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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 2006-2007 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.retry.policy;

import java.lang.ref.SoftReference;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;

import org.springframework.retry.RetryContext;

/**
 * Map-based implementation of {@link RetryContextCache}. The map backing the
 * cache of contexts is synchronized and its entries are soft-referenced, so may
 * be garbage collected under pressure.
 * 
 * @see MapRetryContextCache for non-soft referenced version
 * 
 * @author Dave Syer
 */
public class SoftReferenceMapRetryContextCache implements RetryContextCache {

	/**
	 * Default value for maximum capacity of the cache. This is set to a
	 * reasonably low value (4096) to avoid users inadvertently filling the
	 * cache with item keys that are inconsistent.
	 */
	public static final int DEFAULT_CAPACITY = 4096;

	private Map> map = Collections
			.synchronizedMap(new HashMap>());

	private int capacity;

	/**
	 * Create a {@link SoftReferenceMapRetryContextCache} with default capacity.
	 */
	public SoftReferenceMapRetryContextCache() {
		this(DEFAULT_CAPACITY);
	}

	/**
	 * @param defaultCapacity the default capacity
	 */
	public SoftReferenceMapRetryContextCache(int defaultCapacity) {
		super();
		this.capacity = defaultCapacity;
	}

	/**
	 * Public setter for the capacity. Prevents the cache from growing
	 * unboundedly if items that fail are misidentified and two references to an
	 * identical item actually do not have the same key. This can happen when
	 * users implement equals and hashCode based on mutable fields, for
	 * instance.
	 * 
	 * @param capacity the capacity to set
	 */
	public void setCapacity(int capacity) {
		this.capacity = capacity;
	}

	public boolean containsKey(Object key) {
		if (!map.containsKey(key)) {
			return false;
		}
		if (map.get(key).get() == null) {
			// our reference was garbage collected
			map.remove(key);
		}
		return map.containsKey(key);
	}

	public RetryContext get(Object key) {
		return map.get(key).get();
	}

	public void put(Object key, RetryContext context) {
		if (map.size() >= capacity) {
			throw new RetryCacheCapacityExceededException("Retry cache capacity limit breached. "
					+ "Do you need to re-consider the implementation of the key generator, "
					+ "or the equals and hashCode of the items that failed?");
		}
		map.put(key, new SoftReference(context));
	}

	public void remove(Object key) {
		map.remove(key);
	}
}