I'll go with MyBatis

You've worked hard and developed a bunch of persistence capable entities, data objects to hold projections, a good amount of JPQL/HQL NamedQueries, a few native SQL queries, optimistic locking is still perfect, you've put OpenEntityManagerInViewFilter because of some lazy things do not adhere to transaction demarcation and boundaries, and it works, it works just fine. Then you push it to production wait a month or so open The Slow Query Log, !#@! you think.

I'd advise against JPA/Hibernate especially when you do something highly scalable and highly available (see Sean Hull's 20 Biggest Bottlenecks That Reduce And Slow Down Scalability, Rule Number 9), especially when CQRS and Event Sourcing are a big deal. Ok, one may believe that doing programming with relational database without knowing how to write SQL and what execute plan will be used to run it is a good idea in case you protect yourself with Hibernate. But despite Hibernate abstracts RDB it doesn't remove complexity, take a look at Hibernate ORM documentation. And after all abstractions are leaky and you'll end up debugging SQL and writing native queries.

But you probably do not want to program in JDBC anymore. To make it convenient to work with DB and let DB do its stuff I'd use MyBatis that just removes boilerplate code and doesn't introduce some piece of magic. And yes, it is simple, see MyBatis3 Introduction.

To make you feel what it is like a really minimalistic example below. Mapper xml file src/main/resources/test/persistence/TestMapper.xml

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

<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" 
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="test.persistence.TestMapper">

 <select id="selectOne" parameterType="long" resultType="test">
  SELECT
  t.id, t.name
  FROM test t
  WHERE t.id = #{id}
 </select>
</mapper>

Mapper interface src/main/java/test/persistence/TestMapper.java

package test.persistence;

import test.model.Test;

public interface TestMapper {
 Test selectOne(Long id);
}

Transfer object src/main/java/test/model/Test.java

package test.model;

import java.io.Serializable;

public class Test implements Serializable {

 private Long id;

 private String name;

 public Test() {
  super();
 }

 public Long getId() {
  return id;
 }

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

 public String getName() {
  return name;
 }

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

}

And a piece of code that make use of it

try (SqlSession session = sqlSessionFactory.openSession(TransactionIsolationLevel.REPEATABLE_READ)) {
 TestMapper mapper = session.getMapper(TestMapper.class);
 Test res = mapper.selectOne(1L);
 session.commit();
}

So as you may guess the mapper interface is implemented by MyBatis with the help of provided mapper xml file. See MyBatis3 Getting started.