-
What are application frameworks The idea of a framework applies not only to applications but to application components as 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 component.40419
- 上一篇：SQL Server数据库英文文献和中文翻译
- 下一篇：C#语言与.NET Framework英文文献和中文翻译
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.论文网
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 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 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, just to name a few. Of the seven request methods, GET and POST are by far the most popular.
Once the server has received and serviced the request, it will issue an HTTP response. The first line in the response is called the status line and carries the HTTP protocol version, a numeric status, and a brief description of the status. Following the status line, the server will return a set of HTTP response headers that work in a way similar to the request headers.
As we mentioned, HTTP does not preserve state information between requests.The server logs the request, sends the response, and goes blissfully on to the next request. While simple and efficient, a stateless protocol is problematic for dynamic applications that need to keep track of their users.