org.apache.commons.dbutils.BeanListHandler 是ResultSetHandler接口的实现,负责将ResultSet行转换为Java Bean列表.这个类是线程安全的.
以下是org.apache.commons.dbutils.BeanListHandler的声明class :
public class BeanListHandler<T> extends Object implements ResultSetHandler<List<T>>
第1步 : 创建连接对象.
第2步 : 将ResultSetHandler实现为BeanListHandler对象.
步骤3 : 将resultSetHandler传递给QueryRunner对象,并进行数据库操作.
以下示例将演示如何使用BeanListHandler类读取记录列表.我们将读取Employees Table中的可用记录并将它们映射到Employee bean列表.
List<Employee> empList = queryRunner.query(conn, "SELECT * FROM employees", resultHandler);
其中,
resultHandler : BeanListHandler对象,用于将结果集映射到Employee对象列表.
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 MainApp.java 文件的内容.
import java.sql.Connection; import java.sql.DriverManager; import java.sql.SQLException; import java.util.List; import org.apache.commons.dbutils.DbUtils; import org.apache.commons.dbutils.QueryRunner; import org.apache.commons.dbutils.ResultSetHandler; import org.apache.commons.dbutils.handlers.BeanListHandler; public class MainApp { // 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"; public static void main(String[] args) throws SQLException { Connection conn = null; QueryRunner queryRunner = new QueryRunner(); //Step 1: Register JDBC driver DbUtils.loadDriver(JDBC_DRIVER); //Step 2: Open a connection System.out.println("Connecting to database..."); conn = DriverManager.getConnection(DB_URL, USER, PASS); //Step 3: Create a ResultSet Handler to handle List of Employee Beans ResultSetHandler<List<Employee>> resultHandler = new BeanListHandler<Employee>(Employee.class); try { List<Employee> empList = queryRunner.query(conn, "SELECT * FROM employees", resultHandler); for(Employee emp: empList ) { //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()); } } finally { DbUtils.close(conn); } } }
创建源文件后,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: 100, Age: 18, First: Zara, Last: Ali ID: 101, Age: 25, First: Mahnaz, Last: Fatma ID: 102, Age: 30, First: Zaid, Last: Khan ID: 103, Age: 28, First: Sumit, Last: Mittal