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Frequently Asked Questions regarding Java/COM/DCOM
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PREFACE:
This document is a compilation of frequently asked questions
and their answers about Java/COM/DCOM which have been gathered
from the microsoft.public.visualj/com-support newsgroups.
Although efforts have been made to find obvious errors, there
is no guarantee that the information in this document is
error-free. The FAQ maintainer, or anyone else associated with
this document, assumes NO liability for the content
or use of this document.
Please post a new thread to the appropriate
microsoft.public.java.visualj++ forum if you have follow-up
questions on these issues. If you have a bug report to
submit, please do so at http://www.microsoft.com/visualjSupport.
If you have a question that is not in the FAQ, please post it.
We will be posting FAQ's regularly to this forum. We monitor
the forum traffic. If you have an announcement of value to
other users, please check first to see if anyone else made
the announcement already, then post it. Use common sense.
This kind of discussion adds to the value of the newsgroup.
While much of this material comes directly from newsgroup
discussions, we also rely on your submissions to improve the
quality and inclusiveness of this document. If you have found
a hint, tip, trick, work-around, etc., please write it up and
send it to us! Direct any comments/suggestions to:
radhikar@microsoft.com
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1. I am trying to use an ActiveX automation object written
in Java (the COMCallingJava sample) from Visual Basic but
I keep getting "Out of Memory" errors.
This is normally caused by the Operating System not being
able to find the Java class file that implements the ActiveX
automation server. The class file that implements the Server
must be copied to the java classpath (for instance:
\windows\java\lib) for OLE object creation to work properly
for Java class files. A common example of this is the
COMCallingJava sample application supplied with VJ++. It will
work fine when the sample is first built because the
CEuclid.class is in the local directory (which the Developer
Studio adds to the classpath before running Internet Explorer).
Trying to run the VBDriver Visual Basic sample code supplied
in the VBDriver project subdirectory will then fail with
the "Out of Memory" error. This can be remedied by copying
CEuclid.class to the \windows\java\lib directory. You can
also set the output directory in the project build options
so that the class file is automatically built in the
appropriate classpath directory. This information is also
documented in the following Knowledge Base article;
Q163720: Getting Out Of Memory Error with COMCallingJava.
2. Why does Java misinterpret a Boolean value that is returned
by a COM object?
This is a bug, which has been fixed with the latest Microsoft
Virtual Machine for Java. Please follow the link to
http://www.microsoft.com/java to download the latest Microsoft Virtual
Machine for Java. This version of the VM for Java requires Internet
Explorer 3.01 or later. This information is also documented in the
Microsoft KnowledgeBase article; Q162966: COM Object Returns Incorrect
Value for Bool.
3. Why do I get a "java.lang.ClassFormatError", when I call
Automation methods from VJ++ that takes parameters of
Pointer type BSTR*, long*?
This problem specifically occurs when using Automation
Server methods created with the MFC Class Wizard. This can
be fixed by modifying the .ODL file with [in,out] attributes
on the automation methods that takes pointer type arguments:
methods:
// NOTE - ClassWizard will maintain method
information here.
// Use extreme caution when editing this
section.
//{{AFX_ODL_METHOD(PtrTest)
[id(1)] void TestBstr([in,out]BSTR* arg1);
[id(2)] void TestLong([in,out]long* arg1);
//}}AFX_ODL_METHOD
This allows JavaTlb to generate a valid class file, and the
server works as expected when called from Java or Visual
Basic.
This information is also documented in the following Knowledge Base article;
Q165550 : BUG: JavaTLB Generates Invalid Classes for MFC Server.
4. Why do I get an
"exception:java.lang.ClassCastException:xl5en32/_ExcelApplication"
error, when creating a new _ExcelApplication class and
type-casting it to the Application interface?
Inorder to get to the Application interface you need to call
getDispatch on the Application object. The following code
snippet illustrates how to make an Excel Application visible
from Java and also shows how to get to the Application interface:
This code snippet uses the Excel 5.0 Object Library:
import xl5en32.*;
import com.ms.com.Variant;
public void TestExcel()
{
Application app;
Variant vTemp = new Variant();
// Create A new worksheet
Worksheet wks = (Worksheet)new _ExcelSheet();
// Get hold of a dispatch on the application
vTemp = wks.Application();
app = (Application)vTemp.getDispatch();
// Make Excel Visible
vTemp.putInt(Constants.xlVisible);
app.putVisible(vTemp);
}
This information is also documented in the following Knowledge Base article;
Q169806 : PRB: ClassCastException Error When Using Excel Object in Java.
5. Does the Microsoft VM for Java support Active X Control Containment?
Currently, the Microsoft VM for Java build 1518 does not support
the containment of ActiveX controls. You can't place an
ActiveX control that has a user interface or that sources or
sinks events directly onto an applet without implementing all
of the ActiveX control containment and eventing interfaces
yourself. To be clear, you can use ActiveX automation servers
from Java and you can write ActiveX automation servers
in Java utilizing the Microsoft Java Virtual Machine's ability
to expose Java classes as ActiveX objects. You can also have
ActiveX controls and Java applets on the same Web page and
have them interact (see the OLEControls sample in Visual J++).
However the SDK for Java 2.0 Beta 2 provides ActiveX Control Containment
support through Beans. It exposes any Bean as an ActiveX Control and any
ActiveX Control as a Bean. The SDK also includes samples that illustrates
how to do this. You can download this SDK from
http://www.microsoft.com/java.
6. How do I use the COMCallingJava sample as a DCOM Server?
First you should build the sample and run it as a conventional
(InProcess) automation server. Do this by following the
instructions outlined in the readme.html that is installed
with the sample. More information on how to use this sample
via DCOM, can be found in the KnowledgeBase article;
Q162164: Using Java Servers and DCOM.
7. When I try to use JavaReg with the /surrogate switch
inorder to use my Automation Server written in Java as a
DCOM server, the java console pops up and closes when run on
a remote machine and my client application hangs?
There are various problems that you may experience when you
try to use an Automation Server written in Java
as a DCOM server. These can include hanging, timeouts, out of
memory errors, interface not found errors, and other errors.
These errors are generally caused by not registering the Java
COM object properly on both the client and DCOM server
machines. The JAVAREG(version 1.0) that shipped with
Microsoft Visual J++, versions 1.0 and 1.1 implemented a
surrogate process itself, but it had some bugs making it difficult
to setup Java DCOM servers and clients. This bug is documented in the
KnowledgeBase article Q162164: BUG: Using Java Servers and DCOM.
The DCOM support now in Windows'95 and Windows NT 4.0 with SP2 and SP3
supports a surrogate as part of the system, so the surrogate support
with JAVAREG 1.0 has been dropped.
JAVAREG 2.0 is a new tool that ships with SDK for Java 2.0 Beta 2 and this
tool has fixed the bugs associated with JAVAREG 1.0 and supports remote
access to a Java COM object using the system provided surrogate process.
This information is also documented in the following Knowledge Base article;
Q173790 : HOWTO: Using DllSurrogate support for Java/DCOM servers.
You can download this SDK from http://www.microsoft.com/java.
8. Why do I get "Failed to Create Object" error message, when
trying to instantiate a COM object written in Java?
The following is a checklist that provides some of the common
causes for this error. Make sure:
1. The java class is in the classpath.
2. Your java method is declared 'public'.
3. You need to register the class file (using javareg.exe).
4. Install the latest Java VM from
http://www.microsoft.com/java if you are attempting to
use CreateObject().
5. Follow the steps in the Visual J++ sample named COMCALLINGJAVA.
This information is also documented in the following Knowledge Base
article; Q167953: Possible Reasons for "Failed to create object".
9. Why don't I need to use IDL anymore when creating a
Java com object that is used through IDispatch?
This is due to the new auto IDispatch feature that has been
added to the latest Mirosoft Java VM. JavaTLB was originally
created to generate get/put accessor methods for
propget/propput methods declared in the Type Library. This
Auto IDispatch feature lets all public methods get
automagically exposed via IDispatch and public data members
exposed as properties - you can even utilize this with
javac.exe compiled classes if you use javareg to register
them (or manually create the proper reg entries). Therefore
you don't need to use an IDL/ODL file if you are just using
java com objects through IDispatch - the auto IDispatch
mechanism comes in handy. This information is also documented in
the following Knowledge Base article;
Q172202: INFO: Implementing Java Automation Objects using AutoIDispatch.
10. Is there a way to disable this Auto IDispatch mechanism
of the VM?
You can implement the system interface
com.ms.com.NoAutoScripting to disable the Auto IDispatch
for all instances of a class.
11. I get ComFailException:<80020005h>Type Mismatch error, when
trying to use the Navigate method of the IWebBrowserApp interface?
How do I invoke Internet Explorer from Java and navigate to a URL?
The following code snippet illustrates creating a Java Object
based on the Microsoft Internet Explorer and calling the Navigate
method:
1. Create a default Java Applet or an Application.
2. Run JavaTLB on Microsoft Internet Controls.
import com.ms.com.*;
import shdocvw.*;
public class Navigate
{
IWebBrowserApp testBrowser = null;
public static void main( String args[] )
{
IWebBrowserApp testBrowser = (IWebBrowserApp)new InternetExplorer();
testBrowser.getApplication();
testBrowser.putVisible(true);
Dispatch.call(testBrowser, "Navigate",
"http://www.microsoft.com");
}
}
The Dispatch.call method is documented in the Microsoft SDK for
Java Documentation, which can be found at
http://www.microsoft.com/java/sdk/x/exten025.htm.
12. I am able to automate Excel7.0 from Java, but I am finding the
classes and interfaces to be quite different in Excel8. How do I
automate Excel8.0 from Java?
The following code snippet illustrates how to automate Excel8.0 from Java.
It makes an Excel8.0 application visible and also open an existing .xls
file with data in it. This code snippet uses the Excel 8.0 Object Library:
import excel8.*;
import com.ms.com.*;
_Global globXL=null;
_Application appXL=null;
Workbooks books=null;
_Workbook book = null;
try{
globXL = (_Global)new Global();
appXL = (_Application)globXL.getApplication();
appXL.putVisible(0,true);
books = (Workbooks)appXL.getWorkbooks();
Variant vTemp = new Variant();
vTemp.putString("c:\\book1.xls");
Variant vOptional = new Variant();
vOptional.noParam();
book = (_Workbook)books.Open("c:\\book1.xls",vOptional,vOptional,
vOptional,vOptional,vOptional,vOptional,
vOptional,vOptional,vOptional,vOptional,
vOptional,vOptional,0);
}
catch(ComFailException e)
{
System.out.println(e.getMessage());
}
This information is also documented in the following Knowledge Base article;
Q169796: HOWTO: Automate Excel from Java.
13. When I use JavaTLB to generate classes from some COM object
libraries, I get an error J5008. Should I be concerned?
Often, the cause of this warning is that the method uses a type
that is not supported in Java. All methods that produce a J5008
warning are omitted from the class file. Note that JavaTLB has been
replaced by JACTIVEX in the SDK for Java 2.0 Beta2 release.
14. I get a 'java.lang.NoClassDefFoundError: com/ms/com/LicenseMgr'
error when I run an applet generated by the Database Wizard for Java?
When an applet is run in Internet Explorer and outside of
Developer Studio, the applet is not trusted and does not
have access to ILicenseMgr. This problem is by design since
only trusted applets should have access to the ILicenseMgr.
The ILicenseMgr allows the creation of COM objects on the client.
To fix the problem, create a CAB file that contains the classes of
the applet and digitally sign the CAB with the CodeSign kit.
For more information on Cab and Sign technology, look in the
'Cab&Sign' directory on the Visual J++ CD-ROM.For the latest
info on CAB technology please refer to
'http://www.microsoft.com/workshop/prog/cab'.
This information is also documented in the following Knowledge Base article;
Q169810: PRB: java.lang.NoClassDefFoundError:com/ms/com/LicenseMgr Error.
15. Why does VB crash when calling a Java Object which has a method that
returns a boolean value?
This is a bug with the JavaTLB mapping VT_BOOL to a 4-byte value
for vtable mappings. To workaround the problem change the return
type of the Java function to "short" in the IDL/ODL files with -1
representing TRUE and 0 representing FALSE. This problem has been fixed
for JACTIVEX, where it maps VT_BOOL to a 2-byte value. You can get
JACTIVEX, by installing the SDK for Java 2.0 Beta 2 from
http://www.microsoft.com/java. Note that JavaTLB has been replaced by
JACTIVEX in the SDK for Java 2.0 Beta 2 release.
16. When I run a Java Application that calls a COM object like an
ATL Server, I get a "NoClassDeffoundError" on the COM object. The error
occurs on the line where I create a new COM object in the Java Class.
One reason why you may get this error could be related to missing
parameter attributes for the methods in the ATL servers IDL file.
For Example if you have a method like the one below:
[id(1), helpstring("method GetString")] HRESULT GetString(BSTR* mystr);
JavaTLB executes fine on this TLB. However when you execute your Java
Application that calls this COM object
ie. ISomeInterface m_intf = (ISomeInterface) new CAtlObj, it fails at this
line with a "java.lang.NoClassDeffoundError". To fix the problem, change
the IDL method to include the [out] attribute: For Example the method looks
like:
[id(1), helpstring("method GetString")] HRESULT GetString([out]BSTR*
strGUID);
So check your methods in the IDL file so that they have the right
attributes like [in],[out],[retval] and so on. Once modifying the IDL file,
rebuild your ATL server, and rerun JavaTLB on the ATL Servers Type Library
so that the changes gets reflected.