Transcript Class 16 - Turning Wheel

JAVA DATABASE CONNECTOR
Colorado Technical University
IT420
Tim Peterson
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JDBC Introduction
• JDBC is a JAVA package (java.sql.*).
• The JDBC package contains the base API
class.
• JDBC provides for a common DB interface.
• JDBC is in the public domain.
• Many vendors provide JDBC drivers.
• Focus of JDBC is on executing raw SQL
and retrieving the results.
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JDBC and SQL
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What type of SQL is acceptable?
Many different SQL syntax's exists.
With JDBC, SQL is just passed through.
With JDBC, a query can even pass text and
JDBC will not pass judgment on the text.
• JDBC API consists of a series of abstract
Java interfaces.
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JDBC-ODBC Bridge
• The bridge translates JDBC operations into
ODBC operations.
• Use the sun.jdbc.odbc package to use the
bridge.
• The Bridge is part of the Java SDK.
• The bridge does not work well with applets.
• The bridge is a reference driver so that other
manufacturers can use it as a template.
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JDBC Models
• JDBC supports a two-tier and three-tier
model.
• Two Tier
– Applets are allowed to connect directly to the
database.
– Use in a secure environment such as an
intranet.
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JDBC Models - Cont’d
• Three Tier
– An application server written in Java mediates
access to the database.
– Java applet is downloaded to the client
– This applet then talks to the Java server which
talks to the database.
– Used more for the Internet.
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JDBC vs. ODBC
• JDBC does not use VOID*.
• At one point, developers attempted to map
ODBC into Java.
• Java programming style is to use lots of
smaller methods.
• ODBC uses a smaller number of procedures
with a rich set of flags.
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JDBC Classes
• JDBC consists of various class definitions
in the java.sql package.
• JAVA JDBC Classes
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java.sql.Date
java.sql.DriverManager
java.sql.DriverPropertyInfo
java.sql.Time
java.sql.Timestamp
java.sql.Types
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Main JDBC Interfaces
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java.sql.CallableStatement
java.sql.Connection
java.sql. DatabaseMetaData
java.sql.Driver
java.sql.PreparedStatement
java.sql.ResultSet
java.sql.ResultSetMetaData
java.sql.Statement
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JDBC Exceptions
• java.sql.DataTruncation
• java.sql.SQLException
– Always provides string describing error.
– An error code.
– Chain to next exception.
• java.sql.SQLWarning
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DriverManager Class
• All database connections start with this
class.
• This class keeps track of all loaded JDBC
drivers.
• This class maps database URLs to a specific
driver.
• Once an applet has a connection to a
database, this class is no longer involved.
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Database Connection Example
• Using the JDBC-ODBC bridge, the driver is
loaded as follows:
Class.forName(“sun.jdbc.odbc.JdbcOdbcDriver”);
• Calling Class.forName will register it with the
DriverManager.
• Once driver is loaded, to connect to database:
String url = “jdbc.odbc:NwindDSN”;
Connection con = DriverManager.getConnection (
url, “peterson”, “db_passwd”);
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Database URLs
• JDBC allows you to use the database DSN.
• With JDB, you can also specify the target
node, port, and connection attributes as part
of the database name.
• Standard format for applets is:
– <protocolname>:<subprotocol>:<subname>
– protocolname is always “jdbc”
– subprotocol is database connect mechanism, e.g
“odbc”
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Connection Class
• This class obtains information about a specific
database connection via the instantiated JDBC
driver.
• A connection is a session with a database.
• This is where SQL statements are executed and
results returned.
• With JDBC, multiple connections can be
maintained with a single database.
• Connections can be specified as read only
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Statement Class
String createInventory =
“CREATE TABLE Inventory “ +
“(Inv_ID INTEGER, Item_Name “+
“VARCHAR(50), Price FLOAT, “+
“Cost FLOAT, Sup_ID INTEGER)”;
Statement stmt = con.createStatement();
stmt.executeUpdate(createInventory)
Stmt.executeUpdate(“INSERT INTO Inventory “+
“VALUES (202, ‘Widget A’, 19.95, “+
“16.50, 111)”);
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PreparedStatement Class
PreparedStatement updateInventory =
con.prepareStatement(
“UPDATE Inventory SET Price = Price * ? “ +
“WHERE Item_Name LIKE ?”);
• To use the PreparedStatement, you must supply the values
and the method.
updateInventory.setFloat(1, 1.05);
updateInventory.setString(2, “Wid”);
updateInventory.executeUpdate();
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CallableStatement Class
CallableStatement cs = con.prepareCall(
“{call DISPLAY_INVENTORY}”);
ResultSet rs=cs.executeQuery();
String newProcedure =
“create procedure DISPLAY_INVENTORY as “ +
“select * from INVENTORY order by inv_ID”;
Statement stmt=con.createStatement();
stmt.executeUpdate(newProcedure);
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ResultSet Class
• This class is used to analyze results of a
SQL select.
• A ResultSet maintains that cursor pointing
to the current row of data.
• By using the various get methods, you can
refer to specific columns by index or name.
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ResultSetMetaData Class
• Used to describe a ResultSet object.
• Types of data that can be obtained are:
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Catalog name of a specified column’s table
Number of columns in a ResultSet
Name of a column
Is auto-num on for a column
Can we put null entries in a column
etc
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DatabaseMetaData Class
• Class is used to obtain information about an
entire database.
• Typical types of information include:
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Is database in read-only mode
The name of the database
Determine the database schemas
Obtain database URL
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