DBUtils使用DataSource


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。

句法

QueryRunner queryRunner = new QueryRunner( dataSource );
Employee emp = queryRunner.query("SELECT * FROM employees WHERE first=?", resultHandler, "Sumit");

这里

  • dataSource - 配置的DataSource对象。

  • resultHandler - 将结果集映射到Employee对象的ResultSetHandler对象。

  • queryRunner - 从数据库中读取员工对象的QueryRunner对象。

要理解与DBUtils相关的上述概念,让我们编写一个运行读取查询的示例。要编写我们的示例,让我们创建一个示例应用程序。

以下是 Employee.java 的内容。

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());
   }
}

完成源文件创建后,让我们运行应用程序。如果您的应用程序一切正常,它将打印以下消息。

ID: 103, Age: 33, First: Sumit, Last: Mittal