到目前为止,我们在使用QueryRunner时使用了连接对象.我们也可以无缝地使用数据源.以下示例将演示如何在QueryRunner和数据源的帮助下使用Read查询读取记录.我们将从Employees Table中读取记录.
QueryRunner queryRunner = new QueryRunner( dataSource ); Employee emp = queryRunner.query("SELECT * FROM employees WHERE first=?", resultHandler, "Sumit");
其中,
dataSource : 已配置DataSource对象.
resultHandler : ResultSetHandler对象将结果集映射到Employee对象.
queryRunner : QueryRunner对象从数据库中读取员工对象.
为了理解上面提到的与DBUtils相关的概念,让我们写一个例子来说明运行读取查询.要编写我们的示例,让我们创建一个示例应用程序.
Step | 描述 |
---|---|
1 | 更新文件 MainApp.java . |
2 | 编译并运行应用程序,如下所述. |
以下是
public class Employee { private int id; private int age; private String first; private String last; public int getId() { return id; } public void setId(int id) { this.id = id; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } public String getFirst() { return first; } public void setFirst(String first) { this.first = first; } public String getLast() { return last; } public void setLast(String last) { this.last = last; } }
以下是 CustomDatasource.java 的内容.
import javax.sql.DataSource; import org.apache.commons.dbcp2.BasicDataSource; public class CustomDataSource { // JDBC driver name and database URL static final String JDBC_DRIVER = "com.mysql.jdbc.Driver"; static final String DB_URL = "jdbc:mysql://localhost:3306/emp"; // Database credentials static final String USER = "root"; static final String PASS = "admin"; private static DataSource datasource; private static final BasicDataSource basicDataSource; static { basicDataSource = new BasicDataSource(); basicDataSource.setDriverClassName(JDBC_DRIVER); basicDataSource.setUsername(USER); basicDataSource.setPassword(PASS); basicDataSource.setUrl(DB_URL); } public static DataSource getInstance() { return basicDataSource; } }
以下是 MainApp.java 文件的内容.
import java.sql.SQLException; import org.apache.commons.dbutils.QueryRunner; import org.apache.commons.dbutils.ResultSetHandler; import org.apache.commons.dbutils.handlers.BeanHandler; public class MainApp { public static void main(String[] args) throws SQLException { DbUtils.loadDriver(JDBC_DRIVER); QueryRunner run = new QueryRunner(CustomDataSource.getInstance()); ResultSetHandler<Employee> resultHandler = new BeanHandler<Employee>(Employee.class); Employee emp = queryRunner.query("SELECT * FROM employees WHERE id=?", resultHandler, 103); //Display values System.out.print("ID: " + emp.getId()); System.out.print(", Age: " + emp.getAge()); System.out.print(", First: " + emp.getFirst()); System.out.println(", Last: " + emp.getLast()); } }
完成源文件的创建后,让我们运行应用程序.如果你的申请一切正常,它将打印以下信息.
ID: 103, Age: 33, First: Sumit, Last: Mittal