Spring JDBC - ResultSetExtractor Interface

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Overview

The org.springframework.jdbc.core.ResultSetExtractor interface is a callback interface used by JdbcTemplate's query methods. Implementations of this interface perform the actual work of extracting results from a ResultSet, but don't need to worry about exception handling.

SQLExceptions will be caught and handled by the calling JdbcTemplate. This interface is mainly used within the JDBC framework itself. A RowMapper is usually a simpler choice for ResultSet processing, mapping one result object per row instead of one result object for the entire ResultSet.

Interface Declaration

Following is the declaration for org.springframework.jdbc.core.ResultSetExtractor interface −

public interface ResultSetExtractor

Usage

• Step 1 − Create a JdbcTemplate object using a configured datasource.

• Step 2 − Use JdbcTemplate object methods to make database operations while parsing the resultset using ResultSetExtractor.

Example

Following example will demonstrate how to read a query using JdbcTemplate class and ResultSetExtractor interface. We'll read available record of a student in Student Table.

Syntax

public List<Student> listStudents() {
   String SQL = "select * from Student";
   List <Student> students = jdbcTemplateObject.query(
      SQL, new ResultSetExtractor<List<Student>>(){
         public List<Student> extractData(ResultSet rs) throws SQLException, DataAccessException {
            List<Student> list = new ArrayList<Student>();  
            while(rs.next()){  
               Student student = new Student();
               student.setId(rs.getInt("id"));
               student.setName(rs.getString("name"));
               student.setAge(rs.getInt("age"));
               student.setDescription(rs.getString("description"));
               student.setImage(rs.getBytes("image"));
               list.add(student);  
            }
            return list;  
         }
      }
   );
   return students;
}

Where,

• SQL − Select query to read students.

• jdbcTemplateObject − StudentJDBCTemplate object to read student object from database.

• ResultSetExtractor − ResultSetExtractor object to parse resultset object.

To understand the above-mentioned concepts related to Spring JDBC, let us write an example which will select a query. To write our example, let us have a working Eclipse IDE in place and use the following steps to create a Spring application.

StudentDAO.java

Following is the content of the Data Access Object interface file StudentDAO.java.

package com.tutorialspoint;

import java.util.List;
import javax.sql.DataSource;

public interface StudentDAO {
   /** 
    * This is the method to be used to initialize
    * database resources ie. connection.
   */
   public void setDataSource(DataSource ds);
   
   /** 
    * This is the method to be used to list down
    * all the records from the Student table.
   */
   public List<Student> listStudents();
}

Student.java

Following is the content of the Student.java file.

package com.tutorialspoint;

// Student POJO for Student Table
public class Student {
   private Integer age;
   private String name;
   private Integer id;

   // setter/getter methods
   public void setAge(Integer age) {
      this.age = age;
   }
   public Integer getAge() {
      return age;
   }
   public void setName(String name) {
      this.name = name;
   }
   public String getName() {
      return name;
   }
   public void setId(Integer id) {
      this.id = id;
   }
   public Integer getId() {
      return id;
   }
}

StudentJDBCTemplate.java

Following is the implementation class file StudentJDBCTemplate.java for the defined DAO interface StudentDAO.

package com.tutorialspoint;

import java.util.List;
import java.util.ArrayList;
import javax.sql.DataSource;
import org.springframework.jdbc.core.JdbcTemplate;

// DAO instance to persist Student values
public class StudentJDBCTemplate implements StudentDAO {
   private DataSource dataSource;
   private JdbcTemplate jdbcTemplateObject;
   
   // set the datasource and jdbctemplate
   public void setDataSource(DataSource dataSource) {
      this.dataSource = dataSource;
      this.jdbcTemplateObject = new JdbcTemplate(dataSource);
   }

   // get all the students from the database   
   public List<Student> listStudents() {
      String SQL = "select * from Student";
      List <Student> students = jdbcTemplateObject.query(SQL, 
         new ResultSetExtractor<List<Student>>(){
         public List<Student> extractData(ResultSet rs) throws SQLException, DataAccessException {
            List<Student> list = new ArrayList<Student>();  
            while(rs.next()){  
               Student student = new Student();
               student.setId(rs.getInt("id"));
               student.setName(rs.getString("name"));
               student.setAge(rs.getInt("age"));
               student.setDescription(rs.getString("description"));
               student.setImage(rs.getBytes("image"));
               list.add(student);  
            }
            return list;  
         }    	  
      });
      return students;
   }
}

MainApp.java

Following is the content of the MainApp.java file.

package com.tutorialspoint;

import java.util.List;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class MainApp {
   public static void main(String[] args) {
      // Create the application context by reading Beans.xml  
      ApplicationContext context = new ClassPathXmlApplicationContext("Beans.xml");

      // Create the JDBCTemplate instance from spring context
      StudentJDBCTemplate studentJDBCTemplate = (StudentJDBCTemplate)context.getBean("studentJDBCTemplate");
      
      // get all the students
	  List<Student> students = studentJDBCTemplate.listStudents();
      // print all the students
      for(Student student: students){
         System.out.print("ID : " + student.getId() );
         System.out.println(", Age : " + student.getAge()); 
      }
   }
}

Beans.xml

Following is the configuration file Beans.xml.

<?xml version = "1.0" encoding = "UTF-8"?>
<beans xmlns = "http://www.springframework.org/schema/beans"
   xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance" 
   xsi:schemaLocation = "http://www.springframework.org/schema/beans
   http://www.springframework.org/schema/beans/spring-beans-3.0.xsd ">

   <!-- Initialization for data source -->
   <bean id = "dataSource" 
      class = "org.springframework.jdbc.datasource.DriverManagerDataSource">
      <property name = "driverClassName" value = "com.mysql.cj.jdbc.Driver"/>
      <property name = "url" value = "jdbc:mysql://localhost:3306/TEST"/>
      <property name = "username" value = "root"/>
      <property name = "password" value = "admin"/>
   </bean>

   <!-- Definition for studentJDBCTemplate bean -->
   <bean id = "studentJDBCTemplate" 
      class = "com.tutorialspoint.StudentJDBCTemplate">
      <property name = "dataSource" ref = "dataSource" />    
   </bean>
      
</beans>

Output

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

ID : 1, Age : 17
ID : 3, Age : 18