Home > Articles

Jini and JavaSpaces: Supporting Technologies

  • Print
  • + Share This
sams_sample_chap
This chapter is from the book

Jini is about federating and organizing services on a network and allowing clients to discover and use services. The Jini framework is designed to minimize the amount of human intervention required to manage services.

When you first start establishing a Jini environment, you may doubt that the goal of minimal human intervention was attained. There are a number of services that need to be started in order to deploy a basic Jini network. The initial process can be difficult, especially if you are new to remote method invocation (RMI), but after your network is established, the base services seldom need administration or management.

There are three infrastructure services that will be required somewhere on your Jini network. They are as follows:

  • An HTTP server that supports dynamic downloading of code

  • The Remote Method Invocation daemon (rmid) that provides the distributed remote object lookup and activation mechanism, covered later in this chapter

  • The Jini LUS that provides the service registry and the service lookup capabilities on the Jini network, which is covered in Chapter 4, "Building on Jini Foundation Concepts."

The HTTP Server

The HTTP server should not be new to you. Anyone who has surfed the Web has encountered an HTTP server. It is based on support for the HTTP protocol, which is the standard protocol for fetching Web pages across the Internet. Jini requires that an HTTP server be available on the network—or a server capable of file transport (ftp)—because Jini uses this familiar protocol to transport files (code) from machine to machine.

The HTTP Server is one of the first services that you will start when setting up your Jini network. This enables Jini to transport downloadable code to applications when the applications need it.

You can run one or more HTTP servers on your Jini network. I recommend starting with a single HTTP server. You will want to monitor when the code gets transported across the network by various service requests. It is much easier to start and monitor a single instance of a service until you are comfortable with the service interactions. It might then be appropriate to introduce additional servers to support multiple service configurations, redundancy, scalability, and unique application requirements.

The Role of the HTTP Server and Protocol

Any HTTP server should be able to satisfy the requirements of Jini. The simple and familiar GET method of the HTTP protocol is used to request a specific file (URL) for download. We will discuss the mechanics of requests in the section on RMI, but for now just recognize that requested files are jar or class files necessary to instantiate objects to process distributed requests.

Jini-Supplied

The class com.sun.jini.tool.ClassServer that is supplied with the Jini distribution implements a simple HTTP server for serving up jar and class files.

NOTE

You can download the Jini binaries and source code from the Java Developer Connection at http://developer.java.sun.com/developer/products/jini. Appendix A, "Environment Set Up," provides the necessary links and resources for the Jini distribution.

The HTTP server can be started with the following command on Windows:

java -jar %JINI_HOME%\lib\tools.jar -port 8080 -dir %JWORK_HOME%\lib -trees
 -verbose

where %JINI_HOME% references the Jini implementation directory, for example C:\files\_Jini1_1; and %JWORK_HOME% references the download directory that contains the jar and class files that you will expose to clients. Any files that you want to make available to clients or services should be placed in this directory location.

The other arguments include:

  • [-port port]

  • [-dir dir]

  • [-trees]

  • [-verbose]

The default port is 8080 and can be overridden with the -port option. The default directory on Windows is J: and the default directory on non-Windows systems is /vob/jive/jars. The default can be overridden with the -dir option. By default, all files under the default directory (including all subdirectories) are served up via HTTP.

If the -verbose option is given, then all attempts to download files are output to the console.

The -trees option can be used to serve up individual files stored within jar files, in addition to the files that are served up by default. If this option is used, the server searches all jar files in the top-level directory. If the name of the jar file is name.jar, then any individual file named within that jar file can be downloaded using a URL in the form of http://host:port/name/file.

When this option is used, an open file descriptor and cached information are held for each jar file, for the life of the process.

In the examples, I've set the following Windows variables to define the location of the Jini install directory and the location of files available via the HTTP server. Your setup will probably be different.

set JINI_HOME=D:\files\jini1_1\
set JWORK_HOME=C:\JiniJavaSpaces\services\lib

GUI-Activated

Jini also comes with a GUI-supplied service activation program. It enables you to enter the required and optional parameters to start Jini services in a tabbed pane as an alternative to scripts.

The following command starts the service launcher interface. From the command prompt, type the command:

java -cp %JINI_HOME%\lib\jini-examples.jar com.sun.jini.example.launcher.
StartService

To use the launcher, you can open and edit the properties file located under the /jini1_1/_examples/launcher directory from the file menu. This will generate the tabs shown in Figure 3.1 and enable you to customize the parameters to your environment. There are properties files for both Unix and Windows that supply a list of default values.

After you load the appropriate properties file, your display should look similar to this:

If you are new to Jini, you can use this interface to examine the basic parameters that are available to start Jini services in addition to rmid and the HTTP server. This will help you become familiar with the commands that are used to start the various services.

To start the Web server supplied with Jini, simply select the WebServer tab and set the following properties, as seen in Figure 3.2:

  • Executable jar file: Specify the path to Jini tools.jar

  • Port: Specify the port on which to run the HTTP server

  • Document Area: Specify the path from which to serve jar files

Figure 3.1 A graphical view to starting and stopping Jini services.

Figure 3.2 Example Web Server parameter settings.

Now select the Run tab and start the Web server. On the console you will see the command invoked and a list of the files that are in the directory pointed to by the -dir argument of the Document Area property.

If the service failed to start, you might want to check the "Gotchas and Common Failures" section in Appendix A to troubleshoot the problem.

Alternatives

As mentioned at the start of this section, any HTTP server should be able to perform the functions required to support Jini. In fact, the Jini HTTP server implementation is a minimalist approach to satisfying the startup requirements.

If you already have a Web server, check your server documentation to determine the necessary configuration parameters to access files. This is usually nothing more than a parameter in a startup script indicating a root directory or path where you place Web files.

Now let's take a look at another infrastructure service: remote method invocation (RMI). RMI is often the source of confusion when establishing a Jini environment. For this reason, it is important to understand how RMI fits into the Jini architecture and ensure that you understand the dependencies between RMI and the Jini environment.

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020