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  • LruCache

    2019-10-03 19:36:59
    LruCache 代码如下: 1 public LruCache<String,Bitmap> mMemoryCache; 2 3 void init(){ 4 // 获取应用程序最大可用内存 5 int maxMemory = (int) Runtime.getRuntime().maxMemory...

    LruCache

    代码如下:

     1     public LruCache<String,Bitmap> mMemoryCache;
     2 
     3     void init(){
     4         // 获取应用程序最大可用内存
     5         int maxMemory = (int) Runtime.getRuntime().maxMemory();
     6         int cacheSize = maxMemory / 8;
     7         // 设置图片缓存大小为程序最大可用内存的1/8
     8         mMemoryCache = new LruCache<String, Bitmap>(cacheSize) {
     9             @Override
    10             protected int sizeOf(String key, Bitmap bitmap) {
    11                 return bitmap.getByteCount();
    12             }
    13         };
    14     }
    15     /**
    16      * 给ImageView设置图片。首先从LruCache中取出图片的缓存,设置到ImageView上。如果LruCache中没有该图片的缓存,
    17      * 就给ImageView设置一张默认图片。
    18      * @param imageUrl 图片的URL地址,用于作为LruCache的键。
    19      * @param imageView 用于显示图片的控件。
    20      */
    21     private void setImageView(String imageUrl, ImageView imageView) {
    22         Bitmap bitmap = mMemoryCache.get(imageUrl);
    23         if (bitmap != null) {
    24             imageView.setImageBitmap(bitmap);
    25         } else {
    26             bitmap = getLoacalBitmap(imageUrl);
    27             imageView.setImageResource(R.drawable.empty_photo);
    28         }
    29     }
    30     //...

     

    转载于:https://www.cnblogs.com/sjjg/p/4719619.html

    展开全文
  • LRUCache

    2019-04-08 15:24:00
    public class LRUCache<K, V> extends LinkedHashMap<K, V> { private static final long serialVersionUID = 3125099067311409227L; private Integer cacheSize; public L...
    public class LRUCache<K, V> extends LinkedHashMap<K, V> {
    
        private static final long serialVersionUID = 3125099067311409227L;
    
        private Integer cacheSize;
    
        public LRUCache(Integer cacheSize) {
            super(cacheSize * 3/ 4 + 1, 0.75f, true);
            this.cacheSize = cacheSize;
        }
    
        @Override
        protected boolean removeEldestEntry(Map.Entry<K, V> eldest) {
            if (size() > cacheSize) {
                return true;
            }
            return false;
    
            //return super.removeEldestEntry(eldest);
        }
    
    
    }
    public class MyTest {
    
        public static void main(String[] args) {
    
            Map<String, String> map = new LRUCache<>(4);
            map.put("1", "1");
            map.put("2", "2");
            map.put("3", "3");
            map.put("4", "4");
            map.put("5", "5");
            map.put("6", "6");
            map.put("1", "1");
    
    
            //map.get("3");
            //map.get("6");
            //map.get("1");
    
            for (Map.Entry entry : map.entrySet()) {
                System.out.println(entry.getKey() + "=========" + entry.getValue());
            }
    
        }
    }

    运行结果:

    4=========4
    5=========5
    6=========6
    1=========1

     

    转载于:https://www.cnblogs.com/parkdifferent/p/10670764.html

    展开全文
  • LRuCache

    2018-05-01 16:23:52
    LruCache底层使用LinkedHashMap,因为LruCache中Lru算法的实现就是通过LinkedHashMap来实现的。LinkedHashMap继承于HashMap,它使用了一个双向链表来存储Map中的Entry顺序关系,这种顺序有两种,一种是LRU顺序,一种...

    LruCache底层使用LinkedHashMap,因为LruCache中Lru算法的实现就是通过LinkedHashMap来实现的。LinkedHashMap继承于HashMap,它使用了一个双向链表来存储Map中的Entry顺序关系,这种顺序有两种,一种是LRU顺序,一种是插入顺序,这可以由其构造函数public LinkedHashMap(int initialCapacity,float loadFactor, boolean accessOrder)指定。所以,对于get、put、remove等操作,LinkedHashMap除了要做HashMap做的事情,还做些调整Entry顺序链表的工作。LruCache中将LinkedHashMap的顺序设置为LRU顺序来实现LRU缓存,每次调用get(也就是从内存缓存中取图片),则将该对象移到链表的尾端。调用put插入新的对象也是存储在链表尾端,这样当内存缓存达到设定的最大值时,将链表头部的对象(近期最少用到的)移除。 

    package com.kale.lrucachetest;
    
    import java.util.LinkedHashMap;
    import java.util.Map;
    /**
     * 它的主要算法原理是把最近使用的对象用强引用存储在 LinkedHashMap 中,并且把最近最少使用的对象在缓存值达到预设定值之前从内存中移除。
     */
    
    /**
     * A cache that holds strong references to a limited number of values. Each time
     * a value is accessed, it is moved to the head of a queue. When a value is
     * added to a full cache, the value at the end of that queue is evicted and may
     * become eligible for garbage collection.
     * Cache保存一个强引用来限制内容数量,每当Item被访问的时候,此Item就会移动到队列的头部。
     * 当cache已满的时候加入新的item时,在队列尾部的item会被回收。
     * <p>
     * If your cached values hold resources that need to be explicitly released,
     * override {@link #entryRemoved}. 如果你cache的某个值需要明确释放,重写entryRemoved()
     * <p>
     * If a cache miss should be computed on demand for the corresponding keys,
     * override {@link #create}. This simplifies the calling code, allowing it to
     * assume a value will always be returned, even when there's a cache miss.
     * 如果key相对应的item丢掉啦,重写create().这简化了调用代码,即使丢失了也总会返回。
     * <p>
     * By default, the cache size is measured in the number of entries. Override
     * {@link #sizeOf} to size the cache in different units. For example, this cache
     * is limited to 4MiB of bitmaps: 默认cache大小是测量的item的数量,重写sizeof计算不同item的 大小。
     * 
     * <pre>
     * {@code
     * int cacheSize = 4 * 1024 * 1024; // 4MiB
     * LruCache<String, Bitmap> bitmapCache = new LruCache<String, Bitmap>(cacheSize) {
     * protected int sizeOf(String key, Bitmap value) {
     * return value.getByteCount();
     * }
     * }}
     * </pre>
     *
     * <p>
     * This class is thread-safe. Perform multiple cache operations atomically by
     * synchronizing on the cache:
     * 
     * <pre>
     * {@code
     * synchronized (cache) {
     * if (cache.get(key) == null) {
     * cache.put(key, value);
     * }
     * }}
     * </pre>
     *
     * <p>
     * This class does not allow null to be used as a key or value. A return value
     * of null from {@link #get}, {@link #put} or {@link #remove} is unambiguous:
     * the key was not in the cache. 不允许key或者value为null
     * 当get(),put(),remove()返回值为null时,key相应的项不在cache中
     */
    public class LruCache<K, V> {
        private final LinkedHashMap<K, V> map;
    
        /** Size of this cache in units. Not necessarily the number of elements. */
        private int size; // 已经存储的大小
        private int maxSize; // 规定的最大存储空间
    
        private int putCount; // put的次数
        private int createCount; // create的次数
        private int evictionCount; // 回收的次数
        private int hitCount; // 命中的次数
        private int missCount; // 丢失的次数
    
        /**
         * @param maxSize
         *            for caches that do not override {@link #sizeOf}, this is the
         *            maximum number of entries in the cache. For all other caches,
         *            this is the maximum sum of the sizes of the entries in this
         *            cache.
         */
        public LruCache(int maxSize) {
            if (maxSize <= 0) {
                throw new IllegalArgumentException("maxSize <= 0");
            }
            this.maxSize = maxSize;
            this.map = new LinkedHashMap<K, V>(0, 0.75f, true);
        }
    
        /**
         * Returns the value for {@code key} if it exists in the cache or can be
         * created by {@code #create}. If a value was returned, it is moved to the
         * head of the queue. This returns null if a value is not cached and cannot
         * be created. 通过key返回相应的item,或者创建返回相应的item。相应的item会移动到队列的头部,
         * 如果item的value没有被cache或者不能被创建,则返回null。
         */
        public final V get(K key) {
            if (key == null) {
                throw new NullPointerException("key == null");
            }
    
            V mapValue;
            synchronized (this) {
                mapValue = map.get(key);
                if (mapValue != null) {
                    hitCount++; // 命中
                    return mapValue;
                }
                missCount++; // 丢失
            }
    
            /*
             * Attempt to create a value. This may take a long time, and the map may
             * be different when create() returns. If a conflicting value was added
             * to the map while create() was working, we leave that value in the map
             * and release the created value. 如果丢失了就试图创建一个item
             */
    
            V createdValue = create(key);
            if (createdValue == null) {
                return null;
            }
    
            synchronized (this) {
                createCount++;// 创建++
                mapValue = map.put(key, createdValue);
    
                if (mapValue != null) {
                    // There was a conflict so undo that last put
                    // 如果前面存在oldValue,那么撤销put()
                    map.put(key, mapValue);
                } else {
                    size += safeSizeOf(key, createdValue);
                }
            }
    
            if (mapValue != null) {
                entryRemoved(false, key, createdValue, mapValue);
                return mapValue;
            } else {
                trimToSize(maxSize);
                return createdValue;
            }
        }
    
        /**
         * Caches {@code value} for {@code key}. The value is moved to the head of
         * the queue.
         *
         * @return the previous value mapped by {@code key}.
         */
        public final V put(K key, V value) {
            if (key == null || value == null) {
                throw new NullPointerException("key == null || value == null");
            }
    
            V previous;
            synchronized (this) {
                putCount++;
                size += safeSizeOf(key, value);
                previous = map.put(key, value);
                if (previous != null) { // 返回的先前的value值
                    size -= safeSizeOf(key, previous);
                }
            }
    
            if (previous != null) {
                entryRemoved(false, key, previous, value);
            }
    
            trimToSize(maxSize);
            return previous;
        }
    
        /**
         * @param maxSize
         *            the maximum size of the cache before returning. May be -1 to
         *            evict even 0-sized elements. 清空cache空间
         */
        private void trimToSize(int maxSize) {
            while (true) {
                K key;
                V value;
                synchronized (this) {
                    if (size < 0 || (map.isEmpty() && size != 0)) {
                        throw new IllegalStateException(getClass().getName() + ".sizeOf() is reporting inconsistent results!");
                    }
    
                    if (size <= maxSize) {
                        break;
                    }
    
                    Map.Entry<K, V> toEvict =  map.eldest();
                    if (toEvict == null) {
                        break;
                    }
    
                    key = toEvict.getKey();
                    value = toEvict.getValue();
                    map.remove(key);
                    size -= safeSizeOf(key, value);
                    evictionCount++;
                }
    
                entryRemoved(true, key, value, null);
            }
        }
    
        /**
         * Removes the entry for {@code key} if it exists. 删除key相应的cache项,返回相应的value
         * 
         * @return the previous value mapped by {@code key}.
         */
        public final V remove(K key) {
            if (key == null) {
                throw new NullPointerException("key == null");
            }
    
            V previous;
            synchronized (this) {
                previous = map.remove(key);
                if (previous != null) {
                    size -= safeSizeOf(key, previous);
                }
            }
    
            if (previous != null) {
                entryRemoved(false, key, previous, null);
            }
    
            return previous;
        }
    
        /**
         * Called for entries that have been evicted or removed. This method is
         * invoked when a value is evicted to make space, removed by a call to
         * {@link #remove}, or replaced by a call to {@link #put}. The default
         * implementation does nothing.
         * 当item被回收或者删掉时调用。该方法当value被回收释放存储空间时被remove调用, 或者替换item值时put调用,默认实现什么都没做。
         * <p>
         * The method is called without synchronization: other threads may access
         * the cache while this method is executing.
         *
         * @param evicted
         *            true if the entry is being removed to make space, false if the
         *            removal was caused by a {@link #put} or {@link #remove}.
         *            true---为释放空间被删除;false---put或remove导致
         * @param newValue
         *            the new value for {@code key}, if it exists. If non-null, this
         *            removal was caused by a {@link #put}. Otherwise it was caused
         *            by an eviction or a {@link #remove}.
         */
        protected void entryRemoved(boolean evicted, K key, V oldValue, V newValue) {
        }
    
        /**
         * Called after a cache miss to compute a value for the corresponding key.
         * Returns the computed value or null if no value can be computed. The
         * default implementation returns null. 当某Item丢失时会调用到,返回计算的相应的value或者null
         * <p>
         * The method is called without synchronization: other threads may access
         * the cache while this method is executing.
         *
         * <p>
         * If a value for {@code key} exists in the cache when this method returns,
         * the created value will be released with {@link #entryRemoved} and
         * discarded. This can occur when multiple threads request the same key at
         * the same time (causing multiple values to be created), or when one thread
         * calls {@link #put} while another is creating a value for the same key.
         */
        protected V create(K key) {
            return null;
        }
    
        private int safeSizeOf(K key, V value) {
            int result = sizeOf(key, value);
            if (result < 0) {
                throw new IllegalStateException("Negative size: " + key + "=" + value);
            }
            return result;
        }
    
        /**
         * Returns the size of the entry for {@code key} and {@code value} in
         * user-defined units. The default implementation returns 1 so that size is
         * the number of entries and max size is the maximum number of entries.
         * 返回用户定义的item的大小,默认返回1代表item的数量,最大size就是最大item值
         * <p>
         * An entry's size must not change while it is in the cache.
         */
        protected int sizeOf(K key, V value) {
            return 1;
        }
    
        /**
         * Clear the cache, calling {@link #entryRemoved} on each removed entry.
         * 清空cacke
         */
        public final void evictAll() {
            trimToSize(-1); // -1 will evict 0-sized elements
        }
    
        /**
         * For caches that do not override {@link #sizeOf}, this returns the number
         * of entries in the cache. For all other caches, this returns the sum of
         * the sizes of the entries in this cache.
         */
        public synchronized final int size() {
            return size;
        }
    
        /**
         * For caches that do not override {@link #sizeOf}, this returns the maximum
         * number of entries in the cache. For all other caches, this returns the
         * maximum sum of the sizes of the entries in this cache.
         */
        public synchronized final int maxSize() {
            return maxSize;
        }
    
        /**
         * Returns the number of times {@link #get} returned a value that was
         * already present in the cache.
         */
        public synchronized final int hitCount() {
            return hitCount;
        }
    
        /**
         * Returns the number of times {@link #get} returned null or required a new
         * value to be created.
         */
        public synchronized final int missCount() {
            return missCount;
        }
    
        /**
         * Returns the number of times {@link #create(Object)} returned a value.
         */
        public synchronized final int createCount() {
            return createCount;
        }
    
        /**
         * Returns the number of times {@link #put} was called.
         */
        public synchronized final int putCount() {
            return putCount;
        }
    
        /**
         * Returns the number of values that have been evicted. 返回被回收的数量
         */
        public synchronized final int evictionCount() {
            return evictionCount;
        }
    
        /**
         * Returns a copy of the current contents of the cache, ordered from least
         * recently accessed to most recently accessed. 返回当前cache的副本,从最近最少访问到最多访问
         */
        public synchronized final Map<K, V> snapshot() {
            return new LinkedHashMap<K, V>(map);
        }
    
        @Override
        public synchronized final String toString() {
            int accesses = hitCount + missCount;
            int hitPercent = accesses != 0 ? (100 * hitCount / accesses) : 0;
            return String.format("LruCache[maxSize=%d,hits=%d,misses=%d,hitRate=%d%%]", maxSize, hitCount, missCount, hitPercent);
        }
    }

    展开全文
  • lrucache

    2016-04-19 16:21:44
    --local lrucache = require "resty.lrucache.pureffi" local lrucache = require "resty.lrucache" -- we need to initialize the cache on the lua module level so that -- ...

    local _M = {}

    --local lrucache = require "resty.lrucache.pureffi"
    local lrucache = require "resty.lrucache"

    -- we need to initialize the cache on the lua module level so that
    -- it can be shared by all the requests served by each nginx worker process:
    local c = lrucache.new(200) -- 如果是2,则下面的代码,dog的值会被cat和x覆盖
    if not c then
    return error("failed to create the cache: " .. (err or "unknown"))
    end

    function _M.go()
    c:set("dog", 32)
    c:set("cat", 56)
    ngx.say("dog: ", c:get("dog"))
    ngx.say("cat: ", c:get("cat"))
    c:delete("cat")
    ngx.say("cat: ", c:get("cat"))

    c:set("x", 101, 2) -- expire in 1 sec
    ngx.sleep(1)
    ngx.say("x: ", c:get("x"))
    ngx.sleep(1)
    ngx.say("x: ", c:get("x"))
    end

    _M.go()

    return _M


    dog: 32
    cat: 56
    cat: nil
    x: 101
    x: nil101
    展开全文
  • lruCache

    2016-01-02 23:36:24
    /** * 内存缓存 * @author Administrator * */ public class MemoryCacheUtils { //private HashMap mMemoryCache = new HashMap... private LruCache mMemoryCache; public MemoryCacheUtils(){ long maxM

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