📜  公用DBUtils-BeanListHandler类

📅  最后修改于: 2020-11-18 08:10:51             🧑  作者: Mango


org.apache.commons.dbutils.BeanListHandler是ResultSetHandler接口的实现,负责将ResultSet行转换为Java Bean列表。此类是线程安全的。

类声明

以下是org.apache.commons.dbutils.BeanListHandler类的声明-

public class BeanListHandler
   extends Object implements ResultSetHandler>

用法

  • 步骤1-创建一个连接对象。

  • 步骤2-将ResultSetHandler的实现作为BeanListHandler对象获取。

  • 步骤3-将resultSetHandler传递给QueryRunner对象,并进行数据库操作。

下面的示例将演示如何使用BeanListHandler类读取记录列表。我们将读取雇员表中的可用记录,并将它们映射到雇员Bean列表。

句法

List empList = queryRunner.query(conn, "SELECT * FROM employees", resultHandler);      

哪里,

  • resultHandler -BeanListHandler对象,用于将结果集映射到Employee对象的列表。

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

为了理解与DBUtils有关的上述概念,让我们编写一个示例,该示例将运行读取查询。为了编写示例,让我们创建一个示例应用程序。

Step Description
1 Update the file MainApp.java created under chapter DBUtils – First Application.
2 Compile and run the application as explained below.

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 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> resultHandler = new BeanListHandler(Employee.class);

      try {
         List 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: 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