BAEL-1072 - Difference between Proxy, Decorator, Adapter, and Bridge Patterns (#2390)

* Structural Design Patterns 

Difference between several types of structural design patterns

* Structural Design Pattern

Difference between several types of structural design patterns

* Structural Design Patterns

Difference between several types of structural design patterns

* Structural Design Patterns

Difference between several types of structural design patterns

core-java/pom.xml

@@ -80,7 +80,11 @@
         </dependency>
 
         <!-- logging -->
-
+       <dependency>
+            <groupId>log4j</groupId>
+            <artifactId>log4j</artifactId>
+            <version>1.2.17</version>
+        </dependency>
         <dependency>
             <groupId>org.slf4j</groupId>
             <artifactId>slf4j-api</artifactId>

core-java/src/main/java/com/baeldung/designpatterns/adapter/AdapterPatternDriver.java

@@ -0,0 +1,13 @@
+package com.baeldung.designpatterns.adapter;
+
+import static com.baeldung.designpatterns.util.LogerUtil.LOG;
+
+public class AdapterPatternDriver {
+    
+    public static void main(String args[]) {
+        LuxuryCarsSpeedAdapter luxuryCars = new LuxuryCarsSpeedAdapterImpl();
+        LOG.info("Bugatti Veyron Super Sport's top speed is " + luxuryCars.bugattiVeyronInKMPH() + " Kmph.");
+        LOG.info("McLaren F1 top speed is " + luxuryCars.mcLarenInKMPH() + " Kmph.");
+        LOG.info("Aston Martin One-77 top speed is " + luxuryCars.astonMartinInKMPH() + " Kmph.");
+    }
+}

core-java/src/main/java/com/baeldung/designpatterns/adapter/LuxuryCarsSpeed.java

@@ -0,0 +1,15 @@
+package com.baeldung.designpatterns.adapter;
+
+public class LuxuryCarsSpeed {
+    public double bugattiVeyronInMPH() {
+        return 268;
+    }
+    
+    public double mcLarenInMPH() {
+        return 241;
+    }
+    
+    public double astonMartinInMPH() {
+        return 220;
+    }
+}

core-java/src/main/java/com/baeldung/designpatterns/adapter/LuxuryCarsSpeedAdapter.java

@@ -0,0 +1,7 @@
+package com.baeldung.designpatterns.adapter;
+
+public interface LuxuryCarsSpeedAdapter {
+    public double bugattiVeyronInKMPH();
+    public double mcLarenInKMPH();
+    public double astonMartinInKMPH();
+}

core-java/src/main/java/com/baeldung/designpatterns/adapter/LuxuryCarsSpeedAdapterImpl.java

@@ -0,0 +1,26 @@
+package com.baeldung.designpatterns.adapter;
+
+public class LuxuryCarsSpeedAdapterImpl extends LuxuryCarsSpeed implements LuxuryCarsSpeedAdapter {
+
+    @Override
+    public double bugattiVeyronInKMPH() {
+        double mph = super.bugattiVeyronInMPH();
+        return convertMPHtoKMPH(mph);
+    }
+
+    @Override
+    public double mcLarenInKMPH() {
+        double mph = super.mcLarenInMPH();
+        return convertMPHtoKMPH(mph);
+    }
+
+    @Override
+    public double astonMartinInKMPH() {
+        double mph = super.astonMartinInMPH();
+        return convertMPHtoKMPH(mph);
+    }
+
+    private double convertMPHtoKMPH(double mph) {
+        return mph * 1.60934;
+    }
+}

core-java/src/main/java/com/baeldung/designpatterns/bridge/Blue.java

@@ -0,0 +1,12 @@
+package com.baeldung.designpatterns.bridge;
+
+import static com.baeldung.designpatterns.util.LogerUtil.LOG;
+
+public class Blue implements Color {
+
+    @Override
+    public void fillColor() { 
+        LOG.info("Color : Blue");
+    }
+
+}

core-java/src/main/java/com/baeldung/designpatterns/bridge/BridgePatternDriver.java

@@ -0,0 +1,14 @@
+package com.baeldung.designpatterns.bridge;
+
+public class BridgePatternDriver {
+
+    public static void main(String[] args) {
+        //a square with red color
+        Shape square = new Square(new Red());
+        square.drawShape();
+        
+        //a triangle with blue color
+        Shape triangle = new Triangle(new Blue());
+        triangle.drawShape();
+    }
+}

core-java/src/main/java/com/baeldung/designpatterns/bridge/Color.java

@@ -0,0 +1,5 @@
+package com.baeldung.designpatterns.bridge;
+
+public interface Color {
+    public void fillColor();
+}

core-java/src/main/java/com/baeldung/designpatterns/bridge/Red.java

@@ -0,0 +1,12 @@
+package com.baeldung.designpatterns.bridge;
+
+import static com.baeldung.designpatterns.util.LogerUtil.LOG;
+
+public class Red implements Color {
+
+    @Override
+    public void fillColor() {
+        LOG.info("Color : Red");
+    }
+
+}

core-java/src/main/java/com/baeldung/designpatterns/bridge/Shape.java

@@ -0,0 +1,11 @@
+package com.baeldung.designpatterns.bridge;
+
+public abstract class Shape {
+    protected Color color;
+    
+    public Shape(Color color) {
+        this.color = color;
+    }
+    
+    abstract public void drawShape();
+}

core-java/src/main/java/com/baeldung/designpatterns/bridge/Square.java

@@ -0,0 +1,16 @@
+package com.baeldung.designpatterns.bridge;
+
+import static com.baeldung.designpatterns.util.LogerUtil.LOG;
+
+public class Square extends Shape {
+
+    public Square(Color color) {
+        super(color);
+    }
+
+    @Override
+    public void drawShape() {
+        LOG.info("Square drawn. ");
+        color.fillColor();
+    }
+}

core-java/src/main/java/com/baeldung/designpatterns/bridge/Triangle.java

@@ -0,0 +1,16 @@
+package com.baeldung.designpatterns.bridge;
+
+import static com.baeldung.designpatterns.util.LogerUtil.LOG;
+
+public class Triangle extends Shape {
+
+    public Triangle(Color color) {
+        super(color);
+    }
+
+    @Override
+    public void drawShape() {
+        LOG.info("Triangle drawn. ");
+        color.fillColor();
+    }
+}

core-java/src/main/java/com/baeldung/designpatterns/decorator/BubbleLights.java

@@ -0,0 +1,16 @@
+package com.baeldung.designpatterns.decorator;
+
+public class BubbleLights extends TreeDecorator {
+
+    public BubbleLights(ChristmasTree tree) {
+        super(tree);
+    }
+    
+    public String decorate() {
+        return super.decorate() + decorateWithBubbleLights();
+    }
+    
+    private String decorateWithBubbleLights() {
+        return " with Bubble Lights";
+    }
+}

core-java/src/main/java/com/baeldung/designpatterns/decorator/ChristmasTree.java

@@ -0,0 +1,5 @@
+package com.baeldung.designpatterns.decorator;
+
+public interface ChristmasTree {
+    public String decorate();
+}

core-java/src/main/java/com/baeldung/designpatterns/decorator/ChristmasTreeImpl.java

@@ -0,0 +1,10 @@
+package com.baeldung.designpatterns.decorator;
+
+public class ChristmasTreeImpl implements ChristmasTree {
+
+    @Override
+    public String decorate() {
+        return "Christmas tree";
+    }
+
+}

core-java/src/main/java/com/baeldung/designpatterns/decorator/DecoratorPatternDriver.java

@@ -0,0 +1,20 @@
+package com.baeldung.designpatterns.decorator;
+
+import static com.baeldung.designpatterns.util.LogerUtil.LOG;
+
+public class DecoratorPatternDriver {
+
+    public static void main(String[] args) {
+        //christmas tree with just one Garland
+        ChristmasTree tree1 = new Garland(new ChristmasTreeImpl());
+        LOG.info(tree1.decorate());
+        
+        //christmas tree with two Garlands and one Bubble lights
+        ChristmasTree tree2 = new BubbleLights(new Garland(
+          new Garland(new ChristmasTreeImpl()))
+        );
+        LOG.info(tree2.decorate());
+        
+    }
+
+}

core-java/src/main/java/com/baeldung/designpatterns/decorator/Garland.java

@@ -0,0 +1,16 @@
+package com.baeldung.designpatterns.decorator;
+
+public class Garland extends TreeDecorator {
+
+    public Garland(ChristmasTree tree) {
+        super(tree);
+    }
+    
+    public String decorate() {
+        return super.decorate() + decorateWithGarland();
+    }
+
+    private String decorateWithGarland() {
+        return " with Garland";
+    }
+}

core-java/src/main/java/com/baeldung/designpatterns/decorator/TreeDecorator.java

@@ -0,0 +1,15 @@
+package com.baeldung.designpatterns.decorator;
+
+public abstract class TreeDecorator implements ChristmasTree {
+    private ChristmasTree tree;
+    
+    public TreeDecorator(ChristmasTree tree) {
+        this.tree = tree;
+    }
+    
+    @Override
+    public String decorate() {
+        return tree.decorate();
+    }
+
+}

core-java/src/main/java/com/baeldung/designpatterns/proxy/ExpensiveObject.java

@@ -0,0 +1,5 @@
+package com.baeldung.designpatterns.proxy;
+
+public interface ExpensiveObject {
+    public void process();
+}

core-java/src/main/java/com/baeldung/designpatterns/proxy/ExpensiveObjectImpl.java

@@ -0,0 +1,20 @@
+package com.baeldung.designpatterns.proxy;
+
+import static com.baeldung.designpatterns.util.LogerUtil.LOG;;
+
+public class ExpensiveObjectImpl implements ExpensiveObject {
+
+    public ExpensiveObjectImpl() {
+        heavyInitialConfiguration();
+    }
+    
+    @Override
+    public void process() {
+        LOG.info("processing complete.");
+    }
+    
+    private void heavyInitialConfiguration() {
+        LOG.info("Loading initial configuration...");
+    }
+    
+}

core-java/src/main/java/com/baeldung/designpatterns/proxy/ExpensiveObjectProxy.java

@@ -0,0 +1,13 @@
+package com.baeldung.designpatterns.proxy;
+
+public class ExpensiveObjectProxy implements ExpensiveObject{
+    private static ExpensiveObject object;
+
+    @Override
+    public void process() {
+        if(object == null) {
+            object = new ExpensiveObjectImpl();
+        }
+        object.process();
+    }
+}

core-java/src/main/java/com/baeldung/designpatterns/proxy/ProxyPatternDriver.java

@@ -0,0 +1,9 @@
+package com.baeldung.designpatterns.proxy;
+
+public class ProxyPatternDriver {
+    public static void main(String[] args) {
+        ExpensiveObject object = new ExpensiveObjectProxy();
+        object.process();
+        object.process();
+    }
+}

core-java/src/main/java/com/baeldung/designpatterns/util/LogerUtil.java

@@ -0,0 +1,35 @@
+package com.baeldung.designpatterns.util;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.util.Properties;
+
+import org.apache.log4j.Logger;
+import org.apache.log4j.PropertyConfigurator;
+
+public class LogerUtil {
+
+    public final static Logger LOG = Logger.getLogger("GLOBAL");
+    
+    static {
+    	configuration();
+    }
+    
+    private static void configuration() {
+    	Properties props = new Properties();
+    	try {
+			props.load(
+			  new BufferedReader(
+			    new InputStreamReader(
+			      LogerUtil.class.getResourceAsStream("/log4jstructuraldp.properties")
+			    )
+			  )
+			);
+		} catch (IOException e) {
+			System.out.println("log4jstructuraldp.properties file not configured properly");
+			System.exit(0);
+		}
+    	PropertyConfigurator.configure(props);
+    }
+}

core-java/src/main/resources/log4jstructuraldp.properties

@@ -0,0 +1,9 @@
+
+# Root logger 
+log4j.rootLogger=INFO, file, stdout
+
+# Write to console
+log4j.appender.stdout=org.apache.log4j.ConsoleAppender
+log4j.appender.stdout.Target=System.out
+log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
+log4j.appender.stdout.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n

core-java/src/test/java/com/baeldung/designpatterns/AdapterPatternIntegrationTest.java

@@ -0,0 +1,20 @@
+package com.baeldung.designpatterns;
+
+
+import static org.junit.Assert.*;
+
+import org.junit.Test;
+
+import com.baeldung.designpatterns.adapter.LuxuryCarsSpeedAdapter;
+import com.baeldung.designpatterns.adapter.LuxuryCarsSpeedAdapterImpl;
+
+public class AdapterPatternIntegrationTest {
+    @Test
+    public void givenLuxuryCarsAdapter_WhenConvertingMPHToKMPH_thenSuccessfullyConverted() {
+        LuxuryCarsSpeedAdapter luxuryCars = new LuxuryCarsSpeedAdapterImpl();
+        assertEquals(luxuryCars.bugattiVeyronInKMPH(), 431.30312, 0.00001);
+        assertEquals(luxuryCars.mcLarenInKMPH(), 387.85094, 0.00001);
+        assertEquals(luxuryCars.astonMartinInKMPH(), 354.0548, 0.00001);
+    }
+}
+

core-java/src/test/java/com/baeldung/designpatterns/BridgePatternIntegrationTest.java

@@ -0,0 +1,52 @@
+package com.baeldung.designpatterns;
+
+import static com.baeldung.designpatterns.util.LogerUtil.LOG;
+import static org.hamcrest.CoreMatchers.is;
+import static org.junit.Assert.assertThat;
+
+import java.util.List;
+
+import org.apache.log4j.spi.LoggingEvent;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+
+import com.baeldung.designpatterns.bridge.Blue;
+import com.baeldung.designpatterns.bridge.Red;
+import com.baeldung.designpatterns.bridge.Shape;
+import com.baeldung.designpatterns.bridge.Square;
+import com.baeldung.designpatterns.bridge.Triangle;
+
+public class BridgePatternIntegrationTest {
+    public static TestAppenderDP appender;
+    
+    @Before
+    public void setUp() {
+        appender = new TestAppenderDP();
+        LOG.addAppender(appender);
+    }
+    
+    @Test
+    public void whenBridgePatternInvoked_thenConfigSuccess() {
+        //a square with red color
+        Shape square = new Square(new Red());
+        square.drawShape();
+        
+        //a triangle with blue color
+        Shape triangle = new Triangle(new Blue());
+        triangle.drawShape();
+
+        final List<LoggingEvent> log = appender.getLog();
+        
+        assertThat((String) log.get(0).getMessage(), is("Square drawn. "));
+        assertThat((String) log.get(1).getMessage(), is("Color : Red"));
+        assertThat((String) log.get(2).getMessage(), is("Triangle drawn. "));
+        assertThat((String) log.get(3).getMessage(), is("Color : Blue"));
+    }
+    
+    @After
+    public void tearDown() {
+        LOG.removeAppender(appender);
+    }
+}
+

core-java/src/test/java/com/baeldung/designpatterns/DecoratorPatternIntegrationTest.java

@@ -0,0 +1,28 @@
+package com.baeldung.designpatterns;
+
+import static org.junit.Assert.assertEquals;
+
+import org.junit.Test;
+
+import com.baeldung.designpatterns.decorator.BubbleLights;
+import com.baeldung.designpatterns.decorator.ChristmasTree;
+import com.baeldung.designpatterns.decorator.ChristmasTreeImpl;
+import com.baeldung.designpatterns.decorator.Garland;
+
+public class DecoratorPatternIntegrationTest {
+    private ChristmasTree tree;
+    
+    @Test
+    public void givenDecoratorPattern_WhenDecoratorsInjectedAtRuntime_thenConfigSuccess() {
+        //christmas tree with just one Garland
+        tree = new Garland(new ChristmasTreeImpl());
+        assertEquals(tree.decorate(), "Christmas tree with Garland");
+        
+        //christmas tree with two Garlands and one Bubble lights
+        tree = new BubbleLights(new Garland(
+          new Garland(new ChristmasTreeImpl()))
+        );
+        assertEquals(tree.decorate(), "Christmas tree with Garland with Garland with Bubble Lights");
+    }
+}
+

core-java/src/test/java/com/baeldung/designpatterns/ProxyPatternIntegrationTest.java

@@ -0,0 +1,44 @@
+package com.baeldung.designpatterns;
+
+import static com.baeldung.designpatterns.util.LogerUtil.LOG;
+import static org.hamcrest.CoreMatchers.is;
+import static org.junit.Assert.assertThat;
+
+import java.util.List;
+
+import org.apache.log4j.spi.LoggingEvent;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+
+import com.baeldung.designpatterns.proxy.ExpensiveObject;
+import com.baeldung.designpatterns.proxy.ExpensiveObjectProxy;
+
+public class ProxyPatternIntegrationTest {
+    public static TestAppenderDP appender;
+    
+    @Before
+    public void setUp() {
+        appender = new TestAppenderDP();
+        LOG.addAppender(appender);
+    }
+    
+    @Test
+    public void givenExpensiveObjectProxy_WhenObjectInitialized_thenInitializedOnlyOnce() {
+        ExpensiveObject object = new ExpensiveObjectProxy();
+        object.process();
+        object.process();
+
+        final List<LoggingEvent> log = appender.getLog();
+        
+        assertThat((String) log.get(0).getMessage(), is("Loading initial configuration..."));
+        assertThat((String) log.get(1).getMessage(), is("processing complete."));
+        assertThat((String) log.get(2).getMessage(), is("processing complete."));
+    }
+    
+    @After
+    public void tearDown() {
+        LOG.removeAppender(appender);
+    }
+}
+

core-java/src/test/java/com/baeldung/designpatterns/TestAppenderDP.java

@@ -0,0 +1,29 @@
+package com.baeldung.designpatterns;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.apache.log4j.AppenderSkeleton;
+import org.apache.log4j.spi.LoggingEvent;
+
+public class TestAppenderDP extends AppenderSkeleton {
+    private final List<LoggingEvent> log = new ArrayList<LoggingEvent>();
+
+    @Override
+    public boolean requiresLayout() {
+        return false;
+    }
+
+    @Override
+    protected void append(final LoggingEvent loggingEvent) {
+        log.add(loggingEvent);
+    }
+
+    @Override
+    public void close() {
+    }
+
+    public List<LoggingEvent> getLog() {
+        return new ArrayList<LoggingEvent>(log);
+    }
+}