Populating the Database
To populate the database, we need to execute the main program, as illustrated in Listing 9.
Listing 9 Running the database—populating the data.
C:\java\jpwh-gettingstarted-070401\helloworld-jpa>ant run Buildfile: build.xml compile: copymetafiles: run: [java] 1 message(s) found: [java] Hello World with JPA BUILD SUCCESSFUL
If you compare the program output in Listing 9 with the Java code in Listing 3, you'll see that the following Java code instantiates Message by executing the non-default constructor:
Message message = new Message("Hello World with JPA"); em.persist(message);
The object message is then written (persisted) to the database.
What does the database look like after running the code? Figure 2 illustrates the database contents.
Figure 2 The populated database.
Notice in Figure 2 that the row has been populated with the instance of Message. More of that JPA magic! Notice also that the column NEXT_MESSAGE_ID is blank, because no code was executed to populate the column. However, this is easily fixed by a call to the method setNextMessage().
You now have a great framework with which to explore JPA and persistence.