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Merge pull request #495 from christofferh/feat/cache-aside
Caching pattern: Cache-Aside
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‎caching/README.md

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@@ -27,3 +27,4 @@ Use the Caching pattern(s) when
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* [Write-through, write-around, write-back: Cache explained](http://www.computerweekly.com/feature/Write-through-write-around-write-back-Cache-explained)
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* [Read-Through, Write-Through, Write-Behind, and Refresh-Ahead Caching](https://docs.oracle.com/cd/E15357_01/coh.360/e15723/cache_rtwtwbra.htm#COHDG5177)
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* [Cache-Aside](https://msdn.microsoft.com/en-us/library/dn589799.aspx)

‎caching/etc/caching.png

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‎caching/etc/caching.ucls

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@@ -1,106 +1,90 @@
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<?xml version="1.0" encoding="UTF-8"?>
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<class-diagram version="1.1.8" icons="true" automaticImage="PNG" always-add-relationships="false" generalizations="true"
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realizations="true" associations="true" dependencies="false" nesting-relationships="true">
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<class id="1" language="java" name="main.java.com.wssia.caching.App" project="CachingPatterns"
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file="/CachingPatterns/src/main/java/com/wssia/caching/App.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="249" y="150"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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<class-diagram version="1.1.11" icons="true" automaticImage="PNG" always-add-relationships="false"
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generalizations="true" realizations="true" associations="true" dependencies="false" nesting-relationships="true"
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router="FAN">
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<class id="1" language="java" name="com.iluwatar.caching.CacheStore" project="caching"
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file="/caching/src/main/java/com/iluwatar/caching/CacheStore.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="322" y="444"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</class>
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<class id="2" language="java" name="com.iluwatar.caching.LruCache" project="caching"
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file="/caching/src/main/java/com/iluwatar/caching/LruCache.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="700" y="446"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</class>
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<enumeration id="3" language="java" name="com.iluwatar.caching.CachingPolicy" project="caching"
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file="/caching/src/main/java/com/iluwatar/caching/CachingPolicy.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="943" y="122"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</enumeration>
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<class id="4" language="java" name="com.iluwatar.caching.DbManager" project="caching"
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file="/caching/src/main/java/com/iluwatar/caching/DbManager.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="1011" y="426"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</class>
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<class id="5" language="java" name="com.iluwatar.caching.App" project="caching"
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file="/caching/src/main/java/com/iluwatar/caching/App.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="304" y="95"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</class>
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<class id="6" language="java" name="com.iluwatar.caching.AppManager" project="caching"
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file="/caching/src/main/java/com/iluwatar/caching/AppManager.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="604" y="122"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</class>
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<class id="7" language="java" name="com.iluwatar.caching.UserAccount" project="caching"
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file="/caching/src/main/java/com/iluwatar/caching/UserAccount.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="1161" y="139"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</class>
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<class id="2" language="java" name="main.java.com.wssia.caching.AppManager" project="CachingPatterns"
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file="/CachingPatterns/src/main/java/com/wssia/caching/AppManager.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="502" y="163"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</class>
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<class id="3" language="java" name="main.java.com.wssia.caching.CacheStore" project="CachingPatterns"
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file="/CachingPatterns/src/main/java/com/wssia/caching/CacheStore.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="537" y="436"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</class>
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<enumeration id="4" language="java" name="main.java.com.wssia.caching.CachingPolicy" project="CachingPatterns"
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file="/CachingPatterns/src/main/java/com/wssia/caching/CachingPolicy.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="789" y="162"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</enumeration>
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<class id="5" language="java" name="main.java.com.wssia.caching.DBManager" project="CachingPatterns"
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file="/CachingPatterns/src/main/java/com/wssia/caching/DBManager.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="1137" y="134"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</class>
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<class id="6" language="java" name="main.java.com.wssia.caching.LRUCache" project="CachingPatterns"
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file="/CachingPatterns/src/main/java/com/wssia/caching/LRUCache.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="884" y="435"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</class>
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<class id="7" language="java" name="main.java.com.wssia.caching.UserAccount" project="CachingPatterns"
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file="/CachingPatterns/src/main/java/com/wssia/caching/UserAccount.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="1140" y="405"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</class>
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<class id="8" language="java" name="test.java.com.wssia.caching.AppTest" project="CachingPatterns"
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file="/CachingPatterns/src/test/java/com/wssia/caching/AppTest.java" binary="false" corner="BOTTOM_RIGHT">
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<position height="-1" width="-1" x="251" y="374"/>
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<display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</display>
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</class>
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<association id="9">
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<end type="SOURCE" refId="2" navigable="false">
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<attribute id="10" name="cachingPolicy"/>
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<multiplicity id="11" minimum="0" maximum="1"/>
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</end>
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<end type="TARGET" refId="4" navigable="true"/>
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<display labels="true" multiplicity="true"/>
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</association>
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<association id="12">
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<end type="SOURCE" refId="8" navigable="false">
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<attribute id="13" name="app"/>
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<multiplicity id="14" minimum="0" maximum="1"/>
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</end>
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<end type="TARGET" refId="1" navigable="true"/>
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<display labels="true" multiplicity="true"/>
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</association>
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<association id="15">
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<end type="SOURCE" refId="3" navigable="false">
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<attribute id="16" name="cache"/>
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<multiplicity id="17" minimum="0" maximum="1"/>
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</end>
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<end type="TARGET" refId="6" navigable="true"/>
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<display labels="true" multiplicity="true"/>
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</association>
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<classifier-display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</classifier-display>
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<association id="8">
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<end type="SOURCE" refId="1" navigable="false">
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<attribute id="9" name="cache"/>
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<multiplicity id="10" minimum="0" maximum="1"/>
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</end>
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<end type="TARGET" refId="2" navigable="true"/>
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<display labels="true" multiplicity="true"/>
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</association>
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<association id="11">
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<end type="SOURCE" refId="6" navigable="false">
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<attribute id="12" name="cachingPolicy"/>
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<multiplicity id="13" minimum="0" maximum="1"/>
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</end>
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<end type="TARGET" refId="3" navigable="true"/>
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<display labels="true" multiplicity="true"/>
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</association>
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<classifier-display autosize="true" stereotype="true" package="true" initial-value="false" signature="true"
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sort-features="false" accessors="true" visibility="true">
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<attributes public="true" package="true" protected="true" private="true" static="true"/>
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<operations public="true" package="true" protected="true" private="true" static="true"/>
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</classifier-display>
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<association-display labels="true" multiplicity="true"/>
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</class-diagram>
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</class-diagram>

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

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@@ -26,22 +26,23 @@
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*
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* The Caching pattern describes how to avoid expensive re-acquisition of resources by not releasing
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* the resources immediately after their use. The resources retain their identity, are kept in some
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* fast-access storage, and are re-used to avoid having to acquire them again. There are three main
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* caching strategies/techniques in this pattern; each with their own pros and cons. They are:
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* fast-access storage, and are re-used to avoid having to acquire them again. There are four main
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* caching strategies/techniques in this pattern; each with their own pros and cons. They are;
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* <code>write-through</code> which writes data to the cache and DB in a single transaction,
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* <code>write-around</code> which writes data immediately into the DB instead of the cache, and
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* <code>write-around</code> which writes data immediately into the DB instead of the cache,
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* <code>write-behind</code> which writes data into the cache initially whilst the data is only
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* written into the DB when the cache is full. The <code>read-through</code> strategy is also
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* included in the mentioned three strategies -- returns data from the cache to the caller <b>if</b>
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* it exists <b>else</b> queries from DB and stores it into the cache for future use. These
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* strategies determine when the data in the cache should be written back to the backing store (i.e.
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* Database) and help keep both data sources synchronized/up-to-date. This pattern can improve
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* performance and also helps to maintain consistency between data held in the cache and the data in
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* the underlying data store.
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* written into the DB when the cache is full, and <code>cache-aside</code> which pushes the
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* responsibility of keeping the data synchronized in both data sources to the application itself.
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* The <code>read-through</code> strategy is also included in the mentioned four strategies --
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* returns data from the cache to the caller <b>if</b> it exists <b>else</b> queries from DB and
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* stores it into the cache for future use. These strategies determine when the data in the cache
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* should be written back to the backing store (i.e. Database) and help keep both data sources
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* synchronized/up-to-date. This pattern can improve performance and also helps to maintain
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* consistency between data held in the cache and the data in the underlying data store.
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* <p>
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* In this example, the user account ({@link UserAccount}) entity is used as the underlying
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* application data. The cache itself is implemented as an internal (Java) data structure. It adopts
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* a Least-Recently-Used (LRU) strategy for evicting data from itself when its full. The three
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* a Least-Recently-Used (LRU) strategy for evicting data from itself when its full. The four
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* strategies are individually tested. The testing of the cache is restricted towards saving and
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* querying of user accounts from the underlying data store ( {@link DbManager}). The main class (
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* {@link App} is not aware of the underlying mechanics of the application (i.e. save and query) and
@@ -74,6 +75,7 @@ public static void main(String[] args) {
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app.useReadAndWriteThroughStrategy();
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app.useReadThroughAndWriteAroundStrategy();
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app.useReadThroughAndWriteBehindStrategy();
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app.useCacheAsideStategy();
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}
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/**
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AppManager.find("004");
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System.out.println(AppManager.printCacheContent());
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}
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/**
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* Cache-Aside
144+
*/
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public void useCacheAsideStategy() {
146+
System.out.println("# CachingPolicy.ASIDE");
147+
AppManager.initCachingPolicy(CachingPolicy.ASIDE);
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System.out.println(AppManager.printCacheContent());
149+
150+
UserAccount userAccount3 = new UserAccount("003", "Adam", "He likes food.");
151+
UserAccount userAccount4 = new UserAccount("004", "Rita", "She hates cats.");
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UserAccount userAccount5 = new UserAccount("005", "Isaac", "He is allergic to mustard.");
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AppManager.save(userAccount3);
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AppManager.save(userAccount4);
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AppManager.save(userAccount5);
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System.out.println(AppManager.printCacheContent());
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AppManager.find("003");
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System.out.println(AppManager.printCacheContent());
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AppManager.find("004");
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System.out.println(AppManager.printCacheContent());
162+
}
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}

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

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Original file line numberDiff line numberDiff line change
@@ -64,12 +64,7 @@ public static void initDb(boolean useMongoDb) {
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public static void initCachingPolicy(CachingPolicy policy) {
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cachingPolicy = policy;
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if (cachingPolicy == CachingPolicy.BEHIND) {
67-
Runtime.getRuntime().addShutdownHook(new Thread(new Runnable() {
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@Override
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public void run() {
70-
CacheStore.flushCache();
71-
}
72-
}));
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Runtime.getRuntime().addShutdownHook(new Thread(CacheStore::flushCache));
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}
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CacheStore.clearCache();
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}
@@ -86,6 +81,8 @@ public static UserAccount find(String userId) {
8681
return CacheStore.readThrough(userId);
8782
} else if (cachingPolicy == CachingPolicy.BEHIND) {
8883
return CacheStore.readThroughWithWriteBackPolicy(userId);
84+
} else if (cachingPolicy == CachingPolicy.ASIDE) {
85+
return findAside(userId);
8986
}
9087
return null;
9188
}
@@ -100,10 +97,37 @@ public static void save(UserAccount userAccount) {
10097
CacheStore.writeAround(userAccount);
10198
} else if (cachingPolicy == CachingPolicy.BEHIND) {
10299
CacheStore.writeBehind(userAccount);
100+
} else if (cachingPolicy == CachingPolicy.ASIDE) {
101+
saveAside(userAccount);
103102
}
104103
}
105104

106105
public static String printCacheContent() {
107106
return CacheStore.print();
108107
}
108+
109+
/**
110+
* Cache-Aside save user account helper
111+
*/
112+
private static void saveAside(UserAccount userAccount) {
113+
DbManager.updateDb(userAccount);
114+
CacheStore.invalidate(userAccount.getUserId());
115+
}
116+
117+
/**
118+
* Cache-Aside find user account helper
119+
*/
120+
private static UserAccount findAside(String userId) {
121+
UserAccount userAccount = CacheStore.get(userId);
122+
if (userAccount != null) {
123+
return userAccount;
124+
}
125+
126+
userAccount = DbManager.readFromDb(userId);
127+
if (userAccount != null) {
128+
CacheStore.set(userId, userAccount);
129+
}
130+
131+
return userAccount;
132+
}
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}

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