SQLJ and mapping SQL and Java data types.

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More on the general topic: Architectures Using Databases in the Middle Tier

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