BAEL-871 What is serialVersionUID? (#2203)

* Bean Injection in Spring – ashrafmsokkar@gmail.com

* Bean Injection in Spring – ashrafmsokkar@gmail.com

* BAEL-871: What is serialVersionUID?

* BAEL-871: What is serialVersionUID?

* BAEL-871 What is serialVersionUID?

* BAEL-871 Implemented feedback

core-java/src/main/java/com/baeldung/deserialization/AppleProduct.java

@@ -0,0 +1,26 @@
+package com.baeldung.deserialization;
+
+import java.io.Serializable;
+
+public class AppleProduct implements Serializable {
+
+     private static final long serialVersionUID = 1234567L; // user-defined (i.e. not default or generated)
+//    private static final long serialVersionUID = 7654321L; // user-defined (i.e. not default or generated)
+
+    public String headphonePort;
+    public String thunderboltPort;
+    public String lighteningPort;
+
+    public String getHeadphonePort() {
+        return headphonePort;
+    }
+
+    public String getThunderboltPort() {
+        return thunderboltPort;
+    }
+
+    public static long getSerialVersionUID() {
+        return serialVersionUID;
+    }
+
+}

core-java/src/main/java/com/baeldung/deserialization/DeserializationUtility.java

@@ -0,0 +1,27 @@
+package com.baeldung.deserialization;
+
+import java.io.ByteArrayInputStream;
+import java.io.IOException;
+import java.io.ObjectInputStream;
+import java.util.Base64;
+
+public class DeserializationUtility {
+
+    public static void main(String[] args) throws ClassNotFoundException, IOException {
+
+        String serializedObj = "rO0ABXNyACljb20uYmFlbGR1bmcuZGVzZXJpYWxpemF0aW9uLkFwcGxlUHJvZHVjdAAAAAAAEtaHAgADTAANaGVhZHBob25lUG9ydHQAEkxqYXZhL2xhbmcvU3RyaW5nO0wADmxpZ2h0ZW5pbmdQb3J0cQB+AAFMAA90aHVuZGVyYm9sdFBvcnRxAH4AAXhwdAARaGVhZHBob25lUG9ydDIwMjBwdAATdGh1bmRlcmJvbHRQb3J0MjAyMA==";
+        System.out.println("Deserializing AppleProduct...");
+        AppleProduct deserializedObj = (AppleProduct) deSerializeObjectFromString(serializedObj);
+        System.out.println("Headphone port of AppleProduct:" + deserializedObj.getHeadphonePort());
+        System.out.println("Thunderbolt port of AppleProduct:" + deserializedObj.getThunderboltPort());
+    }
+
+    public static Object deSerializeObjectFromString(String s) throws IOException, ClassNotFoundException {
+        byte[] data = Base64.getDecoder().decode(s);
+        ObjectInputStream ois = new ObjectInputStream(new ByteArrayInputStream(data));
+        Object o = ois.readObject();
+        ois.close();
+        return o;
+    }
+
+}

core-java/src/main/java/com/baeldung/deserialization/SerializationUtility.java

@@ -0,0 +1,30 @@
+package com.baeldung.deserialization;
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.ObjectOutputStream;
+import java.io.Serializable;
+import java.util.Base64;
+
+public class SerializationUtility {
+
+    public static void main(String[] args) throws ClassNotFoundException, IOException {
+
+        AppleProduct macBook = new AppleProduct();
+        macBook.headphonePort = "headphonePort2020";
+        macBook.thunderboltPort = "thunderboltPort2020";
+
+        String serializedObj = serializeObjectToString(macBook);
+        System.out.println("Serialized AppleProduct object to string:");
+        System.out.println(serializedObj);
+    }
+
+    public static String serializeObjectToString(Serializable o) throws IOException {
+        ByteArrayOutputStream baos = new ByteArrayOutputStream();
+        ObjectOutputStream oos = new ObjectOutputStream(baos);
+        oos.writeObject(o);
+        oos.close();
+        return Base64.getEncoder().encodeToString(baos.toByteArray());
+    }
+
+}

core-java/src/test/java/com/baeldung/deserialization/DeserializationUnitTest.java

@@ -0,0 +1,67 @@
+package com.baeldung.deserialization;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotEquals;
+import static org.junit.Assert.assertTrue;
+
+import java.io.IOException;
+import java.io.InvalidClassException;
+
+import org.junit.Ignore;
+import org.junit.Test;
+
+public class DeserializationUnitTest {
+
+    private static final String serializedObj = "rO0ABXNyACljb20uYmFlbGR1bmcuZGVzZXJpYWxpemF0aW9uLkFwcGxlUHJvZHVjdAAAAAAAEtaHAgADTAANaGVhZHBob25lUG9ydHQAEkxqYXZhL2xhbmcvU3RyaW5nO0wADmxpZ2h0ZW5pbmdQb3J0cQB+AAFMAA90aHVuZGVyYm9sdFBvcnRxAH4AAXhwdAARaGVhZHBob25lUG9ydDIwMjBwdAATdGh1bmRlcmJvbHRQb3J0MjAyMA==";
+
+    private static long userDefinedSerialVersionUID = 1234567L;
+
+    /**
+     * Tests the deserialization of the original "AppleProduct" (no exceptions are thrown)
+     * @throws ClassNotFoundException
+     * @throws IOException
+     */
+    @Test
+    public void testDeserializeObj_compatible() throws IOException, ClassNotFoundException {
+
+        assertEquals(userDefinedSerialVersionUID, AppleProduct.getSerialVersionUID());
+        
+        AppleProduct macBook = new AppleProduct();
+        macBook.headphonePort = "headphonePort2020";
+        macBook.thunderboltPort = "thunderboltPort2020";
+        
+        // serializes the "AppleProduct" object
+        String serializedProduct = SerializationUtility.serializeObjectToString(macBook);
+
+        // deserializes the "AppleProduct" object
+        AppleProduct deserializedProduct = (AppleProduct) DeserializationUtility.deSerializeObjectFromString(serializedProduct);
+     
+        assertTrue(deserializedProduct.headphonePort.equalsIgnoreCase(macBook.headphonePort));
+        assertTrue(deserializedProduct.thunderboltPort.equalsIgnoreCase(macBook.thunderboltPort));
+    
+    }
+
+    /**
+     * Tests the deserialization of the modified (non-compatible) "AppleProduct".
+     * The test should result in an InvalidClassException being thrown.
+     * 
+     * Note: to run this test: 
+     *          1. Modify the value of the serialVersionUID identifier in AppleProduct.java
+     *          2. Remove the @Ignore annotation
+     *          3. Run the test individually (do not run the entire set of tests)
+     *          4. Revert the changes made in 1 & 2 (so that you're able to re-run the tests successfully)
+     *          
+     * @throws ClassNotFoundException
+     * @throws IOException
+     */
+    @Ignore
+    @Test(expected = InvalidClassException.class)
+    public void testDeserializeObj_incompatible() throws ClassNotFoundException, IOException {
+
+        assertNotEquals(userDefinedSerialVersionUID, AppleProduct.getSerialVersionUID());
+        
+        // attempts to deserialize the "AppleProduct" object
+        DeserializationUtility.deSerializeObjectFromString(serializedObj);
+    }
+
+}

spring-all/src/main/resources/beanInjection-setter.xml

@@ -11,5 +11,4 @@
 	</bean>
 
 	<bean id="helm" class="org.baeldung.bean.injection.Helm" />
-
 </beans>