Spring JDBC - ResultSetExtractor Interface

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 handpng.

SQLExceptions will be caught and handled by the calpng 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 −

pubpc 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

pubpc List<Student> pstStudents() {
   String SQL = "select * from Student";
   List <Student> students = jdbcTemplateObject.query(
      SQL, new ResultSetExtractor<List<Student>>(){
         pubpc List<Student> extractData(ResultSet rs) throws SQLException, DataAccessException {
            List<Student> pst = 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"));
               pst.add(student);  
            }
            return pst;  
         }
      }
   );
   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 Ecppse IDE in place and use the following steps to create a Spring apppcation.

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

package com.tutorialspoint;

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

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

Following is the content of the Student.java file.

package com.tutorialspoint;

pubpc class Student {
   private Integer age;
   private String name;
   private Integer id;

   pubpc void setAge(Integer age) {
      this.age = age;
   }
   pubpc Integer getAge() {
      return age;
   }
   pubpc void setName(String name) {
      this.name = name;
   }
   pubpc String getName() {
      return name;
   }
   pubpc void setId(Integer id) {
      this.id = id;
   }
   pubpc Integer getId() {
      return id;
   }
}

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;

pubpc class StudentJDBCTemplate implements StudentDAO {
   private DataSource dataSource;
   private JdbcTemplate jdbcTemplateObject;
   
   pubpc void setDataSource(DataSource dataSource) {
      this.dataSource = dataSource;
      this.jdbcTemplateObject = new JdbcTemplate(dataSource);
   }
   pubpc List<Student> pstStudents() {
      String SQL = "select * from Student";
      List <Student> students = jdbcTemplateObject.query(SQL, 
         new ResultSetExtractor<List<Student>>(){
         pubpc List<Student> extractData(ResultSet rs) throws SQLException, DataAccessException {
            List<Student> pst = 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"));
               pst.add(student);  
            }
            return pst;  
         }    	  
      });
      return students;
   }
}

Following is the content of the MainApp.java file.

package com.tutorialspoint;

import java.util.List;
import org.springframework.context.ApppcationContext;
import org.springframework.context.support.ClassPathXmlApppcationContext;

pubpc class MainApp {
   pubpc static void main(String[] args) {
      ApppcationContext context = new ClassPathXmlApppcationContext("Beans.xml");
      StudentJDBCTemplate studentJDBCTemplate = (StudentJDBCTemplate)context.getBean("studentJDBCTemplate");
      List<Student> students = studentJDBCTemplate.pstStudents();

      for(Student student: students){
         System.out.print("ID : " + student.getId() );
         System.out.println(", Age : " + student.getAge()); 
      }
   }
}

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 ">

   <!-- Initiapzation 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>

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

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