Web Development in Java
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Web Development in Java Andrew Simpson
description
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 - PowerPoint PPT Presentation
Transcript of Web Development in Java
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
