SpringData JPA实现CRUD,分页与多参数排序

　　Spring Data 项目的目的是为了简化构建基于 Spring 框架应用的数据访问计数，包括非关系数据库、Map-Reduce 框架、云数据服务等等，SpringData JPA是简化创建 JPA 数据访问层和跨存储的持久层功能，通过一个接口的继承即可实现简单的CRUD。

　　数据库的连接与项目的构建不说了，可以参考：springboot实战SpringDataJPA。我采用的是eclipse构建的普通的springboot项目。

一、创建表与实体类映射

@Entity
@Table(name = "student")
public class Student implements Serializable {
@Id
// id自动生成
@GeneratedValue
@Column(name = "id")
private Long id;
@Column(name = "name")
private String name;
@Column(name = "clas")
private String clas;

@Column(name = "interest")
private String interest;

// 省略了getter(),setter()方法　

二、创建StudentMapper 继承JpaRepository<Student, Long>，第一个参数是实体，第二个参数是主键的类型

public interface StudentMapper extends JpaRepository<Student, Long> {
// int queryCount();
// 自定义的方法实现findAll
@Query(value = "select * from student where id < ?1", nativeQuery = true)
public List<Student> findAll(Long id);
}

三、Controller内的代码如下：

@Resource
private FirstPageService firstPageService;

@RequestMapping(value = "/", method = RequestMethod.GET)
@Fooish(tags = { "this_is_method" })
String home() {
return firstPageService.getString();
}

@RequestMapping(value = "/add", method = RequestMethod.GET)
String addStudent(Student student) {
return firstPageService.addStudent(student);
}

@RequestMapping(value = "/delete", method = RequestMethod.GET)
String deleteStudent(Long id) {
return firstPageService.deleteStudent(id);
}

@RequestMapping(value = "/update", method = RequestMethod.GET)
String updateStudent(Student student) {
return firstPageService.updateStudent(student);
}

@RequestMapping(value = "/list", method = RequestMethod.GET)
List<Student> listStudent() {
return firstPageService.listStudent();
}

// 采用的是自定义的方法
@RequestMapping(value = "/list2", method = RequestMethod.GET)
List<Student> list2Student(Long id) {
return firstPageService.nativeQuery(id);
}

// 分页查询
@RequestMapping(value = "/pageRequest", method = RequestMethod.GET)
List<Student> pageRequest() {

return firstPageService.pageRequest();
}

// 分页与排序查询
@RequestMapping(value = "/pageAndSortRequest", method = RequestMethod.GET)
List<Student> pageAndSortRequest() {

return firstPageService.pageAndSortRequest();
}

四、服务层firstPageService代码如下：

@Resource
private StudentMapper studentMapper;

public String getString() {

// return name;
// int a = studentMapper.queryCount();
// return a + "";
return "Hellow World!";
}

public String addStudent(Student stu) {
studentMapper.save(stu);
return "添加成功";
}

public String deleteStudent(Long id) {
studentMapper.delete(id);
return "删除成功";
}

public String updateStudent(Student stu) {
// 如果有就更新，没有就添加
studentMapper.save(stu);
return "更新成功";
}

public List<Student> listStudent() {

return studentMapper.findAll();
}

public List<Student> nativeQuery(Long id) {
return studentMapper.findAll(id);
}

　　　　// 分页查询
public List<Student> pageRequest() {
PageRequest pageRequest = new PageRequest(1, 3);
Page<Student> stuPage = studentMapper.findAll(pageRequest);
List<Student> stuList = stuPage.getContent();
return stuList;
}

　　　　// 分页与排序
public List<Student> pageAndSortRequest() {
Sort sort1 = new Sort(Sort.Direction.DESC, "id");
Sort sort2 = new Sort(Sort.Direction.ASC, "name");
// 把两个排序的条件取取与
Sort sort = sort1.and(sort2);
PageRequest pageRequest = new PageRequest(1, 2, sort);
Page<Student> stuPage = studentMapper.findAll(pageRequest);
List<Student> stuList = stuPage.getContent();
return stuList;
}

通过源码的继承与实现关系可以看出，JpaRepository接口继承了PagingAndSortingRepository,QueryByExampleExecutor两个接口，PagingAndSortingRepository接口继承了CrudRepository。CrudRepository中包含了简单的数据库增，删，改，查，这四个操作还是比较简单的，下面主要介绍分页与排序；

下面的是PagingAndSortingRepository的源码：

public interface PagingAndSortingRepository extends CrudRepository {

public abstract Iterable findAll(Sort sort);

public abstract Page findAll(Pageable pageable);
}

这个接口提供了分页与排序的基本方法，想要实现分页查询，要实现Pageable接口，而PageRequest是该接口的一个实现类，该类的构造方法：

// 单纯的分页
　　　　public PageRequest(int page, int size) {
this(page, size, null);
}

public transient PageRequest(int page, int size, Sort.Direction direction,
String properties[]) {
this(page, size, new Sort(direction, properties));
}
　　　　　　// 分页与排序，要实现Sort类
public PageRequest(int page, int size, Sort sort) {
super(page, size);
this.sort = sort;
}

五、按照id倒序，name顺序,查询第二页，每页显示两个的查询结果：