Caching pattern: Implementation of Cache-Aside pattern

caching/src/main/java/com/iluwatar/caching/App.java

@@ -74,6 +74,7 @@ public class App {
     app.useReadAndWriteThroughStrategy();
     app.useReadThroughAndWriteAroundStrategy();
     app.useReadThroughAndWriteBehindStrategy();
+    app.useCacheAsideStategy();
   }
 
   /**
@@ -136,4 +137,26 @@ 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());
+  }
 }

caching/src/main/java/com/iluwatar/caching/AppManager.java

@@ -81,6 +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;
   }
@@ -95,10 +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;
+  }
 }

caching/src/main/java/com/iluwatar/caching/CacheStore.java

@@ -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);
+  }
 }

caching/src/main/java/com/iluwatar/caching/CachingPolicy.java

@@ -28,7 +28,7 @@ package com.iluwatar.caching;
  *
  */
 public enum CachingPolicy {
-  THROUGH("through"), AROUND("around"), BEHIND("behind");
+  THROUGH("through"), AROUND("around"), BEHIND("behind"), ASIDE("aside");
 
   private String policy;
 

caching/src/test/java/com/iluwatar/caching/CachingTest.java

@@ -60,4 +60,9 @@ public class CachingTest {
   public void testReadThroughAndWriteBehindStrategy() {
     app.useReadThroughAndWriteBehindStrategy();
   }
+
+  @Test
+  public void testCacheAsideStrategy() {
+    app.useCacheAsideStategy();
+  }
 }