CALIFORNIA SOFTWARE LABS

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1 Wrapping Jini Services in ActiveX CALIFORNIA SOFTWARE LABS R E A L I Z E Y O U R I D E A S California Software Labs 6800 Koll Center Parkway, Suite 100 Pleasanton CA 94566, USA. Phone (925) Fax (925) info@cswl.com

2 Wrapping Jini Services in ActiveX A Technical Report Technical Expertise Level : Intermediate Requires knowledge of : Jini, Java, RMI, VB INDEX INTRODUCTION... 3 BEAN BRIDGE BASICS... 3 JINI BASICS... 4 BUILDING THE BEAN... 4 SECURITY CONSIDERATION... 5 BEAN ARCHITECTURE... 5 OPERATIONS OF THE BEAN... 6 BEAN TO ACTIVEX CONVERSION... 8 INVOKING THE SERVICE METHODS... 9 EXAMPLE USAGE FROM VISUAL BASIC... 9 CONCLUSION CSWL Inc, Pleasanton, California - 2 -

3 Introduction The introduction of JINI by Sun Microsystems has created a spur in the world of Distributed Computing and technology gurus forecast the relevance of this technology for tomorrow. The trend seems to be focus shifting from a PC centric approach to Network centric. This paper illustrates how the JINI services can be encapsulated as an ActiveX component and made to run over a Windows Platform. The basic idea approached to create the system is to create Java Bean that exposes the required Jini service APIs and this bean can be converted into an ActiveX component using the Java Bean Bridge. Bean Bridge basics The Java Bean Bridge is a component that comes along with JRE and as the name goes, it acts as bridge between an ActiveX component and the Java Bean. Initially when a Bean has to be converted into an ActiveX then an ActiveX Packager is used to create an OCX(OLE Control Extension) and its corresponding TLB (Type LiBrary)file. The ActiveX Packager also gives the developer the provision whether the ActiveX control should be registered in the local machine and also generates the.reg (Registry install) file which could be used for installing in another machine. When any component that has been developed using the bean bridge is used in an environment, the component contains the references and methods to start the JRE. During the initialization of the ActiveX component the JVM (Java Virtual Machine) is loaded along with the JRE. The bean that was packed as an OLE is also launched in the JRE memory space. Any method calls on the component made will marshaled over the Bean Bridge which and sent to the Bean that contains the binary code. The method that gets CSWL Inc, Pleasanton, California - 3 -

4 executed in the JRE memory space, the return for the function is unmarshalled by the bridge and given back to the ActiveX component. JINI basics The JINI framework makes a federation of dissimilar devices over the network to communicate and use each other through a standard protocol. The network essentially consists of service providing devices and other devices makes use of the service provided by it. The Jini Lookup Service (JLS) acts as common gateway where a federation of devices registers its services. Any client can browse over the JLS to find for any availability of a service and if any matching services are found then the client device can use the service if needed. Further down the JINI architecture also provides transaction processing. The communication established between the device runs over the RMI Subsystems. Thus JINI ensures the code mobility of the services offered. Building the Bean The initial task that is performed first is to create a Java Bean that will expose all the Jini functionality. The main methods that are exposed are the following: 1. Searching for one or more JLS in the nearby network 2. Registering a service on a JLS 3. Searching for a specified service on one or more JLS 4. Invoking the method of Service offered by a client 5. Un-register a service from a JLS Since the discovery process consists of two methods namely: unicast and multicast discovery both the method of discovery is adopted while searching for a JLS. The end of document contains the API Specification of the bean that is built for this purpose. There are other methods that are just as important when CSWL Inc, Pleasanton, California - 4 -

5 compared to the above five methods. When a client device uses a service object then it may have to execute few methods locally, thus security issues also have to considered. The next passage illustrates how RMI system influences the system s security. The error handling and support functions are also required. There is also the need to set parameters like Time to Live (ttl), if lease has to renewed etc. All these and other method are discussed in the API specification. Security Consideration The main transport protocol on which JINI operates depends extensively on RMI system. Any service object that has to be Remote object and interfaces exposed should be Serializeable. Since the Stub class runs on the client end and few operations may be required do actions locally on the device itself. The RMI introduces the RMISecurityManager that effectively manages the rights or permissions of the stub code when it is installed. The input from the client end will be a policy file that specifies the permission that the stub would have on the client. A method that allows the setting of the policy file is also included in the APIs. Bean Architecture The Bean essentially consists of a collection of independent objects that together coupled together gives the desired output. The major part of the bean contains the JINI enabling classes that are the classes that come along with JINI v1.0 binary. There are classes that load classes and invokes an object s methods etc. Introspection at the figure given below makes the architecture clear. CSWL Inc, Pleasanton, California - 5 -

6 As shown above the BeanInfo class is responsible for giving the details of the Bean namely the methods, events and properties exposed. The FunctionInvoker takes care of invoking the methods of a service object. When this bean is used at device that would be service provider then it should be capable of serving the stub classes to the client using a HTTP server. Thus a class that performs this operation is also included. The service provider may have the service class anywhere in his file system, so the provider can specify the location that contains the specified files. The ClassLoader loads the classes from the location and gives it to the main wrapper class that registers the service in the JLS. Operations of the Bean This section mentions the main aspects of operation of the bean. The scope of explanation will be limited to the discovery of JLS, registration of a service, searching for a service and unregistering a service from a JLS. Lookup Discovery The bean exposes two methods that which performs the unicast and multicast discovery of JLS in the nearby network. It can also discover the JLS that CSWL Inc, Pleasanton, California - 6 -

7 belongs to a particular group. A few considerations in multicast discovery are the maximum time allowed for the finding JLS and Time to live (ttl) value. Separate functions to set the parameters are used. Service Registration When a service provider wishes to offer a service, it then has to make that service to be registered a JLS. Moreover an HTTP server will run at the service provider s end so that its stub classes can be served to any clients which requires a service. All the basic rules of registering a service in Jini are fully complied by this bean. The bean also gives the support to avail lease by the service provider. The user is also given the opportunity to specify the attributes for the service object. Searching Services The search for service can be made in criteria depending on the multicast or unicast discovery of JLS with respect to the attributes of the search service. The search process is made to return a unique service object depending on all attributes rather than many service objects that might partly satisfy few attributes. Unregister Services Any service can be unregistered by the bean from a JLS as long as the same bean registers that service. The bean cancels the lease of the service object thus unregistering the service. CSWL Inc, Pleasanton, California - 7 -

8 Bean to ActiveX conversion The bean is implemented fully and is converted as an ActiveX component using the ActiveX Packager from Sun Microsystems. The steps for this conversion are clearly described in the Javasoft site Now another issue that arises when a cross-language packaging is made is the type conversions. Java language adheres to the latest data type specification and most types are UNICODE compliant. The character is 16 bit long and integer 32 bit and so on. The Table gives the type difference that occurs between the Java and Microsoft languages. Java Sun JavaBeans Bridge for ActiveX 1.0 Type Library Visual Basic Visual C++ Boolean VARIANT_BOOL Boolean BOOL Byte short Integer Short byte array VARIANT Array (Byte) SAFEARRAY (short) Char short Integer Short char array VARIANT Array (Integer) SAFEARRAY (short) Double Double Double Double Float Single Single Single Integer (object) Long Long Long Int Long Long Long Long (8 bytes) Long (4 bytes) Long (4 bytes) Long (4 bytes) Object (or subclass) IDispatch* Object IDispatch* Short Short Integer Short String BSTR String CString (MFC) CSWL Inc, Pleasanton, California - 8 -

9 Invoking the Service Methods The crucial role of the component comes when the client has to use any services of a client. After the search of the service is over which returns the service proxy to the client, the client can invoke any methods exposed by the service object. Since the service object may be a purely a Java object and the client may use the ActiveX component on Visual C++ or Visual Basic environment, the function calls may have to marshalled and unmarshalled accordingly. Most operations are abstracted away for the developer and all that he has to adhere to is the interface definition document that states the usage of the component. The service object s behavior (methods and function parameters) should be known already to the client that uses it. If the client wrongly tries to invoke a service, then an error code is returned. The dynamic invocation of the service object is achieved using the Reflection principles. Example usage from Visual Basic The Jini component after the registration process can be inserted into a Visual Basic project and placed on the form. The name of the component is given as jini and using the jini object variable, methods on this object can be invoked at the form s OnLoad() event as follows: Private Sub Form_Load() set security policy JiniComp.SetSecurityPolicy "E:\\policy" Register a service by discovering the JLS by unicast method JiniComp.RegisterServiceUC "PrinterService", 50, CSWL Inc, Pleasanton, California - 9 -

10 "d:\\printerservice\\", "JPrinterImpl", " ", 4160, Null Returns the status of an operation MsgBox JiniComp.GetStatusMessage() End Sub Private Sub Form_Unload() unregister the printer service JiniComp.UnregisterService "PrinterService" MsgBox JiniComp.GetStatusMessage() End Sub Another client VB application may also use the Jini component and may use the search function to find out whether any JLS has a service called PrinterService registered to it and if found a service object invoke its methods. Private Sub Search() search a service by discovering the JLS by unicast method Set ob = JiniComp.SearchServiceUC ("PrinterService", " ", 4160, Null) If ob Is Nothing Then MsgBox "No Service found" MsgBox JiniComp.GetStatusMessage() Else MsgBox JiniComp.GetStatusMessage() Invoke a print method of the service JiniComp.InvokeMethod ob, "print", Null, Null CSWL Inc, Pleasanton, California

11 End If MsgBox JiniComp.GetStatusMessage() End Sub The description for each of the bean methods is found in the last part of the paper. Conclusion The usage of the Bean bridge enables a Java code run as a Windows program and serves as a valuable tool for developers. The Bean developed exploits the Jini framework to run over a Windows Platform and also be able to maintain interaction towards the Java based Jini Federation Copyright Notice: 2002 California Software Labs. All rights Reserved. The contents on the document are not to be reproduced or duplicated in any form or kind, either in part or full, without the written permission of California Software labs. Product and company names mentioned here in are the trademarks of their respective companies. CSWL Inc, Pleasanton, California