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README.md

README.md

Functional JDBC database interaction in Java

26 Apr 2012

This a collection of Java's take on warm, fuzzy things, to demonstrate environment injection and output accumulation.

Reader

A reader encodes an action to take when given some environmental context. A JdbcAction<A> encapsulates a function which, given a Connection, produces an instance of type A. The encapsulated function implements the Function1 interface:

interface Function1<A, B> {
    B apply(A a) throws SQLException;
}

A JdbcAction wraps this function:

class JdbcAction<A> {

    private final Function1<Connection, A> g;

    JdbcAction(Function1<Connection, A> _g) {
        g = _g;
    }

    A apply(Connection c) throws SQLException {
        return g.apply(c);
    }

Pure functions of type A -> B can be lifted into a JdbcAction:

<B> JdbcAction<B> map(final Function1<A, B> h) {
    return new JdbcAction<B>(new Function1<Connection, B>() {
        public B apply(Connection c) throws SQLException {
            return h.apply(g.apply(c));
        }
    });
}

A function of type A -> JdbcAction<B> can be bound to a JdbcAction<A>:

<B> JdbcAction<B> bind(final Function1<A, JdbcAction<B>> h) {
    return new JdbcAction<B>(new Function1<Connection, B>() {
        public B apply(Connection c) throws SQLException {
            return h.apply(g.apply(c)).apply(c);
        }
    });
}

A JdbcAction can be executed in serial with another JdbcAction:

<B> JdbcAction<B> andThen(final JdbcAction<B> h) {
    return new JdbcAction<B>(new Function1<Connection, B>() {
        public B apply(Connection c) throws SQLException {
            g.apply(c);
            return h.apply(c);
        }
    });
}

See here for more info.

Writer

A writer encodes an action which produces some kind of composable output. See here for more info.

ReaderWriter

Readers and writers can be useful in conjunction to encode actions, which produce some kind of composable output, to take when given some environmental context.