public class UUID extends org.postgresql.util.PGobject {
    public static final long serialVersionUID = 668353936136517917L;
    public UUID(String s) throws java.sql.SQLException {
        super();
        this.setType("uuid");
        this.setValue(s);
    }
}

java.sql.PreparedStatement stmt =
 conn.prepareStatement("UPDATE t SET uid = ? WHERE id = 1");
 stmt.setObject(1, new UUID("a0eebc99-9c0b-4ef8-bb6d-6bb9bd380a11"));
 stmt.executeUpdate();

Connection con = DriverManager.getConnection("jdbc:postgresql://localhost/postgres", "foo", "bar");
con.setAutoCommit(false);
Statement stmt = con.createStatement();
stmt.addBatch("create table foo (id integer, data varchar(100))");
stmt.addBatch("insert into foo values (1, 'one')");
stmt.addBatch("insert into foo values (2, 'two')");
stmt.addBatch("update foo set data = 'one_other' where id = 1");
stmt.executeBatch();
con.commit();

<dependency>
    <groupId>postgresql</groupId>
    <artifactId>postgresql</artifactId>
    <version>8.4-702.jdbc4</version>
</dependency>

pstm.setObject(1, guid); //where pstm is a PreparedStatement and guid is a UUID

//where rs is a ResultSet
UUID myGuid = (UUID) rs.getObject("my_uuid_column_name");

java.util.UUID uuid = java.util.UUID.randomUUID();
…
preparedStatement.setObject( nthPlaceholder++, uuid ); // Pass UUID to database.