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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 2014-2020 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 java.util.Arrays;
import java.util.Collection;

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

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

/**
 * 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;
	private boolean fakesInitialized = false;
    
    @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 (!fakesInitialized) {
	    	for (Specification spec : innerSpecs) {
	    		if (spec instanceof FakeSpecWrapper) {
	        		((FakeSpecWrapper) spec).initializeFakes(root, query, cb);
	        	}
	        	if (spec instanceof Fake) {
	        		spec.toPredicate(root, query, cb);
	        		continue;
	        	}
	    	}
    	}
    	fakesInitialized = true;
    }
    
	@Override
    public Predicate toPredicate(Root root, CriteriaQuery query, CriteriaBuilder cb) {
    	initializeFakes(root, query, cb);
        Specification combinedSpecs = null;
        for (Specification spec : innerSpecs) {
        	if (spec instanceof Fake) {
        		continue;
        	}
            if (combinedSpecs == null) {
                combinedSpecs = Specification.where(spec);
            } else {
                combinedSpecs = combinedSpecs.and(spec);
            }
        }
        return combinedSpecs == null ? null : combinedSpecs.toPredicate(root, query, cb);
    }

    @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 + "]";
	}
}