Dbutils 简明教程

QueryRunner interface

org.apache.commons.dbutils.QueryRunner 类是 DBUtils 库中的核心类。它用可插入的 ResultSet 处理策略执行 SQL 查询。这个类是线程安全的。

The org.apache.commons.dbutils.QueryRunner class is the central class in the DBUtils library. It executes SQL queries with pluggable strategies for handling ResultSets. This class is thread safe.

Class Declaration

以下是 org.apache.commons.dbutils.QueryRunner 类的声明：

Following is the declaration for org.apache.commons.dbutils.QueryRunner class −

public class QueryRunner
   extends AbstractQueryRunner

Usage

  1. Step 1 − Create a connection object.

  2. Step 2 − Use QueryRunner object methods to make database operations.

Example

以下示例将演示如何使用 QueryRunner 类读取记录。我们将读取 employee 表中可用的记录之一。

Following example will demonstrate how to read a record using QueryRunner class. We’ll read one of the available record in employee Table.

Syntax

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 result set to Employee object.

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

为了理解上述与 DBUtils 相关的概念，让我们编写一个将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。

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, 103);
         //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);
      }
   }
}

一旦你创建好源文件，让我们运行应用程序。如果你的应用程序没有问题，它将打印以下消息。

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: 103, Age: 28, First: Sumit, Last: Mittal