Transcript 16 Java Database Connectivity

16 Java Database Connectivity
Objectives
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Understand the JDBC
Understand the steps of the JDBC:
1.) Importing packages
2.) Opening a connection to a database
3.) Working with different types of database drivers
4.) Querying the database
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Creating a Statement object to perform a query ResultSet or
create a PreparedStatement
Executing a query and return a ResultSet object
Differentiating between a Statement and a PreparedStatement
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Objectives (continued)
(Steps of the JDBC, continued)
5.) Processing a ResultSet
6.) Closing the ResultSet and Statement
7.) Importance of closing the connection
• Understand a JBDC row set.
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What is JDBC?
JDBC (Java Database Connectivity)
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A standard Java interface for connecting from Java to
relational databases. The JDBC standard was defined by
Sun Microsystems, allowing individual providers to
implement and extend the standard with their own JDBC
drivers
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Steps in JDBC
1. Import Packages
Import statements at the beginning of your program:
import java.sql.Connection;
import java.sql.SQLException;
or
import java.sql.*;
Import the ff. Oracle packages when you want to access
the extended functionality provided by the Oracle drivers.
import oracle.jdbc.pool.OracleOCIConnectionPool;
or
import oracle.jdbc.*;
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Steps in JDBC
2. Open a Connection to a Database
A call to this method creates an object instance of the
java.sql.Connection class.
The getConnection() method is an overloaded method that takes
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Three parameters, one each for the URL, username, and password
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Only one parameter for the database URL. In this case, the URL
contains the username and password
The ff. lines of code illustrate using the getConnection() method:
Connection conn = DriverManager.getConnection(URL, username,
passwd); Or
Connection conn = DriverManager.getConnetion(URL);
where URL, username and password are of String data types.
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Steps in JDBC
Opening a Connection using the Oracle JDBC OCI:
When using the OCI driver, the database can be specified using the
TNSNAMES entry in the tnsnames.ora.file. For example, to connect to a
database on a particular host as user oratest with password oratest that
has a TNSNAMES entry of oracle.world, use the following code:
Connection conn =
DriverManager.getConnection(“jdbc:oracle:oci9:@oracle.world
”, “oratest”, “oratest”);
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Steps in JDBC
3. Querying the Database
Querying the database involves the following steps:
• Creating a Statement Object
This is to instantiate objects that run the query against the database to which they are
connected. This is done by the createStatement() method of the conn Connection
object created above. A call to this method creates an object instance of the Statement
class. The ff. line of code illustrates this:
Statement sql_stmt = conn.createStatement();
Or
Creating a PreparedStatement
A PreparedStatement is associated as a channel with a connection and a compiled SQL
statement. PreparedStatements are also created with a Connection method. The
following snippet shows how to create a parameterized SQL statement with three input
parameters:
PreparedStatement prepareUpdatePrice = conn.prepareStatement( "UPDATE
Sells SET price = ? WHERE bar = ? AND beer = ?");
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Steps in JDBC
• Executing the Query and Returning a ResultSet
This is done by using the executeQuery() method of the
Statement object. A call to this method takes as parameter
a SQL SELECT statement and returns a JDBC ResultSet
object. The ff. line of code illustrates this using the
sql_stmt object created above:
ResultSet rset = sql_stmt.executeQuery
(“SELECT empno, ename, sal, deptno FROM emp
ORDER BY ename”);
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Steps in JDBC
4. Process the Result Set
Once the query has been executed, there are two steps to be carried
out:
• Processing the output resultSet to fetch the rows
next() method of the ResultSet object
• Retrieving the column values of the current row
getXXX() methods of the JDBC rset object
Here getXXX() corresponds to the getInt(), getString() etc with
XXX being replaced by a Java datatype
while (rset.next())
System.out.println (rset.getString(“ename”));
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Steps in JDBC
5. Closing the ResultSet and Statement
Once the ResultSet and Statement objects have been used,
they must be closed explicitly. This is done by calls to the
close() method of the ResultSet and Statement classes. The
ff. code illustrates this:
rset.close();
sql_stmt.close();
If not closed explicitly, there are two disadvantages:
• Memory leaks can occur
• Maximum Open cursors can be exceeded
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Steps in JDBC
6. Closing the Connection
The last step is to close the database connection after importing the
packages and loading the JDBC drivers. This is done by a call to the
close() method of the Connection class.
The ff. line of code does this:
conn.close();
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Example
package com.jds.architecture.service.dbaccess;
import java.sql.Connection;
import java.sql.SQLException;
Import Packages
import javax.sql.ConnectionPoolDataSource;
import oracle.jdbc.pool.OracleOCIConnectionPool;
public class OracleOCIDBAccess implements
DBAccessInterface {
private static String JDBC_URL =
"jdbc:oracle:oci:@ORCL";
Declaration
private static String USER_ID = "hruser";
private static String PASSWORD = "hruser";
OracleOCIConnectionPool cpool = null;
/**
OCI driver connection pooling functionality,
* constructor
provided by the OracleOCIConnectionPool class,
* @throws DBAccessException
is part of the JDBC client.
*/
protected OracleOCIDBAccess() throws DBAccessException {
dbConnect();
}
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Cont…
public void dbConnect() throws DBAccessException {
try{
Initialize the Database Connection
cpool = new OracleOCIConnectionPool();
cpool.setURL(JDBC_URL);
cpool.setUser(USER_ID);
cpool.setPassword(PASSWORD);
} catch (SQLException e) {
throw new DBAccessException
("dbaccess.sql.connection.exception",e.getCause(),
DBAccessException.ERROR, true);
} catch (Exception e) {
e.printStackTrace();
throw new DBAccessException
("dbaccess.oracle.connection.exception",e.getCause(),DBAccess
Exception.ERROR, true);
}
}
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Cont…
/**
* Returns database connection from oci connection
pool
* @return Connection - database connection
*/
public Connection getConnection() throws
DBAccessException {
Connection conn = null;
try{
conn = cpool.getConnection(); Open a Connection
To a Database
} catch(SQLException e) {
throw new DBAccessException
("dbaccess.getconnection.sql.exception",
e.getCause(), DBAccessException.ERROR,
true);
}
return conn;
}
}
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Row Set
A JDBC RowSet object holds tabular data in a way that makes it more
flexible and easier to use than a result set. A Row Set is an object which
encapsulates a set of rows.
Kinds of RowSet Objects
Connected RowSet object uses a driver based on JDBC technology (“JDBC
Driver”) to make a connection to a relational database and maintains that
connection throughout its life span.
Only one of the standard RowSet implementations is a connected RowSet:
JdbcRowSet. Being always connected to a database, it is very similar to a
ResultSet object and is often used as a wrapper to make an otherwise
nonscrollable and read-only ResultSet object scrollable and updatable.
You can create a JdbcRowSet object in two ways:
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By using the reference implementation constructor that takes a ResultSet object
By using the reference implementation default constructor
Statement stmt = con.createStatement();
ResultSet rs = stmt.executeQuery(select * from COFFEES);
JdbcRowSet jdbcRs = new JdbcRowSetImpl(rs);
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Row Set
Using the Default Constructor
The following line of code creates an empty JdbcRowSet object.
JdbcRowSet jdbcRs2 = new JdbcRowSetImpl();
Disconnected RowSet objects make a connection to a data source only
to read in data from a ResultSet object or to write data back to the data
source.
The other four implementations are disconnected RowSet implementations.
1. A CachedRowSet object has all the capabilities of a JdbcRowSet
object plus it can also do the following:
 Obtain a connection to a data source and execute a query
 Read the data from the resulting ResultSet object and
populate itself with that data
 Manipulate data and make changes to data while it is
disconnected
 Reconnect to the data source to write changes back to it
 Check for conflicts with the data source and resolve those
conflicts
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Row Set
You can create a new CachedRowSet object in two different ways:
– By using the default constructor
CachedRowSet crs = new CacheRowSetImpl();
– By Passing a SyncProvider implementation to the constructor
CachedRowSet crs2 =
CachedRowSetImpl(“com.fred.providers.HighAvailabili
tyProvider”);
2. A WebRowSet object has all the capabilities of a CachedRowSet object plus it
can also do the following:
• Write itself as an XML document
• Read an XML document that describes a WebRowSet object
WebRowSet pricelist = new WebRowSetImpl();
3. A JoinRowSet object has all the capabilities of a WebRowSet object (and
therefore also a CachedRowSet object) plus it can also do the following:
• Form the equivalent of an SQL JOIN without having to connect to a data
source
JoinRowSet jrs = new JoinRowSetImpl();
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Row Set
4. A FilteredRowSet object likewise has all the capabilities of a
WebRowSet object (and therefore also a CachedRowSet object)
plus it can also do the following:
• Apply filtering criteria so that only selected data is visible. This is
equivalent to executing a query on a RowSet object without having to
use a query language or connect to a data source.
FilterRowSet frs = new FilteredRowSetImpl();
This object is initialized with the following:
• The high end of the range within which values must fall
• The low end of the range within which values must fall
• The column name or column number of the value that must fall within
the range of values set by the high and low boundaries
Filter1 range = new Filter(1000, 10999, “STORE_ID”);
The next line of code sets range as the filter for frs.
frs.setFilter(range);
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