Java serialization when object changed 2016-12-01 07:45

It is easy to serialize object to byte array and deserialize byte array to object. Today I will show you how to serialize and deserialize object when it changed.

1. Preparation

The pom file is like following.

<dependencies>
    <dependency>
        <groupId>org.apache.commons</groupId>
        <artifactId>commons-lang3</artifactId>
        <version>3.4</version>
    </dependency>
    <dependency>
        <groupId>commons-io</groupId>
        <artifactId>commons-io</artifactId>
        <version>2.4</version>
    </dependency>
</dependencies>

The first version of User class is like following.

public class User implements Serializable {

    private static final long serialVersionUID = -6704164414515767927L;

    private String name;
    private String address;
    private String age;

    //getter and setter methods

    @Override
    public String toString() {
        return "User{" +
                "name='" + name + '\'' +
                ", address='" + address + '\'' +
                ", age='" + age + '\'' +
                '}';
    }
}

Serialize object to byte array and save it into file.

public class TestSerialize {
    public static void main(String[] args) throws IOException {
        User user = new User();
        user.setName("henry");
        user.setAddress("beijing");
        user.setAge("27");
        FileUtils.writeByteArrayToFile(new File("/user_version1.txt"), SerializationUtils.serialize(user));
    }
}

2. Change fields of User class

Add test field and delete age field.

public class User implements Serializable {

    private static final long serialVersionUID = -6704164414515767927L;

    private String name;
    private String address;
    private String test;

    //getter and setter methods

    @Override
    public String toString() {
        return "User{" +
                "name='" + name + '\'' +
                ", address='" + address + '\'' +
                ", test='" + test + '\'' +
                '}';
    }
}

Read byte array from "user_version1.txt" and deserialize to new version of User.

public class TestDeserialize {
    public static void main(String[] args) throws IOException {
        Path path = Paths.get("/user_version1.txt");
        byte[] data = Files.readAllBytes(path);
        User user = SerializationUtils.deserialize(data);
        System.out.println(user);
    }
}

The output is like following.

User{name='henry', address='beijing', test='null'}

3. Change the value of serialVersionUID

public class User implements Serializable {

    private static final long serialVersionUID = -6L;

    private String name;
    private String address;
    private String age;

    //getter and setter methods

    @Override
    public String toString() {
        return "User{" +
                "name='" + name + '\'' +
                ", address='" + address + '\'' +
                ", age='" + age + '\'' +
                '}';
    }
}

Deserialize this object again. We got the Exception like following.

Exception in thread "main" org.apache.commons.lang3.SerializationException: java.io.InvalidClassException: com.henryxi.serialize.User; local class incompatible: stream classdesc serialVersionUID = -6704164414515767927, local class serialVersionUID = -6
    at org.apache.commons.lang3.SerializationUtils.deserialize(SerializationUtils.java:231)
    at org.apache.commons.lang3.SerializationUtils.deserialize(SerializationUtils.java:267)
    at com.henryxi.serialize.TestDeserialize.main(TestDeserialize.java:14)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)
Caused by: java.io.InvalidClassException: com.henryxi.serialize.User; local class incompatible: stream classdesc serialVersionUID = -6704164414515767927, local class serialVersionUID = -6
    at java.io.ObjectStreamClass.initNonProxy(ObjectStreamClass.java:616)
    at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1623)
    at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1518)
    at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1774)
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1351)
    at java.io.ObjectInputStream.readObject(ObjectInputStream.java:371)
    at org.apache.commons.lang3.SerializationUtils.deserialize(SerializationUtils.java:223)
    ... 7 more

4. Delete the value of serialVersionUID

public class User implements Serializable {

    private String name;
    private String address;
    private String age;

    //getter and setter methods

    @Override
    public String toString() {
        return "User{" +
                "name='" + name + '\'' +
                ", address='" + address + '\'' +
                ", age='" + age + '\'' +
                '}';
    }
}

Deserialize this object again. We got the same Exception.

Exception in thread "main" org.apache.commons.lang3.SerializationException: java.io.InvalidClassException: com.henryxi.serialize.User; local class incompatible: stream classdesc serialVersionUID = -6704164414515767927, local class serialVersionUID = 2510146339395188803
    at org.apache.commons.lang3.SerializationUtils.deserialize(SerializationUtils.java:231)
    at org.apache.commons.lang3.SerializationUtils.deserialize(SerializationUtils.java:267)
    at com.henryxi.serialize.TestDeserialize.main(TestDeserialize.java:14)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)
Caused by: java.io.InvalidClassException: com.henryxi.serialize.User; local class incompatible: stream classdesc serialVersionUID = -6704164414515767927, local class serialVersionUID = 2510146339395188803
    at java.io.ObjectStreamClass.initNonProxy(ObjectStreamClass.java:616)
    at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1623)
    at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1518)
    at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1774)
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1351)
    at java.io.ObjectInputStream.readObject(ObjectInputStream.java:371)
    at org.apache.commons.lang3.SerializationUtils.deserialize(SerializationUtils.java:223)
    ... 7 more

5. Conclusion

1. Deserializing will be success when we only change the field of object. removed field -> lost , new field -> default value.
2. Deserializing will be fail when we change serialVersionUID.
3. Deserializing will be fail when we delete serialVersionUID.

serialVersionUID must be defined in the object when you need serialize and deserialize object. If there is no serialVersionUID or the value of serialVersionUID changed deserializing will be fail.