Spring Data JPA - JpaRepository 中的自定义排序

Question

I am using Spring Data JPA with Spring Data REST and i have created a JpaRepository for my Thing entity.

@Repository
public interface ThingRepository extends JpaRepository<Thing, Long> {

    @RestResource(path = "findByName", rel = "findByName")
    Page findByName(@Param("name") String name, Pageable page);

}

I want to apply sorting. I want to sort the Thing List based on a custom rating algorithm.

List<Thing> sortByRating(List<Thing> things){

    // custom logic

    return things;
};

I would like if possible to use a custom function in order to sort the results. What is the best approach to this kind of thing in Spring JPA? How can i make my Repository use my function to sort the result set?

Answer 1

Spring Data offers basic sorting as seen here . You can also annotate your query with @Query and use order by , but I believe what you need is a more complex sorting logic.

If youre using Java 8 you can use its features to sort your list, this article shows good examples of that, it takes a bit more work but seems like what you're after. Note that in order to convert from stream to list you have to include .collect(Collectors.toList()); at the end of the stream .

Example(taken from the article):

employees.stream().sorted((Employee e1, Employee e2) -> e1.getHireDate()
                        .compareTo(e2.getHireDate())).collect(Collectors.toList());

Edit : I didn't notice you were using pagination. I had a similar problem where I had to do something with the page contents before returning the Page object, so I ended up creating an extension of the PageImpl<T> class:

public class PageImplBean<T> extends PageImpl<T> {

    private static final long serialVersionUID = 1L;
    private int number;
    private int size;
    private int totalPages;
    private int numberOfElements;
    private long totalElements;
    private boolean previousPage;
    private boolean first;
    private boolean nextPage;
    private boolean last;
    private List<T> content;
    @JsonIgnore
    private Sort sort;

    public PageImplBean() {
        super(new ArrayList<T>());
    }

    public PageImplBean(Page pagina){
        super(new ArrayList<T>());
        this.number = pagina.getNumber();
        this.size = pagina.getSize();
        this.totalPages = pagina.getTotalPages();
        this.numberOfElements = pagina.getNumberOfElements();
        this.totalElements = pagina.getTotalElements();
        this.previousPage = pagina.hasPrevious();
        this.first = pagina.isFirst();
        this.nextPage = pagina.hasNext();
        this.last = pagina.isLast();
    }

    public int getNumber() {
        return number;
    }

    public void setNumber(int number) {
        this.number = number;
    }

    public int getSize() {
        return size;
    }

    public void setSize(int size) {
        this.size = size;
    }

    public int getTotalPages() {
        return totalPages;
    }

    public void setTotalPages(int totalPages) {
        this.totalPages = totalPages;
    }

    public int getNumberOfElements() {
        return numberOfElements;
    }

    public void setNumberOfElements(int numberOfElements) {
        this.numberOfElements = numberOfElements;
    }

    public long getTotalElements() {
        return totalElements;
    }

    public void setTotalElements(long totalElements) {
        this.totalElements = totalElements;
    }

    public boolean isPreviousPage() {
        return previousPage;
    }

    public void setPreviousPage(boolean previousPage) {
        this.previousPage = previousPage;
    }

    public boolean isFirst() {
        return first;
    }

    public void setFirst(boolean first) {
        this.first = first;
    }

    public boolean isNextPage() {
        return nextPage;
    }

    public void setNextPage(boolean nextPage) {
        this.nextPage = nextPage;
    }

    public boolean isLast() {
        return last;
    }

    public void setLast(boolean last) {
        this.last = last;
    }

    public List<T> getContent() {
        return content;
    }

    public void setContent(List<T> content) {
        this.content = content;
    }

    public Sort getSort() {
        return sort;
    }

    public void setSort(Sort sort) {
        this.sort = sort;
    }

    public PageImpl<T> pageImpl() {
        return new PageImpl<T>(getContent(), new PageRequest(getNumber(),
                getSize(), getSort()), getTotalElements());
    }
}

What's important here in your case is the setContent method which doesnt exist in the base class. You can use that with your sorting method:

PageImplBean<Thing> page = //call your rest repository
List<Thing> pageContent = page.getContent();
page.setContent(sortByRating(pageContent));

Answer 2

You can customize your object page(Pageable). If you get data of request:

public PageRequest customSort(Args...) {
    String[] newParams = {"newParam"};
    Sort sort = page.getSort();
    Sort.Order dataSort =
        sort.iterator().next();
    Sort newSort = Sort.by(dataSort.getDirection(), newParams);
    return PageRequest.of(page.getPageNumber(), this.getPageSize(), newSort);
}

SQL Before:

order by oldParam ASC/DESC;

SQL After:

order by newParam ASC/DESC;