Transcript Slide
Web Development in Java
Andrew Simpson
Overview
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Background
Language Details
Java Server Pages (JSP)
Servlets
Database Connectivity (JDBC)
Samples and Application
Background
• Java is a compiled language
• Can be server side or client side, servlets
or applets
• Java has many applications outside of
web development
• Java is syntactically very similar to C++
and other compiled languages
Typical Java Code
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class HelloWorld extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws IOException, ServletException
{
response.setContentType("text/html");
PrintWriter out = response.getWriter();
out.println("<html>");
out.println("<head>");
out.println("<title>Hello World!</title>");
out.println("</head>");
out.println("<body>");
out.println("<h1>Hello World!</h1>");
out.println("</body>");
out.println("</html>");
}
}
Primitive Data Types
Keyword
Description
Size/Format
Byte
Byte-length integer
8-bit 2’s complement
Short
Short integer
16-bit 2’s complement
Int
Integer
32-bit 2’s complement
Long
Long integer
64-bit 2’s complement
Float
Single precision float
32-bit IEEE 754
Double
Double precision float
64-bit IEEE 754
Char
A single character
16 bit Unicode char
Boolean
A boolean value
True or false
Java’s Tools
• Similar to the stdlib in C++, Java has many
common data types and other procedures
already implemented
• AbstractCollection, AbstractList, ArrayList,
Array, BitSet, Calendar, Collections,
Currency, Date, Dictionary, HashMap,
HashSet, LinkedHashMap, Properties,
Stack, StringTokenizer, Timer, TreeMap,
TreeSet, Vector
Comparisons
• The usual operators work on the primitive
data types
• Class defined comparisons are required
for all other data types
• Comparator lets the programmer define
their own criteria
• Comparator can be defined for Java to
sort different structures automatically
Error Handling
• Try/Catch Blocks
• Functions can throw exceptions
Public int foo(int x, char y) thows ServletException {
if (x < 0 )
throw new ServletException(“X is negative”);
if (y >= ‘a’ && y <= ‘z’)
throw new ServletException(“Y is not a lower case letter”);
return 1;
}
Java Server Pages (JSP)
• Similar to Perl in that it is not compiled at
first, but rather compiled on the server
• Can contain static HTML/XML components
• Uses “special” JSP tags
• Optionally can have snippets of Java in
the language called scriptlets
JSP Translation
JSP Syntax
There are multiple styles that a JSP translator
recognizes to writing a JSP
• Embedding JAVA into static content
• Creating new dynamic tags to do embedding
• Embedding static content into JAVA
Embedding Java
<table border="1">
<thead>
<td><b> Exp</b></td>
<td><b>Result</b></td>
</thead>
<tr>
<td>\${1}</td>
<td>${1}</td>
</tr>
<tr>
<td>\${1 + 2}</td>
<td>${1 + 2}</td>
</tr>
<tr>
<td>\${1.2 + 2.3}</td>
<td>${1.2 + 2.3}</td>
</tr>
Exp
Result
${1}
1
${1+2}
3
${1.2+2.3}
3.5
Using Dynamic Tags
<%@ taglib prefix="mytag" uri="/WEB-INF/jsp2/jsp2-exampletaglib.tld" %>
<html>
<head>
<title>JSP 2.0 Examples - Hello World SimpleTag
Handler</title>
</head>
<body>
<h1>JSP 2.0 Examples - Hello World SimpleTag
Handler</h1>
<hr>
<p>This tag handler simply echos "Hello, World!" It's an
example of
a very basic SimpleTag handler with no body.</p>
<br>
<b><u>Result:</u></b>
<mytag:helloWorld/>
</body>
</html>
Result: Hello, world!
Tag Library (Pseudo class)
package jsp2.examples.simpletag;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.SimpleTagSupport;
import java.io.IOException;
/**
* SimpleTag handler that prints "Hello, world!"
*/
public class HelloWorldSimpleTag extends SimpleTagSupport {
public void doTag() throws JspException, IOException {
getJspContext().getOut().write( "Hello, world!" );
}
}
Embedding HTML
• This is the more common form that is
actually used
• This form is dominated mostly by scripting
• HTML is a quick and easy output method
far less verbose than trying to use a
servlet to write out the entire output stream
Refer to embedhtml.jsp file for example
Model for Server Handling
Request Handling
General Application Flow
Using A Java Servlet
• Compiled to form a class before being put
on the server
• Does not allow embedded code
• Functions very much like a class in C++
• Has several built in functions specific to
web development that are very useful
JSP vs. Servlets
• JSP is really just an extension of the
Servlet API
• Servlets should be used as an extension
of web server technology, specialized
controller components, database
validation.
• JSP handles text while Servlets can
interface other programs
Servlets and HTML Forms
• Post vs. Get Methods
• Built in handling doPost and doGet
• Good for taking in information in servlet
request, processing it, generating a servlet
response and returning it back to the
browser
• Notion that server always passes a
separate class object for Requests and
Responses between pages which carry a
persisting Session object in many cases.
Session Object for Requests
General Servlet Info
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Similar to C++ class
Member variables/functions
Private and Public options
Usually extension of some other class,
new class inherits functions of extended
class
JDBC
• Java.sql.* package serves as that java
ODBC equivalent
• Basic Methods: Driver, DriverManager,
Connection, Statement,
PreparedStatement, Callable Statement,
ResultSet
• Statements allow JDBC to execute SQL
commands
Starting a Database
• Connect by passing a driver to the
DriverManager
• Obtain a Connection with URL, username
and password
• Pass SQL commands with a Statement
• Examine ResultSet if applicable
• Close the database
View dbsamp.jsp for startup sequence and simple query
Data Navigation and Extraction
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Result.next();
Result.getInt(1);
Result.getString(“Customer”);
Result.getDate(4); (java.sql.Date not
java.util.Date)
Prepared Statements
pstmtU = con.prepareStatement( "UPDATE
myTable SET myStringColumn = ? " +
"WHERE myIntColumn = ?" );
pstmtU.setString( 1, "myString" );
pstmtU.setInt( 2, 1024 );
pstmtU.executeUpdate();
Conclusion
• This is a really general fast overview to
outline the overarching concepts
• Refer to http://java.sun.com for lots of
good documentation, API descriptions
• Excellent collection of basic tutorials at,
http://www.jguru.com/learn/index.jsp
• I will now go over a real example of a Java
web based application