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Interface ServletContext

public interfaceServletContext

Defines a set of methods that a servlet uses to communicate with its servlet container, for example, to get the MIME type of a file, dispatch requests, or write to a log file.

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.

TheServletContext object is contained within theServletConfig object, which the Web server provides the servlet when the servlet is initialized.

See Also:

Servlet.getServletConfig(),ServletConfig.getServletContext()

getContext

publicServletContextgetContext(java.lang.String uripath)

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 obtainRequestDispatcher 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 returnnull for a given URL.

Parameters:

uripath - aString specifying the context path ofanother web application in the container.

Returns:

theServletContext object thatcorresponds to the named URL, or null if eithernone exists or the container wishes to restrict this access.

See Also:

RequestDispatcher

getMajorVersion

public intgetMajorVersion()

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

getMinorVersion

public intgetMinorVersion()

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

getMimeType

public java.lang.StringgetMimeType(java.lang.String file)

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 nameof a file

Returns:

aString specifying the file's MIME type

getResourcePaths

public java.util.SetgetResourcePaths(java.lang.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. 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

getResource

public java.net.URLgetResource(java.lang.String path)                         throws java.net.MalformedURLException

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 andURLConnection objects that are necessary to access the resource.

This method returnsnull 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 thanjava.lang.Class.getResource, which looks up resources based on a class loader. This method does not use class loaders.

Parameters:

path - aString specifyingthe path to the resource

Returns:

the resource located at the named path, ornull if there is no resourceat that path

Throws:

java.net.MalformedURLException - if the pathname is not given in the correct form

getResourceAsStream

public java.io.InputStreamgetResourceAsStream(java.lang.String path)

Returns the resource located at the named path as anInputStream object.

The data in theInputStream 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 viagetResource method is lost when using this method.

The servlet container must implement the URL handlers andURLConnection objects necessary to access the resource.

This method is different fromjava.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 pathto the resource

Returns:

theInputStream returned to the servlet, ornull if no resourceexists at the specified path

getRequestDispatcher

publicRequestDispatchergetRequestDispatcher(java.lang.String path)

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. UsegetContext to obtain aRequestDispatcher for resources in foreign contexts. This method returnsnull if theServletContext cannot return aRequestDispatcher.

Parameters:

path - aString specifying the pathnameto the resource

Returns:

aRequestDispatcher objectthat acts as a wrapper for the resourceat the specified path

See Also:

RequestDispatcher,getContext(java.lang.String)

getNamedDispatcher

publicRequestDispatchergetNamedDispatcher(java.lang.String name)

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 usingServletConfig.getServletName().

This method returnsnull if theServletContext cannot return aRequestDispatcher for any reason.

Parameters:

name - aString specifying the nameof a servlet to wrap

Returns:

aRequestDispatcher objectthat acts as a wrapper for the named servlet

See Also:

RequestDispatcher,getContext(java.lang.String),ServletConfig.getServletName()

getServlet

publicServletgetServlet(java.lang.String name)                   throwsServletException

Deprecated. As of Java Servlet API 2.1, with no direct replacement.

This method was originally defined to retrieve a servlet from aServletContext. 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 theServletContext class and can perform shared business logic by invoking methods on common non-servlet classes.

getServlets

public java.util.EnumerationgetServlets()

Deprecated. As of Java Servlet API 2.0, with no replacement.

This method was originally defined to return anEnumeration 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

public java.util.EnumerationgetServletNames()

Deprecated. As of Java Servlet API 2.1, with no replacement.

This method was originally defined to return anEnumeration 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

public voidlog(java.lang.String msg)

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

log

public voidlog(java.lang.Exception exception,                java.lang.String msg)

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.

log

public voidlog(java.lang.String message,                java.lang.Throwable throwable)

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 exception

throwable - theThrowable error or exception

getRealPath

public java.lang.StringgetRealPath(java.lang.String path)

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 returnsnull 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:

aString specifying the real path, or null if the translation cannot be performed

getServerInfo

public java.lang.StringgetServerInfo()

Returns the name and version of the servlet container on which the servlet is running.

The form of the returned string isservername/versionnumber. For example, the JavaServer Web Development Kit may return the stringJavaServer 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:

aString containing at least the servlet container name and version number

getInitParameter

public java.lang.StringgetInitParameter(java.lang.String name)

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:

aString containing at least the servlet container name and version number

See Also:

ServletConfig.getInitParameter(java.lang.String)

getInitParameterNames

public java.util.EnumerationgetInitParameterNames()

Returns the names of the context's initialization parameters as anEnumeration ofString objects, or an emptyEnumeration if the context has no initialization parameters.

Returns:

anEnumeration ofString objects containing the names of the context's initialization parameters

See Also:

ServletConfig.getInitParameter(java.lang.String)

getAttribute

public java.lang.ObjectgetAttribute(java.lang.String name)

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 ajava.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:

anObject containing the value of the attribute, ornullif no attribute exists matching the givenname

See Also:

getAttributeNames()

getAttributeNames

public java.util.EnumerationgetAttributeNames()

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:

anEnumeration of attribute names

See Also:

getAttribute(java.lang.String)

setAttribute

public voidsetAttribute(java.lang.String name,                         java.lang.Object object)

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 theServletContext the container notifies them accordingly.

If a null value is passed, the effect is the same as callingremoveAttribute().

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

object - anObject representing theattribute to be bound

removeAttribute

public voidremoveAttribute(java.lang.String name)

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 theServletContext the container notifies them accordingly.

Parameters:

name - aString specifying the name of the attribute to be removed

getServletContextName

public java.lang.StringgetServletContextName()

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