QueryRunner interface


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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

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

public class QueryRunner
   extends AbstractQueryRunner

Usage

  • Step 1 − Create a connection object.

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

Example

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");

Where,

  • resultHandler − ResultSetHandler object to map result set to Employee object.

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

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.

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;
   }
}

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);
      }        
   }
}

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
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