org.springframework.data.querydsl.SimpleEntityPathResolver.java Source code

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Here is the source code for org.springframework.data.querydsl.SimpleEntityPathResolver.java

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/*
 * Copyright 2011-2019 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
 *
 *      https://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 org.springframework.data.querydsl;

import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.util.Optional;

import org.springframework.util.Assert;
import org.springframework.util.ClassUtils;
import org.springframework.util.ReflectionUtils;

import com.querydsl.core.types.EntityPath;

/**
 * Simple implementation of {@link EntityPathResolver} to lookup a query class by reflection and using the static field
 * of the same type.
 *
 * @author Oliver Gierke
 * @author Jens Schauder
 */
public class SimpleEntityPathResolver implements EntityPathResolver {

    private static final String NO_CLASS_FOUND_TEMPLATE = "Did not find a query class %s for domain class %s!";
    private static final String NO_FIELD_FOUND_TEMPLATE = "Did not find a static field of the same type in %s!";

    public static final SimpleEntityPathResolver INSTANCE = new SimpleEntityPathResolver("");

    private final String querySuffix;

    /**
     * Creates a new {@link SimpleEntityPathResolver} with the given query package suffix.
     * 
     * @param querySuffix must not be {@literal null}.
     */
    public SimpleEntityPathResolver(String querySuffix) {

        Assert.notNull(querySuffix, "Query suffix must not be null!");

        this.querySuffix = querySuffix;
    }

    /**
     * Creates an {@link EntityPath} instance for the given domain class. Tries to lookup a class matching the naming
     * convention (prepend Q to the simple name of the class, same package) and find a static field of the same type in
     * it.
     *
     * @param domainClass
     * @return
     */
    @SuppressWarnings("unchecked")
    public <T> EntityPath<T> createPath(Class<T> domainClass) {

        String pathClassName = getQueryClassName(domainClass);

        try {

            Class<?> pathClass = ClassUtils.forName(pathClassName, domainClass.getClassLoader());

            return getStaticFieldOfType(pathClass)//
                    .map(it -> (EntityPath<T>) ReflectionUtils.getField(it, null))//
                    .orElseThrow(
                            () -> new IllegalStateException(String.format(NO_FIELD_FOUND_TEMPLATE, pathClass)));

        } catch (ClassNotFoundException e) {
            throw new IllegalArgumentException(
                    String.format(NO_CLASS_FOUND_TEMPLATE, pathClassName, domainClass.getName()), e);
        }
    }

    /**
     * Returns the first static field of the given type inside the given type.
     *
     * @param type
     * @return
     */
    private Optional<Field> getStaticFieldOfType(Class<?> type) {

        for (Field field : type.getDeclaredFields()) {

            boolean isStatic = Modifier.isStatic(field.getModifiers());
            boolean hasSameType = type.equals(field.getType());

            if (isStatic && hasSameType) {
                return Optional.of(field);
            }
        }

        Class<?> superclass = type.getSuperclass();
        return Object.class.equals(superclass) ? Optional.empty() : getStaticFieldOfType(superclass);
    }

    /**
     * Returns the name of the query class for the given domain class.
     *
     * @param domainClass
     * @return
     */
    private String getQueryClassName(Class<?> domainClass) {

        String simpleClassName = ClassUtils.getShortName(domainClass);
        String packageName = domainClass.getPackage().getName();

        return String.format("%s%s.Q%s%s", packageName, querySuffix, getClassBase(simpleClassName),
                domainClass.getSimpleName());
    }

    /**
     * Analyzes the short class name and potentially returns the outer class.
     *
     * @param shortName
     * @return
     */
    private String getClassBase(String shortName) {

        String[] parts = shortName.split("\\.");

        return parts.length < 2 ? "" : parts[0] + "_";
    }
}