Decorator pattern Implementation

src/main/java/com/designpatterns/structural/decorator/CompressingDecorator.java

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+package com.designpatterns.structural.decorator;
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.OutputStream;
+import java.util.zip.GZIPOutputStream;
+
+/**
+ * this is one of the concrete decorators
+ */
+public class CompressingDecorator extends SenderDecorator {
+
+    public CompressingDecorator(Sender sender) {
+        super(sender);
+    }
+
+    @Override
+    public String send(String content) {
+        byte[] compressedBytes = compressContent(content);
+        String compressedContent = new String(compressedBytes);
+        super.send(compressedContent);
+        return compressedContent;
+    }
+
+    private byte[] compressContent(String content) {
+        try (ByteArrayOutputStream baostream = new ByteArrayOutputStream();
+             OutputStream outStream = new GZIPOutputStream(baostream)){
+            outStream.write(content.getBytes());
+            outStream.close();
+            return baostream.toByteArray();
+        } catch (IOException e) {
+            throw new RuntimeException("exception happened while compressing email content");
+        }
+    }
+
+
+}

src/main/java/com/designpatterns/structural/decorator/EmailSender.java

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+package com.designpatterns.structural.decorator;
+
+/**
+ * this is the class which should be decorated without any modification
+ */
+public class EmailSender implements Sender {
+    @Override
+    public String send(String content) {
+        System.out.println("sending \"" + content  + "\" as email");
+        return content;
+    }
+}

src/main/java/com/designpatterns/structural/decorator/EncodingDecorator.java

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+package com.designpatterns.structural.decorator;
+
+import java.util.Base64;
+
+/**
+ * this is another concrete decorator.
+ */
+public class EncodingDecorator extends SenderDecorator {
+
+    public EncodingDecorator(Sender sender) {
+        super(sender);
+    }
+
+    @Override
+    public String send(String content) {
+        String encodedContent = encodeContent(content);
+        super.send(encodedContent);
+        return encodedContent;
+    }
+
+    private String encodeContent(String content){
+        return Base64.getEncoder().encodeToString(content.getBytes());
+    }
+}

src/main/java/com/designpatterns/structural/decorator/Sender.java

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+package com.designpatterns.structural.decorator;
+
+public interface Sender {
+    String send(String content);
+}

src/main/java/com/designpatterns/structural/decorator/SenderDecorator.java

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+package com.designpatterns.structural.decorator;
+
+/**
+ * this is the base decorator.
+ */
+public class SenderDecorator implements Sender {
+    private Sender sender;
+
+    public SenderDecorator(Sender sender) {
+        this.sender = sender;
+    }
+
+    @Override
+    public String send(String content) {
+        return this.sender.send(content);
+    }
+}

src/test/java/com/designpatterns/decorator/DecoratorDemo.java

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+package com.designpatterns.decorator;
+
+import com.designpatterns.structural.decorator.*;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import java.util.Base64;
+
+public class DecoratorDemo {
+
+    @Test
+    public void testDecorator_sendEmailAsPlainText() {
+        String message = "test message";
+        EmailSender sender = new EmailSender();
+        String content = sender.send(message);
+        Assertions.assertEquals(content, message);
+    }
+
+    @Test
+    public void testDecorator_sendEmailAsEncodedText() {
+        String message = "test message";
+        Sender sender = new SenderDecorator(
+                new EncodingDecorator(
+                        new EmailSender()
+                )
+        );
+        String encodedContent = sender.send(message);
+        Assertions.assertEquals(
+                new String(Base64.getDecoder().decode (encodedContent)),
+                message
+        );
+    }
+
+    @Test
+    public void testDecorator_sendEmailAsCompressedText()  {
+        String message = "Java is a general-purpose programming language that is class-based, object-oriented, and designed to have as few implementation dependencies as possible. It is intended to let application developers write once, run anywhere (WORA),[15] meaning that compiled Java code can run on all platforms that support Java without the need for recompilation.[16] Java applications are typically compiled to bytecode that can run on any Java virtual machine (JVM) regardless of the underlying computer architecture. The syntax of Java is similar to C and C++, but it has fewer low-level facilities than either of them. As of 2019, Java was one of the most popular programming languages in use according to GitHub,[17][18] particularly for client-server web applications, with a reported 9 million developers.";
+        Sender sender = new SenderDecorator(
+                new CompressingDecorator(
+                        new EmailSender()
+                )
+        );
+        String compressedContent = sender.send(message);
+        Assertions.assertTrue(message.length()>= compressedContent.length());
+    }
+
+    @Test
+    public void testDecorator_sendEmailAsEncodedCompressedText()  {
+        String message = "Java is a general-purpose programming language that is class-based, object-oriented, and designed to have as few implementation dependencies as possible. It is intended to let application developers write once, run anywhere (WORA),[15] meaning that compiled Java code can run on all platforms that support Java without the need for recompilation.[16] Java applications are typically compiled to bytecode that can run on any Java virtual machine (JVM) regardless of the underlying computer architecture. The syntax of Java is similar to C and C++, but it has fewer low-level facilities than either of them. As of 2019, Java was one of the most popular programming languages in use according to GitHub,[17][18] particularly for client-server web applications, with a reported 9 million developers.";
+        Sender sender = new SenderDecorator(
+                new EncodingDecorator(
+                        new CompressingDecorator(
+                                new EmailSender()
+                        )
+                )
+
+        );
+        String encodedCompressedContent = sender.send(message);
+
+        String decodedCompressed = new String( Base64.getDecoder().decode (encodedCompressedContent));
+        Assertions.assertTrue(message.length()>= decodedCompressed.length());
+    }
+}