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When is a Singleton not a Singleton?

In this article, Joshua Fox describes those phenomenas and how to avoid them. After discussing how to implement the Singleton, Joshua goes over the sometimes surprising causes for the phenomena one by one, showing you how they occur and how you can avoid making those mistakes.

I hope that in the process you will learn about classloading, multithreading, distributed systems, Design Patterns, and other interesting topics, as I did.



Bean Scripting Framework

Bean Scripting Framework (BSF) is a set of Java classes which provides scripting language support within Java applications, and access to Java objects and methods from scripting languages. BSF allows one to write JSPs in languages other than Java while providing access to the Java class library. In addition, BSF permits any Java application to be implemented in part (or dynamically extended) by a language that is embedded within it. This is achieved by providing an API that permits calling scripting language engines from within Java, as well as an object registry that exposes Java objects to these scripting language engines.

 

BSF 2.x supports several scripting languages currently:

 

In addition, the following languages are supported with their own BSF engines:

Information on where to obtain scripting languages for use with BSF is available on the Related Projects page.


Getting Started with Oracle Identity Management

Technical illustration showing Oracle Identity Management Products

Welcome to Oracle Identity Management

The Oracle Identity Management products enable you to manage data about users, devices, and services in an accurate, secure, and cost-effective manner. You use these products to configure and manage the identity data, to synchronize or combine data from different sources, and to share data between domains. These products also enable you to ensure that only users with valid credentials can access online resources.Oracle offers a variety of Identity Management products. Four of these products are included in Oracle Fusion Middleware 11g Release 1.

What do you want to do?

  • Learn the basics
  • Learn to administer the Oracle Identity Management products.

If you are new to Oracle Identity Management, be sure to visit theLearn the basics about Oracle Identity Management 11g Release 1 section. It will introduce you to terms and concepts essential to using the Suite.

Technical illustration showing Oracle Identity Management ProductsTechnical illustration showing Oracle Identity Management components in 11gR1

What Identity Management products are in Oracle Fusion Middleware 11g Release 1?

The following Identity Management products are included in Oracle Fusion Middleware 11g Release 1 and can be installed and set up using one installation CD:

  • Oracle Internet Directory: Add, find, and manage information about users, groups, and other objects.
  • Oracle Directory Integration Platform: Share data in Oracle Internet Directory with other directory servers and applications.
  • Oracle Virtual Directory: Enable applications to make use of data from different vendors’ enterprise data sources, including directory servers and databases, as if only one type was in use.
  • Oracle Identity Federation: Access protected services provided by your partners while retaining full control over your users’ identities. Enable your authenticated users of partner sites to access your protected services.

Technical illustration showing Oracle Internet Directory


Client pull and Server push technologies

Client Pull is a method used to give additional instructions to a Web browser that would not have been sent by the server it is currently browsing. Client Pull is not a language, although it is usually implemented using HTML. You probably have seen Client Pull in action but did not recognize it. A common implementation of Client Pull is to have the browser automatically move to a different page without the user clicking a hyperlink.

To understand what goes on in the background of Client Pull, you need to know about HTTP response headers and the <META> tags.

<HTML>
<HEAD>
<META HTTP-EQUIV="Refresh" CONTENT="20">
<TITLE>My Home Page (Updates every 20 seconds)</TITLE>
</HEAD>
<BODY>
The information on this site changes regularly.  For that reason, this page
will reload itself every twenty seconds.  If you are not using Netscape or
Internet Explorer, you will need to reload this page manually.<BR>
</BODY>
</HTML>


Server Push is similar to Client Pull in that it also includes extra information within the HTML document. Server Push does not rely on the browser to act on the information included in the document but, instead, relies on the server to push the additional information as scheduled. To understand how Server Push works, we must take a more in-depth look into the MIME standard and specifically the MIME content type multipart/mixed.


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