Abstract:
The dynamic mapping from an ActiveX component model to a JavaBean model is disclosed. In one embodiment, an ActiveX compatible object is created at run-time for those JavaBean components that an ActiveX client application wishes to utilize. In another embodiment, upon a call to CoGetClassObject or related methods using class identifiers, a COM-callable wrapper is generated and a mapping table containing COM dispatch identifiers is scanned to ensure the dispatch identifiers are unique. If they are not, the dispatch identifiers associated with JavaBean component interfaces are adjusted to make them unique.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to software component interfaces, and more specifically to dynamic mapping of such interfaces. 
     BACKGROUND OF THE INVENTION 
     The evolution of computer software development has included the introduction of new development techniques and methods. These techniques and methods have included new programming languages, new libraries, new development methodologies, and new development environments. Often these techniques and methods are produced to improve software development productivity or to extend software development capability. 
     Software components are one technique to improve software development productivity and program flexibility. Reusable software components are designed to apply the power and benefit of reusable, interchangeable parts from other industries to the field of software development. Software components have standard interfaces making them interchangeable and reusable. Examples of software components tend to be oriented toward user interface elements. They can be simple like familiar push buttons, text fields list boxes, scrollbars and dialogs, or they can be more complex, such as calculators and spreadsheets. 
     Microsoft&#39;s ActiveX and the JavaBeans specification are two examples of software component models. ActiveX is a component environment commonly used by applications written in Microsoft&#39;s Visual Basic and Visual C++ programming languages. ActiveX can generally be defined as a specification for a software development methodology and an API that allows software components to be dynamically interchanged. ActiveX makes use of the Component Object Model (COM). Further details of COM are described in Dale Rogerson, “Inside COM,” 1997 (ISBN 1-57321-349-8) which is hereby incorporated by reference. 
     The JavaBeans specification for the Java programming language defines an environment for developing components known as “beans.” The JavaBeans specification defines a bean generally as a reusable software component that can be manipulated visually in a builder tool. 
     ActiveX components (also known as “controls”) and beans share the quality that when used within their intended environments, new or alternative components can be substituted for old components without requiring any changes to the application using the component. In addition, software components can be easily incorporated into new programs using software building tools, thereby freeing the developer from writing code to implement the functionality provided by the component. 
     Unfortunately, the interfaces provided by differing programming environments are not always compatible with one another. The reasons for the incompatibility vary, but common causes are incompatible function parameter passing protocols, incompatible data structure definitions and incompatibilities between programming language conventions between different languages or between different vendors&#39; compilers for the same programming language. As a result, it is necessary to convert from one interface to another when incompatibilities are encountered. The process of converting the methods, properties and events of a source class, library or language to methods, properties and events of a differing target class, is generally known as mapping. A specific example where mapping is required because of an incompatibility exists when an application designed to use an ActiveX control desires to use a Java bean component. 
     There are three main reasons why ActiveX controls are incompatible with Java beans. First, the data structures representing ActiveX controls and beans, while containing similar information, are defined differently. These differences include the order of elements in the data structure and the naming convention used for the elements. In addition, elements appearing in one data structure may be missing in the other or may appear in combination with different elements. 
     Second, the data contained within the object data structure are populated at different times. All of the data required to define an object representing an ActiveX control can be determined at the time the source code is compiled or interpreted. However, in JavaBeans, the data required to define a bean interface object cannot be completely determined through the source code alone. The data that cannot be derived via the source code must be supplied at run-time when the source is interpreted by the Java Virtual Machine (VM). The information that must be supplied by the Java VM generally relates to data type identifiers for the methods, properties and events defined by the bean. 
     Third, the interfaces defined by the two component models are different. Interfaces are used to connect objects defined by the component model. ActiveX and the JavaBeans specification define their own interfaces to connect their respective objects together. While they perform similar functions, the two interfaces are different and operate on different objects, and are therefore incompatible. 
     Alternative attempts to allow an ActiveX client to interface with a Java bean have used a technique known as “static mapping” to map between ActiveX controls and Java beans. Static mapping involves invoking a packager application that gathers data based on user input. The packager application also reads the user specified Java source code and scans the source for bean definitions. When a bean is found, the packager application generates three types of files. The first file type is a Java class file that can be interpreted by the Java VM (Virtual Machine). The second file type is a registry file that must be imported into the registry of the computer running an ActiveX client. The third file type is a type library file that contains a COM compatible definition of the methods, properties and events defined by the bean. The files generated by the packager are populated with data gleaned from scanning the source, and include items such as the public methods, properties and events for the top-level class defined in the bean. 
     Static mapping has several disadvantages. First, the packager application can only generate mappings for those classes representing beans defined in the Java source code scanned by the application. It is common in object-oriented languages for a class to propagate its methods, properties and events to lower-level classes that inherit from the top-level class. The end result of static mapping is that only the top-level, or explicitly called out Java classes, have ActiveX compatible objects generated. Mappings can only be generated for top-level classes within the bean, mappings cannot be generated for lower-level classes. As a result, it is possible that a significant number of the methods, properties and events that define classes will be inaccessible to a ActiveX client application. 
     A second disadvantage to static mapping is that the mapping is incomplete. Static mapping methods scan the source code at a particular point in time, and then generate interface files based on the source code. In effect, static mapping produces a snapshot of a bean&#39;s state at a particular point in time. A developer may add methods, properties and events to the bean after the snapshot has been produced by the static mapping method. An ActiveX client using a statically mapped interface will be unable to use the newly defined methods, properties and events. 
     In addition, as discussed above, there is a significant amount of information about a bean that must be provided by the Java VM, and as a result the information is available only during the run-time of a Java program (i.e. while the Java program is executing on the computer). Since the static mapping method scans the files before the Java program is run, not all of the information that must be supplied at run-time is available to the packager application. As a result, a significant portion of the data describing the bean will not be available when the ActiveX client instantiates the bean, resulting in reduced bean functionality. 
     A third disadvantage is that static mapping requires additional system management effort. This is because the static mapping information is contained in several files. These files must be installed as a separate step from the installation of Java or ActiveX. In addition, these files must be located in specific directories specified by the registry file in order for the system to work properly. If the user wishes to move these files, additional work is required to insure that the registry entries point to the correct file location. 
     Therefore, there is a need for a technique that allows software developers to map between component models defined in different development environments that can provide for a more complete mapping of component objects and information within the object, while reducing the development and maintenance overhead of current mapping techniques. 
     SUMMARY OF THE INVENTION 
     The above-mentioned shortcomings, disadvantages and problems are addressed by the present invention, which will be understood by reading and studying the following specification. The invention describes dynamically mapping between class objects representing components defined in two differing software development environments. In one embodiment, a computerized system has an operating system that provides interfaces for controlling two components, with each component interface having methods, properties and events. A client program designed to utilize an interface to one component is combined with a component using a different interface. A mapping from the methods, properties and events of the first interface to the methods, properties and events of the second interface occurs during the run-time of the client program. 
     Thus, dynamic mapping is a process allowing a client process using a particular component interface definition to use an alternative component defined by a different interface. Dynamic mapping occurs at run-time, when all of the information defining the component is available. The desired bean component object can be queried at run-time to provide the desired interface information. This information can then be used to map the bean&#39;s interface elements to semantically equivalent interface elements used in the client program. 
     The dynamic mapping described in the present invention provides for advantages not found in systems employing static mapping methods. First, dynamic mapping methods have access to all of the information about the mapped interface at run-time, and the information reflects the component&#39;s current state. For example, dynamic mapping can take advantage of type information describing objects and their constituent elements that is only available at run-time. Because static mapping occurs before the component&#39;s run-time, it does not have access to all of the component&#39;s data, resulting in reduced functionality. In addition, methods, properties and events added to the mapped component after the static mapping process has taken place are not available to a client program. 
     Second, dynamic mapping has access to methods, properties and events for both top-level class definitions and lower-level class definitions. Because it occurs at run-time, dynamic mapping can query any required object for its methods, properties and event, not just the top-level class object. Static mapping is limited to obtaining information from the source code and the registry, and is therefor only able to acquire data on top-level classes. 
     Finally, dynamic mapping does not require the use of extraneous files that must be administered and maintained. Dynamic mapping is automatically handled by virtual machines common to many interpreted languages. In contrast, static mapping produces files that must be moved to appropriate directories, imported into the computer&#39;s registry, or interpreted in addition to the source files defining the component. Dynamic mapping avoids this overhead because no extraneous files are produced. 
     The present invention describes devices, computers, computer-readable media, and systems of varying scope. In addition to the aspects and advantages of the present invention described here, further aspects and advantages of the invention will become apparent by reference to the drawings and by reading the detailed description that follows. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a diagram of the hardware and operating environment in conjunction with which embodiments of the invention may be practiced; 
     FIGS.  2 ( a ) and  2 ( b ) are diagrams illustrating a system according to one embodiment of the invention as compared to a system employing static mapping; and, 
     FIGS.  3 ( a ) and  3 ( b ) are flowcharts of methods in accordance with an embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following detailed description of exemplary embodiments of the invention, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific exemplary embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that logical, mechanical, electrical and other changes may be made without departing from the spirit or scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims. 
     The detailed description is divided into five sections. In the first section, the hardware and the operating environment in conjunction with which embodiments of the invention may be practiced are described. In the second section, a system level overview of the invention is presented. In the third section, an embodiment is described where the dynamic mapping is invoked for ActiveX methods other than “CoGetClassObject” and other related COM APIs that create instances using a class identifier (CLSID). In the fourth section, an embodiment of the invention describing the case where the dynamic mapping is the result of a call to the “CoGetClassObject” and related APIs using a CLSID is presented. Finally, in the fifth section, a conclusion of the detailed description is provided. 
     Hardware and Operating Environment 
     Referring to FIG. 1, a diagram of the hardware and operating environment in conjunction with which embodiments of the invention may be practiced is shown. The description of FIG. 1 is intended to provide a brief, general description of suitable computer hardware and a suitable computing environment in conjunction with which the invention may be implemented. Although not required, the invention is described in the general context of computer-executable instructions, such as program modules, being executed by a computer, such as a personal computer. Generally, program modules include routines, programs, objects, components, data structures, etc., that perform particular tasks or implement particular abstract data types. 
     Moreover, those skilled in the art will appreciate that the invention may be practiced with other computer system configurations, including hand-held devices, multiprocessor systems, microprocessor-based or programmable consumer electronics, network PCS, minicomputers, mainframe computers, and the like. The invention may also be practiced in distributed computing environments where tasks are performed by remote processing devices that are linked through a communications network. In a distributed computing environment, program modules may be located in both local and remote memory storage devices. 
     The exemplary hardware and operating environment of FIG. 1 for implementing the invention includes a general purpose computing device in the form of a computer  20 , including a processing unit  21 , a system memory  22 , and a system bus  23  that operatively couples various system components include the system memory to the processing unit  21 . There may be only one or there may be more than one processing unit  21 , such that the processor of computer  20  comprises a single central-processing unit (CPU), or a plurality of processing units, commonly referred to as a parallel processing environment. The computer  20  may be a conventional computer, a distributed computer, or any other type of computer; the invention is not so limited. 
     The system bus  23  may be any of several types of bus structures including a memory bus or memory controller, a peripheral bus, and a local bus using any of a variety of bus architectures. The system memory may also be referred to as simply the memory, and includes read only memory (ROM)  24  and random access memory (RAM)  25 . A basic input/output system (BIOS)  26 , containing the basic routines that help to transfer information between elements within the computer  20 , such as during start-up, is stored in ROM  24 . The computer  20  further includes a hard disk drive  27  for reading from and writing to a hard disk, not shown, a magnetic disk drive  28  for reading from or writing to a removable magnetic disk  29 , and an optical disk drive  30  for reading from or writing to a removable optical disk  31  such as a CD ROM or other optical media. 
     The hard disk drive  27 , magnetic disk drive  28 , and optical disk drive  30  are connected to the system bus  23  by a hard disk drive interface  32 , a magnetic disk drive interface  33 , and an optical disk drive interface  34 , respectively. The drives and their associated computer-readable media provide nonvolatile storage of computer-readable instructions, data structures, program modules and other data for the computer  20 . It should be appreciated by those skilled in the art that any type of computer-readable media which can store data that is accessible by a computer, such as magnetic cassettes, flash memory cards, digital video disks, Bernoulli cartridges, random access memories (RAMs), read only memories (ROMs), and the like, may be used in the exemplary operating environment. 
     A number of program modules may be stored on the hard disk, magnetic disk  29 , optical disk  31 , ROM  24 , or RAM  25 , including an operating system  35 , one or more application programs  36 , other program modules  37 , and program data  38 . A user may enter commands and information into the personal computer  20  through input devices such as a keyboard  40  and pointing device  42 . Other input devices (not shown) may include a microphone, joystick, game pad, satellite dish, scanner, or the like. These and other input devices are often connected to the processing unit  21  through a serial port interface  46  that is coupled to the system bus, but may be connected by other interfaces, such as a parallel port, game port, or a universal serial bus (USB). A monitor  47  or other type of display device is also connected to the system bus  23  via an interface, such as a video adapter  48 . In addition to the monitor, computers typically include other peripheral output devices (not shown), such as speakers and printers. 
     The computer  20  may operate in a networked environment using logical connections to one or more remote computers, such as remote computer  49 . These logical connections are achieved by a communication device coupled to or a part of the computer  20 ; the invention is not limited to a particular type of communications device. The remote computer  49  may be another computer, a server, a router, a network PC, a client, a peer device or other common network node, and typically includes many or all of the elements described above relative to the computer  20 , although only a memory storage device  50  has been illustrated in FIG.  1 . The logical connections depicted in FIG. 1 include a local-area network (LAN)  51  and a wide-area network (WAN)  52 . Such networking environments are commonplace in office networks, enterprise-wide computer networks, intranets and the Internet, which are all types of networks. 
     When used in a LAN-networking environment, the computer  20  is connected to the local network  51  through a network interface or adapter  53 , which is one type of communications device. When used in a WAN-networking environment, the computer  20  typically includes a modem  54 , a type of communications device, or any other type of communications device for establishing communications over the wide area network  52 , such as the Internet. The modem  54 , which may be internal or external, is connected to the system bus  23  via the serial port interface  46 . In a networked environment, program modules depicted relative to the personal computer  20 , or portions thereof, may be stored in the remote memory storage device. It is appreciated that the network connections shown are exemplary and other means of and communications devices for establishing a communications link between the computers may be used. 
     The hardware and operating environment in conjunction with which embodiments of the invention may be practiced has been described. The computer in conjunction with which embodiments of the invention may be practiced may be a conventional computer, a distributed computer, or any other type of computer; the invention is not so limited. Such a computer typically includes one or more processing units as its processor, and a computer-readable medium such as a memory. The computer may also include a communications device such as a network adapter or a modem, so that it is able to communicatively couple other computers. 
     System Level Overview 
     FIGS.  2 ( a ) and  2 ( b ) present a system level description of an embodiment of the invention as compared with previous solutions to the mapping problem. FIG.  2 ( a ) shows a diagram of a system, per the prior art, in which the bean object is statically mapped to an ActiveX compatible object through the use of a packager application prior to running an ActiveX client application. FIG.  2 ( b ) shows a diagram of the system according to an embodiment of the invention where bean objects are dynamically mapped at run-time to ActiveX control objects. 
     Referring first to FIG.  2 ( a ), in accordance with the prior art, a Packager application  205  reads a Bean Definition File  200 . The Packager  205  then produces three sets of output, a Type Library  210 , a Registry Text File  215 , and one or more Java Stub Files  220 . The Type Library  210  contains a description of an ActiveX control&#39;s properties, events and methods. The Registry Text File  215  contains an identifier for the mapped object, a file path to the executable for the component and a file path to the type library. As a separate step, the Registry Text File must be imported into the computer&#39;s Registry  225  in order to notify the system that the mapped component is available for use. Java Stub Files  215  contain the computer interpreted instructions that statically map from a bean definition of a component to an ActiveX definition of a component. The Java Virtual Machine  230  is a native program running on an operating system, such as Microsoft Windows 95, that interprets and executes programs written in the Java programming language. The Java Stub Files  220  are read and interpreted by the Java Virtual Machine  230 . Interpretation of Java programs is known in the art. Information regarding Java is described in the reference David Flanagan, “Java in a Nutshell: A Desktop Quick Reference,” 2d edition, 1997 (ISBN 1-56592-262-X), which is hereby incorporated by reference. 
     Referring now to FIG.  2 ( b ), in accordance with an embodiment of the invention, ActiveX Client Process  255  is an application that makes uses of components using an ActiveX Application Program Interface (API). ActiveX Client Process  255  interrogates the computer&#39;s Registry  225  to determine what components are available and for details on how to make use of the components. If ActiveX Client Process  255  desires to use a component that is in fact a bean, it communicates with a Java Virtual Machine  250  to invoke the desired component. Java Virtual Machine  250  is similar to the Java Virtual Machine  230 , however Java Virtual Machine  250  has been modified in accordance with the present invention to dynamically map Java beans to ActiveX controls. Java Virtual Machine  250  then reads Bean Definition File  200  and dynamically maps the bean component definition to an ActiveX control definition. Details on the dynamic mapping process implemented within the Java Virtual Machine are now described in detail with reference to FIGS.  3 ( a ) and  3 ( b ). 
     Methods of an Exemplary Embodiment for Dynamically Mapping a Bean Object to a ActiveX Object 
     The previous section presented a system level description of an embodiment of the invention. In this section, methods within an embodiment of the invention will be described with reference to a flowchart describing steps to be performed by computer programs implementing the method using computer-executable instructions. The computerized method is desirably realized at least in part as one or more programs running on a computer—that is, as a program executed from a computer-readable medium such as a memory by a processor of a computer. The programs are desirably storable on a computer-readable medium such as a floppy disk or a CD-ROM, for distribution and installation and execution on another (suitably equipped) computer. 
     Referring now to FIG.  3 ( a ), a flowchart for a computer implemented method to dynamically map JavaBean components to ActiveX components is presented. This method is executed when an ActiveX Client process  255  invokes an ActiveX method for a component that is implemented by a Java bean. Examples of COM methods which may require mapping a bean are “Itype::GetTypeInfo” and “Itype::GetClassInfo”, each of which require a COM component object as a parameter. The method begins at  300  by determining the component object&#39;s class. This is accomplished by examining the class identifier (CLSID), if any, that was used to create the object. 
     The method then proceeds to  305  which checks whether or not a dynamic mapping has already been established for the CLSID from  300 . If a dynamic mapping does not exist,  310  uses the “java.beans.Introspector” to retrieve the methods, events, properties and other data defined within the bean. 
     Next, at  315 , the method checks the registry for an existing type library associated with the class specified by the CLSID. Preferably, the type library contains information about components and their interfaces, methods, properties, method arguments, and structures. If a type library does exist for the class,  320  applies any COM dispatch identifier (DISPID) assignments from the type library to the runtime mapping of DISPIDs to JavaBeans methods, properties and events. In one embodiment of the invention, the mapped DISPIDs are checked to make sure they do not conflict with commonly used DISPIDs. If there are conflicts, the mapped DISPIDs are adjusted to make them unique. This is generally necessary because some ActiveX clients have pre-defined expectations about the functionality provided by certain DISPID values and were not designed to be flexible. 
     At  325 , an automatic assignment of DISPIDs to JavaBeans methods, properties and events is performed. In one embodiment of the invention, this assignment is based on the naming convention for a bean&#39;s methods, properties and events, and the functional description obtained at run-time from the type library. 
     Finally, at  335  a reference to a COM object is returned to the caller of the method and the method stops. If the check at  305  determined that a dynamic mapping did not already exist, the reference is to the object created at  330 . Otherwise, the reference returned is to an object that was created in a previous dynamic mapping for the CLSID. Re-using the previously generated COM object is desirable because less memory and CPU resources are used. 
     Alternative Method of an Exemplary Embodiment for Dynamically Mapping a JavaBean to a COM Object 
     The previous section described the general case where a COM method is invoked specifying a component that is implemented by a Java bean. This section describes processing that must take place when an ActiveX client calls COM methods that create component instances using a class identifier (CLSID), such as “CoGetClassObject”, “CoCreateInstance”, or other related APIs for a component that is implemented as a Java bean. Because the client only needs to know the CLSID, the client may be unaware that the component is implemented as a bean. The method is similar to that described in the previous section, with two differences. First, the CLSID is already known and does not have to be determined. Second, the method does not need to apply COM DISPID assignments from the type library. 
     Referring now to FIG.  3 ( b ), a flowchart for a computer implemented method to dynamically map a bean invoked as a result of a COM client call to CoGetClassObject and related APIs is presented. The method begins at  350  by checking if a dynamic mapping already exists to the Java class. If not,  355  obtains data on the bean&#39;s methods, properties and events using the “java.beans.Introspector.” The method proceeds to  360  which applies an automatic assignment of DISPIDs to JavaBean methods, properties and events. These values are dynamically mapped in the same manner as described with reference to FIG.  3 ( a ). 
     Next,  370  creates a COM object that implements conventional ItypeLib and ItypeInfo interfaces using and wraps the data gathered at  355  and  365 . 
     Finally,  375  returns a reference to a COM object. If the check at  350  determined a mapping did not already exist, the reference returned is to the object created at  370 . Otherwise, the reference returned is to the previously created object. 
     Conclusion 
     The dynamic mapping of an ActiveX control to a Java bean has been described. In particular, systems and methods of creating a mapping using information gathered at run-time from a Java bean component have been described. Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement which is calculated to achieve the same purpose may be substituted for the specific embodiments shown. For example, the systems and methods described herein could be applied to component model interfaces other than ActiveX or JavaBeans. This application is intended to cover any adaptations or variations of the present invention. Therefore, it is manifestly intended that this invention be limited only by the following claims and equivalents thereof.