Alex Rivera | Logout

Setting outer variable from anonymous inner class

Asked 2011-05-12T12:08:52.790
57

Is there any way to access caller-scoped variables from an anonymous inner class in Java?

Here's the sample code to understand what I need:

public Long getNumber(final String type, final String refNumber, final Long year) throws ServiceException {
    Long result = null;
    try {
        Session session = PersistenceHelper.getSession();
        session.doWork(new Work() {
                public void execute(Connection conn) throws SQLException {
                    CallableStatement st = conn.prepareCall("{ CALL PACKAGE.procedure(?, ?, ?, ?) }");
                    st.setString(1, type);
                    st.setString(2, refNumber);
                    st.setLong(3, year);
                    st.registerOutParameter(4, OracleTypes.NUMBER);
                    st.execute();
                    result = st.getLong(4) ;
                }
            });
    } catch (Exception e) {
        log.error(e);
    }
    return result;
}

The code is in a DAO service class. Obviously it doesn't compile, because it asks that result be final, if it is -- it doesn't compile because I try to modify a final var. I'm bound to JDK5. Other than dropping the doWork() altogether, is there a way to set the result value from within doWork()?

java anonymous-class
Edit
Report

1 Answer

2

The standard solution to this is to return a value. See, for instance, ye olde java.security.AccessController.doPrivileged.

So the code would look something like this:

public Long getNumber(
    final String type, final String refNumber, final Long year
) throws ServiceException {
    try {
        Session session = PersistenceHelper.getSession();
        return session.doWork(new Work<Long>() {
            public Long execute(Connection conn) throws SQLException {
                CallableStatement st = conn.prepareCall("{ CALL PACKAGE.procedure(?, ?, ?, ?) }");
                try {
                    st.setString(1, type);
                    st.setString(2, refNumber);
                    st.setLong(3, year);
                    st.registerOutParameter(4, OracleTypes.NUMBER);
                    st.execute();
                    return st.getLong(4);
                } finally {
                    st.close();
                }
            }
        });
    } catch (Exception e) {
        throw ServiceException(e);
    }
}

(Also fixed the potential resource leak, and returning null for any error.)

Update: So apparently Work is from a third-party library and can't be altered. So I suggest not using it, at least isolate your application from so that you are not using it directly. Something like:

public interface WithConnection<T> {
    T execute(Connection connnection) throws SQLException;
}
public class SessionWrapper {
    private final Session session;
    public SessionWrapper(Session session) {
        session = nonnull(session);
    }
    public <T> T withConnection(final WithConnection<T> task) throws Service Exception {
        nonnull(task);
        return new Work() {
            T result;
            {
                session.doWork(this);
            }
            public void execute(Connection connection) throws SQLExcepti
answered 2011-05-12T13:41:05.263

Your Answer