MELJUN CORTES Web Application and Database

8/11/2019 MELJUN CORTES Web Application and Database

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JDBC OverviewThe JDBC API makes it possible to do

three things:

Establish a connection with a

database or access any tabular data

source

Send SQL statements

Process the results


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Installing the MySQL

DriverTo use the MySQL Connector/J

Driver, you need to download thecomplete distribution.

Once you have extracted thedistribution archive, you can installthe driver by placing mysql-

connector-java-[version]-bin.jar

in your classpath, either by addingthe FULL path to it to yourCLASSPATH enviornment variable.

To use the driver within Tomcat,copy the jar file above to:

[TOMCAT_HOME]\webapps\ROOT\WEB-INF\lib


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Six Steps to Using JDBC

1. Load the JDBC Driver

2. Establish the Database

Connection

3. Create a Statement Object

4. Execute a Query

5. Process the Results

6. Close the Connection


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1) Loading the JDBC

DriverTo use a JDBC driver, you must load

the driver via the Class.forName()method.

In general, the code looks like this: Class.forName("jdbc.DriverXYZ");

where jbdc.DriverXYZ is the JDBC

Driver you want to load.

If you are using a JDBC-ODBCDriver, your code will look like this: Class.forName("sun.jdbc.odbc.Jdb

cOdbcDriver");


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2) Establish the

ConnectionOnce you have loaded your JDBC

driver, the next step is to establish adatabase connection.

The following line of code illustrates

the basic idea:

Connection con =DriverManager.getConnection(url,

"myLogin", "myPassword");

Example in ODBC String url = "jdbc:odbc:basketball"; Connection con =

DriverManager.getConnection(url,admin", adminpasswd");

Example in MySQL String url =

"jdbc:mysql://localhost/basketball"; Connection con =

DriverManager.getConnection(url);


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3) Create a Statement

ObjectThe JDBC Statement object sends

SQL statements to the database.

Statement objects are created fromactive Connection objects.

For example:

Statement stmt =con.createStatement();

With a Statement object, you canissue SQL calls directly to thedatabase.


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4) Execute a QueryexecuteQuery()

Executes the SQL query and returnsthe data in a table (ResultSet)

The resulting table may be emptybut never null

ResultSet results=statement.executeQuery("SELECT a, b FROM table");

executeUpdate() Used to execute for INSERT, UPDATE,

or DELETE SQL statements The return is the number of rows

that were affected in the database Supports Data Definition Language

(DDL) statements CREATE TABLE,DROP TABLE and ALTER TABLE


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Useful Statement

MethodsgetMaxRows/setMaxRows

Determines the number of rows aResultSet may contain

Unless explicitly set, the number ofrows are unlimited (return value of0)

getQueryTimeout/setQueryTimeout Specifies the amount of a time a

driver will wait for a STATEMENT tocomplete before throwing aSQLException


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5) Process the ResultsA ResultSet contains the results of

the SQL query.

Useful Methods All methods can throw a

SQLException

close

Releases the JDBC and database resources The result set is automatically closed

when the associated Statement object

executes a new query

getMetaDataObject

Returns a ResultSetMetaData objectcontaining information about the columns

in the ResultSet


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5) Process the Results

(Continued) next

Attempts to move to the next rowin the

ResultSet

If successful true is returned;otherwise, false

The first call to next positions the

cursor a the first row

findColumn Returns the corresponding integer value

corresponding to the specified columnname

Column numbers in the result set do notnecessarily map to the same columnnumbers in the database


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ResultSet (Continued) getXxx

Returns the value from the columnspecified by column nameor columnindexas anXxxJava type

Returns 0 or null, if the value is a SQL

NULL Legal getXxxtypes:

Double byte int

Date String float

short long Time Object


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6) Close the ConnectionTo close the database connection:

stmt.close();

connection.close();

Note: Some application servers,maintain a pool of databaseconnections.

This is much more efficient, asapplications do not have theoverhead of constantly opening andclosing database connections.


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Designing a Web

Application Using

DatabaseTo build a database application you

must design the relationship

between the model objects and the

corresponding databaserepresentation.

To design the model elements of an

application, you should perform the

following tasks:

Design the domain objects of your

application

Design the database tables that mapto the domain objects

Design the business services to

separate the database code into

classes

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MELJUN CORTES Web Application and Database