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Java example source code file (FailableCache.java)

This example Java source code file (FailableCache.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

cacheloader, errors, errorsexception, failablecache, loadingcache, object, suppresswarnings

The FailableCache.java Java example source code

/**
 * Copyright (C) 2008 Google Inc.
 *
 * 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
 *
 * 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 com.google.inject.internal;

import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.LoadingCache;

/**
 * Lazily creates (and caches) values for keys. If creating the value fails (with errors), an
 * exception is thrown on retrieval.
 *
 * @author jessewilson@google.com (Jesse Wilson)
 */
public abstract class FailableCache<K, V> {
  
  private final LoadingCache<K, Object> delegate = CacheBuilder.newBuilder().build(
      new CacheLoader<K, Object>() {
        public Object load(K key) {
          Errors errors = new Errors();
          V result = null;
          try {
            result = FailableCache.this.create(key, errors);
          } catch (ErrorsException e) {
            errors.merge(e.getErrors());
          }
          return errors.hasErrors() ? errors : result;
        }
      });

  protected abstract V create(K key, Errors errors) throws ErrorsException;
  
  public V get(K key, Errors errors) throws ErrorsException {
    Object resultOrError = delegate.getUnchecked(key);
    if (resultOrError instanceof Errors) {
      errors.merge((Errors) resultOrError);
      throw errors.toException();
    } else {
      @SuppressWarnings("unchecked") // create returned a non-error result, so this is safe
      V result = (V) resultOrError;
      return result;
    }
  }
  
  boolean remove(K key) {
    return delegate.asMap().remove(key) != null;
  }
}

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