Spring JPA - create specification that returns entities in random order (MySql ORDER BY RAND() function)

In this article, we would like to show how in Spring JPA create Specification that provides random order for returned entities (random sorting).

Quick solution:

// CriteriaQuery<?> query = ...
// CriteriaBuilder builder = ...

// put inside toPredicate function following line:
//
query.orderBy(builder.asc(builder.function("RAND", null))); // MySql RAND() function used

// do not use sort parameter using PageRequest:
//
PageRequest pageRequest = PageRequest.of(pageNumber - 1, pageSize);

Practical example

OffersController.java file:

package com.example.controllers;

import org.springframework.data.domain.Page;
import org.springframework.data.domain.PageRequest;
import org.springframework.http.MediaType;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.ResponseBody;

import javax.servlet.http.HttpServletRequest;

import com.example.utils.HttpUtils;
import com.example.database.repositories.OffersRepository; // use your repository here
import com.example.database.specifications.OffersSpecification;
import com.example.database.entities.OfferEntity;

@Controller
public class OffersController {

    @Autowired
    private OffersRepository offersRepository,

    @RequestMapping(
            method = RequestMethod.GET,
            value = "/offers",
            produces = MediaType.APPLICATION_JSON_VALUE
    )
    @ResponseBody
    public List<OfferEntity> getOffers(HttpServletRequest request) {

        int pageNumber = 1;
        int pageSize = 20;

        OffersSpecification offersSpecification = new OffersSpecification();
        PageRequest pageRequest = PageRequest.of(pageNumber - 1, pageSize); // do not add here sort parameter here

        Page<OfferEntity> pagedOffers = this.offersRepository.findAll(offersSpecification, pageRequest);

        return pagedOffers;
    }
}

OffersSpecification.java file:

package com.example.database.specifications;

import org.springframework.data.jpa.domain.Specification;

import javax.persistence.criteria.CriteriaBuilder;
import javax.persistence.criteria.CriteriaQuery;
import javax.persistence.criteria.Predicate;
import javax.persistence.criteria.Root;

import com.example.database.entities.OfferEntity;

public class OffersSpecification implements Specification<OfferEntity> {

    @Override
    public Predicate toPredicate(Root<OfferEntity> root, CriteriaQuery<?> query, CriteriaBuilder builder) {
        Predicate predicate = builder.and();

        // ...

        query.orderBy(builder.asc(builder.function("RAND", null))); // MySql RAND() function used

        return predicate;
    }
}

OfferEntity.java file: 

package com.example.database.entities;

import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Entity;
import javax.persistence.Table;

import java.util.Date;

@Entity
@Table(name = "offers")
public class OfferEntity
{
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    // other fields ...    

    private Long parentId;
    private Date publicationTime;

    // getters and setters ...
}