java - 如何检查h2嵌入式数据库是否已创建？

Question

我有带有嵌入式数据库的app-context文件:

<?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>

我有以下src/META-INF/schema.sql文件:

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;

和src/META-INF/data.sql文件:

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);

ImplReportDao 看起来像这样:

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;
        }
    }
}

并且主类看起来像:

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());
        }
    }
}

但是启动后我收到错误 NullPointerException 因为在 ImplReportDao.findAll() 中 dataSource 为空。如何检查h2嵌入式数据库是否创建？

Answer 1

您在 Spring 中配置数据库，然后使用构造函数创建对象。您没有创建 Spring 上下文，这就是未创建数据库的原因。另外，由于您使用构造函数，Spring 无法将数据源注入(inject)到新创建的对象中，因为 Spring IoC 容器不知道它。

因此您需要对代码和配置 XML 进行一些更改。

首先，要使用 p:dataSource-ref，您需要将此行添加到 XML 文件的标题中: xmlns:p="http://www.springframework.org/schema/p" 就在 xmlns:jdbc="http://www.springframework.org/schema/jdbc" 之后。

其次，您需要像这样实例化 Spring 上下文

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());
    }
  }
}