Server-Side Java Programming

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Server-Side Java Programming
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Java

• 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.

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Java Language

• Java was designed by James Gosling from scratch
  to be a language that is
• Highly object-oriented
• Garbage-collected
• Multithreaded to the core
• Secure/safe/managed
• Dynamic and reflective
• Interpreted (today, Just-In-Time compiled)?
• The approach can be summarized as first, do it
  right, then, improve efficiency.

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Packages and Classes

• 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 ...
• 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).

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Bytecode

• 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.

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Symbols in Bytecode

• Bytecode contains many symbols.
• This allows classes with known interfaces to be
  dynamically loaded and used with ease.
• 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.

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Standard Libraries

• A very large standard library exists, is
  well-documented, and can be assumed available
  anywhere Java is available.
• This helps reduce application code size.
• Java motto is Write once, run anywhere.
• You should quickly learn to read and navigate the
  API documentation.
• We will use both Java SDK and Java EE libraries
  and APIs.

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Java Syntax

• There are no structs or properties in Java.
• Objects are always passed-by-reference.
• 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.

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Server-Side Java

• 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.

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JSP

• 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.

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JSTL

• 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.

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Servlets

• 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.

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EJBs and Entities

• 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.

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Types of EJBs

• 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.

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Enterprise Application Server

• 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.

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JSP Code Examples
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helloworld.jsp

• lt_at_page contentType"text/html gt
• lt_at_page pageEncoding"UTF-8 gt
• lthtmlgt
• ltheadgtlttitlegtJSP Hello World!lt/titlegtlt/headgt
• ltbodygt
• lth1gtJSP Sayslt/h1gt
• lt
• out.println("Hello World!")
• gt
• lt/bodygt
• lt/htmlgt

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helloform.jsp 1/2 JSP Processing

• lt_at_page contentType"text/html gt
• lt_at_page pageEncoding"UTF-8 gt
• lthtmlgt
• ltheadgtlttitlegtJSP Hello Xyzlt/titlegtlt/headgt
• ltbodygt
• lt
• String user request.getParameter("user")
• if (user null)
• user "Stranger"
• gt
• lth1gtHello lt user gtlt/h1gt

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helloform.jsp 2/2 HTML Form

• (JSP processing goes here)
• ltform method"POST" action"helloform.jsp"gt
• Your Name
• ltinput type"text" name"user" size"40"gt
• ltinput type"submit" name"submit" value"OK"gt
• lt/formgt
• lt/bodygt
• lt/htmlgt

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colorbox.jsp Structure

• Colorbox uses nested for loops to create a
  colorful table.
• colorbox.jsp structure
• Page directives at the top
• HTML on the outside
• Initialize formatter to print hexadecimal later.
• Outer for loop for red color
• Nested HTML lttrgt
• Inner loop prints dynamic HTML

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colorbox.jsp 1/2

• lt_at_page contentType"text/html gt
• lt_at_page pageEncoding"UTF-8 gt
• lt_at_page import"java.util.Formatter" gt
• lthtmlgt
• ltheadgtlttitlegtJSP Color Boxlt/titlegtlt/headgt
• ltbodygt
• lttable border"0" cellspacing"0"gt
• lt
• StringBuilder sb new StringBuilder()
• Formatter formatter new Formatter(sb)
• int red, green

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colorbox.jsp 2/2

• for (red 0 red lt 255 red 17)
• // instead of lttrgt below, we can use
  'out.println("lttrgt")' here
• gt
• lttrgt
• lt
• for(green 0 green lt 255 green 17)
• out.println(formatter.format(
• "lttd bgcolor'02x02xff'gtnbspnbspnbsp
  ",
• red, green))
• sb.setLength(0) // avoid appending next
  string
• gt
• lt/bodygtlt/htmlgt