Download Server-Side Java Programming

Server-Side Java Programming
Java
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Java started originally as OAK, for remote
control of peripherals.
Applets, small portable web-page-embeddable
programs made Java look appealing at first.
Today, applets are not very significant to Java's
popularity or success.
Server-side Java has been most important
driving force behind Java's direction.
Java Language
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Java was designed by James Gosling from
scratch to be a language that is:
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Highly object-oriented
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Garbage-collected
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Multithreaded to the core
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Secure/safe/managed
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Dynamic and reflective
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Interpreted (today, Just-In-Time compiled)
The approach can be summarized as “first, do it
right, then, improve efficiency.”
Packages and Classes
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Directory structure parallels package hierarchy.
One .java file contains one public Java class by the
same name.
org/apache/logging/Main.java:
package org.apache.logging;
public class Main { ... }
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Other non-public classes, nested classes and
anonymous classes may also be defined in that same
file.
Java compiles to intermediate “bytecode”; each class
creates one .class file (may be multiple per .java file).
Bytecode
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Unlike platform-specific executables, same bytecode
can run on any platform that supports Java.
Bytecode is often smaller than source code (which is
often much smaller than the corresponding compiled
executable file). This speeds up Java code download
on the network.
All external class references, methods, externally
visible internal methods and fields will have names
recorded in bytecode.
Symbols in Bytecode
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Bytecode contains many symbols.
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This allows classes with known interfaces to be
dynamically loaded and used with ease.
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Often, reverse engineering is quite possible.
Obfuscators can be used to make reverse
engineering harder, but they require all classes to be
gathered and obfuscated together (because public
APIs will be jumbled up).
This eliminates the ability to dynamically load and
use classes.
Standard Libraries
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A very large standard library exists, is welldocumented, and can be assumed available
anywhere Java is available.
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This helps reduce application code size.
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Java motto is “Write once, run anywhere.”
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You should quickly learn to read and navigate
the API documentation.
We will use both Java SDK and Java EE
libraries and APIs.
Java Syntax
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There are no structs or properties in Java.
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Objects are always passed-by-reference.
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Strings and arrays are special types of objects;
other objects can not do operator overloading
(as in C++).
Generics and assertions were added later
without changing the bytecode.
Annotations were added later and they changed
Java significantly.
Server-Side Java
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Lighter-weight three-tier Java “Web Applications”
use Servlets and JSPs (JavaServer Pages).
Heavier-weight four-tier Java “Enterprise
Applications” use EJBs.
In Java EE 5, annotation-based entities that contain
database-persisted data can be used by both of
these types of applications.
Web services and application client containers are
also supported.
JSP
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JSP is much like PHP.
It allows Java code to be embedded within
HTML.
Java code runs on the server side and
produces HTML.
Client only sees the HTML.
JSPs are compiled automatically to Servlets
when a page is requested by a client.
JSTL
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JSP pages used to mix presentation with
business logic.
To separate code from the design, JSTL (JSP
Tag Library) was created.
JSTL tags look like HTML tags, but are backed
by Java code for each tag.
This allows JSP pages to stay smaller and use
less Java code, making accidental change of
code by designers less likely.
Servlets
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Servlets and JavaBeans are often used to have
persistent logic, and page flow control.
JSPs are best used for presentation (more
HTML), Servlets can be used for business logic
(more Java code).
Client sessions can be created and used in both
Servlets and JSPs.
EJBs and Entities
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In four-tier enterprise applications, EJBs usually
handle the business logic.
In this case, JSPs and Servlets are used for
presentation issues.
In Java EE 5, “entity beans” are now replaced with
“entity objects”, which are part of the new JPA (Java
Persistence API).
Entity objects are automatically saved and retrieved
from database.
Enterprise Application Container handles EJB issues
and persistence.
Types of EJBs
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Stateless Session beans don't hold any client
state. They are often pooled and shared
amongst clients.
Stateful Session beans hold client state. They
are created per-client.
Message-Driven beans allow asynchronous
messaging; caller does not wait for a reply.
Enterprise Application Server
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We will use Sun JSAS PE 9.0 (Sun Java System
Application Server Platform Edition 9.0).
Sun JSAS is based on Glassfish open-source
application server.
Java EE 5 greatly simplifies EJB development.
This is mostly due to object-relational mapping that
automates object persistence by using annotations.
The standardized mapping was created by Oracle, in
its open-source product “Toplink Essentials”.
JSP Code Examples
helloworld.jsp
<%@page contentType="text/html“ %>
<%@page pageEncoding="UTF-8“ %>
<html>
<head><title>JSP: Hello World!</title></head>
<body>
<h1>JSP Says:</h1>
<%
out.println("Hello World!");
%>
</body>
</html>
helloform.jsp 1/2: JSP Processing
<%@page contentType="text/html“ %>
<%@page pageEncoding="UTF-8“ %>
<html>
<head><title>JSP: Hello Xyz</title></head>
<body>
<%
String user = request.getParameter("user");
if (user == null)
user = "Stranger";
%>
<h1>Hello <%= user %></h1>
helloform.jsp 2/2: HTML Form
… (JSP processing goes here)
<form method="POST" action="helloform.jsp">
Your Name:
<input type="text" name="user" size="40">
<input type="submit" name="submit" value="OK">
</form>
</body>
</html>
colorbox.jsp Structure
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Colorbox uses nested for loops to create a
colorful table.
colorbox.jsp structure:
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Page directives at the top
HTML on the outside
Initialize formatter to print hexadecimal later.
Outer for loop for red color
Nested HTML “<tr>”
Inner loop prints dynamic HTML
colorbox.jsp 1/2
<%@page contentType="text/html“ %>
<%@page pageEncoding="UTF-8“ %>
<%@page import="java.util.Formatter" %>
<html>
<head><title>JSP: Color Box</title></head>
<body>
<table border="0" cellspacing="0">
<%
StringBuilder sb = new StringBuilder();
Formatter formatter = new Formatter(sb);
int red, green;
colorbox.jsp 2/2
for (red = 0; red <= 255; red += 17) {
// instead of <tr> below, we can use 'out.println("<tr>")' here
%>
<tr>
<%
for(green = 0; green <= 255; green += 17) {
out.println(formatter.format(
"<td bgcolor='%02x%02xff'>&nbsp;&nbsp;&nbsp;",
red, green));
sb.setLength(0);
}
}
%>
// avoid appending next string