Spring - Handling large objects with JdbcTemplate and LobHandler

LobHandler is an abstraction for handling large binary and text fields. This abstraction was mainly created to isolate Oracle peculiar handling of LOBs ( OracleLobHandler implementation). DefaultLobHandler (another implementation) should work with other databases as well.

Example

src/main/resources/createReportTable.sql

CREATE TABLE REPORT(
ID BIGINT PRIMARY KEY AUTO_INCREMENT,
NAME VARCHAR(255) NOT NULL,
CONTENT CLOB,
IMAGE BLOB
);

public class Report {
  private long id;
  private String name;
  private String content;
  private byte[] image;
    .............
}

Using JdbcTemplate and LobHandler

@Repository
public class ReportDao implements Dao<Report> {
  @Autowired
  private DataSource dataSource;
  private JdbcTemplate jdbcTemplate;

  @PostConstruct
  private void postConstruct() {
      jdbcTemplate = new JdbcTemplate(dataSource);
  }

  @Override
  public void save(Report report) {
      String sql = "insert into REPORT (NAME, CONTENT, IMAGE) values (?, ?, ?)";
      LobHandler lobHandler = new DefaultLobHandler();
      jdbcTemplate.execute(sql, new AbstractLobCreatingPreparedStatementCallback(lobHandler) {
          @Override
          protected void setValues(PreparedStatement ps, LobCreator lobCreator)
                  throws SQLException, DataAccessException {

              ps.setString(1, report.getName());
              Reader reader = new StringReader(report.getContent());
              lobCreator.setClobAsCharacterStream(ps, 2, reader,
                      report.getContent().length());

              ByteArrayInputStream inputStream = new ByteArrayInputStream(report.getImage());
              lobCreator.setBlobAsBinaryStream(ps, 3, inputStream, report.getImage().length);
          }
      });
  }
    .............
  @Override
  public List<Report> loadAll() {
      return jdbcTemplate.query("select * from REPORT", (resultSet, i) -> {
          return toReport(resultSet);
      });
  }

  private Report toReport(ResultSet resultSet) throws SQLException {
      Report report = new Report();
      report.setId(resultSet.getLong("ID"));
      report.setName(resultSet.getString("NAME"));

      LobHandler lobHandler = new DefaultLobHandler();
      String content = lobHandler.getClobAsString(resultSet, "CONTENT");
      report.setContent(content);

      byte[] image = lobHandler.getBlobAsBytes(resultSet, "IMAGE");
      report.setImage(image);

      return report;
  }
}

Persisting and loading

@Component
public class ReportClientBean {
  @Autowired
  private Dao<Report> reportDao;

  public void persistReport() {
      Report report = getReport();
      System.out.println("-- persisting report --");
      System.out.println(report);
      reportDao.save(report);
      System.out.println("-- loading all --");
      List<Report> reports = reportDao.loadAll();
      System.out.println(reports);
  }

  private Report getReport() {
      //create dummy report
      Report report = new Report();
      report.setName("dummy report");
      report.setContent("very large dummy content ..");
      report.setImage(new byte[]{1, 4, 3, 3, 3, 5, 5, 3, 6, 7, 6, 7, 9});
      return report;
  }
}

Java Config

@Configuration
@ComponentScan
public class AppConfig {

  @Bean
  public DataSource h2DataSource() {
      return new EmbeddedDatabaseBuilder()
              .setType(EmbeddedDatabaseType.H2)
              .addScript("createReportTable.sql")
              .build();
  }
}

Main class

public class ExampleMain {
  public static void main(String[] args) {
      AnnotationConfigApplicationContext context =
              new AnnotationConfigApplicationContext(AppConfig.class);
      ReportClientBean clientBean = context.getBean(ReportClientBean.class);
      clientBean.persistReport();
  }
}

Output

-- persisting report --
Report{id=0, name='test report', content='dummy large content ..', image=[1, 4, 3, 32, 2, 1, 5, 3, 6, 7, 6, 7]}
-- loading all --
[Report{id=1, name='test report', content='dummy large content ..', image=[1, 4, 3, 32, 2, 1, 5, 3, 6, 7, 6, 7]}]

Example Project

Dependencies and Technologies Used:

• spring-context 4.3.10.RELEASE: Spring Context.
• spring-jdbc 4.3.10.RELEASE: Spring JDBC.
• h2 1.4.196: H2 Database Engine.
• JDK 1.8
• Maven 3.3.9