Apache Commons DBUtils - 读取查询

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以下示例将演示如何在 DBUtils 的帮助下使用读取查询读取记录。我们将从员工表中读取一条记录。

句法

读取查询的语法如下 -

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

在哪里，

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

• queryRunner - QueryRunner 对象从数据库读取员工对象。

为了理解上述与 DBUtils 相关的概念，让我们编写一个运行读取查询的示例。为了编写我们的示例，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MainApp.java文件的内容。

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 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 Employee Beans
      ResultSetHandler<Employee> resultHandler =
         new BeanHandler<Employee>(Employee.class);
      try {
         Employee emp = queryRunner.query(conn,
            "SELECT * FROM employees WHERE id=?", resultHandler, 104);
         //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);
      }
   }
}

创建完源文件后，让我们运行该应用程序。如果您的应用程序一切正常，它将打印以下消息：

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