Basic Features

First Steps in JDBC

This section describes how to get up and running with the Oracle JDBC drivers. When using the Oracle JDBC drivers, you must include certain driver-specific information in your programs. This section describes, in the form of a tutorial, where and how to add the information. The tutorial guides you through creating code to connect to and query a database from the client.

To connect to and query a database from the client, you must provide code for these tasks:

You must supply Oracle driver-specific information for the first three tasks, which allow your program to use the JDBC API to access a database. For the other tasks, you can use standard JDBC Java code as you would for any Java application.

Importing Packages

Regardless of which Oracle JDBC driver you use, you must include the following import statements at the beginning of your program.

import java.sql.*

JDBC packages.

import java.math.*

Java math packages; for example, these are required for the BigDecimal classes.

You will need to add the following Oracle packages to your program when you want to access the extended functionality provided by the Oracle drivers. However, they are not required for the example presented in this section:

oracle.jdbc.driver.* and oracle.sql.*

Add these packages if you use any Oracle-specific extensions to JDBC in your program. For more information on Oracle extensions, see Chapter 4, "Oracle Extensions".

Registering the JDBC Drivers

You must provide the code to register your installed driver with your program. You do this with the static registerDriver() method of the JDBC DriverManager class. This class provides a basic service for managing a set of JDBC drivers.

Note:
Alternatively, you can use the forName() method of the java.lang.Class class to load the JDBC drivers directly. For example:
Class.forName ("oracle.jdbc.driver.OracleDriver");
However, this method is valid only for JDK-compliant Java virtual machines. It is not valid for Microsoft Java virtual machines.

Because you are using one of Oracle's JDBC drivers, you declare a specific driver name string to registerDriver(). You register the driver only once in your Java application.

DriverManager.registerDriver (new oracle.jdbc.driver.OracleDriver());

Note:
If you are registering a Thin driver in an applet, you must enter a driver string that is different from the one used in these examples. For more information on registering a Thin driver for an applet, see "Coding Applets".

Opening a Connection to a Database

You open a connection to the database with the static getConnection() method of the JDBC DriverManager class. This method returns an object of the JDBC Connection class which needs as input a userid, password, connect string that identifies the JDBC driver to use, and the name of the database to which you want to connect.

Connecting to a database is a step where you must enter Oracle JDBC driver-specific information in the getConnection() method. If you are not familiar with this method, continue reading the "Understanding the Forms of getConnection()" section below.

If you are already familiar with the getConnection() method, you can skip ahead to either of these sections, depending on the driver you installed:

"Opening a Connection for the JDBC OCI Driver"
"Opening a Connection for the JDBC Thin Driver"

Note:
The instructions in this section are specific to the client-side drivers only. To find out how to open a database connection using the server-side driver, see "Server-Side Basics".

Understanding the Forms of getConnection()

The getConnection() method is an overloaded method that you declare by the techniques described in these sections:

"Specifying a Database URL and Properties Object"

Note:
You do not have to specify the database name if there is a default connection. For more information about default connections, see "Connecting to the Database with the Server Driver".

If you want to specify a database name in the connection, it must be in one of the following formats:

a Net8 keyword-value pair
a string of the form <host_name>:<port_number>:<sid> (Thin driver only)
a TNSNAMES entry (OCI driver only)

For information on how to specify a keyword-value pair or a TNSNAMES entry, see your Net8 Administrator's Guide.

Specifying a Database URL, Userid, and Password

getConnection(String URL, String user, String password);

where the URL is of the form:

jdbc:oracle:<drivertype>:@<database>

The following example connects user scott with password tiger to a database with SID orcl through port 1521 of host myhost, using the Thin driver.

Connection conn = 
   DriverManager.getConnection ("jdbc:oracle:thin:@myhost:1521:orcl",
       "scott", "tiger");

If you want to use the default connection for an OCI driver, specify either:

Connection conn = DriverManager.getConnection 
     
("jdbc:oracle:oci8:scott/tiger@");

Connection conn = 
     
DriverManager.getConnection ("jdbc:oracle:oci8:@", "scott", "tiger");

For all JDBC drivers you can also specify the database with a Net8 keyword-value pair. The Net8 keyword-value pair substitutes for the TNSNAMES entry. The following example uses the same parameters as the preceding example, but in the keyword-value format:

Connection conn = 
     
DriverManager.getConnection
(jdbc:oracle:oci8:@MyHostString","scott","tiger");

Connection conn = 
DriverManager.getConnection("jdbc:oracle:oci8:@(description=(address=(host= 
myhost)(protocol=tcp)(port=1521))(connect_data=(sid=orcl)))",
"scott", "tiger");

Specifying a Database URL That Includes Userid and Password

getConnection(String URL);

where the URL is of the form:

jdbc:oracle:<drivertype>:<user>/<password>@<database>

The following example connects user scott with password tiger to a database using the OCI driver. In this case, however, the URL includes the userid and password, and is the only input parameter.

Connection conn =   
 DriverManager.getConnection("jdbc:oracle:oci8:scott/tiger@myhost);

Specifying a Database URL and Properties Object

getConnection(String URL, Properties info);

where the URL is of the form:

jdbc:oracle:<drivertype>:@<database>

In addition to the URL, use an object of the standard Java Properties class as input. For example:

java.util.Properties info = new java.util.Properties();
info.put ("user", "scott");
info.put ("password","tiger");
info.put ("defaultRowPrefetch","15");
getConnection ("jdbc:oracle:oci8:@",info);

Oracle Extensions to Connection Properties Object

Oracle has defined several extensions to the connection properties that Oracle JDBC drivers support. For more information on this form of the getConnection() method and the Oracle extensions to the Properties object, see "Oracle Extensions for Connection Properties".

Opening a Connection for the JDBC OCI Driver

For the JDBC OCI driver, you can specify the database by a TNSNAMES entry. You can find the available TNSNAMES entries listed in the file tnsnames.ora on the client computer from which you are connecting. On Windows NT this file is located in [ORACLE_HOME]\NETWORK\ADMIN. On UNIX systems, you can find it in /var/opt/oracle.

For example, if you want to connect to the database on host myhost as user scott with password tiger that has a TNSNAMES entry of MyHostString, enter:

Connection conn = 
     
DriverManager.getConnection ("jdbc:oracle:oci8:@MyHostString",
     
"scott", "tiger");

Note that both the ":" and "@" characters are necessary.

For the JDBC OCI driver (as with the Thin driver), you can also specify the database with a Net8 keyword-value pair. This is less readable than a TNSNAMES entry but does not depend on the accuracy of the TNSNAMES.ORA file. The Net8 keyword-value pair also works with other JDBC drivers.

For example, if you want to connect to the database on host myhost that has a TCP/IP listener up on port 1521, and the SID (system identifier) is orcl, use a statement such as:

Connection conn = 
     
DriverManager.getConnection("jdbc:oracle:oci8:@(description=(address=(host= 
myhost)(protocol=tcp)(port=1521))(connect_data=(sid=orcl)))",
     
"scott", "tiger");

Opening a Connection for the JDBC Thin Driver

Because you can use the JDBC Thin driver in applets that do not depend on an Oracle client installation, you cannot use a TNSNAMES entry to identify the database to which you want to connect. You have to either:

explicitly list the host name, TCP/IP port and Oracle SID of the database to which you want to connect

use a keyword-value pair list

Note:
The JDBC Thin driver supports only the TCP/IP protocol.

For example, use this string if you want to connect to the database on host myhost that has a TCP/IP listener on port 1521 for the database SID (system identifier) orcl. You can logon as user scott, with password tiger:

Connection conn = 
     
DriverManager.getConnection 
("jdbc:oracle:thin:@myhost:1521:orcl", "scott", "tiger");

You can also specify the database with a Net8 keyword-value pair. This is less readable than the first version, but also works with the other JDBC drivers.

Connection conn = 
     
      DriverManager.getConnection 

      ("jdbc:oracle:thin:@(description=(address=(host=myhost)(protocol=tcp)
     
(port=1521))(connect_data=(sid=orcl)))", "scott", "tiger"); 


       






Note:



If you are writing a connection statement for an applet, you must enter a connect string that is different from the one used in these examples. For more information on connecting to a database with an applet, see "Coding Applets".

Creating a Statement Object

Once you connect to the database and, in the process, create your Connection object, the next step is to create a Statement object. The createStatement() method of your JDBC Connection object returns an object of the JDBC Statement class. To continue the example from the previous section where the Connection object conn was created, here is an example of how to create the Statement object:

Statement stmt = conn.createStatement();

Note that there is nothing Oracle-specific about this statement; it follows standard JDBC syntax.

Executing a Query and Returning a Result Set Object

To query the database, use the executeQuery() method of your Statement object. This method takes a SQL statement as input and returns an object of the JDBC ResultSet class.

To continue the example, once you create the Statement object stmt, the next step is to execute a query that populates a ResultSet object with the contents of the ENAME (employee name) column of a table of employees that is named EMP:

ResultSet rset = stmt.executeQuery ("SELECT ename FROM emp");

Again, there is nothing Oracle-specific about this statement; it follows standard JDBC syntax.

Note:
The JDBC drivers actually return an OracleResultSet object, but into a standard ResultSet output variable. If you want to use Oracle extensions to process the result set, then you must cast the output to OracleResultSet. This is further discussed in "Classes of the oracle.jdbc.driver Package".

Processing the Result Set

Once you execute your query, use the next() method of your ResultSet object to iterate through the results. This method loops through the result set row by row, detecting the end of the result set when it is reached.

To pull data out of the result set as you iterate through it, use the various getXXX() methods of the ResultSet object, where XXX corresponds to a Java datatype.

For example, the following code will iterate through the ResultSet object rset from the previous section, and will retrieve and print each employee name:

while (rset.next())
     
System.out.println (rset.getString(1));

Once again, this is standard JDBC syntax. The next() method returns false when it reaches the end of the result set. The employee names are materialized as Java Strings.

Closing the Result Set and Statement Objects

You must explicitly close the ResultSet and Statement objects after you finish using them. This applies to all ResultSet and Statement objects you create when using the Oracle JDBC drivers. The drivers do not have finalizer methods; cleanup routines are performed by the close() method of the ResultSet and Statement classes. If you do not explicitly close your ResultSet and Statement objects, serious memory leaks could occur. You could also run out of cursors in the database. Closing a result set or statement releases the corresponding cursor in the database.

For example, if your ResultSet object is rset and your Statement object is stmt, close the result set and statement with these lines:

rset.close()
stmt.close();

When you close a Statement object that a given Connection object creates, the connection itself remains open.

Closing the Connection

You must close your connection to the database once you finish your work. Use the close() method of the Connection class to do this. For example, if your Connection object is conn, close the connection with this statement:

conn.close();

`import java.sql.*`	JDBC packages.
`import java.math.*`	Java math packages; for example, these are required for the `BigDecimal` classes.