task-14: batch read image db cache and touch only actual hits

backend-java/src/main/java/com/nanri/aiimage/modules/similarasin/service/SimilarAsinImagePrefetchService.java

@@ -144,9 +144,15 @@ public class SimilarAsinImagePrefetchService {
                     cachedHashes.addAll(found);
                 }
             }
+            // Task 14：只对实际命中的 url_hash 更新 last_used_at，未命中不 touch。
             for (int start = 0; start < allHashes.size(); start += CACHE_LOOKUP_BATCH_SIZE) {
-                taskImageCacheMapper.touchLastUsedBatch(allHashes.subList(start,
-                        Math.min(start + CACHE_LOOKUP_BATCH_SIZE, allHashes.size())));
+                List<String> batch = allHashes.subList(start,
+                        Math.min(start + CACHE_LOOKUP_BATCH_SIZE, allHashes.size()));
+                List<String> hitBatch = new ArrayList<>(batch);
+                hitBatch.retainAll(cachedHashes);
+                if (!hitBatch.isEmpty()) {
+                    taskImageCacheMapper.touchLastUsedBatch(hitBatch);
+                }
             }
             hit = cachedHashes.size();
         }
@@ -189,6 +195,75 @@ public class SimilarAsinImagePrefetchService {
                 taskId, urls.size(), hit, miss, fail);
     }
 
+    /**
+     * Task 14：批量直读 DB cache 缩略图。一次 IN 查询返回全部命中字节；
+     * last_used_at 只对实际命中的 url_hash 更新（touch 集合 = 命中集合），
+     * 未命中 url 不产生任何 touch。输入按传入顺序返回，未命中为 null。
+     * 失败/开关关闭返回空列表，由调用方走回退路径。
+     */
+    List<byte[]> lookupBatch(List<String> urls) {
+        List<byte[]> result = new ArrayList<>();
+        if (!properties.isImageDbCacheEnabled()) {
+            return result;
+        }
+        if (urls == null || urls.isEmpty()) {
+            return result;
+        }
+        try {
+            List<String> hashes = new ArrayList<>(urls.size());
+            for (String url : urls) {
+                if (url == null) {
+                    result.add(null);
+                    continue;
+                }
+                String trimmed = url.trim();
+                if (trimmed.isEmpty()) {
+                    result.add(null);
+                    continue;
+                }
+                hashes.add(sha256Hex(trimmed));
+                result.add(null);
+            }
+            if (hashes.isEmpty()) {
+                return result;
+            }
+            Map<String, byte[]> bytesByHash = new LinkedHashMap<>();
+            List<String> hitHashes = new ArrayList<>();
+            for (int start = 0; start < hashes.size(); start += CACHE_LOOKUP_BATCH_SIZE) {
+                List<String> batch = hashes.subList(start,
+                        Math.min(start + CACHE_LOOKUP_BATCH_SIZE, hashes.size()));
+                List<TaskImageCacheEntity> rows = taskImageCacheMapper.selectBytesByUrlHashes(batch);
+                if (rows == null) {
+                    continue;
+                }
+                for (TaskImageCacheEntity row : rows) {
+                    if (row != null && row.getUrlHash() != null && row.getImageBytes() != null
+                            && row.getImageBytes().length > 0) {
+                        if (bytesByHash.putIfAbsent(row.getUrlHash(), row.getImageBytes()) == null) {
+                            hitHashes.add(row.getUrlHash());
+                        }
+                    }
+                }
+            }
+            for (int i = 0; i < hashes.size(); i++) {
+                byte[] bytes = bytesByHash.get(hashes.get(i));
+                if (bytes != null) {
+                    result.set(i, bytes);
+                }
+            }
+            if (!hitHashes.isEmpty()) {
+                for (int start = 0; start < hitHashes.size(); start += CACHE_LOOKUP_BATCH_SIZE) {
+                    taskImageCacheMapper.touchLastUsedBatch(hitHashes.subList(start,
+                            Math.min(start + CACHE_LOOKUP_BATCH_SIZE, hitHashes.size())));
+                }
+            }
+        } catch (Exception ex) {
+            log.debug("[similar-asin] prefetch batch lookup failed urls={} err={}", urls.size(), ex.getMessage());
+            return List.of();
+        }
+        return result;
+    }
+
     /**
      * P2-11：DB cache 直读入口。命中时同步 touchLastUsed，便于 LRU 清理。
      * 失败/未命中返回 null，由调用方走回退路径。

backend-java/src/main/java/com/nanri/aiimage/modules/task/mapper/TaskImageCacheMapper.java

@@ -45,6 +45,14 @@ public interface TaskImageCacheMapper extends BaseMapper<TaskImageCacheEntity> {
     @Select("SELECT image_bytes FROM biz_task_image_cache WHERE url_hash = #{urlHash} LIMIT 1")
     byte[] selectBytesByUrlHash(@Param("urlHash") String urlHash);
 
+    /**
+     * Task 14：批量直读缩略图字节。只 select url_hash + image_bytes 两列，
+     * 避免把整行 entity（含 url 字符串）拉回 JVM；配合 batchSize 分片控制 IN 长度。
+     */
+    @Select("<script>SELECT url_hash, image_bytes FROM biz_task_image_cache WHERE url_hash IN " +
+            "<foreach collection='urlHashes' item='hash' open='(' separator=',' close=')'>#{hash}</foreach></script>")
+    List<TaskImageCacheEntity> selectBytesByUrlHashes(@Param("urlHashes") List<String> urlHashes);
+
     @Select("SELECT COALESCE(SUM(byte_size), 0) FROM biz_task_image_cache")
     Long sumByteSize();