Specification implementation

Specifications offers some glue-code methods to chain and combine Specifications. Thus extending your data access layer is just a matter of creating new Specification implementations and combining them with ones already existing.

ExpenseSpecification.java

package resources.specification;

import java.util.ArrayList;
import java.util.List;

import javax.persistence.criteria.CriteriaBuilder;
import javax.persistence.criteria.CriteriaQuery;
import javax.persistence.criteria.Predicate;
import javax.persistence.criteria.Root;
import javax.ws.rs.QueryParam;

import org.springframework.data.jpa.domain.Specification;

import com.google.common.base.Strings;

import entity.Expense;

public class ExpenseSpecification implements Specification<Expense> {

    private Long id;
    @QueryParam("comment")
    private String comment;
    @QueryParam("totalAmount")
    private Integer totalAmount;
    @QueryParam("taxAmount")
    private Integer taxAmount;

    @Override
    public Predicate toPredicate(Root<Expense> root, CriteriaQuery<?> query,
            CriteriaBuilder cb) {
        List<Predicate> predicates = new ArrayList<Predicate>();
        if (!Strings.isNullOrEmpty(comment)) {
            predicates.add(cb.like(root.<String> get("comment"), "%" + comment
                    + "%"));
        }
        if (totalAmount != null) {
            predicates.add(cb.equal(root.<Integer> get("totalAmount"),
                    totalAmount));
        }
        if (taxAmount != null) {
            predicates
                    .add(cb.equal(root.<Integer> get("taxAmount"), taxAmount));
        }

        if (id != null) {
            predicates.add(cb.equal(root.<Long> get("id"), id));
        }
        if (predicates.isEmpty()) {
            return null;
        }

        return cb.and(predicates.toArray(new Predicate[0]));
    }

    public String getComment() {
        return comment;
    }

    public void setComment(String comment) {
        this.comment = comment;
    }

    public Integer getTotalAmount() {
        return totalAmount;
    }

    public void setTotalAmount(Integer totalAmount) {
        this.totalAmount = totalAmount;
    }

    public Integer getTaxAmount() {
        return taxAmount;
    }

    public void setTaxAmount(Integer taxAmount) {
        this.taxAmount = taxAmount;
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

}