Apache Wink Building Blocks

In order to take full advantage of Apache Wink, a basic understanding of the building blocks that comprise it and their functional integration is required. The following section describes the basic concepts and building blocks of Apache Wink, version 0.1.

This section contains the following sections

Service Implemenatation Building Blocks

• Providers
• URI Dispatching
• Assets
• Annotations
• Url Handling
• Http Methods
• Basic URL Query Parameters
• Apache Wink Building Blocks Summary

Client Components Building Blocks

• RestClient
• Resource
• ClientRequest
• ClientResponse
• ClientConfig
• ClientHandler
• InputStreamAdapter
• OutputStreamAdapter
• EntityType
• ApacheHttpClientConfig

The Apache Wink Runtime

• Request Processor
• Deployment Configuration
• Handler Chain

Service Implementation Building Block Overview

As mentioned in the previous section, Apache Wink 1.0 reflects the design principles of a REST web service. It does so by providing the developer with a set of java classes that enable the implementation of "Resources", "Representations" and the association between them. Wink 1.0 also enables the developer to define the resource URI and the "Uniform methods" that are applicable to the resource.

Resource

A "resource" represents a serviceable component that enables for the retrieval and manipulation of data. A "resource class" is used to implement a resource by defining the "resource methods" that handle requests by implementing the business logic. A resource is bound or anchored to a URI space by annotating the resource class with the @Path annotation.

Providers

A provider is a class that is annotated with the @Provider annotation and implements one or more interfaces defined by the JAX-RS specification. Providers are not bound to any specific resource. The appropriate provider is automatically selected by the Apache Wink runtime according to the JAX-RS specification.
There are three types of providers defined by the JAX-RS specification:

• Entry Providers
• Context Providers
• Exception Mapping Provider

Entity Provider

An "Entity Provider" is a class that converts server data into a specific format requested by the client and or converts a request transmitted by the client into server data. An entity provider can be restricted to support a limited set of media types using the @Produces and @Consumes annotations. An entity provider is configured to handle a specific server data type by implementing the MessageBodyWriter and or MessageBodyReader interfaces.

Figure 2: Entity Provider Diagram

Context Provider

Context providers are used to supply contexts to resource classes and other providers by implementing the context ContextResolver interface. Context providers may restrict the media types that they support using the @Produces annotation.

Figure 3: Context Provider Diagram

Exception Mapping Provider

Exception mapping providers map a checked or runtime exception into an instance of a Response by implementing the ExceptionMapper interface. When a resource method throws an exception for which there is an exception mapping provider, the matching provider is used to obtain a Response instance.

Figure 4: Exception Mapping Provider Diagram

URI Dispatching

Designing an efficient REST web service requires that the application developer understands the resources that comprise the service, how to best identify the resources, and how they relate to one another.
Restful resources are identified by URIs in most cases related resources have URIs that share common path elements.

Figure 5: Apache Wink Logic Flow

Apache Wink Logic Flow

Figure 5 illustrates the Apache Wink logic flow. The Http request sent by the client invokes the "Apache Wink Rest Servlet". The Rest servlet uses the "Request Dispatcher" and the request URI in order to find, match and invoke the correct resource method.

Bookmarks Example

Throughout this document, various project examples are used in order to describe the functionality and processes that comprise the Apache Wink.
In order to explain the Rest design principles used in the Apache Wink this developer guide refers to the "Bookmark" example project found in the examples folder located in the Apache Wink distribution.

Refer to the code (using an IDE application) in the example in conjunction with the following explanations and illustrations in this developer guide.

Apache Wink Servlet and Request Processor

Figure 6:  Apache Wink Rest Servlet and Request Processor for the Bookmark Services

Server and Request Processor

Figure 6 shows the Apache Wink servlet and request Processor concept in the context of the application server. In the "Bookmarks" example in figure 6 there are two Resources, the first Resource is assosiated with the /mybookmarks URI and manages the bookmarks collection, the second resource is assosiated with the /mybookmarks/{bookmark} Resources and manages an individual bookmark within the collection.

The Resources' defined by the web service and managed by Apache Wink are referred to as "URI space". The Resources space is the collection of all URI's that exist in the same context. Figure 6 shows the URI spacew that contains /mybookmarks and /mybookmarks/{bookmarks}.

URI Space

The Bookmarks service URI space consists of the following URI space items and detailed descriptions about their context and functionality.
Table 1: URI Management

Assets

Assets are classes that contain "web service business logic" implemented by the developer. Each Asset is associated with one or more URI. The Apache Wink dispatcher invokes the Asset, which is associated with the URI found in the Http request.

An Asset class can implement one or more methods, each method is associated with a single Http method (GET, HEAD, POST, PUT, DELETE etc).  The methods can be associated with a Mime type of a produced representation. Methods that handle Http verbs of requests with a body (such as PUT, POST) are also associated with the Mime type of the Http request.
The Asset class can be registered to the Apache Wink using the "Spring context xml" or by using a registration API.

Annotations

Annotations are a special text notations, or metadata, added to Java version 1.5. Annotations in Java source code can affect both compilation and runtime behavior of the resulting Java classes.
JAX-RS is implemented by the use of annotations that are defined in the JAX-RS specification. Apache Wink provides a set of additional annotations that enrich the functionality of the JAX-RS enabled application.

The following table describes the additional Apache Wink annotations:

URL Handling

The Apache Wink receives Http requests and then dispatches a wrapped Http request to the appropriate Resource method.
The Http request is match to the Resource method based on the Http request parameters, the Resource method definitions and the Mime type.

Figure 7: URL Request Handling

Request Handling

Figure 7 demonstrates the Http Client request path to the URI dispatcher, once the dispatcher receives the request it is then matched according to the Http method, URL and Mime type and finally the Resource registry definition.

Http Methods - GET, POST, PUT, DELETE and OPTIONS

The common Http 1.1 methods for the Apache Wink are defined in the following section. This set of methods can be expanded.

Method Usage

Table 3: Http Methods

Key - X

• Safe - does not affect the server state
• Idempotent - a repeated application of the same method has the same effect as a single application
• Cacheable - a response to a method is cacheable if it meets the requirements for Http cachin
• * -   Responses to this method are not cacheable, unless the response includes an appropriate Cache-Control or Expires header fields. However, the 303 response can be used to direct the user agent to retrieve a cacheable resource.

GET

The GET method is used to retrieve information from a specified URI and is assumed to be a safe and repeatable operation by browsers, caches and other Http aware components. This means that the operation must have no side effects and GET method requests can be re-issued.

HEAD

The HEAD method is the same as the GET method except for the fact that the HEAD does not contain message body.

POST

The POST method is used for operations that have side effects and cannot be safely repeated. For example, transferring money from one bank account to another has side effects and should not be repeated without explicit approval by the user.

The POST method submits data to be processed, for example, from an  Html form, to the identified resource. The data is included in the body of the request. This may result in the creation of a new resource or the updates of existing resources or both.

PUT

The PUT method requests that the enclosed entity be stored under the supplied Request-URI. If the Request-URI refers to an already existing resource, the enclosed entity should be considered as a modified version of the one residing on the origin server.

If the Request-URI does not point to an existing resource, and that URI is capable of being defined as a new resource by the requesting user agent, the origin server can create the resource with that URI.

DELETE

The DELETE method requests that the origin server delete the resource identified by the Request-URI. This method can be overridden on the origin server.
The client cannot be guaranteed that the operation has been carried out, even if the status code returned from the origin server indicates that the action has been completed successfully.

OPTIONS

The OPTIONS method represents a request for information about the communication options available on the request/response chain identified by the Request-URI.
This method allows the client to determine the options and/or requirements associated with a resource, or the capabilities of a server, without implying a resource action or initiating a resource retrieval.

Basic URL Query Parameters

A URL parameter is a name and value pair appended to a URL. The parameter begins with a question mark "?" and takes the form of name=value.
If more than one URL parameter exists, each parameter is separated by an ampersand "&" symbol. URL parameters enable the client to send data as part of the URL to the server.
When a server receives a request and parameters are appended to the URL of the request, the server uses these parameters as if they were sent as part of the request body. There are several predefined URL parameters recognized by the Symphony SDK. The following table lists the parameters commonly used in web service URLs. These special URL parameters are defined in the "RestConstants" class.

Query Parameters

Table 4: URL Parameters

Combining URL Parameters

A single URL can contain more than one URL parameter, example "?alt=text%2Fjavascript &callback=myfunc"(where "%2F" represents escaped "/").

Apache Wink Building Blocks Summary

The previous section "Service Implementation Building Blocks" outlines the basic precepts and building blocks that comprise the service side of Apache Wink.
In order to understand the relationship between the building blocks that comprise Apache Wink a set of example applications have been designed and built that provide a reference point that demonstrate a rudimentary understanding about the functionality of Apache Wink.

Apache Wink Examples

The following examples applications are used in this "Apache Wink Developer Guide".

• Bookmarks
• HelloWorld
• QADefects

Bookmarks Project

This developer guide uses the bookmarks example application in order to describe the logic flow process within Apache Wink.
Refer to the comments located in the "Bookmarks" example application code for in-depth explanations about the methods used to build the bookmarks application.

HelloWorld Project

Complete the step-by-step "HelloWorld" tutorial in chapter 3 "Getting Started with Apache Wink" and then follow the installation instructions on page xx, in order to view the "Bookmarks" example application from within the Eclipse IDE.

QADefects

The QADefects example application illustrates the advanced functionality of Apache Wink by implementing most of the features provided by the Apache Wink (Runtime) framework.

Apache Wink Client Component Basics Overview

The Apache Wink Client interacts with Rest Web-Services. It maps Rest concepts to Java classes and encapsulates underlying Rest related standards and protocols, as well as providing a plug-in mechanism for raw HTTP streaming data manipulation. This mechanism also provides the ability to embed cross application functionality on the client side, such as security, compression and caching.

Figure 8: Apache Wink Client Simplified Breakdown

Figure 8: The illustration shows the basic elements that comprise the Apache Wink Client. The Apache Wink Client utilizes the providers machanism defined by the JAX-RS specification to perform reading and writing of java objects. The Apache Wink Client is preinitialized with the same providers that are predifined by the Apache Wink JAX-RS server implementation.

Apache Wink Client Components

Apache Wink is comprised of several key elements that together create a simple and convenient framework for the consumption of Rest based web services.

RestClient Class

The RestClient is the entry point for all rest service operations. The RestClient is used to create instances of Resource classes that are used to make the actual invocations to the service. The client can be initialized with a user supplied configuration to specify custom Provider classes, in addition to other configuration options.

The RestClient class is the central access point to Apache Wink. It provides the user with functionality that enables the creation of new resources. The RestClient provides the user with the ability to set different configuration parameters and propagated them, to each resource created. Once the resource is created, it can be manipulated by invoking the Http common methods, GET, PUT, POST and DELETE. The default usage of the Apache Wink is to create and reuse the RestClient object within the application.

Resource

Represents a web resource, enabling the invocation of different http methods.

ClientRequest

Represents a request issued by invoking any one of the invocation methods on a Resource. An instance of a ClientRequest is created at the beginning of an invocation and passed to all the client handlers defined on the client that was used for the invocation.

ClientResponse

Represents an http response that was received after invoking any one of the invocation methods on a Resource. An instance of a ClientResponse is created by the ConnectionHandler at the end of the handler chain, and is returned from every handler on the chain.

ClientConfig

Provides client configuration. The ClientConfig is implemented using the builder pattern so method calls can be easily aggregated. Custom Providers are defined by calling the applications(Application...) method. Custom client handlers are defined by calling the handlers(ClientHandler...) method.

ClientHandler

TBD

InputStreamAdapter

TBD

OutputStreamAdapter

TBD

EntityType

The EntityType is used to specify the class type and the generic type of responses.

Typically, an anonymous "EntityType" instance is created in order to specify the response type, as is shown in the following code example:

Resource resource = client.resource(uri);
                                           List<String> list =
                                                                 resource
                                                                     .get(new EntityType<List<String>>() {
                                                                     });

ApacheHttpClientConfig

The "ApacheHttpClientConfig" Configuration object that wraps Apache HttpClient as an underling Http client. The following code snippet, demonstrates the typical usage:

// create the client that uses Apache DefaultHttpClient as underling Http client.
RestClient client = new RestClient(new ApacheHttpClientConfig(new DefaultHttpClient()));

// create the resource to make invocations on
Resource resource = client.resource("http://myhost:80/my/service");

// invoke GET on the resource and receive the response entity as a string
String entity = resource.get(String.class);
...

The Apache Wink Runtime

The Apache Wink runtime is deployed on a JEE environment and is configured by defining the RestServlet in the web.xml file of the application. This servlet is the entry point of all the Http requests targeted for web services, and passes the request and response instances to the Symphony engine for processing.

Figure 9: Apache Wink Request Processor Architecture

The diagram illustrates the core components of the Apache Wink runtime. The Wink engine is the RequestProcessor. It builds an instance of a MessageContext with all of the required information for the request and passes it through the engine handler chains. The handler chains are responsible for serving the request, invoking the required resource method and finally generating a response.
In case of an error, the RequestProcessor invokes the Error chain with the generated exception for producing the appropriate response.
The Apache Wink runtime maintains providers and resources in two registries, the "providers registry" and the "resource registry" utilizing them during request processing.

Request Processor

The RequestProcessor is the Apache Wink engine, that is initialized by the RestServlet and is populated with an instance of a DeploymentConfiguration.
When a request is passed to the handleRequest() method of the RequestProcessor, a new instance of a  MessageContext is created.
The MessageContext contains all of the information that is required for the Wink runtime to handle the request. The RequestProcessor first invokes the Request Handler Chain and then the Response Handler Chain.

If an exception occurs during any stage of the request processing, the RequestProcessor invokes the Error Handler Chain for processing the exception.

Deployment Configuration

The Apache Wink runtime is initialized with an instance of a Deployment Configuration. The Deployment Configuration holds the runtime configuration, including the handler chains, registries, configuration properties.
The Deployment Configuration is initialized with an instance of a JAX-RS Application used for obtaining user resources and providers.

Customization

The Deployment Configuration is customized by extending the DeplymentConfiguration class, overriding specific methods and specifying the new class in the web.xml file of the application.
In order to specify a different Deployment Configuration class instead of the default Deployment Configuration, the value of the symphony.deploymentConfiguration RestServlet init parameter must be set to be the fully qualified name of the customized configuration class.

<servlet>
 <servlet-name>restSdkService</servlet-name>
 <servlet-class>
 com.hp.wink.server.internal.servlet.RestServlet
 </servlet-class>
 <init-param>
 <param-name>wink.deploymentConfiguration</param-name>
 <param-value>com.hp.example.MyDeploymentConfig</param-value>
 </init-param>
</servlet>

The following table details the customizable methods of the Deployment Configuration class.

Deployment Configuration

Table 5: Deployment Configuration Customizable Methods

Handler Chains

The handler chain pattern is used by the Wink runtime for implementing the core functionalities.
There are three handler chains utilized by the Wink runtime:

• RequestHandlersChain
• ResponseHandlersChain
• ErrorHandlersChain

Registries

The Apache Wink runtime utilizes two registries for maintaining the JAX-RS resources and providers. Both registries maintain their elements in a sorted state according to the JAX-RS specification for increasing performance during request processing. In addition to the JAX-RS specification sorting, Wink supports the prioritization of resources and providers.

Resource Registry

Firgure 10: Resource Registry Architecture

The resources registry maintains all of the root resources in the form of Resource Records.
A Resource Record holds the following:

• URI Template Processor - represents a URI template associated with a resource. Used during the resource matching process.
• Resource Metadata - holds the resource metadata collected from the resource annotations.
• Sub-Resource Records - records of all the sub-resources (methods and locators) collected from the sub-resource annotations.
• Resource Factory - a factory that retrieves an instance of the resource in accordance to the creation method defined for the resource.
  Possible creation methods include:
  • • singleton
    • prototype
    • spring configuration
    • user customizable