QueryRunner interface

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

Class Declaration

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

pubpc 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 apppcation.

Following is the content of the Employee.java.

pubpc class Employee {
   private int id;
   private int age;
   private String first;
   private String last;
   pubpc int getId() {
      return id;
   }
   pubpc void setId(int id) {
      this.id = id;
   }
   pubpc int getAge() {
      return age;
   }
   pubpc void setAge(int age) {
      this.age = age;
   }
   pubpc String getFirst() {
      return first;
   }
   pubpc void setFirst(String first) {
      this.first = first;
   }
   pubpc String getLast() {
      return last;
   }
   pubpc 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;

pubpc 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";

   pubpc 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 apppcation. If everything is fine with your apppcation, it will print the following message.

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