spring data jpa 参数为null查询所有，否则根据参数查询

 分页结果集封装

public class PageResult<T> {
    private long total;//总条数
    private Integer totalPage;//总页数
    private List<T> list;

    public PageResult() {
    }

    public PageResult(long total, List<T> list) {
        this.total = total;
        this.list = list;
    }

    public PageResult(long total, Integer totalPage, List<T> list) {
        this.total = total;
        this.totalPage = totalPage;
        this.list = list;
    }

    public long getTotal() {
        return total;
    }

    public void setTotal(long total) {
        this.total = total;
    }

    public Integer getTotalPage() {
        return totalPage;
    }

    public void setTotalPage(Integer totalPage) {
        this.totalPage = totalPage;
    }

    public List<T> getList() {
        return list;
    }

    public void setList(List<T> list) {
        this.list = list;
    }
}

　　

@RequestMapping(value = "/list",method = RequestMethod.POST)
public Result getBrandList(@RequestBody Map<String,String> map ){
    String search = map.get("search");
    String pageNum = map.get("pageNum");
    String pageSize = map.get("pageSize");
    if (StringUtils.isEmpty(pageNum)){
        pageNum="1";
    }
    if (StringUtils.isEmpty(pageSize)){
        pageSize="5";
    }
    PageResult<Brand> list=brandService.getBrandList(search,Integer.valueOf(pageNum),Integer.valueOf(pageSize));
    return  ResultUtil.success(list);
}

 PageResult<Brand> getBrandList(String search, Integer pageNum, Integer pageSize);

@Autowired
    private BrandDao brandDao;

    @Override
    public PageResult<Brand> getBrandList(String search, Integer pageNum, Integer pageSize) {
        Specification<Brand> specification=new Specification<Brand>() {

            //select * from tb_brand where name like?  limit 0,10;
            @Override
            public Predicate toPredicate(Root<Brand> root, CriteriaQuery<?> criteriaQuery, CriteriaBuilder criteriaBuilder) {
                Path<Object> name = root.get("name");
                List<Predicate> predicateList = new ArrayList<>();
                if (search!=null){
                    Predicate  p1 = criteriaBuilder.like(name.as(String.class),"%"+search+"%");
                    predicateList.add(p1);
                    return criteriaQuery.where(p1).getRestriction();
                }
                Predicate[] pre = new Predicate[predicateList.size()];
                return criteriaQuery.where(predicateList.toArray(pre)).getRestriction();
            }
        };

        Pageable pageable=new PageRequest(pageNum-1,pageSize);
        Page<Brand> page=brandDao.findAll(specification,pageable);
        List<Brand> list = page.getContent();//数据
        int totalPages = page.getTotalPages();//总页数
        long total = page.getTotalElements();//总条数

        return new PageResult<>(total,totalPages,list);
    }

　　

public interface BrandDao extends JpaRepository<Brand,Long>, JpaSpecificationExecutor<Brand> {

}