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6 Months Industrial Training in Spring Framework

The document provides a detailed overview of REST architecture for web services, emphasizing its principles such as statelessness, client-server decoupling, and the use of HTTP methods (GET, POST, PUT, DELETE). It discusses how REST services are implemented in Java using frameworks like Apache CXF and Spring MVC, highlighting their features and how they manage requests and responses. Additionally, it covers annotations used in JAX-RS for binding HTTP methods to Java methods and for parameter mapping.

Education◦
 Representational ◦ Clients possess the information necessary to identify, modify, and/or delete a web resource.  State ◦ All resource state information is stored on the client.  Transfer ◦ Client state is passed from the client to the service through HTTP.
REST stands for Representational State Transfer  It is an architectural pattern for developing web services as opposed to a specification.  REST web services communicate over the HTTP specification, using HTTP vocabulary: ◦ Methods (GET, POST, etc.) ◦ HTTP URI syntax (paths, parameters, etc.) ◦ Media types (xml, json, html, plain text, etc) ◦ HTTP Response codes.
The six characteristics of REST: 1. Uniform interface 2. Decoupled client-server interaction 3. Stateless 4. Cacheable 5. Layered 6. Extensible through code on demand (optional) * Services that do not conform to the above required contstraints are not strictly RESTful web services.
 The HTTP request is sent from the client. ◦ Identifies the location of a resource. ◦ Specifies the verb, or HTTP method to use when accessing the resource. ◦ Supplies optional request headers (name-value pairs) that provide additional information the server may need when processing the request. ◦ Supplies an optional request body that identifies additional data to be uploaded to the server (e.g. form parameters, attachments, etc.)
Sample Client Requests:  A typical client GET request:  A typical client POST request: GET /view?id=1 HTTP/1.1 User-Agent: Chrome Accept: application/json [CRLF] POST /save HTTP/1.1 User-Agent: IE Content-Type: application/x-www-form-urlencoded [CRLF] name=x&id=2 Requested Resource (path and query string) Request Headers Request Body (e.g. form parameters) Requested Resource (typically no query string) Request Headers (no request body)
 The HTTP response is sent from the server. ◦ Gives the status of the processed request. ◦ Supplies response headers (name-value pairs) that provide additional information about the response. ◦ Supplies an optional response body that identifies additional data to be downloaded to the client (html, xml, binary data, etc.)
Sample Server Responses: JSON Response 1:- it is simple and easy to understand 2:- fast processing 3:- contain keys and values in different forms XML Response 1:- most of the news feeds and blog feeds are in xml type 2:- it contain data in the form of tags like html tags
HTTP Methods supported by REST:  GET – Requests a resource at the request URL ◦ Should not contain a request body, as it will be discarded. ◦ May be cached locally or on the server. ◦ May produce a resource, but should not modify on it.  POST – Submits information to the service for processing ◦ Should typically return the new or modified resource.  PUT – Add a new resource at the request URL  DELETE – Removes the resource at the request URL  OPTIONS – Indicates which methods are supported  HEAD – Returns meta information about the request URL
A typical HTTP REST URL:  The protocol identifies the transport scheme that will be used to process and respond to the request.  The host name identifies the server address of the resource.  The path and query string can be used to identify and customize the accessed resource. http://my.store.com/fruits/list?category=fruit&limit=20 protocol host name path to a resource query string
A REST service framework provides a controller for routing HTTP requests to a request handler according to:  The HTTP method used (e.g. GET, POST)  Supplied path information (e.g /service/listItems)  Query, form, and path parameters  Headers, cookies, etc.
REST services in Java web applications can be implemented in several ways:  As a plain Java Servlet ◦ Adequate for very simple REST services. ◦ Requires a lot of “boiler plate” code for complex services.  Using a REST service framework. ◦ Eliminates the need to write “boilerplate” code. ◦ Typically integrates with other technologies, such as Spring. Java provides the JAX-RS specification for use by providers of REST service frameworks.
Although developers may implement REST web services however they choose, the Java Stack team is best equipped to support the following:  Apache CXF ◦ A JAX-RS web service framework  Spring MVC ◦ An MVC framework built upon the Spring Platform (does not implement the JAX-RS specification)
Apache CXF is a robust framework designed specifically for producing and consuming web services:  It is open-source and free to use.  It supports several web service standards and JSR APIs.  It provides tooling and configuration for JAX- WS and JAX-RS services.  It provides integration with the Spring Application Framework, the core technology upon which most of the Java Stack is built.
Apache CXF provides robust support for several web service patterns and specifications:  JSR APIs: JAX-WS, JAX-RS, JSR-181 annotations, SAAJ  WS-* specifications for web service interoperability.  Rich support support for message transports, protocol bindings, content negotiation, data bindings, and so forth.  Flexible, lightweight deployment in a variety of web application containers or stand-alone.  Tooling for code generation  Tools for WSDL and WADL publishing.
Spring MVC is a model-view-controller framework built upon the Spring Application Framework.  Annotation driven  Supports a RESTful pattern of routing requests to web resources using HTTP vocabulary.  Not an implementation of the JAX-RS specification.
JAX-RS HTTP Method Annotations: @GET @POST @PUT @DELETE @OPTIONS @HEAD  Applied to a Java method to bind it to an HTTP method.  Only one HTTP annotation may be applied to a single Java method.  Multiple Java methods may be given the same HTTP method annotation, assuming they are bound to different paths.
 @Path annotations may be supplied to customize the request URI of resource.  @Path on a class defines the base relative path for all resources supplied by that class.  @Path on a Java class method defines the relative path for the resource bound to that method.  @Path on a method is relative to any @Path on the class.  In the absence of @Path on the class or method, the resource is defined to reside at the root of the service.  A leading forward slash (/) is unnecessary as the path is always relative.
 Common JAX-RS Parameter Annotations: ◦ @QueryParam – maps to a query string parameter. ◦ @FormParam – maps to a form POST parameter. ◦ @PathParam – maps to a path segment. ◦ @DefaultValue – supplies a default parameter value.  Most often used on service methods to annotate input parameters.  Can also be used on fields or field setter methods if the service bean has request scope.  Additional parameter annotations are also available. ◦ See the JAX-RS API documentation for details.
@Produces  Used on a class or method to identify the content types that can be produced by that resource class or method.  Method annotation overrides class annotation  If not specified, CXF assumes any type (*/*) can be produced.  CXF responds with HTTP status “406 Not Acceptable” if no appropriate method is found.
@Consumes  Used on a class or method to identify the content types that can be accepted by that resource class or method.  Method annotation overrides class annotation  If not specified, CXF assumes any type (*/*) is acceptable.  CXF responds with HTTP status “406 Not Acceptable” if no appropriate method is found.
Examples of @Produces and @Consumes:  The client submits JSON or XML content with the “Content-Type” header.  The client requests either JSON or XML content through use of the HTTP “Accept” request header. @Path("example") public class ExampleRestService { @POST @Path("items") @Produces({"application/json", "application/xml"}) @Consumes({"application/json", "application/xml"}) public List<Item> editItems(List<Item> items) { // Does something and returns the modified list } }
 As a requirement of JAX-RS, CXF automatically provides support for reading and writing XML to and from JAXB annotated classes.  CXF also provides built-in support for reading and writing JSON to and from JAXB annotated classes. ◦ Default support uses Jettison as the JSON provider ◦ The Stack RS namespace handler will automatically configure Jackson as the JSON provider if it is on the classpath.