JSP外文翻译

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1 JSP application frameworks

What are application frameworks:

A framework is a reusable, semi-complete application that can be specialized to

produce custom applications [Johnson]. Like people, software applications are more

alike than they are different. They run on the same computers, expect input from the 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 sameness between applications. Application frameworks

build on this common ground to provide 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 project.

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 done—but 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 long 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 applications 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 provide

semi-complete versions of a subsystem that can be specialized to provide a custom 毕业设计（论文）外文翻译——原文

2 component.

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 Struts: 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 specific to Struts and underlie every Java web

application. A reason that developers use frameworks like Struts is to hide the nasty details

behind acronyms like HTTP, CGI, and JSP. As a Struts developer, you don’t need to be an

alphabet soup guru, but a working knowledge of these base technologies can help 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 computers 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.

Many 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 the 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 negotiating and retaining a connection,

stateless protocols can handle a large volume of requests. This is one reason why

the 毕业设计（论文）外文翻译——原文

3 Internet 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. 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 location