How to use

readPage

method

in

org.springframework.data.jpa.repository.support.SimpleJpaRepository

/**
 * Reads the given {@link TypedQuery} into a {@link Page} applying the given {@link Pageable} and
 * {@link Specification}.
 *
 * @param query must not be {@literal null}.
 * @param spec can be {@literal null}.
 * @param pageable must not be {@literal null}.
 * @return
 * @deprecated use {@link #readPage(TypedQuery, Class, Pageable, Specification)} instead
 */
@Deprecated
protected Page<T> readPage(TypedQuery<T> query, Pageable pageable, @Nullable Specification<T> spec) {
  return readPage(query, getDomainClass(), pageable, spec);
}

@Override
public Page<T> findAll(@Nullable Specification<T> spec, Pageable pageable) {
  TypedQuery<T> query = getQuery(spec, pageable);
  return isUnpaged(pageable) ? new PageImpl<T>(query.getResultList())
      : readPage(query, getDomainClass(), pageable, spec);
}

@Override
public <S extends T> Page<S> findAll(Example<S> example, Pageable pageable) {
  ExampleSpecification<S> spec = new ExampleSpecification<>(example);
  Class<S> probeType = example.getProbeType();
  TypedQuery<S> query = getQuery(new ExampleSpecification<>(example), probeType, pageable);
  return isUnpaged(pageable) ? new PageImpl<>(query.getResultList()) : readPage(query, probeType, pageable, spec);
}

/**
 * Reads the given {@link TypedQuery} into a {@link Page} applying the given {@link Pageable} and
 * {@link Specification}.
 *
 * @param query must not be {@literal null}.
 * @param spec can be {@literal null}.
 * @param pageable must not be {@literal null}.
 * @return
 * @deprecated use {@link #readPage(TypedQuery, Class, Pageable, Specification)} instead
 */
@Deprecated
protected Page<T> readPage(TypedQuery<T> query, Pageable pageable, @Nullable Specification<T> spec) {
  return readPage(query, getDomainClass(), pageable, spec);
}

public Page<T> findAll(@Nullable Specification<T> spec, Pageable pageable) {
  TypedQuery<T> query = getQuery(spec, pageable);
  return isUnpaged(pageable) ? new PageImpl<T>(query.getResultList())
      : readPage(query, getDomainClass(), pageable, spec);
}

@Override
@Deprecated
protected Page<T> readPage(TypedQuery<T> query, Pageable pageable, Specification<T> spec) {
  Page<T> page = super.readPage(query, pageable, spec);
  return pageable == null ? new WrappedPageImpl<T>(page.getContent())
    : new WrappedPageImpl<T>(page.getContent(), pageable, page.getTotalElements());
}

@Override
public <S extends T> Page<S> findAll(Example<S> example, Pageable pageable) {
  ExampleSpecification<S> spec = new ExampleSpecification<>(example);
  Class<S> probeType = example.getProbeType();
  TypedQuery<S> query = getQuery(new ExampleSpecification<>(example), probeType, pageable);
  return isUnpaged(pageable) ? new PageImpl<>(query.getResultList()) : readPage(query, probeType, pageable, spec);
}

@Override
protected <S extends E> Page<S> readPage(TypedQuery<S> query, Class<S> domainClass, Pageable pageable, @Nullable Specification<S> spec) {
  super.readPage(query, domainClass, pageable, spec);
  //首先查询满足条件的记录数
  Long total = executeCountQuery(getCountQuery(spec, domainClass));
  //检查查询的数据是否超出总记录数，如果超出总记录数，默认查询最后一页，并修改pageable参数
  if (pageable.getOffset() >= total) {
    int pagenum = 0;
    //由于页号是从0开始，所以需要考虑整除的情况
    if (total % pageable.getPageSize() == 0) {
      pagenum = Ints.checkedCast(Math.max(total / pageable.getPageSize() - 1, 0));
    } else {
      pagenum = Ints.checkedCast(total / pageable.getPageSize());
    }
    log.info("总记录数为 {} ，当前页号为 {} 。超出分页查询范围，只返回最后一页（第{}页）的数据。", total, pageable.getPageNumber(), pagenum);
    pageable = PageRequest.of(pagenum, pageable.getPageSize());
  }
  //设置分页查询参数
  query.setFirstResult(Long.valueOf(pageable.getOffset()).intValue());
  query.setMaxResults(pageable.getPageSize());
  List<S> content = total > pageable.getOffset() ? query.getResultList() : Collections.<S>emptyList();
  return new PageImpl<S>(content, pageable, total);
}

@Override
protected <S extends T> Page<S> readPage(TypedQuery<S> query, Class<S> domainClass, Pageable pageable,
                     Specification<S> spec) {
  Page<S> page = super.readPage(query, domainClass, pageable, spec);
  return pageable == null ? new WrappedPageImpl<S>(page.getContent())
    : new WrappedPageImpl<S>(page.getContent(), pageable, page.getTotalElements());
}