Simplifying persistence with Spring

Look at the PhoneBookDerbyDao class. It has 398 lines to support create, read, update, and delete (CRUD) operations. Every method performs almost similar tasks. The following tasks are invoked from the CRUD methods:

  • Passing connection parameters
  • Opening a connection
  • Creating a statement
  • Preparing the statement
  • Executing the statement
  • Iterating through the results (only in the read method)
  • Populating the model objects (only in the read method)
  • Processing any exception
  • Handling transactions
  • Closing the ResultSet (only in the read method)
  • Closing the statement
  • Closing the connection

The Spring framework provides APIs to reduce JDBC code duplication. Spring JDBC hides the low-level details and allows us to concentrate on business logic. We'll implement PhoneBookDao using Spring JDBC.

Download the latest version of JDBC JAR and its dependencies from http://maven.springframework.org/release/org/springframework/spring/.

Follow the ensuing steps to implement Spring JDBC and simplify the code:

  1. Launch Eclipse, open the DatabaseAccess project, and edit .classpath to add the following Spring dependencies shown in the screenshot:
    Simplifying persistence with Spring
  2. Create a PhoneBookDerbySpringDao class that implements the PhoneBookDao interface. The following is the Spring implementation of the create method:
      public class PhoneBookDerbySpringDao  implements
    PhoneBookDao {

  private final JdbcTemplate jdbcTemplate;
  
    public PhoneBookDerbySpringDao(JdbcTemplate jdbcTemplate) {
    this.jdbcTemplate = jdbcTemplate;
    }

    @Override
    public boolean create(PhoneEntry entry) {
      int rowCount = jdbcTemplate.update("insert into PhoneBook values (?,?,?)",
        new Object[]{entry.getPhoneNumber(), entry.getFirstName(),
            entry.getLastName()
        });
      return rowCount == 1;
    }
  }

    JdbcTemplate simplifies the use of JDBC; it handles the resources and helps to avoid common errors such as not closing the connection. It creates and populates the statement object, iterates through the ResultSet object, which leaves the application code to provide SQL, and extracts results. PhoneBookDerbySpringDao contains a JdbcTemplate instance and delegates the database tasks to the jdbcTemplate.

    JdbcTemplate has an update method for insert and update operations. It takes a SQL query and parameters. The new Spring version of the create() method invokes the update() method on jdbcTemplate and passes PhoneEntry details. Now the create method looks simple, just two lines of code. The Spring framework handles the resource life cycle.

  3. Create a JUnit class named PhoneBookDerbySpringDaoTest for unit testing. We'll create a jdbcTemplate mock and pass it to dao. The following is the JUnit implementation:
    @RunWith(MockitoJUnitRunner.class)
public class PhoneBookDerbySpringDaoTest {

  @Mock
  JdbcTemplate mockJdbcTemplate;

  PhoneBookDerbySpringDao springDao;

  @Before
  public void init() {
    springDao = new PhoneBookDerbySpringDao(mockJdbcTemplate);
  }

  @Test
  public void creates_PhoneEntry() throws Exception {
    //create PhoneEntry
    String charlsPhoneNumber = "1234567";
    String charlsFirstName = "Charles";
    String charlsLastName = "Doe";

    PhoneEntry charles = new PhoneEntry();
    charles.setFirstName(charlsFirstName);
    charles.setLastName(charlsLastName);
    charles.setPhoneNumber(charlsPhoneNumber);

    //Stub jdbcTemplate's update to return 1
    when(mockJdbcTemplate.update(anyString(), anyObject(), anyObject(), anyObject())).thenReturn(1);

    //Execute
    assertTrue(springDao.create(charles));

    //Create argument capture
    ArgumentCaptor<Object> varArgs = ArgumentCaptor.forClass(Object.class);

    ArgumentCaptor<String> strArg = ArgumentCaptor.forClass(String.class);

    //Verify update method was called and capture args
    verify(mockJdbcTemplate).update(strArg.capture(),varArgs.capture(),varArgs.capture(), varArgs.capture());
    
    //Verify 1st dynamic argument was the phone number
    assertEquals(charlsPhoneNumber, varArgs.getAllValues().get(0));
    //Verify the name arguments
    assertEquals(charlsFirstName, 
      varArgs.getAllValues().get(1));
    assertEquals(charlsLastName, varArgs.getAllValues().get(2));
  }
}

    Look at the new Spring dao; it is only 54 lines long. The class looks neat, simple, and readable. It doesn't handle resources, it rather concentrates on data access.

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