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A JAP Query By Specification framework.

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package com.github.wenhao.jpa.specification;

import javax.persistence.criteria.CriteriaBuilder;
import javax.persistence.criteria.CriteriaQuery;
import javax.persistence.criteria.From;
import javax.persistence.criteria.Predicate;
import javax.persistence.criteria.Root;

public class EqualSpecification extends AbstractSpecification {
    private final String property;
    private final Object[] values;

    public EqualSpecification(String property, Object... values) {
        this.property = property;
        this.values = values;
    }

    @Override
    public Predicate toPredicate(Root root, CriteriaQuery query, CriteriaBuilder cb) {
        From from = getRoot(property, root);
        String field = getProperty(property);
        if (values == null) {
            return cb.isNull(from.get(field));
        }
        if (values.length == 1) {
            return getPredicate(from, cb, values[0], field);
        }

        Predicate[] predicates = new Predicate[values.length];
        for (int i = 0; i < values.length; i++) {
            predicates[i] = getPredicate(root, cb, values[i], field);
        }
        return cb.or(predicates);
    }

    private Predicate getPredicate(From root, CriteriaBuilder cb, Object value, String field) {
        return value == null ? cb.isNull(root.get(field)) : cb.equal(root.get(field), value);
    }
}