Further study of Spring Data JPA - 深入学习篇（二）

https://github.com/icnws/spring-data-jpa-demo

http://www.spring4all.com

-----------------------------------------------------------这是一条性感的分割线-------------------------------------------------------------------------

在我上一篇文章已经对Spring Data JPA做过了大致上的介绍和分析，Further study of Spring Data JPA - 深入学习篇（一）我们从这篇文章接着对其进行深究，Spring Data JPA为我们提供了JpaSpecificationExecutor接口，只要简单实现toPredicate方法就可以实现复杂的查询，首先我们先看看对JpaSpecificationExecutor接口进行分析：

JpaSpecificationExecutor源码

public interface JpaSpecificationExecutor<T> {

Optional<T> findOne(@Nullable Specification<T> spec);
List<T> findAll(@Nullable Specification<T> spec);
Page<T> findAll(@Nullable Specification<T> spec, Pageable pageable);
List<T> findAll(@Nullable Specification<T> spec, Sort sort);
long count(@Nullable Specification<T> spec);
}

Spring Data JPA通过创建方法名做查询，只能做简单的查询，那如果我们需要做一些复杂查询呢？多见见分页和排序怎么办，这里Spring Data JPA为我们提供了其中JpaSpecificationExecutor接口，该接口提供了对JPA Criteria查询（动态查询）的支持，只要简单实现toPredicate方法就可以实现复杂的查询，该接口包含了常用的单个对象、查询数据集合、查询分页数据集合、查询带排序参数的数据集合、查询数据大小、这些都是产业的数据结果集，因此不需要做其他定义即可直接使用，另外，Specification是我们需要传的参数，它也是一个接口：

public interface Specification<T> extends Serializable {
long serialVersionUID = 1L;

static <T> Specification<T> not(Specification<T> spec) {
return Specifications.negated(spec);
}

static <T> Specification<T> where(Specification<T> spec) {
return Specifications.where(spec);
}

default Specification<T> and(Specification<T> other) {
return Specifications.composed(this, other, CompositionType.AND);
}

default Specification<T> or(Specification<T> other) {
return Specifications.composed(this, other, CompositionType.OR);
}

//提供了toPredicate方法，我们只要按照JPA 2.0 criteria api写好查询条件就可以了
@Nullable
Predicate toPredicate(Root<T> var1, CriteriaQuery<?> var2, CriteriaBuilder var3);
}

定义MyCustomerRepository,并继承于JpaSpecificationExecutor 接口：

@Repository
public interface MyCustomerRepository extends CrudRepository<Customer,Long>, JpaSpecificationExecutor {

}

MyCustomerService：

@Service
public class MyCustomerService {

@Autowired
MyCustomerRepository repository;

/**
* 获取分页列表数据
* @param customer  实体对象
* @return  返回分页数据
*/
public Page<Customer> getPageList(Customer customer){

PageRequest pageable = PageRequest.of(1,10,Sort.Direction.ASC);

//使用Specification复杂查询
return repository.findAll(new Specification() {
@Override
public Predicate toPredicate(Root root, CriteriaQuery cq, CriteriaBuilder cb) {
List<Predicate> predicates = new ArrayList<>();
if (customer.getId()!=null){
predicates.add(cb.equal(root.get("id").as(Long.class),customer.getId()));
}
if (customer.getFirstName()!=null){
predicates.add(cb.like(root.get("firstName").as(String.class),customer.getFirstName()));
}
if (customer.getFirstName()!=null){
predicates.add(cb.like(root.get("lastName").as(String.class),customer.getLastName()));
}
// todo 具体的业务逻辑实现
//                return (Predicate) repository.findAll();
}

},pageable);
}
}

多条件查询

/**
* 多条件查询方式一
* 需求：根据客户firstName和lastName以及年龄条件查询
*/
public void test1(){
Specification specification = new Specification() {
@Override
public Predicate toPredicate(Root root, CriteriaQuery cq, CriteriaBuilder cb) {
Predicate predicateCustomerFirstName = cb.equal(root.get("firstNane"),"Bauer");
Predicate predicateCustomerLastName = cb.equal(root.get("lastName"),"Mdessler");
Predicate predicateCustomerAge = cb.ge(root.get("age"),20);

List<Predicate> list = new ArrayList<>();
list.add(predicateCustomerFirstName);
list.add(predicateCustomerLastName);
list.add(predicateCustomerAge);

Predicate[] arr = new Predicate[list.size()];
return cb.and(list.toArray(arr));
}
};
List<Customer> customerList = this.myCustomerRepository.findAll(specification);
for (Customer customer:customerList){
System.out.println(customer);
}
}

/**
* 多条件查询方式二
* 需求：根据客户firstName或年龄或id为10的查询
*/
public void test2(){

Specification specification = new Specification() {
@Override
public Predicate toPredicate(Root root, CriteriaQuery cq, CriteriaBuilder cb) {
return cb.or(cb.and(cb.equal(root.get("firstName"),"Tony"),
cb.equal(root.get("id"),5),
cb.ge(root.get("age"),25)));
}
};
List<Customer> customerList = this.myCustomerRepository.findAll(specification);
for(Customer customer:customerList){
System.out.println(customer);
}
}

MyCustomerController添加测试方法

• 初始化

@Autowired
MyCustomerRepository repository;

• 单一条件查询

/**
* 单一查询
*/
@RequestMapping("/spec1")
public void specificationQuery1(){
Specification<Customer> spec = SpecificationFactory.containsLike("lastName","Dessler");
Pageable pageable = PageRequest.of(0,5, Sort.Direction.ASC,"id");

Page<Customer> page = repository.findAll(spec, pageable);
System.out.println(page);
System.out.println(page.getTotalElements());
System.out.println(page.getTotalPages());
for (Customer customer:page.getContent()){
System.out.println(customer.toString());
}
}

• 复合条件查询

/**
* 复合条件查询
*/
@RequestMapping(value = "/spec2")
public void specificationQuery2(){
Specification<Customer> spec = Specification
.where(SpecificationFactory.containsLike("firstName","To"))
.or(SpecificationFactory.containsLike("lastName","Dess"));

Pageable pageable =  PageRequest.of(0,5,Sort.Direction.DESC,"id");

Page<Customer> page = repository.findAll(spec, pageable);
System.out.println(page);
System.out.println(page.getTotalPages());
System.out.println(page.getTotalElements());
for (Customer customer:page.getContent()){
System.out.println(customer.toString());
}
}

至此，使用Specification通过Criteria API进行查询，获得查询的结果集。相较于@Query方式的查询定义，更人性化和方便操作，后面在对Criteria API的使用进一步深入，进一步了解他的底层原理和实现。