Java Distributed Computing

Multi-Database Applications

So far we’ve discussed simple local database access from Java using JDBC, and various approaches for connecting Java agents to remote databases. Some simple extensions to these approaches allow you to connect a Java agent to multiple remote databases, and create some interesting possibilities for applications in data analysis and management.

A feature of JDBC that should be obvious from earlier sections is that it insulates the application from the proprietary details of the database. So assuming that we’ve encapsulated the data-access tier of our application well, and that we have local JDBC drivers that can access each database server, we can easily distribute our data across multiple database servers and still pull the data together into a single set of data objects simply by using multiple Connection objects.

As an example, suppose that the tables shown in Figure 7.3 are stored in two separate databases: all tasks and time constraints on tasks are stored in a database named “sequence” on server “data1,” while resource and resource assignment data is stored in a database named “schedule” on server “data2.” Our JDBC-enabled data objects now simply need access to Connections to each of these databases, assuming that the tables in the separate databases are defined the same way they were in the single database. We can modify our DatabaseItem class to contain two Connection objects, as shown in Example 7.13.

Example 7-13. Multi-Database Schedule Data ...