【工具類】系列五 可控大小Cache之 MemberCache

Cache裏經常用到的兩個功能就是：

1 當key對應的值不存在時，加載進來並可以訪問。

2 達到cache的上限後，可以LRU清除。

 

開源包guava自帶的cache就很好的滿足了上面的需求。

 

依賴：

compile 'com.google.guava:guava:18.0'

 

下面的MemberCache只是guava cache裏的一個使用案例：

@Slf4j
public class MemberCache {

    static final String KEY_DELEMILTER = "#";

    // cache trust set of every member, memberSrl --> trust set
    private LoadingCache<String, SortedSet<Activity>> cache;

    public MemberCache(int maxSize) {
        System.out.println("==> member cache max size: " + maxSize);

        cache = CacheBuilder.newBuilder()
                .maximumSize(maxSize)
                .removalListener(new RemoveListener())
                .build(new TrustsetLoader());
    }

    public SortedSet<Activity> getTrustset(String memberSrl, String trustType) throws ExecutionException {
        String key = memberSrl + KEY_DELEMILTER + trustType;
        return cache.get(key);
    }

    public LoadingCache<String, SortedSet<Activity>> getCache() {
        return cache;
    }

    /**
     * listen remove event of cache.
     */
    class RemoveListener implements RemovalListener<String, SortedSet<Activity>> {

        @Override
        public void onRemoval(RemovalNotification<String, SortedSet<Activity>> notification) {
            long free = Runtime.getRuntime().freeMemory();
            final long humanSize = 1024 * 1024;
            System.out.printf("=> up to cache max, system free %d m \n", free / humanSize);
        }
    }

    /**
     * load member's trust set if absent.
     */
    class TrustsetLoader extends CacheLoader<String, SortedSet<Activity>> {

        @Override
        public SortedSet<Activity> load(String key) {

            String[] keys = key.split(KEY_DELEMILTER);
            String memberSrl = keys[0];
            String trustType = keys[1];

            SortedSet<Activity> set = new TreeSet<>();

            try {
                String rowKey = LIMIT_CONTROL.getRowKey(memberSrl);
                Get get = new Get(Bytes.toBytes(rowKey));
                get.addColumn(LIMIT_CONTROL.getCF(), HColumn.valueOf(trustType).getCol());

                // !!! set version is important for limit control table
                get.setMaxVersions(DurationLimit.getLimit(trustType));

                Result[] results = HBaseUtil.get(LIMIT_CONTROL, get);
                for (Result result: results) {
                    CellScanner scanner = result.cellScanner();
                    while (scanner.advance()) {
                        Cell cell = scanner.current();
                        String value = CellUtil.getValue(cell, String.class);
                        long timestamp = cell.getTimestamp();
                        Activity act = Activity.builder()
                                .memberSrl(memberSrl)
                                .trustType(trustType)
                                .value(value)
                                .actTime(timestamp)
                                .build();

                        set.add(act);
                    }
                }
            } catch (Exception e) {
                log.error("load trust set for key: {}, error", key, e);
            }

            System.out.printf("load key: %s, set size: %d \n", key, set.size());

            return set;
        }
    }

}