1. Making Text for the Web part 6
Barb Ericson
Georgia Institute of Technology
March 2006
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2. 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
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3. 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); }
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4. Getting a String for a Query
/**
* Method to execute a query and return a string of the
* first result
query the query to execute
the first result of the query, or null if none */
public String getStringForQuery(String query) {
String result = null;
// try the following
try {
// open the connection to the database
Connection connection =
DriverManager.getConnection(this.urlStr);
// 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); }
// close everything
rs.close();
statement.close();
connection.close();
} catch (SQLException ex) {
SimpleOutput.showError("Trouble with the database " + urlStr);
ex.printStackTrace();
return result;
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5. 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
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6. Write Homepage with Database Info
/**
* Method for writing a homepage for the passed
* first name that displays her/his interests and age
name the person's first name
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");
// get this person's age
String age =
dbManager.getStringForQuery(
"Select Age From Person " +
"Where FirstName='" + name + "'");
// 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>");
// end the page
writeEnd(writer);
// close the writer
writer.close();
} catch (Exception ex) {
ex.printStackTrace(); }
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7. Testing the Homepage Writer
public static void main(String[] args) {
WebPageWriter writer = new WebPageWriter();
writer.writeHomepageV5("Matthew",
"playing video games"); }
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8. 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
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9. 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
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10. 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
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11. 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
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