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Coding a DCOM Server Component from IDL

Author: Gopalan Suresh Raj
Date Submitted: February 10th 2000
Level of Difficulty: Advanced
Subjects Covered: IDL, DCOM, J++
Pre-required Reading: Component Object Model

To work with any of these samples you will need the following:

Microsoft Visual J++ ver 6.0
guidgen.exe and midl.exe from Microsoft Visual C++ ver 6.0

In Visual J++, the most simplest method to create a DCOM server component is to first write your server code in pure Java and then create a COM wrapper for it. However, creating the component from scratch using the IDL will allow you more flexibility and control in coding the server component. Hence, I am presenting here a stock market server component developed from scratch using IDL.

The Steps involved in developing the DCOM Server component from IDL are

Create an empty project
Define your interface in IDL
Compile your IDL and generate the required typelibs necessary
Set the properties for your project
Implement the DCOM server component
Build and register the DCOM server component

1. Create an empty project

Select New Project and from the File menu, choose the Empty project template in Visual J++. Name the project StockDCOM.

2. Define your interface in IDL

Use guidgen.exe where necessary to generate new UUIDs

StockMarketLib.idl

[
uuid(7371a240-2e51-11d0-b4c1-444553540000),
version(1.0)
]
library SimpleStocks {
importlib("stdole32.tlb");
[
    uuid(BC4C0AB0-5A45-11d2-99C5-00A02414C655),
    dual
]
interface IStockMarket : IDispatch {
    HRESULT get_price([in] BSTR p1, [out, retval] float * rtn);
}

[
uuid(BC4C0AB3-5A45-11d2-99C5-00A02414C655),
]
coclass StockMarket {
interface IStockMarket;
};
};

3. Compile the idl file and generate typelibs

Use the midl.exe that comes with your VC++ to compile the IDL files. If the VC++ environment variables are not loaded use the full path to midl.exe. Notice that stockmarketlib.tlb will now appear under the StockDCOM project.

E:\MyProjects\StockDCOM>
E:\MyProjects\StockDCOM>midl StockMarketLib.idl
Microsoft (R) MIDL Compiler Version 5.01.0164
Copyright (c) Microsoft Corp 1991-1997. All rights reserved.
Processing .\StockMarketLib.idl
StockMarketLib.idl
Processing D:\Program Files\Microsoft Visual Studio\VC98\include\oaidl.idl
oaidl.idl
Processing D:\Program Files\Microsoft Visual Studio\VC98\include\objidl.idl
objidl.idl
Processing D:\Program Files\Microsoft Visual Studio\VC98\include\unknwn.idl
unknwn.idl
Processing D:\Program Files\Microsoft Visual Studio\VC98\include\wtypes.idl
wtypes.idl

E:\MyProjects\StockDCOM>

4. Set the properties for your project

From the Project Explorer | StockDCOM | StockDCOM Properties | ClassPath, uncheck the "Merge all Project-specific ........ClassPaths in solution" check box
From the Project Explorer | StockDCOM | StockDCOM Properties | COM Classes check the "Use existing Type Library" ........radio button
Click the "Select" button
Click the "Browse" button
Browse to the newly created StockMarketLib.tlb file in the project directory
Select and open the StockMarketLib.tlb file
Click the "OK" button to confirm the list of COM Components
Click "OK" to confirm StockMarketLib Properties form changes
Notice that the StockMarketLib folder is added to the StockDCOM project
Notice that three java source files have been created:
StockMarket.java, IStockMarket.java, and IStockMarketDefault.java
Rename the generated implementation class, StockMarket.java to StockMarketImpl.java
StockMarket.class will be a COM wrapper automatically generated during the compile phase

5. Implement the DCOM Server Component

Edit StockMarketImpl.java as needed to implement the interface. Notice that when JActiveX created the file it placed skeleton code in place

StockMarketImpl.java

//
// Auto-generated using JActiveX.EXE 5.00.2918
// ("D:\Program Files\Microsoft Visual Studio\VJ98\jactivex.exe" /javatlb /c2j
// /creg /xh /wfc /w /xi /X:rkc /l "F:\TEMP\jvcD.tmp" /nologo /d
// "E:\MyProjects\StockDCOM" "E:\MyProjects\StockDCOM\StockMarketLib.tlb")
//
// WARNING: Do not remove the comments that include "@com" directives.
// This source file must be compiled by a @com-aware compiler.
// If you are using the Microsoft Visual J++ compiler, you must use
// version 1.02.3920 or later. Previous versions will not issue an error
// but will not generate COM-enabled class files.
//

package stockmarketlib;

import com.ms.com.*;
import com.ms.com.IUnknown;
import com.ms.com.Variant;

/** @com.register(clsid=BC4C0AB3-5A45-11D2-99C5-00A02414C655,
* typelib=7371A240-2E51-11D0-B4C1-444553540000,
* version="1.0") */
public class StockMarketImpl implements IUnknown, com.ms.com.NoAutoScripting,
stockmarketlib.IStockMarketDefault {

public float get_price(String symbol) {
float price = 0;

    for( int i = 0; i < symbol.length(); i++ ) {
      price += (int) symbol.charAt(i);
    }

price /= 5;
return price;
}

}

6. Build and register the COM DLL Server component

Project Explorer | StockDCOM | Build

Notice that both StockMarket.class and StockMarketImpl.class are in the project folder

StockMarket.class will be "hidden" using the Project Explorer.

StockMarket is the COM callable wrapper generated by the @com.register directive

StockMarketImpl is the J++ code we defined for the COM object.

Next....Coding a DCOM Client

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