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Apache Commons Lang, a package of Java utility classes for the classes that are in java.lang's hierarchy, or are considered to be so standard as to justify existence in java.lang.

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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.commons.lang3.builder;

import java.util.Collection;

import org.apache.commons.lang3.ClassUtils;

/**
 * Works with {@link ToStringBuilder} to create a "deep" {@code toString}.
 *
 * To use this class write code as follows:
 *
 *  * public class Job {
 *   String title;
 *   ...
 * }
 *
 * public class Person {
 *   String name;
 *   int age;
 *   boolean smoker;
 *   Job job;
 *
 *   ...
 *
 *   public String toString() {
 *     return new ReflectionToStringBuilder(this, new RecursiveToStringStyle()).toString();
 *   }
 * }
 * 
 *
 * This will produce a toString of the format:
 * {@code Person@7f54[name=Stephen,age=29,smoker=false,job=Job@43cd2[title=Manager]]}
 *
 * @since 3.2
 */
public class RecursiveToStringStyle extends ToStringStyle {

    /**
     * Required for serialization support.
     *
     * @see java.io.Serializable
     */
    private static final long serialVersionUID = 1L;

    /**
     * Constructor.
     */
    public RecursiveToStringStyle() {
    }

    @Override
    public void appendDetail(final StringBuffer buffer, final String fieldName, final Object value) {
        if (!ClassUtils.isPrimitiveWrapper(value.getClass()) &&
            !String.class.equals(value.getClass()) &&
            accept(value.getClass())) {
            buffer.append(ReflectionToStringBuilder.toString(value, this));
        } else {
            super.appendDetail(buffer, fieldName, value);
        }
    }

    @Override
    protected void appendDetail(final StringBuffer buffer, final String fieldName, final Collection coll) {
        appendClassName(buffer, coll);
        appendIdentityHashCode(buffer, coll);
        appendDetail(buffer, fieldName, coll.toArray());
    }

    /**
     * Returns whether or not to recursively format the given {@code Class}.
     * By default, this method always returns {@code true}, but may be overwritten by
     * sub-classes to filter specific classes.
     *
     * @param clazz
     *            The class to test.
     * @return Whether or not to recursively format the given {@code Class}.
     */
    protected boolean accept(final Class clazz) {
        return true;
    }
}