SpringDataJpa基础篇3:分页与排序
1、SpringDataJpa中分页相关接口及类
1.1、Pageable接口
【Pageable接口源码】
public interface Pageable {
static Pageable unpaged() {
return Unpaged.INSTANCE;
}
default boolean isPaged() {
return true;
}
default boolean isUnpaged() {
return !isPaged();
}
int getPageNumber();
int getPageSize();
long getOffset();
Sort getSort();
default Sort getSortOr(Sort sort) {
Assert.notNull(sort, "Fallback Sort must not be null!");
return getSort().isSorted() ? getSort() : sort;
}
Pageable next();
Pageable previousOrFirst();
Pageable first();
boolean hasPrevious();
default Optional toOptional() {
return isUnpaged() ? Optional.empty() : Optional.of(this);
}
}
1.2、PageRequest类
PageRequest类是Pageable接口的实现类
import org.springframework.data.domain.Sort.Direction;
import org.springframework.lang.Nullable;
/**
* Basic Java Bean implementation of {@code Pageable}.
*上面一句话是说PageRequest是对Pageable接口的实现
*/
public class PageRequest extends AbstractPageRequest {
private static final long serialVersionUID = -4541509938956089562L;
//排序属性
private final Sort sort;
//@Deprecated表示该构造方法一句过期，不建议使用
@Deprecated
public PageRequest(int page, int size) {
this(page, size, Sort.unsorted());
}
//@Deprecated表示该构造方法一句过期，不建议使用
@Deprecated
public PageRequest(int page, int size, Direction direction, String... properties) {
this(page, size, Sort.by(direction, properties));
}
//@Deprecated表示该构造方法一句过期，不建议使用
@Deprecated
public PageRequest(int page, int size, Sort sort) {
super(page, size);
this.sort = sort;
}
/**
* Creates a new unsorted {@link PageRequest}.
*上面一句话表示创建一个新的未排序
* @param page zero-based page index 当前页，是从0开始.
* @param size the size of the page to be returned 每页多少条记录。
*/
public static PageRequest of(int page, int size) {
return of(page, size, Sort.unsorted());
}
/**
* Creates a new {@link PageRequest} with sort parameters applied.
*上面一句含义创建一个带排序参数的分页
* @param page zero-based page index 当前页，从第0页开始.
* @param size the size of the page to be returned.
* @param sort must not be {@literal null} 设置排序.
* @since 2.0
*/
public static PageRequest of(int page, int size, Sort sort) {
return new PageRequest(page, size, sort);
}
public static PageRequest of(int page, int size, Direction direction, String... properties) {
return of(page, size, Sort.by(direction, properties));
}
public Sort getSort() {
return sort;
}
//下一页
public Pageable next() {
return new PageRequest(getPageNumber() + 1, getPageSize(), getSort());
}
//上一页
public PageRequest previous() {
return getPageNumber() == 0 ? this : new PageRequest(getPageNumber() - 1, getPageSize(), getSort());
}
//第一页是从0开始
public Pageable first() {
return new PageRequest(0, getPageSize(), getSort());
}
@Override
public boolean equals(@Nullable Object obj) {
if (this == obj) {
return true;
}
if (!(obj instanceof PageRequest)) {
return false;
}
PageRequest that = (PageRequest) obj;
return super.equals(that) && this.sort.equals(that.sort);
}
@Override
public int hashCode() {
return 31 * super.hashCode() + sort.hashCode();
}
@Override
public String toString() {
return String.format("Page request [number: %d, size %d, sort: %s]", getPageNumber(), getPageSize(), sort);
}
}
1.3、Page接口
Page接口其实是SpringDataJpa分页结果的一个返回值类型而已。
import java.util.Collections;
import java.util.function.Function;
public interface Page extends Slice {
//创建一个空的Page对象
static Page empty() {
return empty(Pageable.unpaged());
}
//创建一个空的Page对象，且指定pageable分页参数
static Page empty(Pageable pageable) {
return new PageImpl<>(Collections.emptyList(), pageable, 0);
}
//返回总页数
int getTotalPages();
//返回元素的总数
long getTotalElements();
//
Page map(Function converter);
}
2、SpringDataJpa中排序相关接口及类
2.1、Sort类中的内部类Direction
其实在Sort类中有个类部类Direction，而Direction是一个枚举类型。
/**
* Enumeration for sort directions.
* Sort类中内部枚举类
*/
public static enum Direction {
//ASC表示升序，DESC表示降序
ASC, DESC;
/**
* Returns whether the direction is ascending.
* 返回一个升序
* @return
* @since 1.13
*/
public boolean isAscending() {
return this.equals(ASC);
}
/**
* Returns whether the direction is descending.
* 返回一个降序
* @return
* @since 1.13
*/
public boolean isDescending() {
return this.equals(DESC);
}
public static Direction fromString(String value) {
try {
return Direction.valueOf(value.toUpperCase(Locale.US));
} catch (Exception e) {
throw new IllegalArgumentException(String.format(
"Invalid value '%s' for orders given! Has to be either 'desc' or 'asc' (case insensitive).", value), e);
}
}
public static Optional fromOptionalString(String value) {
try {
return Optional.of(fromString(value));
} catch (IllegalArgumentException e) {
return Optional.empty();
}
}
} 2.2、Order类
Order类是Sort类的一个内部类
//sort类的一个内部类
public static class Order implements Serializable {
private static final long serialVersionUID = 1522511010900108987L;
private static final boolean DEFAULT_IGNORE_CASE = false;
private static final NullHandling DEFAULT_NULL_HANDLING = NullHandling.NATIVE;
private final Direction direction;
private final String property;
private final boolean ignoreCase;
private final NullHandling nullHandling;
public Order(@Nullable Direction direction, String property) {
this(direction, property, DEFAULT_IGNORE_CASE, DEFAULT_NULL_HANDLING);
}
public Order(@Nullable Direction direction, String property, NullHandling nullHandlingHint) {
this(direction, property, DEFAULT_IGNORE_CASE, nullHandlingHint);
}
@Deprecated
public Order(String property) {
this(DEFAULT_DIRECTION, property);
}
public static Order by(String property) {
return new Order(DEFAULT_DIRECTION, property);
}
public static Order asc(String property) {
return new Order(Direction.ASC, property, DEFAULT_NULL_HANDLING);
}
public static Order desc(String property) {
return new Order(Direction.DESC, property, DEFAULT_NULL_HANDLING);
}
private Order(@Nullable Direction direction, String property, boolean ignoreCase, NullHandling nullHandling) {
if (!StringUtils.hasText(property)) {
throw new IllegalArgumentException("Property must not null or empty!");
}
this.direction = direction == null ? DEFAULT_DIRECTION : direction;
this.property = property;
this.ignoreCase = ignoreCase;
this.nullHandling = nullHandling;
}
public Direction getDirection() {
return direction;
}
public String getProperty() {
return property;
}
public boolean isAscending() {
return this.direction.isAscending();
}
public boolean isDescending() {
return this.direction.isDescending();
}
public boolean isIgnoreCase() {
return ignoreCase;
}
public Order with(Direction direction) {
return new Order(direction, this.property, this.ignoreCase, this.nullHandling);
}
public Order withProperty(String property) {
return new Order(this.direction, property, this.ignoreCase, this.nullHandling);
}
public Sort withProperties(String... properties) {
return Sort.by(this.direction, properties);
}
public Order ignoreCase() {
return new Order(direction, property, true, nullHandling);
}
public Order with(NullHandling nullHandling) {
return new Order(direction, this.property, ignoreCase, nullHandling);
}
public Order nullsFirst() {
return with(NullHandling.NULLS_FIRST);
}
public Order nullsLast() {
return with(NullHandling.NULLS_LAST);
}
public Order nullsNative() {
return with(NullHandling.NATIVE);
}
public NullHandling getNullHandling() {
return nullHandling;
}
@Override
public int hashCode() {
int result = 17;
result = 31 * result + direction.hashCode();
result = 31 * result + property.hashCode();
result = 31 * result + (ignoreCase ? 1 : 0);
result = 31 * result + nullHandling.hashCode();
return result;
}
@Override
public boolean equals(@Nullable Object obj) {
if (this == obj) {
return true;
}
if (!(obj instanceof Order)) {
return false;
}
Order that = (Order) obj;
return this.direction.equals(that.direction) && this.property.equals(that.property)
&& this.ignoreCase == that.ignoreCase && this.nullHandling.equals(that.nullHandling);
}
@Override
public String toString() {
String result = String.format("%s: %s", property, direction);
if (!NullHandling.NATIVE.equals(nullHandling)) {
result += ", " + nullHandling;
}
if (ignoreCase) {
result += ", ignoring case";
}
return result;
}
}2.3、Sort排序类
【Sort类的部分源码】
public class Sort implements Streamable, Serializable {
private static final long serialVersionUID = 5737186511678863905L;
//
private static final Sort UNSORTED = Sort.by(new Order[0]);
public static final Direction DEFAULT_DIRECTION = Direction.ASC;
private final List orders;
//@Deprecated注解表示该方法已经过期，官方不推荐使用
@Deprecated
public Sort(Order... orders) {
this(Arrays.asList(orders));
}
//@Deprecated注解表示该方法已经过期，官方不推荐使用
@Deprecated
public Sort(List orders) {
Assert.notNull(orders, "Orders must not be null!");
this.orders = Collections.unmodifiableList(orders);
}
//@Deprecated注解表示该方法已经过期，官方不推荐使用
@Deprecated
public Sort(String... properties) {
this(DEFAULT_DIRECTION, properties);
}
public Sort(Direction direction, String... properties) {
this(direction, properties == null ? new ArrayList<>() : Arrays.asList(properties));
}
public Sort(Direction direction, List properties) {
if (properties == null || properties.isEmpty()) {
throw new IllegalArgumentException("You have to provide at least one property to sort by!");
}
this.orders = new ArrayList<>(properties.size());
for (String property : properties) {
this.orders.add(new Order(direction, property));
}
}
public static Sort by(String... properties) {
Assert.notNull(properties, "Properties must not be null!");
return properties.length == 0 ? Sort.unsorted() : new Sort(properties);
}
public static Sort by(List orders) {
Assert.notNull(orders, "Orders must not be null!");
return orders.isEmpty() ? Sort.unsorted() : new Sort(orders);
}
public static Sort by(Order... orders) {
Assert.notNull(orders, "Orders must not be null!");
return new Sort(orders);
}
public static Sort by(Direction direction, String... properties) {
Assert.notNull(direction, "Direction must not be null!");
Assert.notNull(properties, "Properties must not be null!");
Assert.isTrue(properties.length > 0, "At least one property must be given!");
return Sort.by(Arrays.stream(properties)//
.map(it -> new Order(direction, it))//
.collect(Collectors.toList()));
}
public static Sort unsorted() {
return UNSORTED;
}
public Sort descending() {
return withDirection(Direction.DESC);
}
public Sort ascending() {
return withDirection(Direction.ASC);
}
public boolean isSorted() {
return !orders.isEmpty();
}
public boolean isUnsorted() {
return !isSorted();
}
//.............................其他方法及内部类代码省略...................................
} 3、应用例子
3.1、实体类
@Entity
@Table(name="tb_label")
public class Label implements Serializable {
@Id
private String id;//
private String labelname;//标签名称
private String state;//状态
private Long count;//使用数量
private Long fans;//关注数
private String recommend;//是否推荐
public Label() {
}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getLabelname() {
return labelname;
}
public void setLabelname(String labelname) {
this.labelname = labelname;
}
public String getState() {
return state;
}
public void setState(String state) {
this.state = state;
}
public Long getCount() {
return count;
}
public void setCount(Long count) {
this.count = count;
}
public Long getFans() {
return fans;
}
public void setFans(Long fans) {
this.fans = fans;
}
public String getRecommend() {
return recommend;
}
public void setRecommend(String recommend) {
this.recommend = recommend;
}
@Override
public String toString() {
return "Label{" +
"id='" + id + '\'' +
", labelname='" + labelname + '\'' +
", state='" + state + '\'' +
", count=" + count +
", fans=" + fans +
", recommend='" + recommend + '\'' +
'}';
}
}3.2、DAO接口
/**
* JpaRepository基本增删改查操作
* JpaSpecificationExecutor用于复杂查询
*/
public interface LabelDao extends JpaRepository, JpaSpecificationExecutor 3.3、测试代码
@RunWith(SpringRunner.class)
@SpringBootTest(classes = BaseApplication.class)
public class JpaTest {
@Autowired
private LabelDao labelDao;
@Test
public void testPage(){
int pageNo=2;//第二页，注意在springdatajpa中分页是从第0页开始
int size=5;//每页5条
//PageRequest类是Pageable接口的实现类
PageRequest pageRequest = PageRequest.of(pageNo-1, size);
Page