Sequence generator

There are different ways to generate sequence
1) Automatic
2) Custom

1) Automatic

@Id

@GeneratedValue(strategy = GenerationType.SEQUENCE,generator= "countryid-gen")

@SequenceGenerator(name = "countryid-gen", sequenceName = "COUNTRY_SEQ",

              allocationSize = 1, initialValue = 0)

@Column(name = "COUNTRY_ID")

private int id;

2) Custom 

First need to create 

a) Custom Class, then 

b) implement that custom class.

a) Custom Class

package com.pristine.util;

import java.io.Serializable;

import java.sql.Connection;

import java.sql.PreparedStatement;

import java.sql.ResultSet;

import java.sql.SQLException;

import org.apache.commons.lang3.StringUtils;

import org.hibernate.HibernateException;

import org.hibernate.engine.spi.SessionImplementor;

import org.hibernate.id.IdentifierGenerator;

public class EmployeeCodeGenerator implements IdentifierGenerator {

    public Serializable generate(SessionImplementor session, Object object)

            throws HibernateException {

        String prefix = "E";

        Connection connection = session.connection();

        try {

            PreparedStatement ps = connection

                    .prepareStatement("SELECT nextval ('EMPLOYEE_SEQ') as nextval");

            ResultSet rs = ps.executeQuery();

            if (rs.next()) {

                int id = rs.getInt("nextval");

                String code = prefix + StringUtils.leftPad("" + id,3, '0');

                return code;

            }

        } catch (SQLException e) {

            throw new HibernateException(

                    "Unable to generate Stock Code Sequence");

        }

        return null;

    }

}

b) Implementation of Custom Class

@Id

@GenericGenerator(name="seq_id", strategy="com.pristine.util.EmployeeCodeGenerator")

@GeneratedValue(generator="seq_id")

@Column(name = "ID", nullable = false)

private String id;