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Oct 17, 2016
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Caching pattern: Cache-Aside #495

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6ed842e
Caching pattern: Refactor shutdown hook to use method reference
christofferh Sep 22, 2016
865f788
Caching pattern: Refactor LRU cache to avoid NPE and unnecessary cach…
christofferh Sep 22, 2016
e3355d7
Caching pattern: Style fix for null check
christofferh Sep 22, 2016
b31edda
Caching pattern: Implementation of Cache-Aside pattern
christofferh Sep 22, 2016
f114b5b
Caching pattern: Documentation and diagram
christofferh Oct 9, 2016
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1 change: 1 addition & 0 deletions caching/README.md
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Expand Up @@ -27,3 +27,4 @@ Use the Caching pattern(s) when

* [Write-through, write-around, write-back: Cache explained](http://www.computerweekly.com/feature/Write-through-write-around-write-back-Cache-explained)
* [Read-Through, Write-Through, Write-Behind, and Refresh-Ahead Caching](https://docs.oracle.com/cd/E15357_01/coh.360/e15723/cache_rtwtwbra.htm#COHDG5177)
* [Cache-Aside](https://msdn.microsoft.com/en-us/library/dn589799.aspx)
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190 changes: 87 additions & 103 deletions caching/etc/caching.ucls
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@@ -1,106 +1,90 @@
<?xml version="1.0" encoding="UTF-8"?>
<class-diagram version="1.1.8" icons="true" automaticImage="PNG" always-add-relationships="false" generalizations="true"
realizations="true" associations="true" dependencies="false" nesting-relationships="true">
<class id="1" language="java" name="main.java.com.wssia.caching.App" project="CachingPatterns"
file="/CachingPatterns/src/main/java/com/wssia/caching/App.java" binary="false" corner="BOTTOM_RIGHT">
<position height="-1" width="-1" x="249" y="150"/>
<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
sort-features="false" accessors="true" visibility="true">
<attributes public="true" package="true" protected="true" private="true" static="true"/>
<operations public="true" package="true" protected="true" private="true" static="true"/>
</display>
<class-diagram version="1.1.11" icons="true" automaticImage="PNG" always-add-relationships="false"
generalizations="true" realizations="true" associations="true" dependencies="false" nesting-relationships="true"
router="FAN">
<class id="1" language="java" name="com.iluwatar.caching.CacheStore" project="caching"
file="/caching/src/main/java/com/iluwatar/caching/CacheStore.java" binary="false" corner="BOTTOM_RIGHT">
<position height="-1" width="-1" x="322" y="444"/>
<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
sort-features="false" accessors="true" visibility="true">
<attributes public="true" package="true" protected="true" private="true" static="true"/>
<operations public="true" package="true" protected="true" private="true" static="true"/>
</display>
</class>
<class id="2" language="java" name="com.iluwatar.caching.LruCache" project="caching"
file="/caching/src/main/java/com/iluwatar/caching/LruCache.java" binary="false" corner="BOTTOM_RIGHT">
<position height="-1" width="-1" x="700" y="446"/>
<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
sort-features="false" accessors="true" visibility="true">
<attributes public="true" package="true" protected="true" private="true" static="true"/>
<operations public="true" package="true" protected="true" private="true" static="true"/>
</display>
</class>
<enumeration id="3" language="java" name="com.iluwatar.caching.CachingPolicy" project="caching"
file="/caching/src/main/java/com/iluwatar/caching/CachingPolicy.java" binary="false" corner="BOTTOM_RIGHT">
<position height="-1" width="-1" x="943" y="122"/>
<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
sort-features="false" accessors="true" visibility="true">
<attributes public="true" package="true" protected="true" private="true" static="true"/>
<operations public="true" package="true" protected="true" private="true" static="true"/>
</display>
</enumeration>
<class id="4" language="java" name="com.iluwatar.caching.DbManager" project="caching"
file="/caching/src/main/java/com/iluwatar/caching/DbManager.java" binary="false" corner="BOTTOM_RIGHT">
<position height="-1" width="-1" x="1011" y="426"/>
<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
sort-features="false" accessors="true" visibility="true">
<attributes public="true" package="true" protected="true" private="true" static="true"/>
<operations public="true" package="true" protected="true" private="true" static="true"/>
</display>
</class>
<class id="5" language="java" name="com.iluwatar.caching.App" project="caching"
file="/caching/src/main/java/com/iluwatar/caching/App.java" binary="false" corner="BOTTOM_RIGHT">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
<operations public="true" package="true" protected="true" private="true" static="true"/>
</display>
</class>
<class id="6" language="java" name="com.iluwatar.caching.AppManager" project="caching"
file="/caching/src/main/java/com/iluwatar/caching/AppManager.java" binary="false" corner="BOTTOM_RIGHT">
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<operations public="true" package="true" protected="true" private="true" static="true"/>
</display>
</class>
<class id="7" language="java" name="com.iluwatar.caching.UserAccount" project="caching"
file="/caching/src/main/java/com/iluwatar/caching/UserAccount.java" binary="false" corner="BOTTOM_RIGHT">
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<operations public="true" package="true" protected="true" private="true" static="true"/>
</display>
</class>
<class id="2" language="java" name="main.java.com.wssia.caching.AppManager" project="CachingPatterns"
file="/CachingPatterns/src/main/java/com/wssia/caching/AppManager.java" binary="false" corner="BOTTOM_RIGHT">
<position height="-1" width="-1" x="502" y="163"/>
<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
sort-features="false" accessors="true" visibility="true">
<attributes public="true" package="true" protected="true" private="true" static="true"/>
<operations public="true" package="true" protected="true" private="true" static="true"/>
</display>
</class>
<class id="3" language="java" name="main.java.com.wssia.caching.CacheStore" project="CachingPatterns"
file="/CachingPatterns/src/main/java/com/wssia/caching/CacheStore.java" binary="false" corner="BOTTOM_RIGHT">
<position height="-1" width="-1" x="537" y="436"/>
<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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<operations public="true" package="true" protected="true" private="true" static="true"/>
</display>
</class>
<enumeration id="4" language="java" name="main.java.com.wssia.caching.CachingPolicy" project="CachingPatterns"
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<operations public="true" package="true" protected="true" private="true" static="true"/>
</display>
</enumeration>
<class id="5" language="java" name="main.java.com.wssia.caching.DBManager" project="CachingPatterns"
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
<operations public="true" package="true" protected="true" private="true" static="true"/>
</display>
</class>
<class id="6" language="java" name="main.java.com.wssia.caching.LRUCache" project="CachingPatterns"
file="/CachingPatterns/src/main/java/com/wssia/caching/LRUCache.java" binary="false" corner="BOTTOM_RIGHT">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
<operations public="true" package="true" protected="true" private="true" static="true"/>
</display>
</class>
<class id="7" language="java" name="main.java.com.wssia.caching.UserAccount" project="CachingPatterns"
file="/CachingPatterns/src/main/java/com/wssia/caching/UserAccount.java" binary="false" corner="BOTTOM_RIGHT">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
<operations public="true" package="true" protected="true" private="true" static="true"/>
</display>
</class>
<class id="8" language="java" name="test.java.com.wssia.caching.AppTest" project="CachingPatterns"
file="/CachingPatterns/src/test/java/com/wssia/caching/AppTest.java" binary="false" corner="BOTTOM_RIGHT">
<position height="-1" width="-1" x="251" y="374"/>
<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
sort-features="false" accessors="true" visibility="true">
<attributes public="true" package="true" protected="true" private="true" static="true"/>
<operations public="true" package="true" protected="true" private="true" static="true"/>
</display>
</class>
<association id="9">
<end type="SOURCE" refId="2" navigable="false">
<attribute id="10" name="cachingPolicy"/>
<multiplicity id="11" minimum="0" maximum="1"/>
</end>
<end type="TARGET" refId="4" navigable="true"/>
<display labels="true" multiplicity="true"/>
</association>
<association id="12">
<end type="SOURCE" refId="8" navigable="false">
<attribute id="13" name="app"/>
<multiplicity id="14" minimum="0" maximum="1"/>
</end>
<end type="TARGET" refId="1" navigable="true"/>
<display labels="true" multiplicity="true"/>
</association>
<association id="15">
<end type="SOURCE" refId="3" navigable="false">
<attribute id="16" name="cache"/>
<multiplicity id="17" minimum="0" maximum="1"/>
</end>
<end type="TARGET" refId="6" navigable="true"/>
<display labels="true" multiplicity="true"/>
</association>
<classifier-display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
sort-features="false" accessors="true" visibility="true">
<attributes public="true" package="true" protected="true" private="true" static="true"/>
<operations public="true" package="true" protected="true" private="true" static="true"/>
</classifier-display>
<association id="8">
<end type="SOURCE" refId="1" navigable="false">
<attribute id="9" name="cache"/>
<multiplicity id="10" minimum="0" maximum="1"/>
</end>
<end type="TARGET" refId="2" navigable="true"/>
<display labels="true" multiplicity="true"/>
</association>
<association id="11">
<end type="SOURCE" refId="6" navigable="false">
<attribute id="12" name="cachingPolicy"/>
<multiplicity id="13" minimum="0" maximum="1"/>
</end>
<end type="TARGET" refId="3" navigable="true"/>
<display labels="true" multiplicity="true"/>
</association>
<classifier-display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
sort-features="false" accessors="true" visibility="true">
<attributes public="true" package="true" protected="true" private="true" static="true"/>
<operations public="true" package="true" protected="true" private="true" static="true"/>
</classifier-display>
<association-display labels="true" multiplicity="true"/>
</class-diagram>
</class-diagram>
46 changes: 35 additions & 11 deletions caching/src/main/java/com/iluwatar/caching/App.java
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Expand Up @@ -26,22 +26,23 @@
*
* The Caching pattern describes how to avoid expensive re-acquisition of resources by not releasing
* the resources immediately after their use. The resources retain their identity, are kept in some
* fast-access storage, and are re-used to avoid having to acquire them again. There are three main
* caching strategies/techniques in this pattern; each with their own pros and cons. They are:
* fast-access storage, and are re-used to avoid having to acquire them again. There are four main
* caching strategies/techniques in this pattern; each with their own pros and cons. They are;
* <code>write-through</code> which writes data to the cache and DB in a single transaction,
* <code>write-around</code> which writes data immediately into the DB instead of the cache, and
* <code>write-around</code> which writes data immediately into the DB instead of the cache,
* <code>write-behind</code> which writes data into the cache initially whilst the data is only
* written into the DB when the cache is full. The <code>read-through</code> strategy is also
* included in the mentioned three strategies -- returns data from the cache to the caller <b>if</b>
* it exists <b>else</b> 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 <code>cache-aside</code> which pushes the
* responsibility of keeping the data synchronized in both data sources to the application itself.
* The <code>read-through</code> strategy is also included in the mentioned four strategies --
* returns data from the cache to the caller <b>if</b> it exists <b>else</b> 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.
* <p>
* 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
Expand Down Expand Up @@ -74,6 +75,7 @@ public static void main(String[] args) {
app.useReadAndWriteThroughStrategy();
app.useReadThroughAndWriteAroundStrategy();
app.useReadThroughAndWriteBehindStrategy();
app.useCacheAsideStategy();
}

/**
Expand Down Expand Up @@ -136,4 +138,26 @@ public void useReadThroughAndWriteBehindStrategy() {
AppManager.find("004");
System.out.println(AppManager.printCacheContent());
}

/**
* Cache-Aside
*/
public void useCacheAsideStategy() {
System.out.println("# CachingPolicy.ASIDE");
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Is there any reason for not using logging framework like SLF4J or LOG4J Or Common logging?

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@chinnachalam you are right, using a logging framework would give some advantages such as ability to redirect output and filter output based on logging levels. But I think we should handle this issue on a more general level since there are multiple patterns not using a logging framework at the moment. Would you raise an issue about this matter, please?

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());
}
}
36 changes: 30 additions & 6 deletions caching/src/main/java/com/iluwatar/caching/AppManager.java
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Expand Up @@ -64,12 +64,7 @@ public static void initDb(boolean useMongoDb) {
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();
}
Expand All @@ -86,6 +81,8 @@ public static UserAccount find(String userId) {
return CacheStore.readThrough(userId);
} else if (cachingPolicy == CachingPolicy.BEHIND) {
return CacheStore.readThroughWithWriteBackPolicy(userId);
} else if (cachingPolicy == CachingPolicy.ASIDE) {
return findAside(userId);
}
return null;
}
Expand All @@ -100,10 +97,37 @@ public static void save(UserAccount userAccount) {
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;
}
}
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