《关于VisiBroker For Delphi的使用》(3)
-CORBA技术实践(一)
宜昌市中心人民医院 赵普昉
email: 3boy@sohu.com
3,数组对象与简单数据对象的传递
前面提到了一些较为简单的数据操作,我们都可以想象一下,如果操作CORBA对象与操作C/S结构的数据对象一样的方便,那么CORBA又有什么神奇了,不知道看过李维的分布式多层应用系统的书籍时,是否留意到李维对CORBA的评价,无论你看过
还是没有看过,我都要告诉正在使用CORBA编程的朋友们,CORBA比COM/COM+简单,而CORBA的跨平台特性,以及与COM/COM+同样的负载平衡能力,足以让我们将这项分布式技术应用到应用体系的设计之中,其实对于使用Borland的产品开发分布式系统无论你采用CORBA或是COM/COM+其实最核心的技术就是MIDAS,因为
你总可以在CORBA/COM/COM+中看到MIDAS的影子,所以我建议无论你是准备学习CORBA还是学习COM/COM+最好先学习一下MIDAS,本文不涉及MIDAS,关于MIDAS请看李维的《Delphi5.X分布式多层应用—系统篇》。
为什么我从开始就一直要大家使用文本编辑器之类的东西书写IDL,而不用TypeLibrary
来书写IDL,其实我觉得只是为了让刚刚接触CORBA的程序员获得一些更多的IDL方面的知识罢了,在实际的开发中你可以完全很方便的使用TypeLibrary来编写接口规则。
下面我简要的列举几类IDL书写的事例与利用IDL2PAS生成的PASCAL代码。
1、)常量的定义
/**IDL书写**/
module MyCRB{
const long iMyConst=1;
interface myFace {
const long iiMyConst=2;
};
};
/**Pascal**/
unit MyCRB_I;
interface
uses Corba;
const
iMyCOnst:integer=1;
myFace_iiMyConst=2;
2、)不在接口中申明的常量
/**IDL**/
module MyCRB{
const long myconst=1;
};
/*pascal*/
unit MyCRB_I;
interface
const myconst:integer=1;
3、)枚举类型
/*IDL*/
enum MyCRBKind{A,B,C,D,……..}
/*pascal*/
myCRBkind=(A,B,C,D……..);
4、)结构体
/*IDL*/
struct mystructtype{
long X;
string Y;
boolean Z;
};
/*pascal*/
//XXX_I.pas
type mystructtype=interface;
//XXX_C.pas
mystructtype=interface
function _get_X:integer;
function _get_Y:string;
function _get_Z:boolean;
procedure _set_X(const Value:integer);
procedure _set_Y(const Value:string);
procedure _set_Z(const Value:boolean);
property X:integer read _get_X write _Set_X;
property Y:string read _get_Y write _Set_Y;
property Z:boolean read _get_Z write _Set_Z;
…….
还有太多的代码,自己创建一个看一下,为了节约篇幅我就不做详细的翻译了
下面请大家试一下以下的申明会生成什么样的Pascal代码
5、)联合体
union un_exp switch(long)
{
case 1:long x;
case 2:string y;
case 3:st_exp Z;
};
6、sequence(我理解为动态数组)
typedef sequence <long> UnboundeSeq;
typedef sequence <long,42> ShortBoundSeq
7, 数组
const long ArrayBound=10;
typedef long longArray[ArrayBound];
8, 抽象接口
module exp{
interface myface{
long op(in string s);
};
};
9,多重继承
module M{
interface A{
void A1();
void A2();
};
interface B{
void B1();
void B2();
};
interface AB:B,A{
void AB1()
void AB2();
};
};
10,交叉模型定义
module m1{
interface if1;
module m2{
interface if2{
m1::if1 getIf1();
};
interface if1{
m2::if2 getif2()
};
};
};
以上我介绍了一些数据的定义规范,然而我们需要不仅仅是这样的一些比较抽象的接口定义法则,我们要将法则应用到实际的开发中去,那么我们又是如何运用这些法则了,对于接口描述语言的翻译我前面讲到直接使用IDL2PAS就不讲了,以后的章节中也不会在去将如何转换的问题。下面我们实践一下:
编写接口定义一个返回为浮点类型,输入为短整型变量数组对象的方法
typedef short ArrayType[3];
//自定义类型定义长度为3的数组
interface Account {
float InputArray(in ArrayType myArray);//输入为整形数组,返回类型为float的方法
};
//服务端程序的处理xxx_impl.pas
interface
uses
SysUtils,
CORBA,
account_i,
account_c;
type
TAccount = class;
TAccount = class(TInterfacedObject, account_i.Account)
protected
//******************
public
constructor Create;
function InputArray ( const myArray : account_i.ArrayType): Single;
end;
implementation
uses ServerMain;
constructor TAccount.Create;
begin
inherited;
end;
function TAccount. InputArray (const myArray : account_i.ArrayType): Single;
var
j: Integer;
begin
// account_i.ArrayType是指我们自定义的数组类型在account_I单元中
for j := 0 to 2 do
begin
Form1.Memo1.Lines.Add('myArray[' + IntToStr(j) + '] = ' + IntToStr(myArray[j]) );
//接受从客户端传递过来的数组变量并将其依次加入到主窗体的MEMO中
end;
result := random * 100;//返回一个随机数
end;
initialization
randomize;
end.
//服务端程序主单元
unit ServerMain;
interface
uses
Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs, Corba,
Account_I, Account_C, Account_S, Account_Impl, StdCtrls;
type
TForm1 = class(TForm)
Memo1: TMemo;
procedure FormCreate(Sender: TObject);
private
{ private declarations }
protected
{ protected declarations }
Acct : Account; // skeleton 对象
procedure InitCorba;
public
{ public declarations }
end;
var
Form1: TForm1;
implementation
{$R *.dfm}
procedure TForm1.InitCorba;
begin
CorbaInitialize;
// Add CORBA server Code Here
Acct := TAccountSkeleton.Create('Array Server', TAccount.Create);
BOA.ObjIsReady(Acct as _Object);
end;
procedure TForm1.FormCreate(Sender: TObject);
begin
InitCorba;
Memo1.Lines.Add('Account object created...');
Memo1.Lines.Add('Server is ready');
end;
end.
//客户端程序
unit ClientMain;
interface
uses
Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
Corba, StdCtrls, Account_I, Account_C;
type
TForm1 = class(TForm)
Button1: TButton;
Label1: TLabel;
procedure FormCreate(Sender: TObject);
procedure Button1Click(Sender: TObject);
private
{ private declarations }
protected
{ protected declarations }
Acct : Account;
myArray : ArrayType;
procedure InitCorba;
public
{ public declarations }
end;
var
Form1: TForm1;
implementation
{$R *.dfm}
procedure TForm1.InitCorba;
begin
CorbaInitialize;
Acct := TAccountHelper.bind;
end;
procedure TForm1.FormCreate(Sender: TObject);
var
j: Integer;
begin
InitCorba;
for j := 0 to 2 do
myArray[j] := (j + 1) * 100;
end;
procedure TForm1.Button1Click(Sender: TObject);
begin
Label1.Caption := FormatFloat('InputArray = $#,##0.00', Acct.inputArray(myArray));
end;
end.
上面的程序实例很简单我就不一一说明了,下面我们来看一个数据访问的实例
//IDL
interface Employee {
any getEmployeesByName(in string name);
};
接口方法声明单元
//XXX_Impl.pas
interface
uses
SysUtils,
CORBA,
employee_i,
employee_c;
type
TEmployee = class;
TEmployee = class(TInterfacedObject, employee_i.Employee)
public
constructor Create;
function getEmployeesByName ( const name : AnsiString): ANY;
end;
implementation
uses dmEmployee,DMPooler, provider,DSIntf,ServerMain;
constructor TEmployee.Create;
begin
inherited;
end;
function TEmployee.getEmployeesByName ( const name : AnsiString): ANY;
var
DM: TdmEmploy;
RecsOut: Integer;
Options: TGetRecordOptions;
begin
Options := [grMetaData,grReset]; //must specify meta data
DM := ModulePooler.GetModule as TdmEmploy; //Get instance of datamodule from Pool
try
DM.qryEmployee.Close;
DM.qryEmployee.ParamByName('name').AsString:= name + '%';
//显示连接服务器的数量
Inc(Form1.HitCount);
Form1.Label1.Caption := Format('Hit Count = %d', [Form1.HitCount]);
DM.qryEmployee.Open;
Result:=DM.proEmployee.GetRecords(-1, RecsOut, Byte(Options));
DM.qryEmployee.Close;
finally
ModulePooler.FreeModule(DM);//Return instance of DataModule to pool
end;
end;
initialization
//将TdmEmploy对象放入共享池中
ModulePooler.ModuleClass := TdmEmploy;
end.
//共享池的声明单元
主要描述如何提供一个多客户的访问数据提供
unit DMPooler;
interface
uses SysUtils, Classes, Forms, SyncObjs, Windows;
type
//本单元用于为每个客户提供一个独立使用的DataModule对象,相当于我们在以前的CORBA DataModule中选择创建的多线程对象一样的功能
TDataModuleClass = class of TDataModule; //定义类
TPooledModule = record//声明记录类型
Module: TDataModule; //继承标准的TdataModule
InUse: Boolean; //标明上面继承的TdataModule是否在使用
end;
TModulePooler = class
private
FCSect: TCriticalSection; //允许线程自己改变FModules
FModuleClass: TDataModuleClass; //在共享池中类化TDataModule
FModules: array of TPooledModule; //定义一个动态的对象记录数组
FSemaphore: THandle; //限定同时使用的用户规则
public
property ModuleClass: TDataModuleClass read FModuleClass write FModuleClass;
constructor Create;
destructor Destroy; override;
function GetModule: TDataModule;
procedure FreeModule(DataModule: TDataModule);
end;
const
PoolSize = 5;
var
ModulePooler: TModulePooler = nil;
implementation
uses Dialogs;
{ TModulePool }
constructor TModulePooler.Create;
begin
IsMultiThread := True;
FCSect := TCriticalSection.Create;
FSemaphore := CreateSemaphore(nil, PoolSize, PoolSize, nil);
end;
destructor TModulePooler.Destroy;
begin
FCSect.Free;
CloseHandle(FSemaphore);
end;
procedure TModulePooler.FreeModule(DataModule: TDataModule);
var
I: Integer;
begin
FCSect.Enter;
try
for I := 0 to Length(FModules) - 1 do
if FModules[I].Module = DataModule then
FModules[I].InUse := False;
ReleaseSemaphore(FSemaphore, 1, nil);
finally
FCSect.Leave;
end;
end;
function TModulePooler.GetModule: TDataModule;
var
I: Integer;
begin
Result := nil;
if WaitForSingleObject(FSemaphore, 5000) = WAIT_TIMEOUT then
raise Exception.Create('Server too busy');
FCSect.Enter;
try
if Length(FModules) = 0 then
begin
SetLength(FModules, PoolSize);
for I := 0 to PoolSize - 1 do
begin
FModules[I].InUse := False;
FModules[I].Module := FModuleClass.Create(Application);
end;
end;
for I := 0 to Length(FModules) - 1 do
if not FModules[I].InUse then
begin
FModules[I].InUse := True;
Result := FModules[I].Module;
Break;
end;
finally
FCSect.Leave;
end;
//检查曾经是否连接
if not Assigned(Result) then
raise Exception.Create('Pool is out of capacity');
end;
initialization
ModulePooler := TModulePooler.Create;
finalization
ModulePooler.Free;
end.
//本单元是一个通用的方法单元,当然您也可以采用其他的方法来完成这样的一个功能
//DataModule单元
unit dmEmployee;
interface
uses
Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
Db, DBTables, Provider;
type
TdmEmploy = class(TDataModule)
Session1: TSession;
EmployeeDatabase: TDatabase;
qryEmployee: TQuery;
proEmployee: TDataSetProvider;
private
{ Private declarations }
public
{ Public declarations }
end;
var
dmEmploy: TdmEmploy;
implementation
{$R *.DFM}
end.
//服务器的主单元
unit ServerMain;
interface
uses
Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
Grids, DBGrids, Db, DBTables, StdCtrls, Corba, Employee_I, Employee_C,
Employee_S, Employee_Impl;
type
TForm1 = class(TForm)
Label1: TLabel;
procedure FormCreate(Sender: TObject);
private
{ Private declarations }
procedure CorbaInit;
public
{ Public declarations }
hitcount : integer;
end;
var
Form1: TForm1;
myDBServer : Employee;
implementation
{$R *.DFM}
procedure TForm1.CorbaInit;
begin
CorbaInitialize;
myDBServer := TEmployeeSkeleton.Create('myServer', TEmployee.Create);
Boa.ObjIsReady( myDBServer as _Object );
end;
procedure TForm1.FormCreate(Sender: TObject);
begin
CorbaInit;
end;
end.
//客户端程序
interface
uses
Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
StdCtrls, Grids, Corba, Employee_i, Employee_c, Db, DBClient, ExtCtrls,
DBCtrls, DBGrids;
type
TForm1 = class(TForm)
Button1: TButton;
DBGrid1: TDBGrid;
cdsEmployee: TClientDataSet;
DataSource1: TDataSource;
edtEmployeeName: TEdit;
Memo1: TMemo;
Label1: TLabel;
procedure FormCreate(Sender: TObject);
procedure Button1Click(Sender: TObject);
private
{ Private declarations }
myEmployee : Employee;
public
{ Public declarations }
end;
var
Form1: TForm1;
implementation
{$R *.DFM}
procedure TForm1.FormCreate(Sender: TObject);
begin
myEmployee := TEmployeeHelper.bind;
end;
procedure TForm1.Button1Click(Sender: TObject);
begin
cdsEmployee.Data := myEmployee.getEmployeesByName(edtEmployeeName.Text);
cdsEmployee.Open;
end;
end.
我想大家应该可以看得懂上面的程序,如果看不懂也不要紧,下一次我将围绕这个实例展开一系列的问题描述并会同时于COM+/MIDAS进行比较说明,为了让大家留下一个思维的空间我在这里就不多说了。还是那一句话下次再见
我的哲学:“无论是CORBA还是COM+异或是EJB等等最终都是殊途同归”