1.1 Java Servlet and its features
Servlet is the answer of Java technology to CGI programming. The Servlet program runs on the server side and generates web pages dynamically. Compared with traditional CGI and many other CGI-like technologies, Java Servlets are more efficient, easier to use, more powerful, more portable, and more investment-saving (more importantly, Servlet programmers earn more than Perl programmers :-):
Efficient.
In traditional CGI, each request needs to start a new process. If the execution time of the CGI program itself is short, the overhead required to start the process is likely to exceed the actual execution time. In Servlets, each request is handled by a lightweight Java thread (rather than a heavyweight operating system process).
In traditional CGI, if there are N concurrent requests to the same CGI program, the code of the CGI program is repeatedly loaded N times in memory; for Servlets, N threads are processing the request, and only one Servlet class code is required. In terms of performance optimization, Servlets also have more choices than CGI, such as buffering previous calculation results, maintaining database connection activity, etc.
convenient.
Servlets provide a large number of practical routines, such as automatically parsing and decoding HTML form data, reading and setting HTTP headers, processing cookies, tracking session status, etc.
Powerful.
In Servlets, many tasks that are difficult to accomplish with traditional CGI programs can be easily accomplished. For example, Servlets can interact directly with web servers, while ordinary CGI programs cannot. Servlets can also share data between programs, making it easy to implement functions such as database connection pools.
Good portability.
Servlets are written in Java, and the Servlet API has complete standards. Therefore, Servlets written for I-Planet Enterprise Server can be ported to Apache, Microsoft IIS, or WebStar without any substantial changes. Almost all mainstream servers support Servlets directly or through plug-ins.
Save investment.
Not only are there many cheap or even free web servers available for personal or small-scale websites, but for existing servers, if it does not support Servlets, this feature is often free (or requires very little investment).
1.2 JSP and its features
JavaServer Pages (JSP) is a technology that implements mixed encoding of ordinary static HTML and dynamic HTML. For descriptions of the basic concepts of JSP, please refer to the "Introduction to JSP Technology".
Most of the pages generated by CGI programs are still static HTML, and dynamic content only appears in a few limited parts of the page. But most CGI technologies and their variants, including Servlets, always generate the entire page through the program. JSP allows us to create these two parts separately. For example, here is a simple JSP page:
＜!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"＞
＜HTML＞
＜HEAD＞＜TITLE＞Welcome to the online store＜/TITLE＞＜/HEAD＞
＜BODY＞
＜H1＞Welcome＜/H1＞
＜SMALL＞Welcome,
＜!-- The user name for the first visit is "New User" -->
＜% ((request)); %＞
To set up account information, click
＜A HREF=""＞Here＜/A>＜/SMALL＞
＜P＞
The rest of the page. .
＜/BODY＞＜/HTML＞
Here is a simple comparison of JSP and other similar or related technologies:
Compared with Active Server Pages (ASP)
Microsoft's ASP is a technology similar to JSP. Compared with ASP, JSP has two advantages. First, the dynamic part is written in Java, rather than VB Script or other Microsoft languages, not only is it more powerful but also easier to use. Second, JSP applications can be ported to other operating systems and non-Microsoft web servers.
Compared with pure Servlets
JSP does not add any features that cannot be implemented essentially with Servlets. However, it is more convenient to write static HTML in JSP, and there is no need to use the println statement to output each line of HTML code. More importantly, with the help of the separation of content and appearance, tasks of different natures in page production can be conveniently separated: for example, HTML design is performed by page design experts, while leaving room for Servlet programmers to insert dynamic content.
Compared with JSP and server-side inclusion (Server-Side Include, SSI)
SSI is a widely supported technology to introduce external code in static HTML. JSP supports this more perfectly because it can generate dynamic content using Servlets instead of independent programs. Additionally, SSI is only used for simple inclusion, not for "real" programs that can handle form data and access databases.
Compared with JSP and JavaScript
JavaScript can generate HTML dynamically on the client side. While JavaScript is useful, it can only handle dynamic information based on the client environment. Apart from cookies, HTTP status and form submission data are not available to JavaScript. In addition, since it is running on the client side, JavaScript cannot access server-side resources, such as database, directory information, etc.
Servlet is the answer of Java technology to CGI programming. The Servlet program runs on the server side and generates web pages dynamically. Compared with traditional CGI and many other CGI-like technologies, Java Servlets are more efficient, easier to use, more powerful, more portable, and more investment-saving (more importantly, Servlet programmers earn more than Perl programmers :-):
Efficient.
In traditional CGI, each request needs to start a new process. If the execution time of the CGI program itself is short, the overhead required to start the process is likely to exceed the actual execution time. In Servlets, each request is handled by a lightweight Java thread (rather than a heavyweight operating system process).
In traditional CGI, if there are N concurrent requests to the same CGI program, the code of the CGI program is repeatedly loaded N times in memory; for Servlets, N threads are processing the request, and only one Servlet class code is required. In terms of performance optimization, Servlets also have more choices than CGI, such as buffering previous calculation results, maintaining database connection activity, etc.
convenient.
Servlets provide a large number of practical routines, such as automatically parsing and decoding HTML form data, reading and setting HTTP headers, processing cookies, tracking session status, etc.
Powerful.
In Servlets, many tasks that are difficult to accomplish with traditional CGI programs can be easily accomplished. For example, Servlets can interact directly with web servers, while ordinary CGI programs cannot. Servlets can also share data between programs, making it easy to implement functions such as database connection pools.
Good portability.
Servlets are written in Java, and the Servlet API has complete standards. Therefore, Servlets written for I-Planet Enterprise Server can be ported to Apache, Microsoft IIS, or WebStar without any substantial changes. Almost all mainstream servers support Servlets directly or through plug-ins.
Save investment.
Not only are there many cheap or even free web servers available for personal or small-scale websites, but for existing servers, if it does not support Servlets, this feature is often free (or requires very little investment).
1.2 JSP and its features
JavaServer Pages (JSP) is a technology that implements mixed encoding of ordinary static HTML and dynamic HTML. For descriptions of the basic concepts of JSP, please refer to the "Introduction to JSP Technology".
Most of the pages generated by CGI programs are still static HTML, and dynamic content only appears in a few limited parts of the page. But most CGI technologies and their variants, including Servlets, always generate the entire page through the program. JSP allows us to create these two parts separately. For example, here is a simple JSP page:
＜!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"＞
＜HTML＞
＜HEAD＞＜TITLE＞Welcome to the online store＜/TITLE＞＜/HEAD＞
＜BODY＞
＜H1＞Welcome＜/H1＞
＜SMALL＞Welcome,
＜!-- The user name for the first visit is "New User" -->
＜% ((request)); %＞
To set up account information, click
＜A HREF=""＞Here＜/A>＜/SMALL＞
＜P＞
The rest of the page. .
＜/BODY＞＜/HTML＞
Here is a simple comparison of JSP and other similar or related technologies:
Compared with Active Server Pages (ASP)
Microsoft's ASP is a technology similar to JSP. Compared with ASP, JSP has two advantages. First, the dynamic part is written in Java, rather than VB Script or other Microsoft languages, not only is it more powerful but also easier to use. Second, JSP applications can be ported to other operating systems and non-Microsoft web servers.
Compared with pure Servlets
JSP does not add any features that cannot be implemented essentially with Servlets. However, it is more convenient to write static HTML in JSP, and there is no need to use the println statement to output each line of HTML code. More importantly, with the help of the separation of content and appearance, tasks of different natures in page production can be conveniently separated: for example, HTML design is performed by page design experts, while leaving room for Servlet programmers to insert dynamic content.
Compared with JSP and server-side inclusion (Server-Side Include, SSI)
SSI is a widely supported technology to introduce external code in static HTML. JSP supports this more perfectly because it can generate dynamic content using Servlets instead of independent programs. Additionally, SSI is only used for simple inclusion, not for "real" programs that can handle form data and access databases.
Compared with JSP and JavaScript
JavaScript can generate HTML dynamically on the client side. While JavaScript is useful, it can only handle dynamic information based on the client environment. Apart from cookies, HTTP status and form submission data are not available to JavaScript. In addition, since it is running on the client side, JavaScript cannot access server-side resources, such as database, directory information, etc.