# Programming with SQL Relay using JDBC

The SQL Relay distribution does not provide a native JBCD driver, but by using the JDBC-ODBC bridge provided by most Java distributions, applications which use JDBC on Unix or Linux may access databases through SQL Relay via the ODBC driver.

Note that the JDBC-ODBC bridge is not available in OpenJDK and was removed from Oracle Java in version 8. To use the JDBC-ODBC bridge, you must use Oracle Java 7 or earlier.

See Programming with SQL Relay using ODBC for instructions detailing how to access SQL Relay through ODBC. Once that is working, you can access databases through SQL Relay via JDBC as well.

A good program to test this with is HenPlus, a JDBC command line client. After downloading and installing HenPlus, you can run it as follows:

> henplus jdbc:odbc:sqlrexample

When you run it, you might get an error like:

> /usr/java/jdk1.7.0_10/bin/java: symbol lookup error: /usr/java/jdk1.7.0_10/jre/lib/i386/libJdbcOdbc.so: undefined symbol: SQLAllocEnv

If so, this is because the JDBC-ODBC library wasn't linked properly, a common problem. It can be fixed by preloading the ODBC driver manager library as follows:

> export LD_PRELOAD=/usr/lib/libodbc.so

(Replacing /usr/lib with the path to libodbc.so on your system)

Here is a sample henplus session:

>     [dmuse@fedora bin]$ ./henplus jdbc:odbc:sqlrexample
>     no readline found (no JavaReadline in java.library.path). Using simple stdin.
>     using GNU readline (Brian Fox, Chet Ramey), Java wrapper by Bernhard Bablok
>     henplus config at /home/dmuse/.henplus
>     ----------------------------------------------------------------------------
>      HenPlus II 0.9.8 "Yay Labor Day"
>      Copyright(C) 1997..2009 Henner Zeller <H.Zeller@acm.org>
>      HenPlus is provided AS IS and comes with ABSOLUTELY NO WARRANTY
>      This is free software, and you are welcome to redistribute it under the
>      conditions of the GNU Public License <http://www.gnu.org/licenses/gpl2.txt>
>     ----------------------------------------------------------------------------
>     HenPlus II connecting
>      url 'jdbc:odbc:sqlrexample'
>      driver version 2.1
>      oracle - Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production
>     With the Partitioning, OLAP, Data Mining and Real Application Testing options
>     @odbc> create table exampletable (col1 int, col2 varchar2(20));
>     affected 0 rows (301 msec)
>     @odbc> insert into exampletable values (1,'hello');
>     affected 1 rows (71 msec)
>     @odbc> insert into exampletable values (2,'goodbye');
>     affected 1 rows (1 msec)
>     @odbc> select * from exampletable;
>     ------+---------+
>      COL1 |  COL2   |
>     ------+---------+
>         1 | hello   |
>         2 | goodbye |
>     ------+---------+
>     2 rows in result (first row: 56 msec; total: 57 msec)
>     @odbc> update exampletable set col2='bye' where col1=2;
>     affected 1 rows (2 msec)
>     @odbc> select * from exampletable;
>     ------+-------+
>      COL1 | COL2  |
>     ------+-------+
>         1 | hello |
>         2 | bye   |
>     ------+-------+
>     2 rows in result (first row: 1 msec; total: 2 msec)
>     @odbc> delete from exampletable where col1=1;
>     affected 1 rows (2 msec)
>     @odbc> select * from exampletable;
>     ------+------+
>      COL1 | COL2 |
>     ------+------+
>         2 | bye  |
>     ------+------+
>     1 row in result (first row: 1 msec; total: 1 msec)
>     @odbc> drop table exampletable;
>     affected 0 rows (3.637 sec)
>     @odbc> quit
>     storing settings..
>     [dmuse@fedora bin]$

Similarly, any program that uses JDBC can be configured to use SQL Relay via JDBC by setting its database url to jdbc:odbc:DSN where DSN is replaced with the ODBC DSN defined in /etc/odbc.ini.

Developing applications which use JDBC is beyond the scope if this document but many examples and tutorials may be found on the web.