org.apache.wicket.injection.Injector.java Source code

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Here is the source code for org.apache.wicket.injection.Injector.java

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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 org.apache.wicket.injection;

import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.List;

import org.apache.wicket.Application;
import org.apache.wicket.MetaDataKey;
import org.apache.wicket.util.collections.ClassMetaCache;

/**
 * Injector scans fields of an object instance and checks if the specified
 * {@link IFieldValueFactory} can provide a value for a field; if it can, the field is set to that
 * value. Injector will ignore all non-null fields.
 * 
 * @author Igor Vaynberg (ivaynberg)
 * 
 */
public abstract class Injector {
    private static final MetaDataKey<Injector> KEY = new MetaDataKey<Injector>() {
        private static final long serialVersionUID = 1L;
    };

    private final ClassMetaCache<Field[]> cache = new ClassMetaCache<>();

    /**
     * Binds current instance of the injector to the Application. After this method is called this
     * instance of injector will be returned from subsequent calls to {@link #get()} whenever the
     * specified application object is active in the thread.
     * 
     * @param application
     */
    public void bind(final Application application) {
        application.setMetaData(KEY, this);
    }

    /**
     * @return Injector associated with the application instance
     */
    public static Injector get() {
        return Application.get().getMetaData(KEY);
    }

    /**
     * Injects the specified object. This method is usually implemented by delegating to
     * {@link #inject(Object, IFieldValueFactory)} with some {@link IFieldValueFactory}
     * 
     * @param object
     * 
     * @see #inject(Object, IFieldValueFactory)
     */
    public abstract void inject(Object object);

    /**
     * traverse fields in the class hierarchy of the object and set their value with a locator
     * provided by the locator factory.
     * 
     * @param object
     * @param factory
     */
    protected void inject(final Object object, final IFieldValueFactory factory) {
        final Class<?> clazz = object.getClass();

        Field[] fields = null;

        // try cache
        fields = cache.get(clazz);

        if (fields == null) {
            // cache miss, discover fields
            fields = findFields(clazz, factory);

            // write to cache
            cache.put(clazz, fields);
        }

        for (final Field field : fields) {
            if (!field.isAccessible()) {
                field.setAccessible(true);
            }
            try {

                if (field.get(object) == null) {

                    Object value = factory.getFieldValue(field, object);

                    if (value != null) {
                        field.set(object, value);
                    }
                }
            } catch (IllegalArgumentException e) {
                throw new RuntimeException("error while injecting object [" + object.toString() + "] of type ["
                        + object.getClass().getName() + "]", e);
            } catch (IllegalAccessException e) {
                throw new RuntimeException("error while injecting object [" + object.toString() + "] of type ["
                        + object.getClass().getName() + "]", e);
            }
        }
    }

    /**
     * Returns an array of fields that can be injected using the given field value factory
     * 
     * @param clazz
     * @param factory
     * @return an array of fields that can be injected using the given field value factory
     */
    private Field[] findFields(Class<?> clazz, final IFieldValueFactory factory) {
        List<Field> matched = new ArrayList<>();

        while (clazz != null) {
            Field[] fields = clazz.getDeclaredFields();
            for (final Field field : fields) {
                if (factory.supportsField(field)) {
                    matched.add(field);
                }
            }
            clazz = clazz.getSuperclass();
        }

        return matched.toArray(new Field[matched.size()]);
    }

}