On the road to openness: the Java EE Foundation of ASP Developers (i)

If you are an ASP developer who is looking to migrate an existing e-business application to Java EE, or an ASP developer who is writing a new Java EE application from scratch, but does not want to experience "overload information" to begin writing programs. So this road map is for you. This roadmap is designed for ASP developers who want to quickly turn to Java EE, a platform-independent open standard set that uses the Java language to develop WEB applications and other types of distributed applications. At the same time, we'll introduce you to Java EE, how to program in the java-based language, how to develop an EE WEB application, and how to relate that knowledge to your experience in writing ASP, COM objects, and ISAPI filters for IIS and Windows environments.

Why turn to the Java EE?

If you are not very keen to venture into the Java EE development environment, consider the following benefits of the Java EE:

Choice, more options: Because Java EE is a well-defined set of standards, there are a number of Java EE implementations to choose from when deploying your own code. As long as you stick to the standard API and avoid vendor-specific extensions, applications can run on a variety of implementations without changing the code.

Are we talking about choice? : Java EE implementations are available on a variety of platforms from mainframes to Wintel, UNIX, and Linux. Once you write an application, you can deploy it on a variety of platforms.

Can't we just be complacent? : Java EE contains a standard API for accessing many legacy EIS systems such as CICS, IMS, ERP, and CRM. It also includes Web service support, so you can integrate. NET systems and other systems that support industry WEB service standards. Java EE also supports the standard messaging API (the java-based message Service; JMS) and for accessing relational databases (Java database connectivity; JDBC) API. This broad selection allows you to integrate a variety of existing systems without losing your investment in them.

The engine room was no longer smoky: experts from around the world developed Java Community Process (JCP) specification. JCP issued a preliminary draft of the code for public comment. Even if you don't take the initiative, you will always know which future specifications are being prepared. The specification also includes a reference implementation that you can use to check the new technology before you decide to implement it.

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Introduction to Java EE

Java 2 Enterprise Edition This specification consists of a number of component specifications related to developing distributed applications in the Java language. You can use the Java EE component to write web-based applications and traditional client-server applications, and to use standard APIs to connect to legacy resources such as relational databases. If you have a iis/asp development background, then the Java servlets and JavaServer Pages (JSP) technologies are the most useful components for you.

Porting to the Java platform

If you develop. NET, Windows client/server applications, and ASP applications, and want to quickly cross the Java EE platform, a series of articles on the Open Road will guide you through this process, leveraging your existing development knowledge, paving the way for you to follow open standards based programming.

Java Servlet

The Java Servlet is a Java class that runs as an extension to Web servers such as IIS or Apache Web server. The Java Servlet is similar to an ISAPI filter or Cgi-bin program/script. The servlet runs when the client browser invokes a specially configured URL, either directly or indirectly. The servlet can access the information in the HTTP request and process the request directly by providing content that is returned to the client. Alternatively, the servlet can redirect the client browser to another resource. Most Java EE Web applications use the servlet primarily as a target for HTML forms to handle user input and then handle them accordingly. The generation of response pages is typically delegated to a JSP page.

JavaServer Page Technology

JSP pages are similar to ASP pages. That is, they are HTML pages that contain script elements that will run on the server when the user requests the page. One key difference between ASP pages and JSP pages is that ASP uses VBScript or JScript as the scripting language, while JSP pages use the Java language. Typical JSP pages contain Java snippets and some special class HTML tags defined in the JSP specification that are intertwined with standard HTML to provide a combination of static content and dynamic content. The difference between the Java Servlet and the JavaServer page technology is conceptually similar to the difference between an ISAPI filter and an ASP page. In both cases, the former is a piece of code that can be used to send HTML directly or indirectly to other resources, followed by an HTML document that can contain embedded code.

Web Server and Application server

As an ASP developer, you know that ASP pages are executed by the scripting engine invoked by IIS. You can also add ISAPI filters and COM components to the WEB application for IIS to invoke. This approach makes it easy to deploy WEB applications on IIS. However, this is limited to the Windows platform, the only platform that IIS can run. Java EE uses a different approach because it is designed to run on a variety of operating systems, including Windows. Instead of trying to embed code that runs Java Servlet and JSP pages directly into a WEB server, it runs them using a separate server component called an application server. Most application servers, such as IBM WebSphere, also have a separate insert component that bridges the application server to a particular WEB server. For example, WebSphere comes with a separate plug-in for IIS and the Apache Web server. This allows you to use the WEB server of your choice when you run the Java EE component.