Circular Dependencies between Immutable Objects; the Freeze Pattern

Question

Generally, I structure small threadsafe immutable objects like this:

public class SmallObject {
    private final String state;
    public SmallObject(final String state) {
        this.state = state;
    }

    // ...
}

And then wire these up in Spring like this:

<bean name="SmallObjectForThisThing" class="my.package.SmallObject">
    <constructor-arg name="state" value="in practice this is usually a ref"/>
</bean>

However, this leads to complications with circular dependencies. To keep the immutability when this happens, I use a "freeze" pattern, where the variables are set once. This is what I want reviewed:

public class SmallObject {
    private String state = null;

    public void setState(String state) {
        if (this.state != null) {
            throw new IllegalStateException("state already set: '" + state + "'.");
        }
        this.state = state;
    }

    private void ensureInitialized() {
        if (this.state == null) {
            throw new IllegalStateException(
                "state must be set before this instance is used."
            );
        }
    }

    // ... For every additional method on the object, I call 
    // ensureInitialized() first.
}

And then wire them up like this:

<bean name="SmallObjectForThisThing" class="my.package.SmallObject">
    <property name="state" value="in practice this is usually a ref"/>
</bean>