Add gallery spider

app/src/main/java/com/hippo/ehviewer/EhCacheKeyFactory.java

@@ -0,0 +1,26 @@
+package com.hippo.ehviewer;
+
+public class EhCacheKeyFactory {
+
+    public static String getThumbKey(int gid) {
+        return "thumb:" + gid;
+    }
+
+    /**
+     * @param index start from 0
+     */
+    public static String getNormalPreviewKey(int gid, int index) {
+        return "preview:normal:" + gid + ":" + index;
+    }
+
+    /**
+     * @param index start from 0
+     */
+    public static String getLargePreviewKey(int gid, int index) {
+        return "preview:large:" + gid + ":" + index;
+    }
+
+    public static String getImageKey(int gid, int index) {
+        return "image:" + gid + ":" + index;
+    }
+}