DBUtils讀取查詢

以下示例將演示如何在DBUtils的幫助下，使用讀取查詢來讀取數據庫表中的記錄。這裏演示從員工表中讀取一條記錄。

語法

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

其中，

• resultHandler − ResultSetHandler對象將結果集映射到Employee對象。
• queryRunner − QueryRunner對象在數據庫中插入Employee對象。

爲了理解上述與DBUtils相關的概念，我們編寫一個將運行讀取查詢的示例。創建一個示例應用程序。

• 更新在DBUtils入門應用中創建的文件MainApp.java。
• 編譯並運行應用程序，如下所述。

以下是Employee.java文件的內容。

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文件的內容。

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);
      }        
   }
}

完成創建源文件後，運行該應用程序。 如果應用程序一切正常，它將打印下面的消息。

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