alvinalexander.com | career | drupal | java | mac | mysql | perl | scala | uml | unix  

Java example source code file (TestingCacheLoaders.java)

This example Java source code file (TestingCacheLoaders.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

annotation, atomicinteger, cacheloader, constantloader, exception, gwtcompatible, gwtincompatible, identityloader, incrementingloader, listenablefuture, map, object, override, util

The TestingCacheLoaders.java Java example source code

/*
 * Copyright (C) 2011 The Guava 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
 *
 * 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.common.cache;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.collect.Maps;
import com.google.common.util.concurrent.Futures;
import com.google.common.util.concurrent.ListenableFuture;

import java.util.Map;
import java.util.concurrent.atomic.AtomicInteger;

import javax.annotation.Nullable;

/**
 * Utility {@link CacheLoader} implementations intended for use in testing.
 *
 * @author mike nonemacher
 */
@GwtCompatible(emulated = true)
class TestingCacheLoaders {

  /**
   * Returns a {@link CacheLoader} that implements a naive {@link CacheLoader#loadAll}, delegating
   * {@link CacheLoader#load} calls to {@code loader}.
   */
  static <K, V> CacheLoader bulkLoader(final CacheLoader loader) {
    checkNotNull(loader);
    return new CacheLoader<K, V>() {
      @Override
      public V load(K key) throws Exception {
        return loader.load(key);
      }

      @Override
      public Map<K, V> loadAll(Iterable keys) throws Exception {
        Map<K, V> result = Maps.newHashMap(); // allow nulls
        for (K key : keys) {
          result.put(key, load(key));
        }
        return result;
      }
    };
  }

  /**
   * Returns a {@link CacheLoader} that returns the given {@code constant} for every request.
   */
  static <K, V> ConstantLoader constantLoader(@Nullable V constant) {
    return new ConstantLoader<K, V>(constant);
  }

  /**
   * Returns a {@link CacheLoader} that returns the given {@code constant} for every request.
   */
  static IncrementingLoader incrementingLoader() {
    return new IncrementingLoader();
  }

  /**
   * Returns a {@link CacheLoader} that throws the given error for every request.
   */
  static <K, V> CacheLoader errorLoader(final Error e) {
    checkNotNull(e);
    return new CacheLoader<K, V>() {
      @Override
      public V load(K key) {
        throw e;
      }
    };
  }

  /**
   * Returns a {@link CacheLoader} that throws the given exception for every request.
   */
  static <K, V> CacheLoader exceptionLoader(final Exception e) {
    checkNotNull(e);
    return new CacheLoader<K, V>() {
      @Override
      public V load(K key) throws Exception {
        throw e;
      }
    };
  }

  /**
   * Returns a {@link CacheLoader} that returns the key for every request.
   */
  static <T> IdentityLoader identityLoader() {
    return new IdentityLoader<T>();
  }

  /**
   * Returns a {@code new Object()} for every request, and increments a counter for every request.
   * The count is accessible via {@link #getCount}.
   */
  static class CountingLoader extends CacheLoader<Object, Object> {
    private final AtomicInteger count = new AtomicInteger();

    @Override
    public Object load(Object from) {
      count.incrementAndGet();
      return new Object();
    }

    public int getCount() {
      return count.get();
    }
  }

  static final class ConstantLoader<K, V> extends CacheLoader {
    private final V constant;

    ConstantLoader(V constant) {
      this.constant = constant;
    }

    @Override
    public V load(K key) {
      return constant;
    }
  }

  /**
   * Returns a {@code new Object()} for every request, and increments a counter for every request.
   * An {@code Integer} loader that returns the key for {@code load} requests, and increments the
   * old value on {@code reload} requests. The load counts are accessible via {@link #getLoadCount}
   * and {@link #getReloadCount}.
   */
  static class IncrementingLoader extends CacheLoader<Integer, Integer> {
    private final AtomicInteger countLoad = new AtomicInteger();
    private final AtomicInteger countReload = new AtomicInteger();

    @Override
    public Integer load(Integer key) {
      countLoad.incrementAndGet();
      return key;
    }

    @GwtIncompatible // reload
    @Override
    public ListenableFuture<Integer> reload(Integer key, Integer oldValue) {
      countReload.incrementAndGet();
      return Futures.immediateFuture(oldValue + 1);
    }

    public int getLoadCount() {
      return countLoad.get();
    }

    public int getReloadCount() {
      return countReload.get();
    }
  }

  static final class IdentityLoader<T> extends CacheLoader {
    @Override
    public T load(T key) {
      return key;
    }
  }
}

Other Java examples (source code examples)

Here is a short list of links related to this Java TestingCacheLoaders.java source code file:

... this post is sponsored by my books ...

#1 New Release!

FP Best Seller

 

new blog posts

 

Copyright 1998-2021 Alvin Alexander, alvinalexander.com
All Rights Reserved.

A percentage of advertising revenue from
pages under the /java/jwarehouse URI on this website is
paid back to open source projects.