Interface ServletContext
There is one context per "web application" per Java Virtual Machine. (A
"web application" is a collection of servlets and content installed under a
specific subset of the server's URL namespace such as /catalog
and possibly installed via a .war
file.)
In the case of a web application marked "distributed" in its deployment descriptor, there will be one context instance for each virtual machine. In this situation, the context cannot be used as a location to share global information (because the information won't be truly global). Use an external resource like a database instead.
The ServletContext
object is contained within
the ServletConfig
object, which the Web server provides the
servlet when the servlet is initialized.
- Version:
- $Version$
- Author:
- Various
- See Also:
-
Method Summary
Modifier and TypeMethodDescriptiongetAttribute
(String name) Returns the servlet container attribute with the given name, ornull
if there is no attribute by that name.Returns anEnumeration
containing the attribute names available within this servlet context.getContext
(String uripath) Returns aServletContext
object that corresponds to a specified URL on the server.getInitParameter
(String name) Returns aString
containing the value of the named context-wide initialization parameter, ornull
if the parameter does not exist.Returns the names of the context's initialization parameters as anEnumeration
ofString
objects, or an emptyEnumeration
if the context has no initialization parameters.int
Returns the major version of the Java Servlet API that this servlet container supports.getMimeType
(String file) Returns the MIME type of the specified file, ornull
if the MIME type is not known.int
Returns the minor version of the Servlet API that this servlet container supports.getNamedDispatcher
(String name) Returns aRequestDispatcher
object that acts as a wrapper for the named servlet.getRealPath
(String path) Returns aString
containing the real path for a given virtual path.getRequestDispatcher
(String path) Returns aRequestDispatcher
object that acts as a wrapper for the resource located at the given path.getResource
(String path) Returns a URL to the resource that is mapped to a specified path.getResourceAsStream
(String path) Returns the resource located at the named path as anInputStream
object.getResourcePaths
(String path) Returns a directory-like listing of all the paths to resources within the web application whose longest sub-path matches the supplied path argument.Returns the name and version of the servlet container on which the servlet is running.getServlet
(String name) Deprecated.As of Java Servlet API 2.1, with no direct replacement.Returns the name of this web application correponding to this ServletContext as specified in the deployment descriptor for this web application by the display-name element.Deprecated.As of Java Servlet API 2.1, with no replacement.Deprecated.As of Java Servlet API 2.0, with no replacement.void
Deprecated.As of Java Servlet API 2.1, uselog(String message, Throwable throwable)
instead.void
Writes the specified message to a servlet log file, usually an event log.void
Writes an explanatory message and a stack trace for a givenThrowable
exception to the servlet log file.void
removeAttribute
(String name) Removes the attribute with the given name from the servlet context.void
setAttribute
(String name, Object object) Binds an object to a given attribute name in this servlet context.
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Method Details
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getContext
Returns aServletContext
object that corresponds to a specified URL on the server.This method allows servlets to gain access to the context for various parts of the server, and as needed obtain
RequestDispatcher
objects from the context. The given path must be begin with "/", is interpreted relative to the server's document root and is matched against the context roots of other web applications hosted on this container.In a security conscious environment, the servlet container may return
null
for a given URL.- Parameters:
uripath
- aString
specifying the context path of another web application in the container.- Returns:
- the
ServletContext
object that corresponds to the named URL, or null if either none exists or the container wishes to restrict this access. - See Also:
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getMajorVersion
int getMajorVersion()Returns the major version of the Java Servlet API that this servlet container supports. All implementations that comply with Version 2.3 must have this method return the integer 2.- Returns:
- 2
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getMinorVersion
int getMinorVersion()Returns the minor version of the Servlet API that this servlet container supports. All implementations that comply with Version 2.3 must have this method return the integer 3.- Returns:
- 3
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getMimeType
Returns the MIME type of the specified file, ornull
if the MIME type is not known. The MIME type is determined by the configuration of the servlet container, and may be specified in a web application deployment descriptor. Common MIME types are"text/html"
and"image/gif"
.- Parameters:
file
- aString
specifying the name of a file- Returns:
- a
String
specifying the file's MIME type
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getResourcePaths
Returns a directory-like listing of all the paths to resources within the web application whose longest sub-path matches the supplied path argument. Paths indicating subdirectory paths end with a '/'. The returned paths are all relative to the root of the web application and have a leading '/'. For example, for a web application containing
/welcome.html
/catalog/index.html
/catalog/products.html
/catalog/offers/books.html
/catalog/offers/music.html
/customer/login.jsp
/WEB-INF/web.xml
/WEB-INF/classes/com.acme.OrderServlet.class,
getResourcePaths("/") returns {"/welcome.html", "/catalog/", "/customer/", "/WEB-INF/"}
getResourcePaths("/catalog/") returns {"/catalog/index.html", "/catalog/products.html", "/catalog/offers/"}.- Parameters:
the
- partial path used to match the resources, which must start with a /- Returns:
- a Set containing the directory listing, or null if there are no resources in the web application whose path begins with the supplied path.
- Since:
- Servlet 2.3
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getResource
Returns a URL to the resource that is mapped to a specified path. The path must begin with a "/" and is interpreted as relative to the current context root.This method allows the servlet container to make a resource available to servlets from any source. Resources can be located on a local or remote file system, in a database, or in a
.war
file.The servlet container must implement the URL handlers and
URLConnection
objects that are necessary to access the resource.This method returns
null
if no resource is mapped to the pathname.Some containers may allow writing to the URL returned by this method using the methods of the URL class.
The resource content is returned directly, so be aware that requesting a
.jsp
page returns the JSP source code. Use aRequestDispatcher
instead to include results of an execution.This method has a different purpose than
java.lang.Class.getResource
, which looks up resources based on a class loader. This method does not use class loaders.- Parameters:
path
- aString
specifying the path to the resource- Returns:
- the resource located at the named path,
or
null
if there is no resource at that path - Throws:
MalformedURLException
- if the pathname is not given in the correct form
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getResourceAsStream
Returns the resource located at the named path as anInputStream
object.The data in the
InputStream
can be of any type or length. The path must be specified according to the rules given ingetResource
. This method returnsnull
if no resource exists at the specified path.Meta-information such as content length and content type that is available via
getResource
method is lost when using this method.The servlet container must implement the URL handlers and
URLConnection
objects necessary to access the resource.This method is different from
java.lang.Class.getResourceAsStream
, which uses a class loader. This method allows servlet containers to make a resource available to a servlet from any location, without using a class loader.- Parameters:
name
- aString
specifying the path to the resource- Returns:
- the
InputStream
returned to the servlet, ornull
if no resource exists at the specified path
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getRequestDispatcher
Returns aRequestDispatcher
object that acts as a wrapper for the resource located at the given path. ARequestDispatcher
object can be used to forward a request to the resource or to include the resource in a response. The resource can be dynamic or static.The pathname must begin with a "/" and is interpreted as relative to the current context root. Use
getContext
to obtain aRequestDispatcher
for resources in foreign contexts. This method returnsnull
if theServletContext
cannot return aRequestDispatcher
.- Parameters:
path
- aString
specifying the pathname to the resource- Returns:
- a
RequestDispatcher
object that acts as a wrapper for the resource at the specified path - See Also:
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getNamedDispatcher
Returns aRequestDispatcher
object that acts as a wrapper for the named servlet.Servlets (and JSP pages also) may be given names via server administration or via a web application deployment descriptor. A servlet instance can determine its name using
ServletConfig.getServletName()
.This method returns
null
if theServletContext
cannot return aRequestDispatcher
for any reason.- Parameters:
name
- aString
specifying the name of a servlet to wrap- Returns:
- a
RequestDispatcher
object that acts as a wrapper for the named servlet - See Also:
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getServlet
Deprecated.As of Java Servlet API 2.1, with no direct replacement.This method was originally defined to retrieve a servlet from a
ServletContext
. In this version, this method always returnsnull
and remains only to preserve binary compatibility. This method will be permanently removed in a future version of the Java Servlet API.In lieu of this method, servlets can share information using the
ServletContext
class and can perform shared business logic by invoking methods on common non-servlet classes.- Throws:
ServletException
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getServlets
Enumeration getServlets()Deprecated.As of Java Servlet API 2.0, with no replacement.This method was originally defined to return an
Enumeration
of all the servlets known to this servlet context. In this version, this method always returns an empty enumeration and remains only to preserve binary compatibility. This method will be permanently removed in a future version of the Java Servlet API. -
getServletNames
Enumeration getServletNames()Deprecated.As of Java Servlet API 2.1, with no replacement.This method was originally defined to return an
Enumeration
of all the servlet names known to this context. In this version, this method always returns an emptyEnumeration
and remains only to preserve binary compatibility. This method will be permanently removed in a future version of the Java Servlet API. -
log
Writes the specified message to a servlet log file, usually an event log. The name and type of the servlet log file is specific to the servlet container.- Parameters:
msg
- aString
specifying the message to be written to the log file
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log
Deprecated.As of Java Servlet API 2.1, uselog(String message, Throwable throwable)
instead.This method was originally defined to write an exception's stack trace and an explanatory error message to the servlet log file.
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log
Writes an explanatory message and a stack trace for a givenThrowable
exception to the servlet log file. The name and type of the servlet log file is specific to the servlet container, usually an event log.- Parameters:
message
- aString
that describes the error or exceptionthrowable
- theThrowable
error or exception
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getRealPath
Returns aString
containing the real path for a given virtual path. For example, the path "/index.html" returns the absolute file path on the server's filesystem would be served by a request for "http://host/contextPath/index.html", where contextPath is the context path of this ServletContext..The real path returned will be in a form appropriate to the computer and operating system on which the servlet container is running, including the proper path separators. This method returns
null
if the servlet container cannot translate the virtual path to a real path for any reason (such as when the content is being made available from a.war
archive).- Parameters:
path
- aString
specifying a virtual path- Returns:
- a
String
specifying the real path, or null if the translation cannot be performed
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getServerInfo
String getServerInfo()Returns the name and version of the servlet container on which the servlet is running.The form of the returned string is servername/versionnumber. For example, the JavaServer Web Development Kit may return the string
JavaServer Web Dev Kit/1.0
.The servlet container may return other optional information after the primary string in parentheses, for example,
JavaServer Web Dev Kit/1.0 (JDK 1.1.6; Windows NT 4.0 x86)
.- Returns:
- a
String
containing at least the servlet container name and version number
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getInitParameter
Returns aString
containing the value of the named context-wide initialization parameter, ornull
if the parameter does not exist.This method can make available configuration information useful to an entire "web application". For example, it can provide a webmaster's email address or the name of a system that holds critical data.
- Parameters:
name
- aString
containing the name of the parameter whose value is requested- Returns:
- a
String
containing at least the servlet container name and version number - See Also:
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getInitParameterNames
Enumeration getInitParameterNames()Returns the names of the context's initialization parameters as anEnumeration
ofString
objects, or an emptyEnumeration
if the context has no initialization parameters.- Returns:
- an
Enumeration
ofString
objects containing the names of the context's initialization parameters - See Also:
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getAttribute
Returns the servlet container attribute with the given name, ornull
if there is no attribute by that name. An attribute allows a servlet container to give the servlet additional information not already provided by this interface. See your server documentation for information about its attributes. A list of supported attributes can be retrieved usinggetAttributeNames
.The attribute is returned as a
java.lang.Object
or some subclass. Attribute names should follow the same convention as package names. The Java Servlet API specification reserves names matchingjava.*
,javax.*
, andsun.*
.- Parameters:
name
- aString
specifying the name of the attribute- Returns:
- an
Object
containing the value of the attribute, ornull
if no attribute exists matching the given name - See Also:
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getAttributeNames
Enumeration getAttributeNames()Returns anEnumeration
containing the attribute names available within this servlet context. Use thegetAttribute(java.lang.String)
method with an attribute name to get the value of an attribute.- Returns:
- an
Enumeration
of attribute names - See Also:
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setAttribute
Binds an object to a given attribute name in this servlet context. If the name specified is already used for an attribute, this method will replace the attribute with the new to the new attribute.If listeners are configured on the
ServletContext
the container notifies them accordingly.If a null value is passed, the effect is the same as calling
removeAttribute()
.Attribute names should follow the same convention as package names. The Java Servlet API specification reserves names matching
java.*
,javax.*
, andsun.*
.- Parameters:
name
- aString
specifying the name of the attributeobject
- anObject
representing the attribute to be bound
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removeAttribute
Removes the attribute with the given name from the servlet context. After removal, subsequent calls togetAttribute(java.lang.String)
to retrieve the attribute's value will returnnull
.If listeners are configured on the
ServletContext
the container notifies them accordingly.- Parameters:
name
- aString
specifying the name of the attribute to be removed
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getServletContextName
String getServletContextName()Returns the name of this web application correponding to this ServletContext as specified in the deployment descriptor for this web application by the display-name element.- Returns:
- The name of the web application or null if no name has been declared in the deployment descriptor.
- Since:
- Servlet 2.3
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