How to handle a Findbugs “Non-transient non-serializable instance field in serializable class”?

Question

Consider the class below. If I run Findbugs against it it will give me an error (\"Non-transient non-serializable instance field in serializable class\") on line 5 but not o

Answer 1

I use a findbugs-exclude Filter for collection-Fields:

<Match>
    <Field type="java.util.Map" />
    <Bug pattern="SE_BAD_FIELD" />
</Match>
<Match>
    <Field type="java.util.Set" />
    <Bug pattern="SE_BAD_FIELD" />
</Match>
<Match>
    <Field type="java.util.List" />
    <Bug pattern="SE_BAD_FIELD" />
</Match>

See http://findbugs.sourceforge.net/manual/filter.html

Answer 2

Use a concrete Serializable set for your internal representation, but make any public interfaces use the Set interface.

public class TestClass implements Serializable {
    private static final long serialVersionUID = 1905162041950251407L;

    private HashSet<Integer> mySet;

    public TestClass(Set<Integer> s) {
        super();
        setMySet(s);
    }

    public void setMySet(Set<Integer> s) {
        mySet = (s == null) ? new HashSet<>() : new HashSet<>(s);
    }
}