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
	}