write-through which writes data to the cache and DB in a single transaction,
- * write-around which writes data immediately into the DB instead of the cache, and
+ * write-around which writes data immediately into the DB instead of the cache,
* write-behind which writes data into the cache initially whilst the data is only
- * written into the DB when the cache is full. The read-through strategy is also
- * included in the mentioned three strategies -- returns data from the cache to the caller if
- * it exists else queries from DB and stores it into the cache for future use. These
- * strategies determine when the data in the cache should be written back to the backing store (i.e.
- * Database) and help keep both data sources synchronized/up-to-date. This pattern can improve
- * performance and also helps to maintain consistency between data held in the cache and the data in
- * the underlying data store.
+ * written into the DB when the cache is full, and cache-aside which pushes the
+ * responsibility of keeping the data synchronized in both data sources to the application itself.
+ * The read-through strategy is also included in the mentioned four strategies --
+ * returns data from the cache to the caller if it exists else queries from DB and
+ * stores it into the cache for future use. These strategies determine when the data in the cache
+ * should be written back to the backing store (i.e. Database) and help keep both data sources
+ * synchronized/up-to-date. This pattern can improve performance and also helps to maintain
+ * consistency between data held in the cache and the data in the underlying data store.
*
* In this example, the user account ({@link UserAccount}) entity is used as the underlying
* application data. The cache itself is implemented as an internal (Java) data structure. It adopts
- * a Least-Recently-Used (LRU) strategy for evicting data from itself when its full. The three
+ * a Least-Recently-Used (LRU) strategy for evicting data from itself when its full. The four
* strategies are individually tested. The testing of the cache is restricted towards saving and
* querying of user accounts from the underlying data store ( {@link DbManager}). The main class (
* {@link App} is not aware of the underlying mechanics of the application (i.e. save and query) and
@@ -74,6 +75,7 @@ public class App {
app.useReadAndWriteThroughStrategy();
app.useReadThroughAndWriteAroundStrategy();
app.useReadThroughAndWriteBehindStrategy();
+ app.useCacheAsideStategy();
}
/**
@@ -136,4 +138,26 @@ public class App {
AppManager.find("004");
System.out.println(AppManager.printCacheContent());
}
+
+ /**
+ * Cache-Aside
+ */
+ public void useCacheAsideStategy() {
+ System.out.println("# CachingPolicy.ASIDE");
+ AppManager.initCachingPolicy(CachingPolicy.ASIDE);
+ System.out.println(AppManager.printCacheContent());
+
+ UserAccount userAccount3 = new UserAccount("003", "Adam", "He likes food.");
+ UserAccount userAccount4 = new UserAccount("004", "Rita", "She hates cats.");
+ UserAccount userAccount5 = new UserAccount("005", "Isaac", "He is allergic to mustard.");
+ AppManager.save(userAccount3);
+ AppManager.save(userAccount4);
+ AppManager.save(userAccount5);
+
+ System.out.println(AppManager.printCacheContent());
+ AppManager.find("003");
+ System.out.println(AppManager.printCacheContent());
+ AppManager.find("004");
+ System.out.println(AppManager.printCacheContent());
+ }
}
diff --git a/caching/src/main/java/com/iluwatar/caching/AppManager.java b/caching/src/main/java/com/iluwatar/caching/AppManager.java
index 2967c759f..2d6a424a3 100644
--- a/caching/src/main/java/com/iluwatar/caching/AppManager.java
+++ b/caching/src/main/java/com/iluwatar/caching/AppManager.java
@@ -64,12 +64,7 @@ public final class AppManager {
public static void initCachingPolicy(CachingPolicy policy) {
cachingPolicy = policy;
if (cachingPolicy == CachingPolicy.BEHIND) {
- Runtime.getRuntime().addShutdownHook(new Thread(new Runnable() {
- @Override
- public void run() {
- CacheStore.flushCache();
- }
- }));
+ Runtime.getRuntime().addShutdownHook(new Thread(CacheStore::flushCache));
}
CacheStore.clearCache();
}
@@ -86,6 +81,8 @@ public final class AppManager {
return CacheStore.readThrough(userId);
} else if (cachingPolicy == CachingPolicy.BEHIND) {
return CacheStore.readThroughWithWriteBackPolicy(userId);
+ } else if (cachingPolicy == CachingPolicy.ASIDE) {
+ return findAside(userId);
}
return null;
}
@@ -100,10 +97,37 @@ public final class AppManager {
CacheStore.writeAround(userAccount);
} else if (cachingPolicy == CachingPolicy.BEHIND) {
CacheStore.writeBehind(userAccount);
+ } else if (cachingPolicy == CachingPolicy.ASIDE) {
+ saveAside(userAccount);
}
}
public static String printCacheContent() {
return CacheStore.print();
}
+
+ /**
+ * Cache-Aside save user account helper
+ */
+ private static void saveAside(UserAccount userAccount) {
+ DbManager.updateDb(userAccount);
+ CacheStore.invalidate(userAccount.getUserId());
+ }
+
+ /**
+ * Cache-Aside find user account helper
+ */
+ private static UserAccount findAside(String userId) {
+ UserAccount userAccount = CacheStore.get(userId);
+ if (userAccount != null) {
+ return userAccount;
+ }
+
+ userAccount = DbManager.readFromDb(userId);
+ if (userAccount != null) {
+ CacheStore.set(userId, userAccount);
+ }
+
+ return userAccount;
+ }
}
diff --git a/caching/src/main/java/com/iluwatar/caching/CacheStore.java b/caching/src/main/java/com/iluwatar/caching/CacheStore.java
index 5903f8219..c2b95a1bd 100644
--- a/caching/src/main/java/com/iluwatar/caching/CacheStore.java
+++ b/caching/src/main/java/com/iluwatar/caching/CacheStore.java
@@ -40,7 +40,7 @@ public class CacheStore {
* Init cache capacity
*/
public static void initCapacity(int capacity) {
- if (null == cache) {
+ if (cache == null) {
cache = new LruCache(capacity);
} else {
cache.setCapacity(capacity);
@@ -121,7 +121,7 @@ public class CacheStore {
* Clears cache
*/
public static void clearCache() {
- if (null != cache) {
+ if (cache != null) {
cache.clear();
}
}
@@ -153,4 +153,25 @@ public class CacheStore {
sb.append("----\n");
return sb.toString();
}
+
+ /**
+ * Delegate to backing cache store
+ */
+ public static UserAccount get(String userId) {
+ return cache.get(userId);
+ }
+
+ /**
+ * Delegate to backing cache store
+ */
+ public static void set(String userId, UserAccount userAccount) {
+ cache.set(userId, userAccount);
+ }
+
+ /**
+ * Delegate to backing cache store
+ */
+ public static void invalidate(String userId) {
+ cache.invalidate(userId);
+ }
}
diff --git a/caching/src/main/java/com/iluwatar/caching/CachingPolicy.java b/caching/src/main/java/com/iluwatar/caching/CachingPolicy.java
index 490113baa..5ad32f699 100644
--- a/caching/src/main/java/com/iluwatar/caching/CachingPolicy.java
+++ b/caching/src/main/java/com/iluwatar/caching/CachingPolicy.java
@@ -24,11 +24,11 @@ package com.iluwatar.caching;
/**
*
- * Enum class containing the three caching strategies implemented in the pattern.
+ * Enum class containing the four caching strategies implemented in the pattern.
*
*/
public enum CachingPolicy {
- THROUGH("through"), AROUND("around"), BEHIND("behind");
+ THROUGH("through"), AROUND("around"), BEHIND("behind"), ASIDE("aside");
private String policy;
diff --git a/caching/src/main/java/com/iluwatar/caching/DbManager.java b/caching/src/main/java/com/iluwatar/caching/DbManager.java
index c12461d0c..455302106 100644
--- a/caching/src/main/java/com/iluwatar/caching/DbManager.java
+++ b/caching/src/main/java/com/iluwatar/caching/DbManager.java
@@ -82,7 +82,7 @@ public final class DbManager {
}
return null;
}
- if (null == db) {
+ if (db == null) {
try {
connect();
} catch (ParseException e) {
@@ -106,7 +106,7 @@ public final class DbManager {
virtualDB.put(userAccount.getUserId(), userAccount);
return;
}
- if (null == db) {
+ if (db == null) {
try {
connect();
} catch (ParseException e) {
@@ -126,7 +126,7 @@ public final class DbManager {
virtualDB.put(userAccount.getUserId(), userAccount);
return;
}
- if (null == db) {
+ if (db == null) {
try {
connect();
} catch (ParseException e) {
@@ -148,7 +148,7 @@ public final class DbManager {
virtualDB.put(userAccount.getUserId(), userAccount);
return;
}
- if (null == db) {
+ if (db == null) {
try {
connect();
} catch (ParseException e) {
diff --git a/caching/src/main/java/com/iluwatar/caching/LruCache.java b/caching/src/main/java/com/iluwatar/caching/LruCache.java
index 5c5549afd..00e27ccf1 100644
--- a/caching/src/main/java/com/iluwatar/caching/LruCache.java
+++ b/caching/src/main/java/com/iluwatar/caching/LruCache.java
@@ -73,7 +73,6 @@ public class LruCache {
}
/**
- *
* Remove node from linked list.
*/
public void remove(Node node) {
@@ -90,7 +89,6 @@ public class LruCache {
}
/**
- *
* Move node to the front of the list.
*/
public void setHead(Node node) {
@@ -136,10 +134,11 @@ public class LruCache {
* Invalidate cache for user
*/
public void invalidate(String userId) {
- System.out.println("# " + userId + " has been updated! Removing older version from cache...");
- Node toBeRemoved = cache.get(userId);
- remove(toBeRemoved);
- cache.remove(userId);
+ Node toBeRemoved = cache.remove(userId);
+ if (toBeRemoved != null) {
+ System.out.println("# " + userId + " has been updated! Removing older version from cache...");
+ remove(toBeRemoved);
+ }
}
public boolean isFull() {
@@ -160,7 +159,6 @@ public class LruCache {
}
/**
- *
* Returns cache data in list form.
*/
public List