diff --git a/dirty-flag/README.md b/dirty-flag/README.md new file mode 100644 index 000000000..36c92f0e2 --- /dev/null +++ b/dirty-flag/README.md @@ -0,0 +1,26 @@ +--- +layout: pattern +title: Dirty Flag +folder: dirty-flag +permalink: /patterns/dirty-flag/ +categories: Other +tags: + - Java + - Difficulty-Easy + - Performance +--- + +## Intent +To avoid expensive re-acquisition of resources. The resources retain their identity, are kept in some +fast-access storage, and are re-used to avoid having to acquire them again. + +![alt text](./etc/dirty-flag.png "Dirty Flag") + +## Applicability +Use the Dirty Flag pattern when + +* Repetitious acquisition, initialization, and release of the same resource causes unnecessary performance overhead. + +## Credits + +* [Design Patterns: Dirty Flag](https://www.takeupcode.com/podcast/89-design-patterns-dirty-flag/) diff --git a/dirty-flag/etc/dirty-flag.png b/dirty-flag/etc/dirty-flag.png new file mode 100644 index 000000000..98d4f679d Binary files /dev/null and b/dirty-flag/etc/dirty-flag.png differ diff --git a/dirty-flag/etc/dirty-flag.ucls b/dirty-flag/etc/dirty-flag.ucls new file mode 100644 index 000000000..760d456f7 --- /dev/null +++ b/dirty-flag/etc/dirty-flag.ucls @@ -0,0 +1,45 @@ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + \ No newline at end of file diff --git a/dirty-flag/pom.xml b/dirty-flag/pom.xml new file mode 100644 index 000000000..a50381a56 --- /dev/null +++ b/dirty-flag/pom.xml @@ -0,0 +1,30 @@ + + + 4.0.0 + + com.iluwatar + java-design-patterns + 1.20.0-SNAPSHOT + + com.iluwatar + dirty-flag + 1.20.0-SNAPSHOT + dirty-flag + http://maven.apache.org + + UTF-8 + + + + org.junit.jupiter + junit-jupiter-api + test + + + org.junit.jupiter + junit-jupiter-engine + test + + + diff --git a/dirty-flag/src/main/java/com/iluwatar/dirtyflag/App.java b/dirty-flag/src/main/java/com/iluwatar/dirtyflag/App.java new file mode 100644 index 000000000..4d72b34da --- /dev/null +++ b/dirty-flag/src/main/java/com/iluwatar/dirtyflag/App.java @@ -0,0 +1,82 @@ +/** + * The MIT License + * Copyright (c) 2014-2016 Ilkka Seppälä + *

+ * Permission is hereby granted, free of charge, to any person obtaining a copy + * of this software and associated documentation files (the "Software"), to deal + * in the Software without restriction, including without limitation the rights + * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell + * copies of the Software, and to permit persons to whom the Software is + * furnished to do so, subject to the following conditions: + *

+ * The above copyright notice and this permission notice shall be included in + * all copies or substantial portions of the Software. + *

+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE + * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, + * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN + * THE SOFTWARE. + */ +package com.iluwatar.dirtyflag; + +import java.util.List; +import java.util.concurrent.Executors; +import java.util.concurrent.ScheduledExecutorService; +import java.util.concurrent.TimeUnit; + +/** + * + * This application demonstrates the Dirty Flag pattern. The dirty flag behavioral pattern allows you to avoid + * expensive operations that would just need to be done again anyway. This is a simple pattern that really just explains + * how to add a bool value to your class that you can set anytime a property changes. This will let your class know that + * any results it may have previously calculated will need to be calculated again when they’re requested. Once the + * results are re-calculated, then the bool value can be cleared. + * + * There are some points that need to be considered before diving into using this pattern:- there are some things you’ll + * need to consider:- (1) Do you need it? This design pattern works well when the results to be calculated are difficult + * or resource intensive to compute. You want to save them. You also don’t want to be calculating them several times in + * a row when only the last one counts. (2) When do you set the dirty flag? Make sure that you set the dirty flag within + * the class itself whenever an important property changes. This property should affect the result of the calculated + * result and by changing the property, that makes the last result invalid. (3) When do you clear the dirty flag? It + * might seem obvious that the dirty flag should be cleared whenever the result is calculated with up-to-date + * information but there are other times when you might want to clear the flag. + * + * In this example, the {@link DataFetcher} holds the dirty flag. It fetches and re-fetches from world.txt + * when needed. {@link World} mainly serves the data to the front-end. + */ +public class App { + /** + * Program execution point + */ + public void run() { + + final ScheduledExecutorService executorService = Executors.newSingleThreadScheduledExecutor(); + executorService.scheduleAtFixedRate(new Runnable() { + @Override + public void run() { + World world = new World(); + List countries = world.fetch(); + System.out.println("Our world currently has the following countries:-"); + for (String country : countries) { + System.out.println("\t" + country); + } + } + }, 0, 15, TimeUnit.SECONDS); // Run at every 15 seconds. + } + + /** + * Program entry point + * + * @param args + * command line args + */ + public static void main(String[] args) { + App app = new App(); + + app.run(); + } + +} diff --git a/dirty-flag/src/main/java/com/iluwatar/dirtyflag/DataFetcher.java b/dirty-flag/src/main/java/com/iluwatar/dirtyflag/DataFetcher.java new file mode 100644 index 000000000..9123bf32d --- /dev/null +++ b/dirty-flag/src/main/java/com/iluwatar/dirtyflag/DataFetcher.java @@ -0,0 +1,59 @@ +package com.iluwatar.dirtyflag; + +import java.io.BufferedReader; +import java.io.File; +import java.io.FileReader; +import java.io.IOException; +import java.util.ArrayList; +import java.util.List; + +/** + * A mock database manager -- Fetches data from a raw file. + * + * @author swaisuan + * + */ +public class DataFetcher { + + private final String filename = "world.txt"; + private long lastFetched; + + public DataFetcher() { + this.lastFetched = -1; + } + + private boolean isDirty(long fileLastModified) { + if (lastFetched != fileLastModified) { + lastFetched = fileLastModified; + return true; + } + return false; + } + + /** + * Fetches data/content from raw file. + * + * @return List of strings + */ + public List fetch() { + ClassLoader classLoader = getClass().getClassLoader(); + File file = new File(classLoader.getResource(filename).getFile()); + + if (isDirty(file.lastModified())) { + System.out.println(filename + " is dirty! Re-fetching file content..."); + + List data = new ArrayList(); + try (BufferedReader br = new BufferedReader(new FileReader(file))) { + String line; + while ((line = br.readLine()) != null) { + data.add(line); + } + } catch (IOException e) { + e.printStackTrace(); + } + return data; + } + + return new ArrayList(); + } +} diff --git a/dirty-flag/src/main/java/com/iluwatar/dirtyflag/World.java b/dirty-flag/src/main/java/com/iluwatar/dirtyflag/World.java new file mode 100644 index 000000000..d356e6581 --- /dev/null +++ b/dirty-flag/src/main/java/com/iluwatar/dirtyflag/World.java @@ -0,0 +1,36 @@ +package com.iluwatar.dirtyflag; + +import java.util.ArrayList; +import java.util.List; + +/** + * + * A middle-layer app that calls/passes along data from the back-end. + * + * @author swaisuan + * + */ +public class World { + + private List countries; + private DataFetcher df; + + public World() { + this.countries = new ArrayList(); + this.df = new DataFetcher(); + } + + /** + * + * Calls {@link DataFetcher} to fetch data from back-end. + * + * @return List of strings + */ + public List fetch() { + List data = df.fetch(); + + countries = data.isEmpty() ? countries : data; + + return countries; + } +} diff --git a/dirty-flag/src/main/resources/world.txt b/dirty-flag/src/main/resources/world.txt new file mode 100644 index 000000000..280ea3702 --- /dev/null +++ b/dirty-flag/src/main/resources/world.txt @@ -0,0 +1,3 @@ +UNITED_KINGDOM +MALAYSIA +UNITED_STATES \ No newline at end of file diff --git a/dirty-flag/src/test/java/org/dirty/flag/AppTest.java b/dirty-flag/src/test/java/org/dirty/flag/AppTest.java new file mode 100644 index 000000000..50f107cd5 --- /dev/null +++ b/dirty-flag/src/test/java/org/dirty/flag/AppTest.java @@ -0,0 +1,40 @@ +/** + * The MIT License + * Copyright (c) 2014-2016 Ilkka Seppälä + * + * Permission is hereby granted, free of charge, to any person obtaining a copy + * of this software and associated documentation files (the "Software"), to deal + * in the Software without restriction, including without limitation the rights + * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell + * copies of the Software, and to permit persons to whom the Software is + * furnished to do so, subject to the following conditions: + * + * The above copyright notice and this permission notice shall be included in + * all copies or substantial portions of the Software. + * + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE + * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, + * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN + * THE SOFTWARE. + */ +package org.dirty.flag; + +import java.io.IOException; + +import org.junit.jupiter.api.Test; + +import com.iluwatar.dirtyflag.App; + +/** + * Tests that Dirty-Flag example runs without errors. + */ +public class AppTest { + @Test + public void test() throws IOException { + String[] args = {}; + App.main(args); + } +} diff --git a/dirty-flag/src/test/java/org/dirty/flag/DirtyFlagTest.java b/dirty-flag/src/test/java/org/dirty/flag/DirtyFlagTest.java new file mode 100644 index 000000000..8f651b267 --- /dev/null +++ b/dirty-flag/src/test/java/org/dirty/flag/DirtyFlagTest.java @@ -0,0 +1,54 @@ +/** + * The MIT License + * Copyright (c) 2014-2016 Ilkka Seppälä + * + * Permission is hereby granted, free of charge, to any person obtaining a copy + * of this software and associated documentation files (the "Software"), to deal + * in the Software without restriction, including without limitation the rights + * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell + * copies of the Software, and to permit persons to whom the Software is + * furnished to do so, subject to the following conditions: + * + * The above copyright notice and this permission notice shall be included in + * all copies or substantial portions of the Software. + * + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE + * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, + * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN + * THE SOFTWARE. + */ +package org.dirty.flag; + +import static org.junit.jupiter.api.Assertions.assertTrue; + +import java.util.List; + +import org.junit.jupiter.api.Test; + +import com.iluwatar.dirtyflag.DataFetcher; + +/** + * + * Application test + * + */ +public class DirtyFlagTest { + + @Test + public void testIsDirty() { + DataFetcher df = new DataFetcher(); + List countries = df.fetch(); + assertTrue(!countries.isEmpty()); + } + + @Test + public void testIsNotDirty() { + DataFetcher df = new DataFetcher(); + df.fetch(); + List countries = df.fetch(); + assertTrue(countries.isEmpty()); + } +} diff --git a/pom.xml b/pom.xml index 965c8f37c..e1d025c13 100644 --- a/pom.xml +++ b/pom.xml @@ -158,7 +158,8 @@ eip-splitter eip-aggregator retry - trampoline + dirty-flag + trampoline serverless