1,JSP的运行原理
(1)WEB容器JSP页面的访问请求时,它将把该访问请求交给JSP引擎去处理。Tomcat中的JSP引擎就是一个Servlet程序,它负责解释和执行JSP页面。
(2)每个JSP页面在第一次被访问时,JSP引擎先将它翻译成一个Servlet源程序,接着再把这个Servlet源程序编译成Servlet的class类文件,然后再由WEB容器像调用普通Servlet程序一样的方式来装载和解释执行这个由JSP页面翻译成的Servlet程序。
(3)Tomcat 5把为JSP页面创建的Servlet源文件和class类文件放置在“apache-tomcat-5.5.26\work\Catalina\localhost\<应用程序名>\”目录中,Tomcat将JSP页面翻译成的Servlet的包名为org.apache.jsp(即:apache-tomcat-5.5.26\work\Catalina\localhost\org\apache\jsp\文件下)
例子:
HelloJSP.jsp:(文件目录:D:\apache-tomcat-5.5.26\webapps\test_jsp\HelloJSP.jsp)
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<%@ pagelanguage=
"java"
import
=
"java.util.*"
pageEncoding=
"gb2312"
%>
<title>简单JSP页面示例</title>
这是一个简单的 JSP页面示例——HelloJSP <br>
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HelloJSP.jsp页面被请求时,Web服务器中JSP编译器会编译生成对应的Java文件,如下:
HelloJSP_jsp.java:(文件目录:D:\apache-tomcat-5.5.26\work\Catalina\localhost\test_jsp\org\apache\jsp\HelloJSP_jsp.java)
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<pre
class
=
"brush:java;"
>
package
org.apache.jsp;
import
javax.servlet.*;
import
javax.servlet.http.*;
import
javax.servlet.jsp.*;
import
java.util.*;
public
final
class
HelloJSP_jsp
extends
org.apache.jasper.runtime.HttpJspBase
implements
org.apache.jasper.runtime.JspSourceDependent {
private
static
java.util.List _jspx_dependants;
public
Object getDependants() {
return
_jspx_dependants;
}
public
void
_jspService(HttpServletRequest request, HttpServletResponse response)
throws
java.io.IOException, ServletException {
JspFactory _jspxFactory =
null
;
PageContext pageContext =
null
;
HttpSession session =
null
;
ServletContext application =
null
;
ServletConfig config =
null
;
JspWriter out =
null
;
Object page =
this
;
JspWriter _jspx_out =
null
;
PageContext _jspx_page_context =
null
;
try
{
_jspxFactory = JspFactory.getDefaultFactory();
response.setContentType(
"text/html;charset=gb2312"
);
pageContext = _jspxFactory.getPageContext(
this
, request, response,
null
,
true
,
8192
,
true
);
_jspx_page_context = pageContext;
application = pageContext.getServletContext();
config = pageContext.getServletConfig();
session = pageContext.getSession();
out = pageContext.getOut();
_jspx_out = out;
out.write(
"\r\n"
);
out.write(
"\r\n"
);
out.write(
"\t\r\n"
);
out.write(
" \t<title>简单JSP页面示例</title>\r\n"
);
out.write(
"\t\r\n"
);
out.write(
"\r\n"
);
out.write(
"\t这是一个简单的 JSP页面示例――HelloJSP <br>\r\n"
);
out.write(
"\t\r\n"
);
out.write(
"\r\n"
);
}
catch
(Throwable t) {
if
(!(t
instanceof
SkipPageException)){
out = _jspx_out;
if
(out !=
null
&& out.getBufferSize() !=
0
)
out.clearBuffer();
if
(_jspx_page_context !=
null
) _jspx_page_context.handlePageException(t);
}
}
finally
{
if
(_jspxFactory !=
null
) _jspxFactory.releasePageContext(_jspx_page_context);
}
}
}</pre>
<pre
class
=
"brush:java;"
></pre>
<p></p>
<p><br>
</p>
<p>上面这段代码就是HelloJSP.jsp编译生成的Java代码,它的路径(我的电脑)为:D:\apache-tomcat-
5.5
.
26
\work\Catalina\localhost\test_jsp\org\apache\jsp中(其中:test_jsp为我的项目名称)。在这个目录下会有两个对应的文件,一个是
class
文件一个是java</p>
<p>文件如下:</p>
<p><img style=
"width: 164px; height: 42px; display: inline;"
alt=
"\" src="
http:
//www.2cto.com/uploadfile/Collfiles/20140417/20140417092148150.png"><br>
</p>
<p><br>
</p>
<h1><strong>
2
</strong><strong>,<喎�
"http://www.2cto.com/kf/ware/vc/"
target=
"_blank"
class
=
"keylink"
>vc3Ryb25nPjxzdHJvbmc+SlNQPC9zdHJvbmc+PHN0cm9uZz61xNa00NC5/bPMPC9zdHJvbmc+PC9oMT4KPHA+SlNQtcTWtNDQuf2zzNb30qq/ydLUt9bOqtLUz8K8uLXjo7o8L3A+CjxwPjGjqb/Nu6e2y7eis/bH68fzoaM8L3A+CjxwPjKjqVdlYsjdxve9q0pTUNeq0uuzyVNlcnZsZXTUtLT6wuuhozwvcD4KPHA+M6OpV2ViyN3G972rsvrJ+rXE1LS0+sLrvfjQ0LHg0uuhozwvcD4KPHA+NKOpV2ViyN3G97zT1Nix4NLruvO1xLT6wuuyota00NChozwvcD4KPHA+NaOpsNHWtNDQveG5+
8
/s06bWwb/Nu6e2y6GjPC9wPgo8cD48aW1nIHNyYz0=
"http://www.2cto.com/uploadfile/Collfiles/20140417/20140417092148152.jpg"
alt=
""
><br>
<p></p>
<p><br>
</p>
</strong></h1><strong><h1>
3
,总结</h1>
<strong>JSP执行过程:</strong>
<p>
1
)首先,客户端发出请求(request ),请求访问JSP网页</p>
<p>
2
)接着,JSP Container将要访问的.JSP文件 转译成Servlet的源代码(.java文件)</p>
<p>
3
)然后,将产生的Servlet的源代码(.java文件)经过编译,生成.
class
文件,并加载到内存执行</p>
<p>
4
)最后把结果响应(response )给客户端</p>
<p> 执行JSP网页文件时,需要经过两个时期:转译时期(Translation Time)和请求时期(Request
Time)。</p>
<p> 转译时期:JSP转译成Servlet类(.
class
文件)。</p>
<p> 请求时期:Servlet类(.
class
文件)执行后,响应结果至客户端。</p>
<p><br>
</p>
<p> 转译期间主要做了两件事情:</p>
<p> (
1
)将JSP网页转译为Servlet源代码(.java),此段称为转译时期(Translation
time);</p>
<p> (
2
)将Servlet源代码(.java)编译成Servlet类(.
class
),此阶段称为编译时期(Compilation
time)。</p>
<p></p>
<p>其实,JSP就是一个Servlet。</p>
<br>
<p><br>
</p> </strong>
|