.NET Remoting and Delphi - Implementing the Server
(Page 10 of 11 )
The server is composed of two parts:
The project source file in which we will open an HTTP remoting channel and register the class that implements the IBankManager interface.
A unit that contains the class TBankManager. This class implements the IBankManager interface.
We've added a new unit to the server project and saved it as BankServer_Impl.pas. This unit is shown in Listing 29.2.
Listing 29.2 The BankServer_Impl.pas Unit
1: unit BankServer_Impl;
2:
3: interface
4:
5: uses
6: BankShared;
7:
8: type
9: TBankManager = class(MarshalByRefObject, IBankManager)
10: private
11: fAccount1,
12: fAccount2 : TAccount;
13: protected
14: // IBankManager
15: function GetAccountNumbers : TAccountNumberArray;
16: function GetAccount(const AccountNumber : integer) : TAccount;
17: procedure TransferMoney(const Origin, Destination : integer;
18: const Amount : double);
19: public
20: constructor Create;
21: end;
22:
23: implementation
24:
25: { TBankManager }
26:
27: constructor TBankManager.Create;
28: begin
29: inherited Create;
30: fAccount1 := TAccount.Create(1, 'John Smith', 1999);
31: fAccount2 := TAccount.Create(2, 'Jack Rockwell', 249);
32: end;
33:
34: function TBankManager.GetAccount(const AccountNumber: integer): TAccount;
35: begin
36: case AccountNumber of
37: 1 : result := fAccount1;
38: 2 : result := fAccount2;
39: else raise Exception.Create('Invalid account number!');
40: end;
41:
42: Console.WriteLine('A client requested account '+result.Number.ToString+
43: ' ('+result.Name+')');
44: end;
45:
46: function TBankManager.GetAccountNumbers: TAccountNumberArray;
47: begin
48: SetLength(result, 2);
49: result[0] := fAccount1.Number;
50: result[1] := fAccount2.Number;
51:
52: Console.WriteLine('A client requested the list of accounts');
53: end;
54:
55: procedure TBankManager.TransferMoney(const Origin, Destination: integer;
56: const Amount: double);
57: var origin_acct, destination_acct : TAccount;
58: begin
59: origin_acct := GetAccount(Origin);
60: destination_acct := GetAccount(Destination);
61:
62: if (origin_acct.Balance<Amount) or (Amount<0)
63: then raise Exception.Create('Insufficient funds or invalid amount specified');
64:
65: destination_acct.Balance := destination_acct.Balance+Amount;
66: origin_acct.Balance := origin_acct.Balance-Amount;
67:
68: Console.WriteLine('Transferred ${0} from account {1} to account {2}',
69: Amount.ToString, origin_acct.Number.ToString,
70: destination_acct.Number.ToString);
71: end;
72:
73: end.
Find the code on the CD: \Code\Chapter 29\Ex01.
Pay attention to the declaration of TBankManager at line 9. MarshalByRefObject is the base class for objects that communicate across application domain boundaries by exchanging messages using a proxy.
The proxy is created the first time the object is accessed. Subsequent calls on the proxy are marshaled back to the object residing in the server application domain.
Classes must inherit from MarshalByRefObject when their instances need to be used across application domains, and their state doesn't need to be or cannot be copied.
In the project source file (see Listing 29.3 later), we've added the namespaces System.Runtime.Remoting, System.Runtime.Remoting.Channels, and System.Runtime.Remoting.Channels.HTTP. The project source file now contains
uses
BankServer_Impl in 'BankServer_Impl.pas',
System.Runtime.Remoting,
System.Runtime.Remoting.Channels,
System.Runtime.Remoting.Channels.HTTP;
We've also defined a variable of type HTTPChannel called Channel and initialized it as follows:
var def_HTTPPort : integer = 8099;
Channel : HttpChannel;
Begin
[..]
Channel := HttpChannel.Create(def_HTTPPort);
ChannelServices.RegisterChannel(Channel);
Finally, we registered the type TBankManager by using the RemotingConfiguration class:
RemotingConfiguration.RegisterWellKnownServiceType(
typeOf(TBankManager),
'BankManager.soap',
WellKnownObjectMode.Singleton);
// Starts accepting requests
Writeln('Waiting for requests...');
Readln;
The complete source for the BankServer.dpr file is shown in Listing 29.3.
Listing 29.3 BankServer.dpr File
1: program BankServer;
2:
3: {$APPTYPE CONSOLE}
4:
5: {%DelphiDotNetAssemblyCompiler 'BankPackage.dll'}
6: {%DelphiDotNetAssemblyCompiler [..]}
7: {%DelphiDotNetAssemblyCompiler [..]}
8:
9: uses
10: BankServer_Impl in 'BankServer_Impl.pas',
11: System.Runtime.Remoting,
12: System.Runtime.Remoting.Channels,
13: System.Runtime.Remoting.Channels.HTTP;
14:
15: var def_HTTPPort : integer = 8099;
16: Channel : HttpChannel;
17: begin
18: Console.WriteLine('Initializing server...');
19:
20: // Initializes the server to listen for HTTP requests on a specific port
21: Channel := HttpChannel.Create(def_HTTPPort);
22: ChannelServices.RegisterChannel(Channel);
23: Console.WriteLine('HTTP channel created. Listening on port '+
24: System.Convert.ToString(def_HTTPPort));
25:
26: // Registers the TBankManager service
27: RemotingConfiguration.RegisterWellKnownServiceType(
28: typeOf(TBankManager),
29: 'BankManager.soap',
30: WellKnownObjectMode.Singleton);
31:
32: // Starts accepting requests
33: Console.WriteLine('Waiting for requests...');
34: Console.ReadLine;
35: end.
Find the code on the CD: \Code\Chapter 29\Ex01.
Lines 21–22 show how to make the server application create a remoting channel that listens for HTTP messages on port 8099. Lines 27–30 register the object TBankManager as a singleton ready to be remotely accessed.
Notice how you do not need to associate a class to a channel. If you have other remote classes, you would just need to register them as we did with TBankManager (lines 27–30). The HTTP channel that was previously created listens for any type of remoting message coming from clients and forwards it to the correct target object.
At this point, you can compile the server application and launch it outside the IDE. It will display the contents as shown in Figure 29.12.
Figure 29.12
Server application output.
 This chapter is from Delphi for .NET Developer's Guide, by Xavier Pacheco (Sams, 2004, ISBN: 0-672-32443-1). Check it out at your favorite bookstore today.
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