Criteria API (projaction)

 For retrieving specific column from  database we  are using PROJECTION(criteria api) for this requirement we have to follow the following steps

Step 1: Create table from your database(i am using MYSQL )

for doing any operations in hibernate we have to  create table with primary key

create table employee(id int(10)  primary key(id),name varchar(30),address varchar(30));

now table is created as below

Step 2: create POJO class with table fields

package a;

public class Employee {

    int id;
    String name;
    String address;

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }


}

Step 3: generate hibernate configuration file (hibernate.cfg.xml)

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">

<hibernate-configuration>

  <session-factory>

    <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>

    <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>

    <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/xxx</property>

    <property name="hibernate.connection.username">root</property>

    <property name="hibernate.connection.password">root</property>

    <mapping resource="a/Employee.hbm.xml"/>

  </session-factory>

</hibernate-configuration>

Step 4: create a class with projection logic

package a;

import java.util.ArrayList;
import java.util.Iterator;
import org.hibernate.Criteria;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.hibernate.criterion.Order;
import org.hibernate.criterion.ProjectionList;
import org.hibernate.criterion.Projections;
import org.hibernate.criterion.Restrictions;

public class EmployeeServlet {

public static void main(String ar[]){
Configuration cfg=new Configuration();
cfg.configure();
SessionFactory sf=cfg.buildSessionFactory();
Session hsession=sf.openSession();



//c.add(Restrictions.between("salary", 20000, 34000));
//c.addOrder(Order.asc("id"));


Criteria c = hsession.createCriteria(Employee.class);
ProjectionList pl = Projections.projectionList();
pl.add(Projections.property("name"));

c.setProjection(pl);

ArrayList list=(ArrayList)c.list();
Iterator itr=list.iterator();
while(itr.hasNext()){
   
   String e = (String)itr.next();
       
System.out.println(e);


}

}

}
   
   

Step 5: generate hibernate mapping file from database table 

<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"

"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<!-- Generated Oct 8, 2013 10:36:24 AM by Hibernate Tools 3.2.1.GA -->

<hibernate-mapping>

    <class name="a.Employee" table="employee" catalog="xxx">

        <id name="id" type="int">

            <column name="id" />

            <generator class="assigned" />

        </id>

        <property name="name" type="string">

            <column name="name" length="30" />

        </property>

        <property name="address" type="string">

            <column name="address" length="30" />

        </property>

    </class>

</hibernate-mapping>

Step 6: now run the application  we will get