如何检查h2嵌入式数据库是否已创建？

Question

I have app-context file with embedded database:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:jdbc="http://www.springframework.org/schema/jdbc"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
    http://www.springframework.org/schema/jdbc
    http://www.springframework.org/schema/jdbc/spring-jdbc.xsd">

    <jdbc:embedded-database id="dataSource" type="H2">
        <jdbc:script location="classpath:META-INF/schema.sql" />
        <jdbc:script location="classpath:META-INF/data.sql" />
    </jdbc:embedded-database>

    <bean id="reportDao" 
          class="jdbc.dao.ImplReportDao"
          p:dataSource-ref="dataSource" />

</beans>

And I have the following src/META-INF/schema.sql file:

USE `reports`;

/*Table structure for table `reports` */

DROP TABLE IF EXISTS `reports`;

CREATE TABLE `reports` (
  `id` int(9) unsigned zerofill NOT NULL,
  `parent_id` int(9) unsigned zerofill NOT NULL DEFAULT '0000',
  `name` varchar(99) NOT NULL,
  `is_category` tinyint(1) NOT NULL DEFAULT '1',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=cp1251;

and src/META-INF/data.sql file:

insert  into `reports`.`reports`(`id`,`parent_id`,`name`,`is_category`) 
values 
(0000,0000,'Reports',1),
(0001,0000,'Card emission',1),
(0002,0000,'Technical reports',1);

And ImplReportDao looks like this:

public class ImplReportDao implements ReportDao {
    private DataSource dataSource;

    public void setDataSource(DataSource dataSource) {
        this.dataSource = dataSource;
    }

    @Override
    public List<Report> findAll() {
        System.out.println("find all");
        List<Report> result = new ArrayList<Report>();
        Connection conn = null;     
        try {
            if (dataSource != null) {
                System.out.println("dataSource != null");
            } else {
                System.out.println("dataSource == null");
            }

            conn = dataSource.getConnection();
            PreparedStatement statement = conn.prepareStatement("select * from reports");
            ResultSet resultSet = statement.executeQuery();
            while (resultSet.next()) {
                Report report = new Report();
                report.setId(resultSet.getInt("id"));
                report.setParentId(resultSet.getInt("parent_id"));
                report.setName(resultSet.getString("name"));
                result.add(report);
            }
            return result;
        } catch (Exception ex) {
            return null;
        }
    }
}

And Main class looks like:

public class Main {
    private static ReportDao reportDao = new ImplReportDao();

    public static void main(String[] args) {
        List<Report> reports = reportDao.findAll();
        for (Report report : reports) {
            System.out.println("report: " + report.getName());
        }
    }
}

But after launch I've got the error NullPointerException because in ImplReportDao.findAll() dataSource is null. How can I check whether h2 embedded database is created?

Answer 1

You configure your databae in Spring but then create object using constructor. You do not create Spring context that is why database is not created. Also because you use constructor Spring cannot inject datasource into your newly created object because Spring IoC container doesn't know about it.

So you need to make several changes in your code and config XML.

First, to use p:dataSource-ref you need to add this line into heade of your XML file: xmlns:p="http://www.springframework.org/schema/p" right after xmlns:jdbc="http://www.springframework.org/schema/jdbc" .

Second you need to instantiate Spring context like this

public class Main {

  public static void main(String[] args) {
    ClassPathXmlApplicationContext ctx = new ClassPathXmlApplicationContext("app-context.xml"); //assuming app-context.xml is in classpath of project
    ReportDao reportDao = ctx.getBean(ReportDao.class); //Ask Spring to gice you DAO object with injected dataSource
    List<Report> reports = reportDao.findAll();
    for (Report report : reports) {
        System.out.println("report: " + report.getName());
    }
  }
}