Requirements of Java EE 7 Enterprise Applications

The Java EE technology elements

Java EE specifications incorporates a group of other technologies and specifications to provide server-side functionalities for enterprise application developers

• application components: these components allow creation of application business logic and control elements
• integration: integration elements allow to interact with the functionalities from other applications and systems
• container management: these elements provide runtime support for Java EE application components

Creating a Simple Maven Project

1 Generating a simple project with Maven and Eclipse

To generate a project with maven from command line:

 mvn -B archetype:generate \
  -DgroupId=com.company.application \
  -DartifactId=project \
  -Dpackage=com.company.application \
  -Dversion=1.0 
  -DarchetypeGroupId=org.apache.maven.archetypes \
  -DarchetypeArtifactId=maven-archetype-quickstart \

• the maven command mvn archetype:generate executes the generate goal of the archetype plugin
• an archetype is defined as a "model from which similar thing are patterned; a prototype"
• when you run the archetype:generate goal you pass the goal parameter: archetypeArtifactId=maven-archetype-quickstart
• you can select the maven archetypes that fits your purpose
• the maven-archetype-quickstart is the most basic archetype to create a java project

Serializing Java Objects with JAXB

Java Model

The model class Team

package j2s.team;

import java.util.ArrayList;
import java.util.List;

import javax.xml.bind.annotation.XmlAccessType;
import javax.xml.bind.annotation.XmlAccessorType;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlElementWrapper;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.XmlType;

/* 
 * As the class Team is annotated with @XmlRootElement, JAXB transforms a Team 
 * instance into an XML document whose root element is <team> 
 */
@XmlRootElement(name="team")
@XmlType(propOrder={"name","description","playerList"})
@XmlAccessorType(XmlAccessType.FIELD)
public class Team {

 // fields
 private String name;
 private String description;

 @XmlElement(name = "player")
 @XmlElementWrapper(name = "players")
 private List<Player> playerList;

 public Team(String name, String description) {
  this.name = name;
  this.description = description;
  this.playerList = new ArrayList<Player>();
 }

 // default constructor required by JAXB
 public Team() {
  this("team name", "team descr");
 }

 public String getName() {
  return name;
 }

 public void setName(String name) {
  this.name = name;
 }

 public String getDescription() {
  return description;
 }

 public void setDescription(String description) {
  this.description = description;
 }

 public List<Player> getPlayers() {
  return playerList;
 }

 public void setPlayers(List<Player> playerList) {
  this.playerList = playerList;
 }

 public void addPlayer(Player dev) {
  playerList.add(dev);
 }

 @Override
 public String toString() {
  return "Team [name=" + name + ", description=" + description + ", players=" + playerList + "]";
 }

}

Web Services Introduction

Common definitions

Hypermedia systems are systems where text, pictures, audio, video and other media are stored in network hosts and connected through hyperlinks. The web is the example of hypermedia system.

The TCP-IP protocol stack makes it possible the data communication within a network of computer. The protocol stack is arranged in abstraction layers. From lowest to highest, the layers are: the link layer (for communication within a single network segment or link) the internet layer (for communication between independent networks) the transport layer (for communication host-to-host) and the application layer (for communication between two running application programs or processes: for example a client and a server). - (Internet_protocol_suite on wikipedia)

The HyperText Transfer Protocol or HTTP is an application-level protocol for hypermedia information systems.
HTTP is used by the World Wide Web with Hypertext to transfer data from servers to clients. HTTP is a generic protocol which can be used for many tasks beyond hypertext (such as Domain Name System and distributed object systems, like CORBA) through extension of its request methods, error codes and headers. (HTTP on wikipedia, HTTP on mozilla , rfc2616)

In computer networking, a communication channel is a logical connection that allows to transport information, from transmitters to receivers. A communication endpoint is an abstract object or interface that is the final point of a communication path; the transmitter writes to the endpoint and the receiver reads from the endpoint. For example, in operating systems, a software port is a communication endpoint managed by a computer's operating system, which identifies a specific process or a type of network service.

Web Service definitions

• A web service is a distributed software whose components can be deployed and executed on distinct devices.
• A web service consists of a service (a.k.a. producer) and a client (a.k.a. consumer or requester).

Web Service compared to Website

• both web services and websites are examples of distributed systems.
• websites deliver HMTL payloads whereas web services deliver XML or JSON payloads

Web service terminology

• endpoint: a web service endpoint is an association between a binding and a network address, specified by a URI, that may be used to communicate with an instance of a service.
• message: the basic unit of communication between a web service and a requester; data to be communicated to or from a web service as a single logical transmission.
• operation: a description of an action supported by the service; a set of messages related to a single web service action.
• synchronous: an interaction is said to be synchronous when the participating agents must be available to receive and process the associated messages from the time the interaction is initiated until all messages are actually received or some failure condition is determined.
• asynchronous: an interaction is said to be asynchronous when the associated messages are chronologically and procedurally decoupled.

Web Service communication layer

• A web service typically communicates over HTTP. A web service over HTTP is a web service that uses HTTP to transport web service messages (we say that HTTP protocol and HTTP messages are infrastructure). HTTP messages follow four kinds of conversational pattern: request/response, solicit/response, one-way and subscribe/notify
• the communication payloads are structured text, usually XML or JSON documents. XML and JSON are web service data interchange formats that provide an intermediary level and handle the differences in data types between different programming languages.

Web Service architecture

• The architecture of a simple web service is a client and a server.
• The architecture of a complicated web service have many clients and a service composed of other services.
• Example: an e-commerce service can be composed of multiple software components (each hosted on a separate web server) and any combination of PCs, tablets, mobile phones and other networked devices may host programs that make requests to the service.

Web services come in two flavors: SAOP-based and REST-style.

• SOAP is an XML dialect with a grammar that specifies the structure that documents must follow in order to be accepted as SOAP messages. SOAP-based services are transport neutral, but HTTP is the most common trasport for SOAP-based services
• REST-style services use HTTP not only as service transport protocol but also as service messaging system.

Why using web services?

• interoperability: clients and services can interact despite differences in programming languages, operating systems and hardware platforms.
• system integration: web services offers software integration for legacy system or databases. For example, you can write a web service that integrates with a legacy system written in COBOL or a web service that integrates with a RDBMS.

How to validate an xml document against a schema

STEP 1: Create the XML

To create a new XML file, start eclipse IDE and choose File->New->Other->XML file->Create XML file from XML template.
Model the data of interest in the XML file. In my case, I have created the following XML.

The teams.xml file

<?xml version="1.0" encoding="UTF-8"?>
<team>
 <name>the great team</name>
 <description>these team was recruited by google to develop a secret product</description>
 <developers>
  <developer role="frontend">
   <name>John Carrot</name>
  </developer>
  <developer role="backend">
   <name>Joshua Allock</name>
  </developer>
  <developer role="frontend">
   <name>Brendan Tich</name>
  </developer>
 </developers>
</team>

XML Schema Primer

Table of Contents

1 Introduction
2 Basic Concepts: The Purchase Order
    2.1 The Purchase Order Schema
    2.2 Complex Type Definitions, Element & Attribute Declarations
    2.3 Simple Types
    2.4 Anonymous Type Definitions
3 Advanced Concepts I: Namespaces, Schemas & Qualification
    3.1 Target Namespaces & Unqualified Locals
    3.2 Qualified Locals
    3.3 Global vs. Local Declarations
    3.4 Undeclared Target Namespaces

1 Introduction

Basic Concepts: The Purchase Order (§2) covers the basic mechanisms of XML Schema. It describes how to declare the elements and attributes that appear in XML documents, the distinctions between simple and complex types, defining complex types, the use of simple types for element and attribute values, schema annotation, a simple mechanism for re-using element and attribute definitions, and nil values.

Advanced Concepts I: Namespaces, Schemas & Qualification (§3), explains the basics of how namespaces are used in XML and schema documents.

2 Basic Concepts: The Purchase Order

The purpose of XML schemas

• a schema defines a class of XML documents (is a description of an XML document)
• an instance document is an XML document that conforms to a particular schema

The instance document, the po.xml file, describes a purchase order that may be generated by a product ordering application.

Example

The Purchase Order, po.xml

<?xml version="1.0"?>
<purchaseOrder orderDate="1999-10-20">
   <shipTo country="US">
      <name>Alice Smith</name>
      <street>123 Maple Street</street>
      <city>Mill Valley</city>
      <state>CA</state>
      <zip>90952</zip>
   </shipTo>
   <billTo country="US">
      <name>Robert Smith</name>
      <street>8 Oak Avenue</street>
      <city>Old Town</city>
      <state>PA</state>
      <zip>95819</zip>
   </billTo>
   <comment>Hurry, my lawn is going wild!</comment>
   <items>
      <item partNum="872-AA">
         <productName>Lawnmower</productName>
         <quantity>1</quantity>
         <USPrice>148.95</USPrice>
         <comment>Confirm this is electric</comment>
      </item>
      <item partNum="926-AA">
         <productName>Baby Monitor</productName>
         <quantity>1</quantity>
         <USPrice>39.98</USPrice>
         <shipDate>1999-05-21</shipDate>
      </item>
   </items>
</purchaseOrder>

The purchase order's elements have simple types or complex types

• the purchase order consists of a main element purchaseOrder and the subelements {shipTo, billTo, comment, items}.
• subelements can contain other subelements or data
• elements that contain subelements or carry attributes are said to have complex types
• elements that contain numbers, strings, dates and no subelements are said to have simple types, attributes always have simple types

Where to find the definitions of the types in the instance document

• the complex types in the instance document are defined in the schema for purchase orders
• the simple types in the instance document are defined either in the schema for purchase orders or are part of the built-in simple types of XML Schema

What is the association between the instance document and the the purchase order schema?

• an instance document does not need to refer to a schema
• the purchase order does not reference the purchase order schema