89 lines
3.2 KiB
Plaintext
89 lines
3.2 KiB
Plaintext
- ADO Wrapper for JACOB - Copyright 1999, Dan Adler
|
|
|
|
This sample shows how to generate more strongly typed wrapper classes
|
|
for the JACOB automation classes. These are pure java classes which
|
|
extend com.jacob.com.Dispatch and delegate all the methods to the
|
|
unedrlying IDispatch pointer. This methodology is similar to the way
|
|
MFC does automation wrappers, rather than using the @com directives
|
|
to invisibly delegate the calls, as the Microsoft VM does.
|
|
|
|
The ADO wrappers in this directory are not a part of the JACOB
|
|
distribution, however, they demonstrate the preferred way to create
|
|
wrappers around the core functionality. The wrappers included here are
|
|
not a complete set, but they could easily be extended to provide all
|
|
the functionality of the com.ms.wfc.data classes.
|
|
|
|
The code in test.java demonstrates two ways to get a Recordset
|
|
from SQL Server. In this case, I query for the authors in the 'pubs'
|
|
database once by opening a Recordset object directly, and once by
|
|
using the Command and Connection objects. The same code, using the WFC
|
|
wrappers can be found in ms\testms.java in case you want to compare
|
|
the performace. You can run the test.java demo in the MS VM as well.
|
|
|
|
The constructor of the wrapper is used to create an instance.
|
|
For example, the user can write:
|
|
|
|
Connection c = new Connection();
|
|
|
|
The code for the Connection constructor is shown here:
|
|
|
|
public Connection()
|
|
{
|
|
super("ADODB.Connection");
|
|
}
|
|
|
|
it simply delegates to the com.jacob.com.Dispatch constructor which
|
|
takes a ProgID.
|
|
|
|
Since I don't have a tool like JACTIVEX yet to create the wrappers
|
|
automatically from the type library, I created them by hand by using
|
|
the JACTIVEX'ed version as a starting point, and replacing the @com
|
|
calls with delegated calls to JACOB classes. A simple PERL program
|
|
could probably be used to automate this step.
|
|
|
|
In order to return strongly typed wrappers from method calls, I had to
|
|
create a special constructor which constructs the wrapper class instance
|
|
and copies over the IDispatch pointer. This is because I can't cast a
|
|
java Dispatch object to a super class object.
|
|
|
|
For example, the Command class has a method like this:
|
|
|
|
public Connection getActiveConnection();
|
|
|
|
Ideally, I would like the wrapper code to say:
|
|
|
|
public Connection getActiveConnection()
|
|
{
|
|
// this doesn't work
|
|
return (Connection)Dispatch.get(this, "ActiveConnection").toDispatch());
|
|
}
|
|
|
|
Thereby wrapping the returned Dispatch pointer in a Connection object.
|
|
But, since I can't cast in this way, I use the following construct:
|
|
|
|
public Connection getActiveConnection()
|
|
{
|
|
// this works
|
|
return new Connection(Dispatch.get(this, "ActiveConnection").toDispatch());
|
|
}
|
|
|
|
Which uses a special constructor inserted into the Connection class:
|
|
|
|
/**
|
|
* This constructor is used instead of a case operation to
|
|
* turn a Dispatch object into a wider object - it must exist
|
|
* in every wrapper class whose instances may be returned from
|
|
* method calls wrapped in VT_DISPATCH Variants.
|
|
*/
|
|
public Connection(Dispatch d)
|
|
{
|
|
// take over the IDispatch pointer
|
|
m_pDispatch = d.m_pDispatch;
|
|
// null out the input's pointer
|
|
d.m_pDispatch = 0;
|
|
}
|
|
|
|
I have to add this constructor to any class whose instances I want
|
|
to return from wrapped calls.
|
|
|