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Spring Retry provides an abstraction around retrying failed operations, with an emphasis on declarative control of the process and policy-based behaviour that is easy to extend and customize. For instance, you can configure a plain POJO operation to retry if it fails, based on the type of exception, and with a fixed or exponential backoff.

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/*
 * Copyright 2006-2022 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.classify;

import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;

/**
 * A {@link Classifier} for exceptions that has only two classes (true and false).
 * Classifies objects according to their inheritance relation with the supplied types. If
 * the object to be classified is one of the provided types, or is a subclass of one of
 * the types, then the non-default value is returned (usually true).
 *
 * @see SubclassClassifier
 * @author Dave Syer
 * @author Gary Russell
 *
 */
@SuppressWarnings("serial")
public class BinaryExceptionClassifier extends SubclassClassifier {

	private boolean traverseCauses;

	public static BinaryExceptionClassifierBuilder builder() {
		return new BinaryExceptionClassifierBuilder();
	}

	public static BinaryExceptionClassifier defaultClassifier() {
		// create new instance for each call due to mutability
		return new BinaryExceptionClassifier(
				Collections., Boolean>singletonMap(Exception.class, true), false);
	}

	/**
	 * Create a binary exception classifier with the provided default value.
	 * @param defaultValue defaults to false
	 */
	public BinaryExceptionClassifier(boolean defaultValue) {
		super(defaultValue);
	}

	/**
	 * Create a binary exception classifier with the provided classes and their
	 * subclasses. The mapped value for these exceptions will be the one provided (which
	 * will be the opposite of the default).
	 * @param exceptionClasses the exceptions to classify among
	 * @param value the value to classify
	 */
	public BinaryExceptionClassifier(Collection> exceptionClasses, boolean value) {
		this(!value);
		if (exceptionClasses != null) {
			Map, Boolean> map = new HashMap<>();
			for (Class type : exceptionClasses) {
				map.put(type, !getDefault());
			}
			setTypeMap(map);
		}
	}

	/**
	 * Create a binary exception classifier with the default value false and value mapping
	 * true for the provided classes and their subclasses.
	 * @param exceptionClasses the exception types to throw
	 */
	public BinaryExceptionClassifier(Collection> exceptionClasses) {
		this(exceptionClasses, true);
	}

	/**
	 * Create a binary exception classifier using the given classification map and a
	 * default classification of false.
	 * @param typeMap the map of types
	 */
	public BinaryExceptionClassifier(Map, Boolean> typeMap) {
		this(typeMap, false);
	}

	/**
	 * Create a binary exception classifier using the given classification map and the
	 * given value for default class.
	 * @param defaultValue the default value to use
	 * @param typeMap the map of types to classify
	 */
	public BinaryExceptionClassifier(Map, Boolean> typeMap, boolean defaultValue) {
		super(typeMap, defaultValue);
	}

	/**
	 * Create a binary exception classifier.
	 * @param defaultValue the default value to use
	 * @param typeMap the map of types to classify
	 * @param traverseCauses if true, throwable's causes will be inspected to find
	 * non-default class
	 */
	public BinaryExceptionClassifier(Map, Boolean> typeMap, boolean defaultValue,
			boolean traverseCauses) {
		super(typeMap, defaultValue);
		this.traverseCauses = traverseCauses;
	}

	public void setTraverseCauses(boolean traverseCauses) {
		this.traverseCauses = traverseCauses;
	}

	@Override
	public Boolean classify(Throwable classifiable) {
		Boolean classified = super.classify(classifiable);
		if (!this.traverseCauses) {
			return classified;
		}

		/*
		 * If the result is the default, we need to find out if it was by default or so
		 * configured; if default, try the cause(es).
		 */
		if (classified.equals(this.getDefault())) {
			Throwable cause = classifiable;
			do {
				if (this.getClassified().containsKey(cause.getClass())) {
					return classified; // non-default classification
				}
				cause = cause.getCause();
				classified = super.classify(cause);
			}
			while (cause != null && classified.equals(this.getDefault()));
		}

		return classified;
	}

}