javax.servlet
Interface ServletContext

All Known Implementing Classes:

Application, ServletContextImpl, WebApp

public interface ServletContext

ServletContexts encapsulate applications. Applications are generalized virtual hosts; a URL prefix defines a distinct application. So /myapp and /yourapp could define different applications. As a degenerate case, each virtual host has its own ServletContext.

Each application is entirely distinct. Each has its own:

• Class loader -- each application gets its own beans and servlets.
• ServletContext attributes
• Servlets and servlet mappings (e.g. *.jsp could map to different servlets in different applications.)
• File root
• Mime mapping
• Real-path mapping (aliases)

URIs are relative to the application root (e.g. /myapp) for most ServletContext methods. So you can define user workspaces with identical JSP files and servlets in different applications.

Including and forwarding

Forwarding and including files, the Servlet equivalent of SSI are handled by the RequestDispatcher methods.

Global initialization

There is no direct equivalent of a global.jsa. To initialize and cleanup shared classes on start and stop, use a load-on-startup servlet. The init() method will be called when the application starts and the destroy() method will be called when the application finishes.

   <servlet servlet-name='global'
            servlet-class='test.InitServlet'
            load-on-startup/>
 

Basic configuration

In the resin.conf, to define the /myapp application with a document root in /www/myweb, add the following to the resin.conf.

   <web-app id='/myapp' app-dir='/www/myweb'/>
 

Servlet and Bean locations (class loaders)

Each application has its own directories to load application servlets and beans. By default these are WEB-APP/classes and WEB-APP/lib. To add a servlet test.MyServlet, create the java file: /www/myweb/WEB-APP/classes/test/MyServlet.java

Load balancing

When using load balancing with a web server, each JVM will have its own application object. The attributes are not shared. In contrast, sessions are always sent to the same JVM.

So the application object is best used as a cache rather than as a way for servlets to communicate.

Method Summary

void	addFilter(java.lang.String filterName, java.lang.String description, java.lang.String className, java.util.Map<java.lang.String,java.lang.String> initParam) Adds a filter.
void	addFilterMapping(java.lang.String filterName, java.lang.String[] urlPatterns, java.lang.String[] servletNames, java.util.EnumSet<DispatcherType> dispatcherTypes, boolean isMatchAfter) Adds a filter mapping.
void	addServlet(java.lang.String servletName, java.lang.String description, java.lang.String className, java.util.Map<java.lang.String,java.lang.String> initParam, int loadOnStartup) Adds a runtime servlet.
void	addServletMaping(java.lang.String servletName, java.lang.String[] urlPatterns) Adds a runtime servlet mapping
java.lang.Object	getAttribute(java.lang.String name) Returns an attribute value.
java.util.Enumeration	getAttributeNames() Returns an enumeration of all the attribute names.
ServletContext	getContext(java.lang.String uri) Returns the ServletContext for the uri.
java.lang.String	getContextPath() Returns the context-path for the web-application.
java.lang.String	getInitParameter(java.lang.String name) Returns the value of an initialization parameter from the configuration file.
java.util.Enumeration	getInitParameterNames() Returns an enumeration of all init parameter names.
int	getMajorVersion() Returns the major version of the servlet API.
java.lang.String	getMimeType(java.lang.String uri) Returns the mime type for the given uri.
int	getMinorVersion() Returns the minor version of the servlet API.
RequestDispatcher	getNamedDispatcher(java.lang.String servletName) Returns a request dispatcher based on a servlet name.
java.lang.String	getRealPath(java.lang.String uri) Returns the real file path for the given uri.
RequestDispatcher	getRequestDispatcher(java.lang.String uri) Returns a request dispatcher for later inclusion or forwarding.
java.net.URL	getResource(java.lang.String uri) Returns the resource for the given uri.
java.io.InputStream	getResourceAsStream(java.lang.String path) Returns the resource as a stream.
java.util.Set	getResourcePaths(java.lang.String prefix) Returns the set all resources held by the application.
java.lang.String	getServerInfo() Returns a server-specific string identifying the servlet engine.
Servlet	getServlet(java.lang.String name) Deprecated.
java.lang.String	getServletContextName() Returns the URL prefix for the ServletContext.
java.util.Enumeration	getServletNames() Deprecated.
java.util.Enumeration	getServlets() Deprecated.
SessionCookieConfig	getSessionCookieConfig() Sets the session cookie configuration
java.util.EnumSet<SessionTrackingMode>	getSessionTrackingModes() The session tracking mode
void	log(java.lang.Exception exception, java.lang.String msg) Deprecated.
void	log(java.lang.String msg) Logs a message.
void	log(java.lang.String message, java.lang.Throwable throwable) Logs a message and a stack trace.
void	removeAttribute(java.lang.String name) Removes an attribute.
void	setAttribute(java.lang.String name, java.lang.Object value) Sets an attribute value.
void	setSessionCookieConfig(SessionCookieConfig cookieConfig) The session cookie configuration
void	setSessionTrackingModes(java.util.EnumSet<SessionTrackingMode> modes) The session tracking mode

Method Detail

getServletContextName

java.lang.String getServletContextName()

Returns the URL prefix for the ServletContext.

getServerInfo

java.lang.String getServerInfo()

Returns a server-specific string identifying the servlet engine.

getMajorVersion

int getMajorVersion()

Returns the major version of the servlet API.

getMinorVersion

int getMinorVersion()

Returns the minor version of the servlet API.

getInitParameter

java.lang.String getInitParameter(java.lang.String name)

Returns the value of an initialization parameter from the configuration file. The Resin configuration looks something like:

 <web-app id='/myapp' app-dir='/www/myapp'>
   <context-param name1='value1'/>
   <context-param name2='value2'/>
 </web-app>
 

Parameters:

name - init parameter name

Returns:

init parameter value

getInitParameterNames

java.util.Enumeration getInitParameterNames()

Returns an enumeration of all init parameter names.

getContext

ServletContext getContext(java.lang.String uri)

Returns the ServletContext for the uri. Note: the uri is not relative to the application.

Parameters:

uri - path relative to the root

Returns:

the ServletContext responsible for the given uri.

getContextPath

java.lang.String getContextPath()

Returns the context-path for the web-application.

getRealPath

java.lang.String getRealPath(java.lang.String uri)

Returns the real file path for the given uri. The file path will be in native path format (with native path separators.)

See ServletRequest to return the real path relative to the request uri.

Parameters:

uri - path relative to the application root to be translated.

Returns:

native file path for the uri.

getRequestDispatcher

RequestDispatcher getRequestDispatcher(java.lang.String uri)

Returns a request dispatcher for later inclusion or forwarding. This is the servlet API equivalent to SSI includes. The uri is relative to the application root.

The following example includes the result of executing inc.jsp into the output stream. If the context path is /myapp, the equivalent uri is /myapp/inc.jsp

   RequestDispatcher disp;
   disp = getRequestDispatcher("/inc.jsp?a=b");
   disp.include(request, response);
 

See ServletRequest to return a request dispatcher relative to the request uri.

Parameters:

uri - path relative to the app root (including query string) for the included file.

Returns:

RequestDispatcher for later inclusion or forwarding.

getNamedDispatcher

RequestDispatcher getNamedDispatcher(java.lang.String servletName)

Returns a request dispatcher based on a servlet name.

Parameters:

servletName - the servlet name to include or forward to.

Returns:

RequestDispatcher for later inclusion or forwarding.

getMimeType

java.lang.String getMimeType(java.lang.String uri)

Returns the mime type for the given uri.

Parameters:

uri - path relative to the application root.

getAttribute

java.lang.Object getAttribute(java.lang.String name)

Returns an attribute value.

Parameters:

name - of the attribute.

Returns:

stored value

getAttributeNames

java.util.Enumeration getAttributeNames()

Returns an enumeration of all the attribute names.

setAttribute

void setAttribute(java.lang.String name,
                  java.lang.Object value)

Sets an attribute value. Because servlets are multithreaded, setting ServletContext attributes will generally need synchronization.

A typical initialization of an application attribute will look like:

 ServletContext app = getServletContext();
 Object value;
 synchronized (app) {
   value = app.getAttribute("cache");
   if (value == null) {
     value = new Cache();
     app.setAttribute("cache", value);
   }
 }
 

Parameters:

name - of the attribute.

value - value to store

removeAttribute

void removeAttribute(java.lang.String name)

Removes an attribute. Because servlets are multithreaded, removing ServletContext attributes will generally need synchronization.

Parameters:

name - of the attribute.

log

void log(java.lang.String msg)

Logs a message.

log

void log(java.lang.String message,
         java.lang.Throwable throwable)

Logs a message and a stack trace.

getResource

java.net.URL getResource(java.lang.String uri)
                         throws java.net.MalformedURLException

Returns the resource for the given uri. In general, the RequestDispatcher routines are more useful.

Parameters:

uri - path relative to the application root.

Throws:

java.net.MalformedURLException

getResourcePaths

java.util.Set getResourcePaths(java.lang.String prefix)

Returns the set all resources held by the application.

getResourceAsStream

java.io.InputStream getResourceAsStream(java.lang.String path)

Returns the resource as a stream. In general, the RequestDispatcher routines are more useful.

Parameters:

uri - path relative to the application root.

Returns:

InputStream to the resource.

getServlet

Servlet getServlet(java.lang.String name)
                   throws ServletException

Deprecated.

Throws:

ServletException

getServlets

java.util.Enumeration getServlets()

Deprecated.

getServletNames

java.util.Enumeration getServletNames()

Deprecated.

log

void log(java.lang.Exception exception,
         java.lang.String msg)

Deprecated.

addServlet

void addServlet(java.lang.String servletName,
                java.lang.String description,
                java.lang.String className,
                java.util.Map<java.lang.String,java.lang.String> initParam,
                int loadOnStartup)

Adds a runtime servlet.

addServletMaping

void addServletMaping(java.lang.String servletName,
                      java.lang.String[] urlPatterns)

Adds a runtime servlet mapping

addFilter

void addFilter(java.lang.String filterName,
               java.lang.String description,
               java.lang.String className,
               java.util.Map<java.lang.String,java.lang.String> initParam)

Adds a filter.

addFilterMapping

void addFilterMapping(java.lang.String filterName,
                      java.lang.String[] urlPatterns,
                      java.lang.String[] servletNames,
                      java.util.EnumSet<DispatcherType> dispatcherTypes,
                      boolean isMatchAfter)

Adds a filter mapping.

setSessionCookieConfig

void setSessionCookieConfig(SessionCookieConfig cookieConfig)

The session cookie configuration

getSessionCookieConfig

SessionCookieConfig getSessionCookieConfig()

Sets the session cookie configuration

setSessionTrackingModes

void setSessionTrackingModes(java.util.EnumSet<SessionTrackingMode> modes)

The session tracking mode

getSessionTrackingModes

java.util.EnumSet<SessionTrackingMode> getSessionTrackingModes()

The session tracking mode