DBUtils - 读取操作(Read)

下面的示例将演示如何读取(Read)数据，无涯教程将从员工表中读取一条记录。

ResultSetHandler<Employee> resultHandler=new BeanHandler<Employee>(Employee.class);
Employee emp=queryRunner.query(conn, "SELECT * FROM employees WHERE first=?", resultHandler, "Sumit");

• resultHandler  -  将输出集映射到Employee对象的ResultSetHandler对象 。

• queryRunner   -   QueryRunner对象 ，用于从数据库读取员工对象 。

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 MainApp.java 文件的内容。

链接：https://www.learnfk.comhttps://www.learnfk.com/dbutils/dbutils-read-query.html

来源：LearnFk无涯教程网

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

import org.apache.commons.dbutils.DbUtils;
import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.ResultSetHandler;
import org.apache.commons.dbutils.handlers.BeanHandler;

public class MainApp {
   //JDBC 驱动程序名称和数据库 URL
   static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";  
   static final String DB_URL = "jdbc:mysql://localhost:3306/emp";

   //连接数据库凭据
   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();
      //第一步：注册JDBC驱动
      DbUtils.loadDriver(JDBC_DRIVER);

      //第二步：打开连接
      System.out.println("Connecting to database...");
      conn = DriverManager.getConnection(DB_URL, USER, PASS);

      //第三步：创建一个 ResultSet Handler 来处理 Employee 对象
      ResultSetHandler<Employee> resultHandler = 
         new BeanHandler<Employee>(Employee.class);

      try {
         Employee emp = queryRunner.query(conn, "SELECT * FROM employees WHERE id=?",
            resultHandler, 104);
         //显示对象信息
         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);
      }        
   }
}

创建完源文件后，让无涯教程运行该应用程序。如果您的应用程序一切正常，它将打印以下消息。

无涯教程网

ID: 104, Age: 30, First: Learnfk, Last: Kumar