Databases: Connectivity
Dr Andy Evans
Databases
Flat file, relational, or object orientated stores of data records
and their relationships.
Oracle
MySQL
MS SQL Server
PostgreSQL ("Postgres")
Access (~format used by Arc Geodatabases)
Java DB: “Derby”
Comes free with Java 7, or from:
http://www.oracle.com/technetwork/java/javadb/overview/index.html
Can add the jar files to any java project.
Nice, small, DB system, which can be rolled into even small
mobile apps, and distributed.
Jar it up with your classfiles, by sticking them in the same
directory and using the following Manifest to make a
automatically running file:
Manifest-Version: 1.0
Main-Class: YourClass
Class-Path: derby.jar
Software connections
Software can be written in many different languages.
Languages can represent even basic data types in
different ways.
We therefore need something to do the translation.
Inter-process communication
To communicate we can:
Ensure everyone uses the same type of compiled
code : JVM, .Net
Ensure everyone uses the same types of objects and
give some way of invoking methods in a OS
framework: COM
Supply software that can translate the binary code of
one into the binary code of the other : CORBA, bridge
drivers
Translation drivers
For Java Database communication we have various options:
Java → database with java interface/driver.
Derby Driver
Java — standard protocol [PC or Network] → database
that accepts standard protocols.
MySQL Connector/J
Java → standardized driver → database
ODBC (Open Database Connectivity)
Database packages
Java Database Connectivity (JDBC)
Packages:
java.sql
javax.sql
Opening a connection
1)
2)
3)
4)
Load the driver
Open the connection
Issue SQL
Close the connection
Database drivers
If the manufacturer supplied a java driver, you should be able to
load it.
MySQL: http://www.mysql.com/products/connector/
DriverManager.registerDriver(new com.mysql.jdbc.Driver());
Oracle database: http://www.orafaq.com/wiki/JDBC
DriverManager.registerDriver(new
oracle.jdbc.driver.OracleDriver());
SQL Server: http://msdn.microsoft.com/en-us/sqlserver/aa937724
DriverManager.registerDriver(new
com.microsoft.sqlserver.jdbc.SQLServerDriver());
Postgres: https://jdbc.postgresql.org/
DriverManager.registerDriver(new org.postgresql.Driver());
Alternative method
As an alternative, you can load the driver into the JVM and
DriverManager will find it. The following code uses the default
classloader to do this:
Java DB:
Class.forName("org.apache.derby.jdbc.EmbeddedDriver");
Opening a connection
Connection conn = null;
try {
conn = DriverManager.getConnection
("jdbc:xxxx:URL");
} catch (SQLException e) {}
xxxx = DB driver (“mysql”, “derby”, “oracle:thin”, “sqlserver”,
“postgresql”)
URL is a URL string or file:
"jdbc:derby: " + "//" + serverName + ":" + portNumber + "/" + dbName
Where serverName can be "localhost", or you can give a real
database directory:
"jdbc:derby:c:\\databases\\myDB"
Closing a connection
As usual with connections to things, it is polite to close
them:
try {
conn.close();
} catch (SQLException e) {}
ODBC
(Open Database Connectivity)
Use where no driver available.
Driver Manager keeps a list of data sources.
ODBC Driver Manager opens a driver that communicates
with a database when requested.
JDBC-ODBC bridge used to ask the Driver Manager to open
a driver connection.
ODBC Data Source Manager
Driver managers in Windows and Mac.
Windows: odbcad32.exe
ODBC Data Source Manager
Give the source a name
and (for Excel) select the
workbook.
Note under “Options>>” that
the default is “Read Only”.
Access
The same kinds of
options, but some
additional ones for
databases.
Under “Advanced” you
can set default
passwords to use.
Opening/closing ODBC connection
Connection conn = null;
try {
conn = DriverManager.getConnection
("jdbc:odbc:sourceName");
} catch (SQLException e) {}
try {
conn.close();
} catch (SQLException e) {}
ODBC Pros
Common to most machines and driver supplied.
As long as the ODBC data is uptodate, you can refer to the
database by name, not location.
ODBC Cons
Rather inefficient:
Program → Bridge → Driver → Database
JBDC-ODBC bridge was meant to be a stop-gap and doesn’t
implement all the JDBC methods.
Issues with Strings and Access. On Excel and text, see also:
http://support.microsoft.com/kb/178717
javax.sql.DataSource
What happens if the URL changes and you are using another
driver?
Nice thing about ODBC is that you call the database by name.
There is a java database registration setup called the Java
Naming and Directory Interface (JNDI).
You can use this, with a driver, to get a DataSource object, which
replaces the DriverManager. Databases are registered by name –
if the location changes, the JND can be updated.
java.util.Properties
What is there are access restrictions on the database?
To understand this, we need to understand Properties.
Properties : convenience class for storing key:value
String pairs.
Useful for loading and saving things like regionalised text
in different languages and user settings.
Properties
Properties p = new Properties();
p.setProperty(key, value); // both Strings
String a = p.getProperty(key);
store() : methods taking in various output streams.
load() : method taking in various input streams.
java.util.ResourceBundle
String a =
ResourceBundle.getBundle("setup").getString
("keyString");
Where setup.properties is a text file like this:
# This is a comment
keyString=Text
anotherKey=Text can\nhave escape characters
anotherKeyString=Some more text
in the directory the class files are in.
java.util.ResourceBundle
Good for regionalisation
# Filemenu resource bundle
saveMenu=Save
closeMenu=Close
String saveMenuText =
ResourceBundle.getBundle("en-gb")
.getString("saveMenu");
Can be set up in more complex way in families for e.g.
language regionalisation.
Connection properties
Using a password:
Properties p = new Properties();
p.setProperty("user", userName);
p.setProperty("password", password);
conn = DriverManager.getConnection
("jdbc:derby:c:\\databases\myDB", p);
Creating Databases
Connection conn = null;
String strUrl =
"jdbc:derby:c:\\databases\\myDB;create=true";
try {
conn = DriverManager.getConnection(strUrl);
} catch (SQLException sqle) {
sqle.printStackTrace();
}