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1、JSP application frameworksWhat are application frameworks:A framework is a reusable, semi-complete application that can be specialized toproduce custom applications Johnson. Like people, software applications are more alike than they are different. They run on the same computers, expect input from t
2、he same devices, output to the same displays, and save data to the same hard disks. Developers working on conventional desktop applications are accustomed to toolkits and development environments that leverage the samenessbetween applications. Application frameworks build on this common ground to pr
3、ovide developers with a reusable structure that can serve as the foundation for their own products.A framework provides developers with a set of backbone components that have the following characteristics:1.They are known to work well in other applications.2. They are ready to use with the next proj
4、ect.3. They can also be used by other teams in the organization.Frameworks are the classic build-versus-buy proposition. If you build it, you will understand it when you are donebut how long will it be before you can roll your own? If you buy it, you will have to climb the learning curve and how lon
5、g is that going to take? There is no right answer here, but most observers would agree that frameworks such as Struts provide a significant return on investment compared to starting from scratch, especially for larger projects.Other types of frameworks:The idea of a framework applies not only to app
6、lications but to application componentsas well. Throughout this article, we introduce other types of frameworks that you can use with Struts. These include the Lucene search engine, the Scaffold toolkit, the Struts validator, and the Tiles tag library. Like application frameworks, these tools provid
7、e semi-complete versions of a subsystem that can be specialized to provide a custom1component.Some frameworks have been linked to a proprietary development environment. This is not the case with Struts or any of the other frameworks shown in this book. You can use any development environment with St
8、ruts: Visual Age for Java, JBuilder, Eclipse, Emacs, and Textpad are all popular choices among Struts developers. If you can use it with Java, you can use it with Struts.Enabling technologies:Applications developed with Struts are based on a number of enabling technologies.These components are not s
9、pecific to Struts and underlie every Java web application. A reason that developers use frameworks like Struts is to hide the nasty detailsbehind acronyms like HTTP, CGI, and JSP. As a Struts developer, you don t need to b alphabet soup guru, but a working knowledge of these base technologies can he
10、lp you devise creative solutions to tricky problems.Hypertext Transfer Protocol (HTTP):When mediating talks between nations, diplomats often follow a formal protocol.Diplomatic protocols are designed to avoid misunderstandings and to keep negotiations from breaking down. In a similar vein, when comp
11、uters need to talk, they also follow a formal protocol. The protocol defines how data is transmitted and how to decode it once it arrives. Web applications use the Hypertext Transfer Protocol (HTTP) to move data between the browser running on your computer and the application running on the server.M
12、any server applications communicate using protocols other than HTTP. Some of these maintain an ongoing connection between the computers. The application server knows exactly who is connected at all times and can tell when a connection is dropped. Because they know the state of each connection and th
13、e identity of each person using it, these are known as stateful protocols.By contrast, HTTP is known as a stateless protocol. An HTTP server will accept any request from any client and will always provide some type of response, even if the response is just to say no. Without the overhead of negotiat
14、ing and retaining a connection, stateless protocols can handle a large volume of requests. This is one reason why the2Internet has been able to scale to millions of computers.Another reason HTTP has become the universal standard is its simplicity. An HTTP request looks like an ordinary text document
15、. This has made it easy for applications to make HTTP requests. You can even send an HTTP request by hand using a standard utility such as Telnet. When the HTTP response comes back, it is also in plain text that developers can read.The first line in the HTTP request contains the method, followed by the locationof the requested resource and the version of HTTP. Zero or more HTTP request headers follow the initial line. The HTTP headers provide additional information to the server. This can include the browser type and version, acceptable document types, and the browser s cookies,
