Spring Boot JPA分页查询

1、UML类图

2、接口方法

/*
 * Copyright 2008-2020 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.springframework.data.repository;

import org.springframework.data.domain.Page;
import org.springframework.data.domain.Pageable;
import org.springframework.data.domain.Sort;

/**
 * Extension of {@link CrudRepository} to provide additional methods to retrieve entities using the pagination and
 * sorting abstraction.
 *
 * @author Oliver Gierke
 * @see Sort
 * @see Pageable
 * @see Page
 */
@NoRepositoryBean
public interface PagingAndSortingRepository<T, ID> extends CrudRepository<T, ID> {

  /**
   * Returns all entities sorted by the given options.
   *
   * @param sort
   * @return all entities sorted by the given options
   */
  Iterable<T> findAll(Sort sort);

  /**
   * 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);
}

（1）根据排序取所有对象的集合。
（2）根据分页和排序进行查询，并用Page对象封装。Pageable对象包含分页和Sort对象。

3、接口实现

/*
   * (non-Javadoc)
   * @see org.springframework.data.jpa.repository.JpaRepository#findAll(org.springframework.data.domain.Sort)
   */
  @Override
  public List<T> findAll(Sort sort) {
    return getQuery(null, sort).getResultList();
  }

  /*
   * (non-Javadoc)
   * @see org.springframework.data.repository.PagingAndSortingRepository#findAll(org.springframework.data.domain.Pageable)
   */
  @Override
  public Page<T> findAll(Pageable pageable) {

    if (isUnpaged(pageable)) {
      return new PageImpl<T>(findAll());
    }

    return findAll((Specification<T>) null, pageable);
  }

4、使用示例

4.1 继承PagingAndSortingRepository

/**
 * 用户DAO接口层
 * @author zhuhuix
 * @date 2020-04-03
 */
public interface UserRepository extends PagingAndSortingRepository<User,Long>

4.2 测试

@Test
    void test4(){
        UserRepository userRepository = SpringContextHolder.getBean(UserRepository.class);
       Page<User> page1= userRepository.findAll( PageRequest.of(0,10));
       page1.forEach(user -> System.out.println(user.toString()));
       Page<User> page2= userRepository.findAll( PageRequest.of(0,10,Sort.by("id")));
       page2.forEach(user -> System.out.println(user.toString()));
    }

结果如下：

4.2 注意点：PageRequest

代替分页功能的方法是不要new PageRequest，而是直接调用PageRequest.of这个方法，并根据你的有需求选择参数
/**
* Creates a new {@link PageRequest} with sort parameters applied.
*
* @param page zero-based page index, must not be negative.
* @param size the size of the page to be returned, must be greater than 0.
* @param sort must not be {@literal null}, use {@link Sort#unsorted()} instead.
*/
protected PageRequest(int page, int size, Sort sort) {

  super(page, size);

  Assert.notNull(sort, "Sort must not be null!");

  this.sort = sort;
}

/**
 * Creates a new unsorted {@link PageRequest}.
 *
 * @param page zero-based page index, must not be negative.
 * @param size the size of the page to be returned, must be greater than 0.
 * @since 2.0
 */
public static PageRequest of(int page, int size) {
  return of(page, size, Sort.unsorted());
}

/**
 * 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 must not be {@literal null}, use {@link Sort#unsorted()} instead.
 * @since 2.0
 */
public static PageRequest of(int page, int size, Sort sort) {
  return new PageRequest(page, size, sort);
}