Custom JPA repo

CustomJPARepository.java

package com.jpa.demo.repo;

import com.jpa.demo.entities.Customer;

import java.util.List;

/**
 *
 * The class that implements  should contain the IMPL postfix for spring recognise and provide implementation during run time
 *
 * */

/**
 * mimic how spring data provides implementation durinhg runtime when we extend to JPA REPO
 *
 * */
public interface CustomJPARepository<T> {

  Iterable<T> retriveAll();

  //PROVIDING CUSTOM SAVE IMPLEMENATION.
  // this has higher precendence over save method from CRUD REPO
  // if return type is defined as T directly, we can either use T class or a sub class of T
  // when u say S extends T, a  DTO can be passed  which need not be extending to T,
  // the save method however returns an new object which is extended to T
    <S extends T> S save(S entity);


}

CustomJPARepositoryImpl.java

package com.jpa.demo.repo;


import com.jpa.demo.entities.Customer;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.jdbc.core.JdbcTemplate;

import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import javax.transaction.Transactional;
import java.util.Arrays;
import java.util.List;
import java.util.Optional;

/**
 *
 * The class that implements  should contain the IMPL postfix for spring recognise and provide implementation during run time
 *
 * */
/**
 * mimic how spring data provides implementation durinhg runtime when we extend to JPA REPO
 * spring data searches for the implementation with IMPL postfix and uses it as implementation at run time
 * */

// add <T> as <Customer>
public class CustomJPARepositoryImpl implements CustomJPARepository<Customer> {

    private  static  final Logger log = LoggerFactory.getLogger(CustomJPARepositoryImpl.class);

    @Autowired
    JdbcTemplate jdbc;

    @PersistenceContext
    EntityManager entityManager;

    @Override
    public List<Customer> retriveAll() {
        log.info("query being executed from customrepoimpl");
        return jdbc.query("Select * from customers c order by c.customer_id",(rs, rowNum) -> {
           return new Customer(rs.getLong("customer_id"),rs.getString("first_name"), rs.getString("last_name"));
        });

    }

    @Override
    @Transactional
    public Customer save(Customer entity) {
        log.info("saving entity "+ entity);
        entityManager.persist(entity);
        return entity;


    }
}

FuturesTester.java

package com.jpa.demo.service;

import com.jpa.demo.entities.Customer;
import com.jpa.demo.repo.CustomerRepository;
import net.bytebuddy.asm.Advice;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

import javax.persistence.criteria.Predicate;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.*;
import java.util.stream.Collectors;
import java.util.stream.Stream;

/**
 * refer : http://www.baeldung.com/java-completablefuture
 */
@Component
public class FuturesTester {

    @Autowired
    CustomerRepository repo;

    private static final Logger log = LoggerFactory.getLogger(FuturesTester.class);

    
    /**
    * retriveAll is picked up from CustomRepositoryImpl during runtime
    */
    public CompletableFuture<List<Customer>> fetchAllUsingCustomRepo(){
        CompletableFuture cf = CompletableFuture.supplyAsync(() -> repo.retriveAll());
        return cf;
    }
    
    /**
    * save is picked up from CustomRepositoryImpl during runtime
    */
    //overiging with custom save behaviour
    public CompletableFuture<Customer> customSave(Customer customer){
        // custom repo CustomerRepoImpl's save
        return CompletableFuture.supplyAsync(() -> repo.save(customer));
    }







}