What is the difference between JDBC and JDBI?

(I am the primary author of jDBI)

jDBI is a convenience library built on top of JDBC. JDBC works very well but generally seems to optimize for the database vendors (driver writers) over the users. jDBI attempts to expose the same functionality, but in an API optimized for users.

It is much lower level than things like Hibernate or JPA. The closest similar library is probably MyBatis (forked successor to iBATIS).

jDBI supports two style APIs, an older fluent style, which looks like:

List<Something> r = h.createQuery("select * from something where name = :name and id = :id")
                .bind(0, "eric")
                .bind("id", 1)
                .map(Something.class)
                .list();

A newer SQL Object API does much more reflective type stuff and really does start to abstract a bunch of JDBC stuff:

interface TheBasics
{
    @SqlUpdate("insert into something (id, name) values (:id, :name)")
    int insert(@BindBean Something something);

    @SqlQuery("select id, name from something where id = :id")
    Something findById(@Bind("id") long id);
}

@Test
public void useTheBasics() throws Exception
{
    TheBasics dao = dbi.onDemand(TheBasics.class);

    dao.insert(new Something(7, "Martin"));

    Something martin = dao.findById(7);
}

The library has good reference docs (javadoc) and some reasonable tutorial style documentation at http://jdbi.org/. It has been around since 2004, and is used by a relatively small number of folks (some few dozen people I know of personally, and maybe a dozen companies) but it works very well for them. Most of the folks who work on it are A+ folks, and are primarily concerned with building a tool that works well for them -- that it is open source is largely a side effect.

JDBC is a long-established standard used in Java to access SQL databases. DB Vendors implement a JDBC driver so that all DBs can be accessed in a uniform manner. Practically everything done with databases in Java uses JDBC.

JDBI seems to be some sort of abstraction layer on top of JDBC, but it's hard to tell since it's poorly documented. It's certainly not widely used and this is the first time I've heard of it.

Do you mean https://jdbi.org ?

jDBI is designed to provide convenient tabular data access in Java(tm). It uses the Java collections framework for query results, provides a convenient means of externalizing sql statements, and provides named parameter support for any database being used.

JDBI uses JDBC, if you don't know if you need JDBI, I would suggest you don't use it.