Tuesday, October 13, 2009

Tomcat Java Servlets Manager

Tomcat Java Servlets Manager

In many production environments, it is very useful to have the capability to deploy a new web application, or undeploy an existing one, without having to shut down and restart the entire container. In addition, you can request an existing application to reload itself, even if you have not declared it to be reloadable in the Tomcat 5 server configuration file.

To support these capabilities, Tomcat 5 includes a web application (installed by default on context path /manager) that supports the following functions:

* List the currently deployed web applications, as well as the sessions that are currently active for those web apps.
* Reload an existing web application, to reflect changes in the contents of /WEB-INF/classes or /WEB-INF/lib.
* List the OS and JVM property values.
* List the available security roles defined in the user database.
* Remove an installed web application.
* Start a stopped application (thus making it available again).
* Stop an existing application (so that it becomes unavailable), but do not undeploy it.
* Undeploy a deployed web application and delete its document base directory.

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Java Server Pages (JSP) scripting elements and variables

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Java Server Pages (JSP) scripting elements and variables

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JSP scripting elements and variables
Standard scripting variables
The following scripting variables are always available:

* out The JSPWriter used to write the data to the response stream.
* page The servlet itself.
* pageContext A PageContext instance that contains data associated with the whole page. A given HTML page may be passed among multiple JSPs.
* request The HTTP request object.
* response The HTTP response object.
* session The HTTP session object that can be used to track information about a user from one request to another.

Scripting elements
There are three basic kinds of scripting elements that allow java code to be inserted directly into the servlet.

* A declaration tag places a variable definition inside the body of the java servlet class. Static data members may be defined as well.
<%! int serverInstanceVariable = 1; %>
* A scriptlet tag places the contained statements inside the _jspService() method of the java servlet class.
<% int localStackBasedVariable = 1; out.println(localStackBasedVariable); %>
* An expression tag places an expression to be evaluated inside the java servlet class. Expressions should not be terminated with a semi-colon.
<%= "expanded inline data " + 1 %>

Tomcat 5 Servlet/JSP container.

Tomcat 5 Servlet/JSP container.

Tomcat 5 implements the Servlet 2.4 and JavaServer Pages 2.0 specifications from Java Software, and includes many additional features that make it a useful platform for developing and deploying web applications and web services.

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Java Server Pages (JSP)
(JSP) A freely available specification for extending the Java Servlet API to generate dynamic web pages on a web server. The JSP specification was written by industry leaders as part of the Java development program.

JSP assists developers in creating HTML or XML pages that combine static (fixed) page templates with dynamic content. Separating the user interface from content generation allows page designers to change the page layout without having to rewrite program code. JSP was designed to be simpler than pure servlets or CGI scripting.

JSP uses XML-like tags and scripts written in Java to generate the page content. HTML or XML formatting tags are passed back to the client. Application logic can live on the server, e.g. in JavaBeans.

JSP is a cross-platform alternative to Microsoft's Active Server Pages, which only runs in IIS on Windows NT.

Applications written to the JSP specification can be run on compliant web servers, and web servers such as Apache, Netscape Enterprise Server, and Microsoft IIS that have had Java support added.