WiRL Project

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Introduction ​

Delphi RESTful Library

WiRL is an attempt to write a simple REST library in Delphi using the new features of the language (such as generics, anonymous methods, attributes, record helpers and so on).

JAX-RS ​

WiRL it's inspired by the Java API for RESTful Web Services (JAX-RX), the "de facto" standard in the Java world to build a REST API.

The goals of the JAX-RS API (and therefore also WiRL) are:

  • POJO-based: To provide a collection of classes and associated annotations to be used with POJOs (Plain Old Java Object) so as to expose them as Web resources.

  • HTTP-centric: To use HTTP as the underlying network protocol and provide a clear mapping between HTTP and URI elements and the corresponding API classes and annotations.

  • Content Negotiation: To be applicable to a wide variety of HTTP entity body content types and provide the necessary pluggability to allow additional types to be added.

The main components of a JAX-RS (and WiRL) are:

  • MessageBody Readers & Writers (Clients & Servers)
  • Filters (Clients & Servers)
  • Annotations (Attributes)
  • POJO for resources
  • Serializer Engine for Entities
  • HTTP verbs as actions
  • Pluggable Auth

WiRL Main Features ​

WiRL wants to be a standard and clean way to build true RESTful services adhering to the famous 6 constraint of the REST Architecure:

REST Constraints

  1. Client/Server
  2. Stateless
  3. Cache
  4. Uniform interface
  5. Layered system
  6. Code on demand (optional)

if your service adopts the above constraints, it will benefit from the following properties:

  • Scalability of components
  • Reliability in the resistance to failure
  • Visibility of communication between components
  • Simplicity of a uniform interface
  • Portability of components by moving program code with the data
  • Modifiability of components to meet changing needs
  • Performance in component interactions

The main feature of WiRL is the mapping of a Delphi class in a web resource using some attributes.

pascal
[Path('customers')]
TCustomerResource = class
public
  [GET]
  [Produces('TMediaType.APPLICATION_JSON')]
  function SelectCustomers: TCustomerList;

  [POST]
  [Consumes('TMediaType.APPLICATION_JSON')]
  [Produces('TMediaType.APPLICATION_JSON')]
  function InsertCustomer(ACustomer: TCustomer): TCustomer;
end;

Every class decorated with the [Path] attribute and registered in the TWiRLResourceRegistry is a web resource associated with a specific path. The input parameters of the methods are read from the HTTP request, WiRL try to find the right parameter value using some built-in attributes: [PathParam], [QueryParam], [BodyParam] and many others. Then inject the correct value into the parameters. If the parameter type is an object WiRL try to build the object using a Message Body Reader a special customizable class factory. The result type is handled in the same way but with a Message Body Writer.