RecursiveToStringStyle.java
/*
* 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
*
* 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.apache.commons.lang3.builder;
import java.util.Collection;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.function.Supplier;
import org.apache.commons.lang3.ClassUtils;
import org.apache.commons.lang3.mutable.MutableBoolean;
/**
* Works with {@link ToStringBuilder} to create a "deep" {@code toString}.
* <p>
* To use this class write code as follows:
* </p>
*
* <pre>
* 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();
* }
* }
* </pre>
* <p>
* This will produce a toString of the format: {@code Person@7f54[name=Stephen,age=29,smoker=false,job=Job@43cd2[title=Manager]]}
* </p>
* <p>
* Graph safety: within one top-level {@code toString()} call, each object is rendered in detail at most once. A second (identity-equal) occurrence of an object
* (whether through a true cycle or through a shared (acyclic) reference) is rendered in the abbreviated {@code Object.toString()} format instead of being
* re-traversed. This keeps traversal cost linear in the size of the object graph; without it, shared references (reference "diamonds") would be re-traversed
* exponentially. An optional output-length limit can be set via {@link RecursiveToStringStyle.Builder#setMaxOutputLength(int)}; once the produced string
* reaches the limit, further nested objects are replaced by a {@code "...<truncated>"} marker.
* </p>
*
* @since 3.2
*/
public class RecursiveToStringStyle extends ToStringStyle {
/**
* Builder for {@link RecursiveToStringStyle} instances.
*/
public static class Builder implements Supplier<RecursiveToStringStyle> {
private int maxOutputLength;
private Builder() {
this.maxOutputLength = 0;
}
@Override
public RecursiveToStringStyle get() {
return new RecursiveToStringStyle(this);
}
/**
* Sets the maximum length the output buffer may reach before nested objects are elided with {@link #TRUNCATED_TEXT}; {@code 0} (the default) means
* unlimited. This is a throttle, not an exact bound: objects already being rendered may still append their shallow content.
*
* @param maxOutputLength once the produced string reaches this length, further nested objects are replaced by a {@code "...<truncated>"} marker;
* {@code 0} means unlimited.
* @return this builder for chaining.
*/
public Builder setMaxOutputLength(final int maxOutputLength) {
this.maxOutputLength = maxOutputLength;
return this;
}
}
/**
* Required for serialization support.
*
* @see java.io.Serializable
*/
private static final long serialVersionUID = 1L;
/**
* Marker appended in place of a nested object once {@link #maxOutputLength} is reached.
*/
private static final String TRUNCATED_TEXT = "...<truncated>";
/**
* Creates a new {@link Builder} for {@link RecursiveToStringStyle} instances.
*
* @return a new {@link Builder} for {@link RecursiveToStringStyle} instances.
*/
public static Builder builder() {
return new Builder();
}
/**
* Maximum length the output buffer may reach before nested objects are elided with
* {@link #TRUNCATED_TEXT}; {@code 0} (the default) means unlimited. This is a throttle,
* not an exact bound: objects already being rendered may still append their shallow content.
*/
private final int maxOutputLength;
/**
* Constructs a new instance with no output-length limit.
*/
public RecursiveToStringStyle() {
this(RecursiveToStringStyle.builder());
}
private RecursiveToStringStyle(final Builder builder) {
this.maxOutputLength = builder.maxOutputLength;
}
/**
* Constructs a new instance with an output-length limit.
*
* @param maxOutputLength once the produced string reaches this length, further nested
* objects are replaced by a {@code "...<truncated>"} marker; {@code 0} means unlimited.
* @since 3.21.0
*/
public RecursiveToStringStyle(final int maxOutputLength) {
this.maxOutputLength = maxOutputLength;
}
/**
* Tests whether or not to recursively format the given {@link Class}.
* <p>
* By default, this method always filters out the following:
* </p>
* <ul>
* <li><a href="https://docs.oracle.com/javase/specs/jls/se25/html/jls-5.html#jls-5.1.7">Boxed primitives</a>, see {@link ClassUtils#isPrimitiveWrapper(Class)}
* <li>{@link String}</li>
* <li>{@link Number} subclasses</li>
* <li>{@link AtomicBoolean}</li>
* <li>{@link MutableBoolean}</li>
* </ul>
*
* @param clazz The class to test.
* @return Whether or not to recursively format instances of the given {@link Class}.
*/
protected boolean accept(final Class<?> clazz) {
// @formatter:off
return !ClassUtils.isPrimitiveWrapper(clazz) &&
!String.class.equals(clazz) &&
!Number.class.isAssignableFrom(clazz) &&
!AtomicBoolean.class.equals(clazz) &&
!MutableBoolean.class.equals(clazz);
// @formatter:on
}
@Override
protected void appendDetail(final StringBuffer buffer, final String fieldName, final Collection<?> coll) {
appendClassName(buffer, coll);
appendIdentityHashCode(buffer, coll);
appendDetail(buffer, fieldName, coll.toArray());
}
@Override
public void appendDetail(final StringBuffer buffer, final String fieldName, final Object value) {
if (value != null && accept(value.getClass())) {
buffer.append(ReflectionToStringBuilder.toString(value, this));
} else {
super.appendDetail(buffer, fieldName, value);
}
}
/**
* {@inheritDoc}
*
* <p>In addition to the cycle check performed by the superclass, this implementation keeps a
* per-thread set of objects already rendered in detail during the current top-level call.
* Values that this style would traverse structurally (see {@link #accept(Class)}) are rendered
* in detail at most once; later identity-equal occurrences are appended in the abbreviated
* {@code Object.toString()} format. This bounds the traversal to one visit per object, so
* shared (acyclic) references cannot cause exponential re-traversal. If an output-length limit
* was configured and the buffer has reached it, a {@code "...<truncated>"} marker is appended
* instead of the value.</p>
*/
@Override
protected void appendInternal(final StringBuffer buffer, final String fieldName, final Object value, final boolean detail) {
if (detail && value != null && accept(value.getClass())
&& !(value instanceof Number || value instanceof Boolean || value instanceof Character)) {
if (isVisited(value)) {
appendCyclicObject(buffer, fieldName, value);
return;
}
if (maxOutputLength > 0 && buffer.length() >= maxOutputLength) {
buffer.append(TRUNCATED_TEXT);
return;
}
markVisited(value);
}
super.appendInternal(buffer, fieldName, value, detail);
}
}