How to stop ProGuard from stripping the Serializable interface from a class

Question

Is there an explicit way to stop ProGuard from changing a class from implementing an interface?

I have a class that implements java.io.Serializable, let's call it com.my.package.name.Foo. I've found that after running through ProGuard, it no longer implements Serializable. I get null after I cast from Serializable to Foo and false if I check an instance with instanceof Serializable. I've made sure to set ProGuard to ignore this class:

-keep class com.my.package.name.Foo

I've also tried:

-keep class com.my.package.name.Foo { *; }

and I've also tried the whole package by doing this:

-keep class com.my.package.name.** { *; }

or:

-keep class com.my.package.** { *; }

and also just to keep all Serializable classes:

-keep class * implements java.io.Serializable { *; }

but to no avail. I have another class in a sibling package (roughly: com.my.package.name2.Bar) that also implements Serializable and is used similarly but has no issues.

I'm not sure it's relevant, but I'm packing this in a jar for use with Android. The code that uses these classes include putting them in Bundles which is why I need Serializable. I considered that perhaps somehow ProGuard thinks that Foo is never used as a Serializable but that seems unlikely given that I pass it as a parameter to Bundle.putSerializable(String, Serializable) and also I do an implicit cast: Serializable serializable = foo;. In fact, when I debug, I can see the Foo get put into the Bundle and I can examine the Bundle and see the instance of Foo there, but when retrieving it the cast fails.

Answer 1

I had the same issue fixed using below config.

-keepnames class * implements java.io.Serializable
-keepclassmembers class * implements java.io.Serializable {
    static final long serialVersionUID;
    private static final java.io.ObjectStreamField[] serialPersistentFields;
    !static !transient <fields>;
    private void writeObject(java.io.ObjectOutputStream);
    private void readObject(java.io.ObjectInputStream);
    java.lang.Object writeReplace();
    java.lang.Object readResolve();
}

Official Documentation http://proguard.sourceforge.net/manual/examples.html#serializable