Web Development in Java Andrew Simpson. Overview Background Language Details Java Server Pages (JSP) Servlets Database Connectivity (JDBC) Samples and

Web Development in Java

Andrew Simpson

Overview

• 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 Codeimport 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

• Embedding JAVA into static content

• Creating new dynamic tags to do embedding

• Embedding static content into JAVA

There are multiple styles that a JSP translator recognizes to writing a JSP

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-example-taglib.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

Refer to embedhtml.jsp file for example

• 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

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

• 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

• 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

http://java.sun.com/

http://www.jguru.com/learn/index.jsp

Documents

Web Development in Java Andrew Simpson. Overview Background Language Details Java Server Pages (JSP) Servlets Database Connectivity (JDBC) Samples and