Making Text for the Web
part 6
Barb Ericson
Georgia Institute of Technology
March 2006
Georgia Institute of Technology
Doing a Join Query
• Add aliases for the table names
– Picture as pict, Person as per, PicturePerson
as pictPer
• Use the alias in front of the field name
– per.FirstName, pict.FileName
• Use And to join conditions
Where per.firstName = 'Jennifer' And
pictPer.PersonID = per.PersonID And
pict.PictureID = pictPer.PictureID
Georgia Institute of Technology
Finding Jennifer
/* main for testing */
public static void main(String[] args)
{
// create the database manager for an Access database
DatabaseManager dbManager =
new DatabaseManager("sun.jdbc.odbc.JdbcOdbcDriver",
"jdbc:odbc:person");
// create the database manager for a MySQL database
// new DatabaseManager("com.mysql.jdbc.Driver",
//
"jdbc:mysql://localhost:3306/person");
// test a query
dbManager.testQuery("Select per.FirstName, " +
"pict.FileName From " +
"Picture as pict, Person as per, " +
"PicturePerson as pictPer " +
"Where per.FirstName = 'Jennifer' And " +
"pictPer.PersonID = per.PersonID And " +
"pict.PictureID = pictPer.PictureID", 2);
}
Georgia Institute of Technology
Getting a String for a Query
/**
* Method to execute a query and return a string of the
* first result
* @param query the query to execute
* @return the first result of the query, or null if none
*/
public String getStringForQuery(String query)
{
String result = null;
// create a statement
Statement statement = connection.createStatement();
// execute the query
ResultSet rs = statement.executeQuery(query);
// print out the results
if (rs.next())
{
result = rs.getString(1);
}
// try the following
try {
// close everything
rs.close();
statement.close();
connection.close();
// open the connection to the database
Connection connection =
DriverManager.getConnection(this.urlStr);
} catch (SQLException ex) {
SimpleOutput.showError("Trouble with the database " +
urlStr);
ex.printStackTrace();
}
return result;
}
Georgia Institute of Technology
Adding Database Info to a Homepage
• Now we can use a database to get
information for an HTML page
• Modify the writeHomepage method to get
the person's age from the database
– Use the DatabaseManager class to get it
Georgia Institute of Technology
Write Homepage with Database Info
/**
* Method for writing a homepage for the passed
* first name that displays her/his interests and age
* @param name the person's first name
* @param interests a list of the person's interests
*/
public void writeHomepageV5(String name,
String interests)
{
// Get a DatabaseManager object
DatabaseManager dbManager =
new DatabaseManager("sun.jdbc.odbc.JdbcOdbcDriver",
"jdbc:odbc:person");
// try the following
try {
// open a file for writing
BufferedWriter writer =
new BufferedWriter(new FileWriter(name + ".html"));
// write the start
writeStart(writer);
// write the header
writeHead(writer,name + "'s Homepage");
// write the body
writeBody(writer,"<h1>Welcome to " + name +
"'s Homepage</h1>" +
"<p> I am interested in " + interests +
".</p><p>I am " + age + " years old</p>");
// get this person's age
String age =
dbManager.getStringForQuery(
"Select Age From Person " +
"Where FirstName='" + name + "'");
// end the page
writeEnd(writer);
// close the writer
writer.close();
} catch (Exception ex) {
ex.printStackTrace();
}
}
Georgia Institute of Technology
Testing the Homepage Writer
public static void main(String[] args)
{
WebPageWriter writer = new WebPageWriter();
writer.writeHomepageV5("Matthew",
"playing video games");
}
Georgia Institute of Technology
Exercise
• Create a writeHomepageV6 method that looks
up the person's name in the database and adds
thumbnails of pictures of that person to the page
• Add information to the database for your pictures
– Add to the Person table
– Add to the Picture table
– Add to the PicturePerson table
• Use the writeHomepage method to generate a
homepage for you
– With your pictures on it
Georgia Institute of Technology
Servlets and JSP
• Some database access is done through
JavaServer Pages (JSPs)
– HTML pages with special tags that allow Java
code to be executed
– JSP pages are translated into servlets
• Small programs like applets
– But they run on the server
• Servlets connect to the database and get
information
– Which is displayed in the HTML
Georgia Institute of Technology
Summary
• HTML is the language of the Web
– Not a programming language
– You can use Java programs to create HTML
• Helper methods are often private methods that
are used by other public methods
– To break a task into parts (procedural abstraction)
• Throwing an exception
– A method can throw an exception using the throws
keyword followed by the exception name
• The Unnamed Package
– All classes are put in a package. If you don't specify
a package the "unnamed" one is used
Georgia Institute of Technology
Summary Continued
• Maps store key and value pairs
– Map is an interface
– HashMap, Hashtable, and TreeMap are classes that implement
Map
• Generics allow you to declare the types of things in
collection classes
– and eliminate the need to downcast when you take items back
out of a collection
• Iterators let you walk through each item in a collection
• Using classes in the java.sql package you can access
information in a database
– SQL is the standard language to use to communicate with a
database
Georgia Institute of Technology