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An alternative API for filtering data with Spring MVC and Spring Data JPA. This library provides a custom HandlerMethodArgumentResolver that transforms HTTP parameters into a Specification object ready to use with Spring Data repositories.

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/**
 * Copyright 2014-2022 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package net.kaczmarzyk.spring.data.jpa.domain;

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

import javax.persistence.criteria.CriteriaBuilder;
import javax.persistence.criteria.CriteriaQuery;
import javax.persistence.criteria.Predicate;
import javax.persistence.criteria.Root;
import java.util.*;

import static java.util.stream.Collectors.toList;

/**
 * Helper for easier joining lists of specs with {@code AND} operator
 *
 * @author Tomasz Kaczmarzyk
 */
public class Conjunction implements Specification, FakeSpecWrapper {

	private static final long serialVersionUID = 1L;

	private Collection> innerSpecs;

	/**
	 * In case of paged search, method {@link #toPredicate(Root, CriteriaQuery, CriteriaBuilder)}
	 * will be executed on the same object in two different contexts.
	 *
	 * The first time during standard search.
	 * The second time during count(*) query which is executed for paging purposes.
	 *
	 * Fakes should be initialized in both.
	 */
	private Set> queriesWithInitializedFakes = new HashSet<>();

	@SafeVarargs
	public Conjunction(Specification... innerSpecs) {
		this(Arrays.asList(innerSpecs));
	}

	public Conjunction(Collection> innerSpecs) {
		this.innerSpecs = innerSpecs;
	}

	@SuppressWarnings("unchecked")
	@Override
	public void initializeFakes(Root root, CriteriaQuery query, CriteriaBuilder cb) {
		if (!queriesWithInitializedFakes.contains(query)) {
			for (Specification spec : innerSpecs) {
				if (spec instanceof FakeSpecWrapper) {
					((FakeSpecWrapper) spec).initializeFakes(root, query, cb);
				}
				if (spec instanceof Fake) {
					spec.toPredicate(root, query, cb);
					continue;
				}
			}
		}
		queriesWithInitializedFakes.add(query);
	}

	@Override
	public Predicate toPredicate(Root root, CriteriaQuery query, CriteriaBuilder cb) {
    	initializeFakes(root, query, cb);

		return cb.and(
				innerSpecs.stream()
						.filter(spec -> !(spec instanceof Fake))
						.map(spec -> spec.toPredicate(root, query, cb))
						.filter(Objects::nonNull)
						.collect(toList()).toArray(new Predicate[]{})
		);
	}

	@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + ((innerSpecs == null) ? 0 : innerSpecs.hashCode());
		return result;
	}

	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (obj == null)
			return false;
		if (getClass() != obj.getClass())
			return false;
		Conjunction other = (Conjunction) obj;
		if (innerSpecs == null) {
			if (other.innerSpecs != null)
				return false;
		} else if (!innerSpecs.equals(other.innerSpecs))
			return false;
		return true;
	}

	@Override
	public String toString() {
		return "Conjunction [innerSpecs=" + innerSpecs + "]";
	}
}