Web Services Made Easy With Delphi

WSDL is a document that is written in XML. Its primary purpose is to describe a web service. It holds the following information about a web service:

• The location of the service or the URL.
  
• The methods it uses and the parameters that it takes.
  
• The results of the methods and type (string, float, etc.).

Here's an example WSDL file (converted to Pascal/Delphi code) that describes the location and methods that you need to use to access the service:

// *************************************************************** //

// The types declared in this file were generated from data read from the

// WSDL File described below:

// WSDL     : http://www.webservicex.net/WeatherForecast.asmx?WSDL

// Encoding : utf-8

// Version  : 1.0

// (10/08/2006 16:26:14 - 1.33.2.5)

// *************************************************************** //

unit WeatherForecast;

interface

uses InvokeRegistry, SOAPHTTPClient, Types, XSBuiltIns;

type

  // *************************************************************** //

  // The following types, referred to in the WSDL document are not being represented

  // in this file. They are either aliases[@] of other types represented or were referred

  // to but never[!] declared in the document. The types from the latter category

  // typically map to predefined/known XML or Borland types; however, they could also

  // indicate incorrect WSDL documents that failed to declare or import a schema type.

  // *************************************************************** //

  // !:string          - "http://www.w3.org/2001/XMLSchema"

  // !:float           - "http://www.w3.org/2001/XMLSchema"

  WeatherData          = class;                 { "http://www.webservicex.net" }

  WeatherForecasts     = class;                 { "http://www.webservicex.net" }

  // *************************************************************** //

  // Namespace : http://www.webservicex.net

  // ************************************************************** //

  WeatherData = class(TRemotable)

  private

    FDay: WideString;

    FWeatherImage: WideString;

    FMaxTemperatureF: WideString;

    FMinTemperatureF: WideString;

    FMaxTemperatureC: WideString;

    FMinTemperatureC: WideString;

  published

    property Day: WideString read FDay write FDay;

    property WeatherImage: WideString read FWeatherImage write FWeatherImage;

    property MaxTemperatureF: WideString read FMaxTemperatureF write FMaxTemperatureF;

    property MinTemperatureF: WideString read FMinTemperatureF write FMinTemperatureF;

    property MaxTemperatureC: WideString read FMaxTemperatureC write FMaxTemperatureC;

    property MinTemperatureC: WideString read FMinTemperatureC write FMinTemperatureC;

  end;

  ArrayOfWeatherData = array of WeatherData;    { "http://www.webservicex.net" }

  // ************************************************************** //

  // Namespace : http://www.webservicex.net

  // ************************************************************** //

  WeatherForecasts = class(TRemotable)

  private

    FLatitude: Single;

    FLongitude: Single;

    FAllocationFactor: Single;

    FFipsCode: WideString;

    FPlaceName: WideString;

    FStateCode: WideString;

    FStatus: WideString;

    FDetails: ArrayOfWeatherData;

  public

    destructor Destroy; override;

  published

    property Latitude: Single read FLatitude write FLatitude;

    property Longitude: Single read FLongitude write FLongitude;

    property AllocationFactor: Single read FAllocationFactor write FAllocationFactor;

    property FipsCode: WideString read FFipsCode write FFipsCode;

    property PlaceName: WideString read FPlaceName write FPlaceName;

    property StateCode: WideString read FStateCode write FStateCode;

    property Status: WideString read FStatus write FStatus;

    property Details: ArrayOfWeatherData read FDetails write FDetails;

  end;

  // *************************************************************** //

  // Namespace : http://www.webservicex.net

  // soapAction: http://www.webservicex.net/%operationName%

  // transport : http://schemas.xmlsoap.org/soap/http

  // style     : document

  // binding   : WeatherForecastSoap

  // service   : WeatherForecast

  // port      : WeatherForecastSoap

  // URL       : http://www.webservicex.net/WeatherForecast.asmx

  // *************************************************************** //

  WeatherForecastSoap = interface(IInvokable)

  ['{45A46EB0-5550-8C38-49AC-AE13AD113F74}']

    function  GetWeatherByZipCode(const ZipCode: WideString): WeatherForecasts; stdcall;

    function  GetWeatherByPlaceName(const PlaceName: WideString): WeatherForecasts; stdcall;

  end;

function GetWeatherForecastSoap(UseWSDL: Boolean=System.False; Addr: string=''; HTTPRIO: THTTPRIO = nil): WeatherForecastSoap;

implementation

function GetWeatherForecastSoap(UseWSDL: Boolean; Addr: string; HTTPRIO: THTTPRIO): WeatherForecastSoap;

const

  defWSDL = 'http://www.webservicex.net/WeatherForecast.asmx?WSDL';

  defURL  = 'http://www.webservicex.net/WeatherForecast.asmx';

  defSvc  = 'WeatherForecast';

  defPrt  = 'WeatherForecastSoap';

var

  RIO: THTTPRIO;

begin

  Result := nil;

  if (Addr = '') then

  begin

    if UseWSDL then

      Addr := defWSDL

    else

      Addr := defURL;

  end;

  if HTTPRIO = nil then

    RIO := THTTPRIO.Create(nil)

  else

    RIO := HTTPRIO;

  try

    Result := (RIO as WeatherForecastSoap);

    if UseWSDL then

    begin

      RIO.WSDLLocation := Addr;

      RIO.Service := defSvc;

      RIO.Port := defPrt;

    end else

      RIO.URL := Addr;

  finally

    if (Result = nil) and (HTTPRIO = nil) then

      RIO.Free;

  end;

end;

destructor WeatherForecasts.Destroy;

var

  I: Integer;

begin

  for I := 0 to Length(FDetails)-1 do

    if Assigned(FDetails[I]) then

      FDetails[I].Free;

  SetLength(FDetails, 0);

  inherited Destroy;

end;

initialization

  InvRegistry.RegisterInterface(TypeInfo(WeatherForecastSoap), 'http://www.webservicex.net', 'utf-8');

  InvRegistry.RegisterDefaultSOAPAction(TypeInfo(WeatherForecastSoap), 'http://www.webservicex.net/%operationName%');

  InvRegistry.RegisterInvokeOptions(TypeInfo(WeatherForecastSoap), ioDocument);

  RemClassRegistry.RegisterXSClass(WeatherData, 'http://www.webservicex.net', 'WeatherData');

  RemClassRegistry.RegisterXSInfo(TypeInfo(ArrayOfWeatherData), 'http://www.webservicex.net', 'ArrayOfWeatherData');

  RemClassRegistry.RegisterXSClass(WeatherForecasts, 'http://www.webservicex.net', 'WeatherForecasts');

end.

When you read the information above, it is pretty easy to see what methods are available and how you can read them.

Conclusion

In this first part of the series we've covered what a web service is and how it works. We have also looked at some examples of what XML and SOAP messages look like. In the next installment we will be looking into building our own web service and client.