BAEL-5283: Serialize a lambda in Java

core-java-modules/core-java-lambdas/src/main/java/com/baeldung/java8/lambda/serialization/NotSerializableLambdaExpression.java

@@ -0,0 +1,8 @@
+package com.baeldung.java8.lambda.serialization;
+
+public class NotSerializableLambdaExpression {
+    public static Object getLambdaExpressionObject() {
+        Runnable r = () -> System.out.println("please serialize this message");
+        return r;
+    }
+}

core-java-modules/core-java-lambdas/src/main/java/com/baeldung/java8/lambda/serialization/SerializableLambdaExpression.java

@@ -0,0 +1,10 @@
+package com.baeldung.java8.lambda.serialization;
+
+import java.io.Serializable;
+
+public class SerializableLambdaExpression {
+    public static Object getLambdaExpressionObject() {
+        Runnable r = (Runnable & Serializable) () -> System.out.println("please serialize this message");
+        return r;
+    }
+}

core-java-modules/core-java-lambdas/src/test/java/com/baeldung/java8/lambda/serialization/LambdaSerializationUnitTest.java

@@ -0,0 +1,77 @@
+package com.baeldung.java8.lambda.serialization;
+
+import org.junit.Test;
+
+import java.io.*;
+import java.nio.file.Files;
+import java.util.function.Consumer;
+import java.util.function.Function;
+
+import static org.junit.Assert.assertTrue;
+
+public class LambdaSerializationUnitTest {
+    @Test(expected = NotSerializableException.class)
+    public void givenRunnable_whenNoCapturing_thenSerializationFailed() throws IOException, ClassNotFoundException {
+        Object obj = NotSerializableLambdaExpression.getLambdaExpressionObject();
+        writeAndReadObject(obj, Runnable.class);
+    }
+
+    @Test
+    public void givenIntersectionType_whenNoCapturing_thenSerializationSuccess() throws IOException, ClassNotFoundException {
+        Object obj = SerializableLambdaExpression.getLambdaExpressionObject();
+        writeAndReadObject(obj, Runnable.class);
+    }
+
+    @Test
+    public void givenSerializableRunnable_whenNoCapturing_thenSerializationSuccess() throws IOException, ClassNotFoundException {
+        SerializableRunnable obj = () -> System.out.println("please serialize this message");
+        writeAndReadObject(obj, SerializableRunnable.class);
+    }
+
+    @Test
+    public void givenSerializableFunction_whenNoCapturing_thenSerializationSuccess() throws IOException, ClassNotFoundException {
+        SerializableFunction<String, String> obj = message -> String.format("Hello %s", message);
+        writeAndReadObject(obj, SerializableFunction.class);
+    }
+
+    @Test
+    public void givenSerializableConsumer_whenNoCapturing_thenSerializationSuccess() throws IOException, ClassNotFoundException {
+        SerializableConsumer<String> obj = System.out::println;
+        writeAndReadObject(obj, SerializableConsumer.class);
+    }
+
+    @Test(expected = NotSerializableException.class)
+    public void givenSerializableConsumer_whenCapturingNotSerializable_thenSerializationFailed() throws IOException, ClassNotFoundException {
+        SerializableConsumer<String> obj = System.out::println;
+        writeAndReadObject(obj, SerializableConsumer.class);
+    }
+
+    private <T> void writeAndReadObject(Object obj, Class<T> clazz) throws IOException, ClassNotFoundException {
+        File file = Files.createTempFile("lambda", "ser").toFile();
+        try (
+                FileOutputStream fos = new FileOutputStream(file);
+                ObjectOutputStream oos = new ObjectOutputStream(fos)
+        ) {
+            oos.writeObject(obj);
+        }
+
+        try (
+                FileInputStream fis = new FileInputStream(file);
+                ObjectInputStream ois = new ObjectInputStream(fis)
+        ) {
+            Object newObj = ois.readObject();
+            boolean isInstance = clazz.isInstance(newObj);
+
+            assertTrue(isInstance);
+        }
+    }
+
+    interface SerializableRunnable extends Runnable, Serializable {
+    }
+
+    interface SerializableFunction<T, R> extends Function<T, R>, Serializable {
+    }
+
+    interface SerializableConsumer<T> extends Consumer<T>, Serializable {
+    }
+}