Spring Data JPA(2)--利用PagingAndSortingRespository实现分页和排序

通过查看PagingAndSortingRepository接口源码,我们可以看到有两个方法来实现功能:

/**
* Returns all entities sorted by the given options.
*
* @param sort
* @return all entities sorted by the given options
*/
Iterable<T> findAll(Sort sort);//升序或者降序的查询所有

/**
* Returns a {@link Page} of entities meeting the paging restriction provided in the {@code Pageable} object.
*
* @param pageable
* @return a page of entities
*/
Page<T> findAll(Pageable pageable);//分页查询,传入Pageable对象,返回一个Page对象

下面通过实例来说明如何实现分页和排序的功能,并了解Sort对象,Pageable对象,Page对象如何声明实现.

1.Student实体类

@Entity
public class Student {
private int sno;
private String sname;
private int sage;
@Override
public String toString() {
return "Student [sno=" + sno + ", sname=" + sname + ", sage=" + sage
+ "]";
}
@GeneratedValue
@Id
public int getSno() {
return sno;
}

getter,setter...

2.创建一个接口,继承PagingAndSortingRepository

public interface StudentPagingAndSortingRepository extends PagingAndSortingRepository<Student, Integer>{

}

3.测试类进行单元测试,代码

public class StudentPagingAndSortingRepositoryTest {
private ApplicationContext ctx = null;
private StudentPagingAndSortingRepository studentPagingAndSortingRepository = null;
@Before
public void setUp(){
ctx = new ClassPathXmlApplicationContext("beans.xml");
studentPagingAndSortingRepository = ctx.getBean(StudentPagingAndSortingRepository.class);
System.out.println("setup");
}
@After
public void tearDown(){
ctx = null;
System.out.println("teardown");
}
//PagingAndSortingRepository
//分页
@Test
public void testPage(){
System.out.println("start");
//PageRequest(page,size)  page从index0开始
Pageable pageable = new PageRequest(0,2);
Page<Student> page = studentPagingAndSortingRepository.findAll(pageable);
System.out.println("查询的总页数:"+page.getTotalPages());
System.out.println("查询的记录数:"+page.getTotalElements());
System.out.println("查询当前的第几页:"+(page.getNumber()+1));
System.out.println("查询当前页面的集合:"+page.getContent());
System.out.println("查询当前页面的记录数:"+page.getNumberOfElements());
System.out.println("started");
}
//分页加排序
@Test
public void testPageAndSort(){
System.out.println("start");
Order order = new Order(Direction.ASC,"sage");
Sort sort = new Sort(order);
Pageable pageable = new PageRequest(0,2,sort);
Page<Student> page = studentPagingAndSortingRepository.findAll(pageable);
System.out.println("查询的总页数:"+page.getTotalPages());
System.out.println("查询的记录数:"+page.getTotalElements());
System.out.println("查询当前的第几页:"+(page.getNumber()+1));
System.out.println("查询当前页面的集合:"+page.getContent());
System.out.println("查询当前页面的记录数:"+page.getNumberOfElements());
System.out.println("started");
}
}

这样就实现了分页与排序的功能.

我们回头看看实现的过程:

Pageable接口的实现方法,通过源码发现,它有两个子类PageRequest和QPageRequest,我们选用常用的PageRequest来实现它.

PageRequest继承了AbstractPageRequest类,它提供了
c224
一系列的方法,常用的有:

/**
* Creates a new {@link PageRequest}. Pages are zero indexed, thus providing 0 for {@code page} will return the first
* page.
*
* @param page zero-based page index.
* @param size the size of the page to be returned.
*/
public PageRequest(int page, int size) {
this(page, size, null);//从哪一页开始(从0开始),页面容量
}

/**
* Creates a new {@link PageRequest} with sort parameters applied.
*
* @param page zero-based page index.
* @param size the size of the page to be returned.
* @param direction the direction of the {@link Sort} to be specified, can be {@literal null}.
* @param properties the properties to sort by, must not be {@literal null} or empty.
*/
public PageRequest(int page, int size, Direction direction, String... properties) {
this(page, size, new Sort(direction, properties));//开始页面,页面容量,排序方向,按照什么字段排序
}

/**
* Creates a new {@link PageRequest} with sort parameters applied.
*
* @param page zero-based page index.
* @param size the size of the page to be returned.
* @param sort can be {@literal null}.
*/
public PageRequest(int page, int size, Sort sort) {
super(page, size);
this.sort = sort;//开始页面,页面容量,排序方向
}

/*
* (non-Javadoc)
* @see org.springframework.data.domain.Pageable#getSort()
*/
public Sort getSort() {
return sort;
}

/*
* (non-Javadoc)
* @see org.springframework.data.domain.Pageable#next()
*/
public Pageable next() {
return new PageRequest(getPageNumber() + 1, getPageSize(), getSort());//下一页
}

/*
* (non-Javadoc)
* @see org.springframework.data.domain.AbstractPageRequest#previous()
*/
public PageRequest previous() {
return getPageNumber() == 0 ? this : new PageRequest(getPageNumber() - 1, getPageSize(), getSort());//是否存在页面
}

/*
* (non-Javadoc)
* @see org.springframework.data.domain.Pageable#first()
*/
public Pageable first() {
return new PageRequest(0, getPageSize(), getSort());//第一页
}

Sort类源码:

/**
* Creates a new {@link Sort} instance using the given {@link Order}s.
*
* @param orders must not be {@literal null}.
*/
public Sort(Order... orders) {
this(Arrays.asList(orders));//Sort的构建需要先实例化Order对象,Order order = new Order(Direction.ASC,"sage");ASC升序,DESC降序
}