data

Accessing a database directly from JSP page
Will cover 1) on next course. Good for larger applications. Will use 2) for development purposes. (Useful for smaller applications - but does not support connection pooling) Using option 2): • Can use java code (via scriptlets) OR JSTL <SQL> tags to access databases. We’ll use JSTL here. • Full description of <SQL> tags in JSTL documentation • Note: To use JSTL <sql> tags, need to include the appropriate <taglib> directive into the JSP page
Column
customer ID 1 2 3
Name John Liz Rory
Phone 879687 975645 321544
Row
SELECT * from customers? SELECT name, phone from customers where customer_ID = 2 ?
Relational DBs
INSERT INSERT INTO CUSTOMERS (customer_ID, name, phone) VALUES (5, “JOHN”, “875895”) UPDATE UPDATE CUSTOMERS SET NAME = “Robert” WHERE CUSTOMER_ID = 1 DELETE DELETE FROM CUSTOMERS WHERE CUSTOMER_ID = 2
Some Database concepts
• • To access a database from a web application, need a path or connection to the database To support multiple connections to the same database - have connection pooling. Works like a group of connections that are used by clients as needed and “put back” in the pool as needed. Each database engine (e.g. Oracle, SQLServer, Access) needs its own database driver (The driver is just a piece of software that translate SQL calls between the web application to the database). Web applications have to “load” the appropriate driver in order to connect to the database
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Datasource names (DSNs)
• • • To SET UP a data source name in Windows: Go to Windows control panel / administrative tools / user DSN Add a new database source, selecting appropriate driver Note: Will use microsoft access for development purposes – it’s an ODBC database and supports DSNs
Accessing a database from JSP with a Data source name
setDataSource tag has seven attributes:
Will use this name in any other SQL statements <sql:setDataSource To access the Db var=“productsdb" driver=“sun.jdbc.odbc.JdbcOdbcDriver" url="jdbc:odbc:products” user = “cindy” DSN password = “DIT” scope = “session” datasource = .. />
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Some Database concepts
• Java provides the JDBC API (Java Database Connectivity API) to enable a uniform interface to different database engines JDBC enables java code that accesses a databases to be portable from one database to another (provided the correct driver is used). Many databases have an ODBC (Open Database Connectivity) interface (e.g. access) Sun provides a JDBC-ODBC driver for development purposes
DT228/2 Web Development
Databases
Database
• • • • • Almost all web application on the net access a database e.g. shopping sites, message boards, search engines Relational databases (uses tables) are the most common type used Small application may use just one table, larger applications may have have hundreds of tables In JSP, database access can be done using scriplets or using JSTL JSTL supplies the SQL library to enable database access
Accessing a database directly from JSP page
•Use the <SQL:setDataSource> action from the JSTL SQL library and specify the attributes it needs •The <SQL:setDataSource> action creates a database connection in the background •Note: Can use the datasource name in the action, if available – as shown on next page. Otherwise, have to specify direct database and drivertabase from JSP
• Need to identify and connect to the database to be used with the JSP page: 1) Global datasource: Can specifying a default datasource in a Tomcat configuration file for the application called the web.xml file. The datasource will automatically be made available to the JSP if done this way – Good approach for larger applications. OR 2) Direct from JSP: by specifying the database details directly within the JSP page. Use instead of (1) all the time OR just to override the default data source specified in (1)
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Some Database concepts
•JDBC-ODBC driver enables java (and JSP) applications to connect to ODBC databases, using the JDBC API •Note: In production environment, should use a production quality driver from the database vendor
Datasource names (DSNs)
• To use a database in a web application need to say: - What the database is called - Where is resides - What driver is required by the database ODBC databases allow a Data source name to be used as a quick way to specify the above within the applicaton e.g. , rather than saying “I want to connect to an Access2000 database named Exams.mdb in d:\samples\database directory in every JSP page that uses the particular database, will rather create a DSN named Exams Note: not all databases will support DSNs.
Databases and web application
•Variety of databases available for use by web applications •typically will use relational database with support for Structured Query Language •Examples of common databases used: SQL server, MySQL, Oracle, Access
Relational DBs
Data is stored in tables. Rows and columns in tables can be related to rows and columns in other tables in the dB Each table usually has a primary key Structured Query Language (SQL) is used to query the database Common SQL Statements: SELECT, INSERT, UPDATE, DELETE