Dbutils 简明教程

Apache Commons DBUtils - Read Query

以下示例将演示如何使用 DBUtils 借助 Read 查询来读取记录。我们将读取 Employees 表中的记录。

The following example will demonstrate how to read a record using Read query with the help of DBUtils. We will read a record from Employees Table.

Syntax

读取查询的语法如下 −

The syntax for read query is mentioned below −

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

其中，

Where,

  1. resultHandler − ResultSetHandler object to map the result set to Employee object.

  2. queryRunner − QueryRunner object to read an employee object from database.

为了理解与 DBUtils 相关的以上概念，我们来编写一个示例，该示例将运行一个读取查询。为了编写示例，我们来创建一个示例应用程序。

To understand the above mentioned concepts related to DBUtils, let us write an example which will run a read query. To write our example, let us create a sample application.

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。

Following is the content of the Employee.java.

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。

Following is the content of the MainApp.java file.

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);
      }
   }
}

一旦完成创建源文件，我们就来运行应用程序。如果你的应用程序一切正常，它将打印出以下消息：

Once you are done creating the source files, let us run the application. If everything is fine with your application, it will print the following message:

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