org.springframework.data.util.AnnotationDetectionFieldCallback.java Source code

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Here is the source code for org.springframework.data.util.AnnotationDetectionFieldCallback.java

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/*
 * Copyright 2012-2019 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.util;

import java.lang.annotation.Annotation;
import java.lang.reflect.Field;

import org.springframework.core.annotation.AnnotatedElementUtils;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.ReflectionUtils;
import org.springframework.util.ReflectionUtils.FieldCallback;

/**
 * A {@link FieldCallback} that will inspect each field for a given annotation. This field's type can then be accessed
 * afterwards.
 *
 * @author Oliver Gierke
 * @author Christoph Strobl
 */
public class AnnotationDetectionFieldCallback implements FieldCallback {

    private final Class<? extends Annotation> annotationType;
    private @Nullable Field field;

    /**
     * Creates a new {@link AnnotationDetectionFieldCallback} scanning for an annotation of the given type.
     *
     * @param annotationType must not be {@literal null}.
     */
    public AnnotationDetectionFieldCallback(Class<? extends Annotation> annotationType) {

        Assert.notNull(annotationType, "AnnotationType must not be null!");

        this.annotationType = annotationType;
    }

    /*
     * (non-Javadoc)
     * @see org.springframework.util.ReflectionUtils.FieldCallback#doWith(java.lang.reflect.Field)
     */
    public void doWith(Field field) throws IllegalArgumentException, IllegalAccessException {

        if (this.field != null) {
            return;
        }

        if (AnnotatedElementUtils.findMergedAnnotation(field, annotationType) != null) {

            ReflectionUtils.makeAccessible(field);
            this.field = field;
        }
    }

    /**
     * Returns the detected field.
     *
     * @return the field
     */
    @Nullable
    public Field getField() {
        return field;
    }

    /**
     * Returns the field that was detected.
     *
     * @return
     * @throws IllegalStateException in case no field with the configured annotation was found.
     */
    public Field getRequiredField() {

        Field field = this.field;

        if (field == null) {
            throw new IllegalStateException(String.format("No field found for annotation %s!", annotationType));
        }

        return field;
    }

    /**
     * Returns the type of the field.
     *
     * @return
     */
    @Nullable
    public Class<?> getType() {

        Field field = this.field;

        return field == null ? null : field.getType();
    }

    /**
     * Returns the type of the field or throws an {@link IllegalArgumentException} if no field could be found.
     *
     * @return
     * @throws IllegalStateException in case no field with the configured annotation was found.
     */
    public Class<?> getRequiredType() {
        return getRequiredField().getType();
    }

    /**
     * Retrieves the value of the field by reflection.
     *
     * @param source must not be {@literal null}.
     * @return
     */
    @Nullable
    @SuppressWarnings("unchecked")
    public <T> T getValue(Object source) {

        Assert.notNull(source, "Source object must not be null!");

        Field field = this.field;

        if (field == null) {
            return null;
        }

        return (T) ReflectionUtils.getField(field, source);
    }
}