MapListHandler Class

The org.apache.commons.dbutils.MapListHandler is the implementation of ResultSetHandler interface and is responsible to convert the ResultSet rows into pst of Maps. This class is thread safe.

Class Declaration

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

pubpc class MapListHandler
   extends AbstractListHandler<Map<String,Object>>

Usage

Step 1 − Create a connection object.

Step 2 − Get implementation of ResultSetHandler as MapListHandler object.

Step 3 − Pass resultSetHandler to QueryRunner object, and make database operations.

Example

Following example will demonstrate how to read a pst of records using MapListHandler class. We ll read available records in Employees Table as pst of maps.

Syntax

List<Map<String, Object>> result = queryRunner.query(conn, "SELECT * FROM employees", new MapListHandler());

Where,

resultHandler − MapListHandler object to map result sets to pst of maps.

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 java.util.List;
import java.util.Map;

import org.apache.commons.dbutils.DbUtils;
import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.MapListHandler;

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);        

      try {
         List<Map<String, Object>> result = queryRunner.query(
            conn, "SELECT * FROM employees", new MapListHandler());      
         System.out.println(result);
      } 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.

Connecting to database...
[{id=100, age=18, first=Zara, last=Ap}, 
{id=101, age=25, first=Mahnaz, last=Fatma}, 
{id=102, age=30, first=Zaid, last=Khan}, 
{id=103, age=33, first=Sumit, last=Mittal}]