Web services

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Java-Examples

What is java

Java is a programming language originally developed by James Gosling at Sun Microsystems (which has since merged into Oracle Corporation) and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++, but it has fewer low-level facilities than either of them. Java applications are typically compiled to bytecode (class file) that can run on any Java virtual machine (JVM) regardless of computer architecture. Java is a general-purpose, concurrent, class-based, object-oriented language that is specifically designed to have as few implementation dependencies as possible. It is intended to let application developers "write once, run anywhere" (WORA), meaning that code that runs on one platform does not need to be recompiled to run on another. Java is as of 2012 one of the most popular programming languages in use, particularly for client-server web applications, with a reported 10 million users.[10][11] The original and reference implementation Java compilers, virtual machines, and class libraries were developed by Sun from 1991 and first released in 1995. As of May 2007, in compliance with the specifications of the Java Community Process, Sun relicensed most of its Java technologies under the GNU General Public License. Others have also developed alternative implementations of these Sun technologies, such as the GNU Compiler for Java and GNU Classpath.

why we use java

Java is a programming language and computing platform first released by Sun Microsystems in 1995. It is the underlying technology that powers state-of-the-art programs including utilities, games, and business applications. Java runs on more than 850 million personal computers worldwide, and on billions of devices worldwide, including mobile and TV devices.
Why do I need Java?
There are lots of applications and websites that won't work unless you have Java installed, and more are created every day. Java is fast, secure, and reliable. From laptops to datacenters, game consoles to scientific supercomputers, cell phones to the Internet, Java is everywhere!

Usage

Java technology is a high-level programming and a platform independent language. Java is designed to work in the distributed environment on the Internet. Java has a GUI features that provides you better "look and feel" over the C++ language, moreover it is easier to use than C++ and works on the concept of object-oriented programming model. Java enable us to play online games, video, audio, chat with people around the world, Banking Application, view 3D image and Shopping Cart. Java find its extensive use in the intranet applications and other e-business solutions that are the grassroots of corporate computing. Java , regarded as the most well described and planned language to develop an applications for the Web. Java is a well known technology which allows you for software designed and written only once for an "virtual machine" to run on a different computers, supports various Operating System like Windows PCs, Macintoshes, and Unix computers. On the web aspect, Java is popular on web servers, used by many of the largest interactive websites. Java is used to create standalone applications which may run on a single computer or in distributed network. It is also be used to create a small application program based on applet, which is further used for Web page. Applets make easy and possible to interact with the Web page.

Introduction to webservices

Web services are client and server applications that communicate over the World Wide Web's (WWW) HyperText Transfer Protocol (HTTP). As described by the World Wide Web Consortium (W3C), web services provide a standard means of interoperating between software applications running on a variety of platforms and frameworks. Web services are characterized by their great interoperability and extensibility, as well as their machine-processable descriptions, thanks to the use of XML. Web services can be combined in a loosely coupled way to achieve complex operations. Programs providing simple services can interact with each other to deliver sophisticated added-value services.

Types of Web Services

On the conceptual level, a service is a software component provided through a network-accessible endpoint. The service consumer and provider use messages to exchange invocation request and response information in the form of self-containing documents that make very few assumptions about the technological capabilities of the receiver. On a technical level, web services can be implemented in various ways. The two types of web services discussed in this section can be distinguished as "big" web services and "RESTful" web services.
Big- Web Services
In Java EE 6, JAX-WS provides the functionality for "big" web services, which are described in Chapter 19, Building Web Services with JAX-WS. Big web services use XML messages that follow the Simple Object Access Protocol (SOAP) standard, an XML language defining a message architecture and message formats. Such systems often contain a machine-readable description of the operations offered by the service, written in the Web Services Description Language (WSDL), an XML language for defining interfaces syntactically. The SOAP message format and the WSDL interface definition language have gained widespread adoption. Many development tools, such as NetBeans IDE, can reduce the complexity of developing web service applications. A SOAP-based design must include the following elements. A formal contract must be established to describe the interface that the web service offers. WSDL can be used to describe the details of the contract, which may include messages, operations, bindings, and the location of the web service. You may also process SOAP messages in a JAX-WS service without publishing a WSDL. The architecture must address complex nonfunctional requirements. Many web service specifications address such requirements and establish a common vocabulary for them. Examples include transactions, security, addressing, trust, coordination, and so on. The architecture needs to handle asynchronous processing and invocation. In such cases, the infrastructure provided by standards, such as Web Services Reliable Messaging (WSRM), and APIs, such as JAX-WS, with their client-side asynchronous invocation support, can be leveraged out of the box.

RESTful Web Services

In Java EE 6, JAX-RS provides the functionality for Representational State Transfer (RESTful) web services. REST is well suited for basic, ad hoc integration scenarios. RESTful web services, often better integrated with HTTP than SOAP-based services are, do not require XML messages or WSDL service-API definitions. Project Jersey is the production-ready reference implementation for the JAX-RS specification. Jersey implements support for the annotations defined in the JAX-RS specification, making it easy for developers to build RESTful web services with Java and the Java Virtual Machine (JVM). Because RESTful web services use existing well-known W3C and Internet Engineering Task Force (IETF) standards (HTTP, XML, URI, MIME) and have a lightweight infrastructure that allows services to be built with minimal tooling, developing RESTful web services is inexpensive and thus has a very low barrier for adoption. You can use a development tool such as NetBeans IDE to further reduce the complexity of developing RESTful web services. A RESTful design may be appropriate when the following conditions are met. The web services are completely stateless. A good test is to consider whether the interaction can survive a restart of the server. A caching infrastructure can be leveraged for performance. If the data that the web service returns is not dynamically generated and can be cached, the caching infrastructure that web servers and other intermediaries inherently provide can be leveraged to improve performance. However, the developer must take care because such caches are limited to the HTTP GET method for most servers. The service producer and service consumer have a mutual understanding of the context and content being passed along. Because there is no formal way to describe the web services interface, both parties must agree out of band on the schemas that describe the data being exchanged and on ways to process it meaningfully. In the real world, most commercial applications that expose services as RESTful implementations also distribute so-called value-added toolkits that describe the interfaces to developers in popular programming languages. Bandwidth is particularly important and needs to be limited. REST is particularly useful for limited-profile devices, such as PDAs and mobile phones, for which the overhead of headers and additional layers of SOAP elements on the XML payload must be restricted. Web service delivery or aggregation into existing web sites can be enabled easily with a RESTful style. Developers can use such technologies as JAX-RS and Asynchronous JavaScript with XML (AJAX) and such toolkits as Direct Web Remoting (DWR) to consume the services in their web applications. Rather than starting from scratch, services can be exposed with XML and consumed by HTML pages without significantly refactoring the existing web site architecture. Existing developers will be more productive because they are adding to something they are already familiar with rather than having to start from scratch with new technology. RESTful web services are discussed in Chapter 20, Building RESTful Web Services with JAX-RS. This chapter contains information about generating the skeleton of a RESTful web service using both NetBeans IDE and the Maven project
management tool.

Building Web Services with JAX-WS

Java API for XML Web Services (JAX-WS) is a technology for building web services and clients that communicate using XML. JAX-WS allows developers to write message-oriented as well as Remote Procedure Call-oriented (RPC-oriented) web services.
In JAX-WS, a web service operation invocation is represented by an XML-based protocol, such as SOAP. The SOAP specification defines the envelope structure, encoding rules, and conventions for representing web service invocations and responses. These calls and responses are transmitted as SOAP messages (XML files) over HTTP.
Although SOAP messages are complex, the JAX-WS API hides this complexity from the application developer. On the server side, the developer specifies the web service operations by defining methods in an interface written in the Java programming language. The developer also codes one or more classes that implement those methods. Client programs are also easy to code. A client creates a proxy (a local object representing the service) and then simply invokes methods on the proxy. With JAX-WS, the developer does not generate or parse SOAP messages. It is the JAX-WS runtime system that converts the API calls and responses to and from SOAP messages.
With JAX-WS, clients and web services have a big advantage: the platform independence of the Java programming language. In addition, JAX-WS is not restrictive: A JAX-WS client can access a web service that is not running on the Java platform, and vice versa. This flexibility is possible because JAX-WS uses technologies defined by the W3C: HTTP, SOAP, and WSDL. WSDL specifies an XML format for describing a service as a set of endpoints operating on messages.

Building restful Web Services with JAX-RS


Building RESTful Web Services with JAX-RS

This chapter describes the REST architecture, RESTful web services, and the Java API for RESTful Web Services (JAX-RS, defined in JSR 311). Jersey, the reference implementation of JAX-RS, implements support for the annotations defined in JSR 311, making it easy for developers to build RESTful web services by using the Java programming language. If you are developing with GlassFish Server, you can install the Jersey samples and documentation by using the Update Tool. Instructions for using the Update Tool can be found in Java EE 6 Tutorial Component. The Jersey samples and documentation are provided in the Available Add-ons area of the Update Tool.

JAX-RS: Advanced Topics and Example


Example Applications for JAX-RS

This section provides an introduction to creating, deploying, and running your own JAX-RS applications. This section demonstrates the steps that are needed to create, build, deploy, and test a very simple web application that uses JAX-RS annotations.
A RESTful Web Service

This section explains how to use NetBeans IDE to create a RESTful web service. NetBeans IDE generates a skeleton for the application, and you simply need to implement the appropriate methods. If you do not use an IDE, try using one of the example applications that ship with Jersey as a template to modify. You can find a version of this application at tut-install/examples/jaxrs/HelloWorldApplication/.
To Create a RESTful Web Service Using NetBeans IDE
    In NetBeans IDE, create a simple web application. This example creates a very simple "Hello, World" web application.
    From the File menu, choose New Project.
    From Categories, select Java Web. From Projects, select Web Application. Click Next.

Note - For this step, you could also create a RESTful web service in a Maven web project by selecting Maven as the category and Maven Web Project as the project. The remaining steps would be the same.
Type a project name, HelloWorldApplication, and click Next.

Make sure that the Server is GlassFish Server (or similar wording).
Click Finish.
The project is created. The file index.jsp appears in the Source pane.
Right-click the project and select New; then select RESTful Web Services from Patterns.
Select Simple Root Resource and click Next.
Type a Resource Package name, such as helloWorld.
Type helloworld in the Path field. Type HelloWorld in the Class Name field. For MIME Type, select text/html.
Click Finish.
The REST Resources Configuration page appears.
Click OK.
A new resource, HelloWorld.java, is added to the project and appears in the Source pane. This file provides a template for creating a RESTful web service.
In HelloWorld.java, find the getHtml() method. Replace the //TODO comment and the exception with the following text, so that the finished product resembles the following method.
Note - Because the MIME type produced is HTML, you can use HTML tags in your return statement.
/**
* Retrieves representation of an instance of helloWorld.HelloWorld
* @return an instance of java.lang.String
*/
@GET
@Produces("text/html")
public String getHtml() {
return "
";
}
Test the web service. To do this, right-click the project node and click Test RESTful Web Services.
This step deploys the application and brings up a test client in the browser.
When the test client appears, select the helloworld resource in the left pane, and click the Test button in the right pane.
The words Hello, World!! appear in the Response window below.
Set the Run Properties:
Right-click the project node and select Properties.
In the dialog, select the Run category.
Set the Relative URL to the location of the RESTful web service relative to the Context Path, which for this example is resources/helloworld.
Tip - You can find the value for the Relative URL in the Test RESTful Web Services browser window. In the top of the right pane, after Resource, is the URL for the RESTful web service being tested. The part following the Context Path (http://localhost:8080/HelloWorldApp) is the Relative URL that needs to be entered here.
If you don't set this property, the file index.jsp will appear by default when the application is run. As this file also contains Hello World as its default value, you might not notice that your RESTful web service isn't running, so just be aware of this default and the need to set this property, or update index.jsp to provide a link to the RESTful web service.
Right-click the project and select Deploy.
Right-click the project and select Run.
A browser window opens and displays the return value of Hello, World!!