我有Map<Range<Double>, String>
检查特定Double
值(得分)映射到String
(级别)的位置。最终用户希望能够动态地更改此映射,从长远来看,我们希望有一个基于Web的GUI
来控制它,但是从短期来看,他们很高兴文件是在S3
中,并在需要更改时进行编辑。我不想为每个请求点击S3
并希望缓存它,因为它不会太频繁地更改(每周一次左右)。我不想让代码更改并退回我的服务。
以下是我的想法 -
public class Mapper() {
private LoadingCache<Score, String> scoreToLevelCache;
public Mapper() {
scoreToLevelCache = CacheBuilder.newBuilder()
.expireAfterWrite(10, TimeUnit.MINUTES)
.build(new CacheLoader<Score, String>() {
public String load(Score score) {
Map<Range<Double>, String> scoreToLevelMap = readMappingFromS3(); //readMappingFromS3 omitted for brevity
for(Range<Double> key : scoreToLevelMap.keySet()) {
if(key.contains(score.getCount())) { return scoreToLevelMap.get(key); }
}
throw new IllegalArgumentException("The score couldn't be mapped to a level. Either the score passed in was incorrect or the mapping is incorrect");
}
});
}
public String getContentLevelForScore(Score Score) {
try {
return scoreToLevelCache.get(Score);
} catch (ExecutionException e) { throw new InternalServerException(e); }
}
}
当我这样做时,这种方法的明显问题在于load
方法
Map<Range<Double>, String> scoreToLevelMap = readMappingFromS3();
对于每个键,我一遍又一遍地加载整个地图。这不是性能问题,但是当尺寸增加时它可能会变成一个,无论如何这不是一种有效的方法。
我认为将整个地图保留在缓存中会更好,但我不知道该怎么做。任何人都可以帮助解决这个问题,或者提出一种更优雅的方法来实现这一目标。
答案 0 :(得分:6)
Guava对“只包含一个值的缓存”有不同的机制;它被称为Suppliers.memoizeWithExpiration
。
private Supplier<Map<Range<Double>, String> cachedMap =
Suppliers.memoizeWithExpiration(
new Supplier<Map<Range<Double>, String>() {
public Map<Range<Double>, String> get() {
return readMappingFromS3();
}
}, 10, TimeUnit.MINUTES);
public String getContentLevelForScore(Score score) {
Map<Range<Double>, String> scoreMap = cachedMap.get();
// etc.
}
答案 1 :(得分:2)
不要混用缓存和业务逻辑。 除非您的分数映射很大并且您可以加载单个部分,例如使用readMappingFromS3(Double d) - 只需缓存整个地图。
public static final String MAGIC_WORD = "oh please please give me my data!!!";
private final LoadingCache<String, Map<Range<Double>, String>> scoreToLevelCache;
public Mapper() {
scoreToLevelCache = CacheBuilder.newBuilder()
.expireAfterWrite(10, TimeUnit.MINUTES)
.build(new CacheLoader<String, Map<Range<Double>, String>>() {
public Map<Range<Double>, String> load(String score) {
return readMappingFromS3(); //readMappingFromS3 omitted for brevity
}
});
}
public Map<Range<Double>, String> getScoreMap() {
try {
return scoreToLevelCache.get(MAGIC_WORD);
} catch (ExecutionException e) {
throw new InternalServerException(e);
}
}
像这样获取级别名称
public String findLevel(final Double score) {
final Map<Range<Double>, String> scoreMap = getScoreMap();
for (final Range<Double> key : scoreMap.keySet()) {
if (key.contains(score)) {
return scoreMap.get(key);
}
}
...
}
答案 2 :(得分:0)
这是一个解决方案,可以一次读取整个地图,并通过refreshing it asynchronouzly as needed保留asyncReloading。
它会在refresh期间返回旧值而不会阻止多个读取器线程,例如Suppliers.memoizeWithExpiration
does。
private static final Object DUMMY_KEY = new Object();
private static final LoadingCache<Object, Map<Range<Double>, String>> scoreToLevelCache =
CacheBuilder.newBuilder()
.maximumSize(1)
.refreshAfterWrite(10, TimeUnit.MINUTES)
.build(CacheLoader.asyncReloading(
new CacheLoader<Object, Map<Range<Double>, String>>() {
public Map<Range<Double>, String> load(Object key) {
return readMappingFromS3();
}
},
Executors.newSingleThreadExecutor()));
public String getContentLevelForScore(Score score) {
try {
Map<Range<Double>, String> scoreMap = scoreToLevelCache.get(DUMMY_KEY);
// traverse scoreMap ranges
return level;
} catch (ExecutionException e) {
Throwables.throwIfUnchecked(e);
throw new IllegalStateException(e);
}
}
另请考虑将Map<Range<Double>, String>
替换为RangeMap <Double, String>
,以执行有效的远程查找。
答案 3 :(得分:0)
到目前为止,我找不到一种方法来动态存储由番石榴缓存的地图值,看起来所有值都需要在缓存地图初始化期间加载一次。尽管您需要随时间推移加载地图,但是一种解决方案是使用org.apache.commons.collections4.map库中的“ PassiveExpiringMap”
private static Map<String, String> cachedMap = new PassiveExpiringMap<>(30, TimeUnit.SECONDS);
将给定时间的高速缓存键添加到地图中。