Interface ServletContext


  • public interface ServletContext
    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.

    The ServletContext object is contained within the ServletConfig object, which the Web server provides the servlet when the servlet is initialized.

    See Also:
    Servlet.getServletConfig(), ServletConfig.getServletContext()
    • Field Summary

      Fields 
      Modifier and Type Field Description
      static java.lang.String ORDERED_LIBS
      The name of the ServletContext attribute that holds the ordered list of web fragments for this web application.
      static java.lang.String TEMPDIR
      The name of the ServletContext attribute that holds the temporary file location for the web application.
    • Field Detail

      • TEMPDIR

        static final java.lang.String TEMPDIR
        The name of the ServletContext attribute that holds the temporary file location for the web application.
        See Also:
        Constant Field Values
      • ORDERED_LIBS

        static final java.lang.String ORDERED_LIBS
        The name of the ServletContext attribute that holds the ordered list of web fragments for this web application.
        Since:
        Servlet 3.0
        See Also:
        Constant Field Values
    • Method Detail

      • getContextPath

        java.lang.String getContextPath()
        Return the main path associated with this context.
        Returns:
        The main context path
        Since:
        Servlet 2.5
      • getContext

        ServletContext getContext​(java.lang.String uripath)
        Returns a ServletContext 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 - a String 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:
        RequestDispatcher
      • getMajorVersion

        int getMajorVersion()
        Returns the major version of the Java Servlet API that this servlet container supports. All implementations that comply with Version 5.0 must have this method return the integer 5.
        Returns:
        5
      • getMinorVersion

        int getMinorVersion()
        Returns the minor version of the Servlet API that this servlet container supports. All implementations that comply with Version 5.0 must have this method return the integer 0.
        Returns:
        0
      • getMimeType

        java.lang.String getMimeType​(java.lang.String file)
        Returns the MIME type of the specified file, or null 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 - a String specifying the name of a file
        Returns:
        a String specifying the file's MIME type
      • getResourcePaths

        java.util.Set<java.lang.String> getResourcePaths​(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:
        path - 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

        java.net.URL getResource​(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 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 a RequestDispatcher 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 - a String 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:
        java.net.MalformedURLException - if the pathname is not given in the correct form
      • getResourceAsStream

        java.io.InputStream getResourceAsStream​(java.lang.String path)
        Returns the resource located at the named path as an InputStream object.

        The data in the InputStream can be of any type or length. The path must be specified according to the rules given in getResource. This method returns null 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:
        path - a String specifying the path to the resource
        Returns:
        the InputStream returned to the servlet, or null if no resource exists at the specified path
      • getRequestDispatcher

        RequestDispatcher getRequestDispatcher​(java.lang.String path)
        Returns a RequestDispatcher object that acts as a wrapper for the resource located at the given path. A RequestDispatcher 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 a RequestDispatcher for resources in foreign contexts. This method returns null if the ServletContext cannot return a RequestDispatcher.

        Parameters:
        path - a String specifying the pathname to the resource
        Returns:
        a RequestDispatcher object that acts as a wrapper for the resource at the specified path, or null if the ServletContext cannot return a RequestDispatcher
        See Also:
        RequestDispatcher, getContext(java.lang.String)
      • getNamedDispatcher

        RequestDispatcher getNamedDispatcher​(java.lang.String name)
        Returns a RequestDispatcher 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 the ServletContext cannot return a RequestDispatcher for any reason.

        Parameters:
        name - a String specifying the name of a servlet to wrap
        Returns:
        a RequestDispatcher object that acts as a wrapper for the named servlet, or null if the ServletContext cannot return a RequestDispatcher
        See Also:
        RequestDispatcher, getContext(java.lang.String), ServletConfig.getServletName()
      • getServlet

        @Deprecated
        Servlet getServlet​(java.lang.String name)
                    throws ServletException
        Deprecated.
        As of Java Servlet API 2.1, with no direct replacement.
        Do not use. This method was originally defined to retrieve a servlet from a ServletContext. In this version, this method always returns null 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.

        Parameters:
        name - Not used
        Returns:
        Always null
        Throws:
        ServletException - never
      • getServlets

        @Deprecated
        java.util.Enumeration<Servlet> getServlets()
        Deprecated.
        As of Java Servlet API 2.0, with no replacement.
        Do not use. 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.
        Returns:
        Always and empty Enumeration
      • getServletNames

        @Deprecated
        java.util.Enumeration<java.lang.String> getServletNames()
        Deprecated.
        As of Java Servlet API 2.1, with no replacement.
        Do not use. 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 empty Enumeration and remains only to preserve binary compatibility. This method will be permanently removed in a future version of the Java Servlet API.
        Returns:
        Always and empty Enumeration
      • log

        void log​(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 - a String specifying the message to be written to the log file
      • log

        @Deprecated
        void log​(java.lang.Exception exception,
                 java.lang.String msg)
        Deprecated.
        As of Java Servlet API 2.1, use log(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.

        Do not use.
        Parameters:
        exception - The exception to log
        msg - The message to log with the exception
      • log

        void log​(java.lang.String message,
                 java.lang.Throwable throwable)
        Writes an explanatory message and a stack trace for a given Throwable 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 - a String that describes the error or exception
        throwable - the Throwable error or exception
      • getRealPath

        java.lang.String getRealPath​(java.lang.String path)
        Returns a String 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 - a String specifying a virtual path
        Returns:
        a String specifying the real path, or null if the translation cannot be performed
      • getServerInfo

        java.lang.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
      • getInitParameter

        java.lang.String getInitParameter​(java.lang.String name)
        Returns a String containing the value of the named context-wide initialization parameter, or null 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 web site administrator's email address or the name of a system that holds critical data.

        Parameters:
        name - a String containing the name of the parameter whose value is requested
        Returns:
        a String containing the value of the initialization parameter
        Throws:
        java.lang.NullPointerException - If the provided parameter name is null
        See Also:
        ServletConfig.getInitParameter(java.lang.String)
      • getInitParameterNames

        java.util.Enumeration<java.lang.String> getInitParameterNames()
        Returns the names of the context's initialization parameters as an Enumeration of String objects, or an empty Enumeration if the context has no initialization parameters.
        Returns:
        an Enumeration of String objects containing the names of the context's initialization parameters
        See Also:
        ServletConfig.getInitParameter(java.lang.String)
      • setInitParameter

        boolean setInitParameter​(java.lang.String name,
                                 java.lang.String value)
        Set the given initialisation parameter to the given value.
        Parameters:
        name - Name of initialisation parameter
        value - Value for initialisation parameter
        Returns:
        true if the call succeeds or false if the call fails because an initialisation parameter with the same name has already been set
        Throws:
        java.lang.IllegalStateException - If initialisation of this ServletContext has already completed
        java.lang.UnsupportedOperationException - If called from a ServletContextListener.contextInitialized(ServletContextEvent) method of a ServletContextListener that was not defined in a web.xml file, a web-fragment.xml file nor annotated with WebListener. For example, a ServletContextListener defined in a TLD would not be able to use this method.
        java.lang.NullPointerException - If the provided parameter name is null
        Since:
        Servlet 3.0
      • getAttribute

        java.lang.Object getAttribute​(java.lang.String name)
        Returns the servlet container attribute with the given name, or null 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 using getAttributeNames.

        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 matching java.*, javax.*, and sun.*.

        Parameters:
        name - a String specifying the name of the attribute
        Returns:
        an Object containing the value of the attribute, or null if no attribute exists matching the given name
        Throws:
        java.lang.NullPointerException - If the provided attribute name is null
        See Also:
        getAttributeNames()
      • getAttributeNames

        java.util.Enumeration<java.lang.String> getAttributeNames()
        Returns an Enumeration containing the attribute names available within this servlet context. Use the getAttribute(java.lang.String) method with an attribute name to get the value of an attribute.
        Returns:
        an Enumeration of attribute names
        See Also:
        getAttribute(java.lang.String)
      • setAttribute

        void setAttribute​(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 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.*, and sun.*.

        Parameters:
        name - a String specifying the name of the attribute
        object - an Object representing the attribute to be bound
        Throws:
        java.lang.NullPointerException - If the provided attribute name is null
      • removeAttribute

        void removeAttribute​(java.lang.String name)
        Removes the attribute with the given name from the servlet context. After removal, subsequent calls to getAttribute(java.lang.String) to retrieve the attribute's value will return null.

        If listeners are configured on the ServletContext the container notifies them accordingly.

        Parameters:
        name - a String specifying the name of the attribute to be removed
      • getServletContextName

        java.lang.String getServletContextName()
        Returns the name of this web application corresponding 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
      • addServlet

        ServletRegistration.Dynamic addServlet​(java.lang.String servletName,
                                               java.lang.String className)
        Register a servlet implementation for use in this ServletContext.
        Parameters:
        servletName - The name of the servlet to register
        className - The implementation class for the servlet
        Returns:
        The registration object that enables further configuration
        Throws:
        java.lang.IllegalStateException - If the context has already been initialised
        java.lang.UnsupportedOperationException - If called from a ServletContextListener.contextInitialized(ServletContextEvent) method of a ServletContextListener that was not defined in a web.xml file, a web-fragment.xml file nor annotated with WebListener. For example, a ServletContextListener defined in a TLD would not be able to use this method.
        Since:
        Servlet 3.0
      • addServlet

        ServletRegistration.Dynamic addServlet​(java.lang.String servletName,
                                               Servlet servlet)
        Register a servlet instance for use in this ServletContext.
        Parameters:
        servletName - The name of the servlet to register
        servlet - The Servlet instance to register
        Returns:
        The registration object that enables further configuration
        Throws:
        java.lang.IllegalStateException - If the context has already been initialised
        java.lang.UnsupportedOperationException - If called from a ServletContextListener.contextInitialized(ServletContextEvent) method of a ServletContextListener that was not defined in a web.xml file, a web-fragment.xml file nor annotated with WebListener. For example, a ServletContextListener defined in a TLD would not be able to use this method.
        Since:
        Servlet 3.0
      • addJspFile

        ServletRegistration.Dynamic addJspFile​(java.lang.String jspName,
                                               java.lang.String jspFile)
        Parameters:
        jspName - The servlet name under which this JSP file should be registered
        jspFile - The path, relative to the web application root, for the JSP file to be used for this servlet
        Returns:
        a ServletRegistration.Dynamic object that can be used to further configure the servlet
        Since:
        Servlet 4.0
      • getServletRegistration

        ServletRegistration getServletRegistration​(java.lang.String servletName)
        Obtain the details of the named servlet.
        Parameters:
        servletName - The name of the Servlet of interest
        Returns:
        The registration details for the named Servlet or null if no Servlet has been registered with the given name
        Throws:
        java.lang.UnsupportedOperationException - If called from a ServletContextListener.contextInitialized(ServletContextEvent) method of a ServletContextListener that was not defined in a web.xml file, a web-fragment.xml file nor annotated with WebListener. For example, a ServletContextListener defined in a TLD would not be able to use this method.
        Since:
        Servlet 3.0
      • getClassLoader

        java.lang.ClassLoader getClassLoader()
        Get the web application class loader associated with this ServletContext.
        Returns:
        The associated web application class loader
        Throws:
        java.lang.UnsupportedOperationException - If called from a ServletContextListener.contextInitialized(ServletContextEvent) method of a ServletContextListener that was not defined in a web.xml file, a web-fragment.xml file nor annotated with WebListener. For example, a ServletContextListener defined in a TLD would not be able to use this method.
        java.lang.SecurityException - if access to the class loader is prevented by a SecurityManager
        Since:
        Servlet 3.0
      • declareRoles

        void declareRoles​(java.lang.String... roleNames)
        Add to the declared roles for this ServletContext.
        Parameters:
        roleNames - The roles to add
        Throws:
        java.lang.UnsupportedOperationException - If called from a ServletContextListener.contextInitialized(ServletContextEvent) method of a ServletContextListener that was not defined in a web.xml file, a web-fragment.xml file nor annotated with WebListener. For example, a ServletContextListener defined in a TLD would not be able to use this method.
        java.lang.IllegalArgumentException - If the list of roleNames is null or empty
        java.lang.IllegalStateException - If the ServletContext has already been initialised
        Since:
        Servlet 3.0
      • getVirtualServerName

        java.lang.String getVirtualServerName()
        Get the primary name of the virtual host on which this context is deployed. The name may or may not be a valid host name.
        Returns:
        The primary name of the virtual host on which this context is deployed
        Since:
        Servlet 3.1
      • setSessionTimeout

        void setSessionTimeout​(int sessionTimeout)
        Set the default session timeout. This method may only be called before the ServletContext is initialised.
        Parameters:
        sessionTimeout - The new default session timeout in minutes.
        Throws:
        java.lang.UnsupportedOperationException - If called from a ServletContextListener.contextInitialized(ServletContextEvent) method of a ServletContextListener that was not defined in a web.xml file, a web-fragment.xml file nor annotated with WebListener. For example, a ServletContextListener defined in a TLD would not be able to use this method.
        java.lang.IllegalStateException - If the ServletContext has already been initialised
        Since:
        Servlet 4.0
      • getRequestCharacterEncoding

        java.lang.String getRequestCharacterEncoding()
        Get the default character encoding for reading request bodies.
        Returns:
        The character encoding name or null if no default has been specified
        Throws:
        java.lang.UnsupportedOperationException - If called from a ServletContextListener.contextInitialized(ServletContextEvent) method of a ServletContextListener that was not defined in a web.xml file, a web-fragment.xml file nor annotated with WebListener. For example, a ServletContextListener defined in a TLD would not be able to use this method.
        Since:
        Servlet 4.0
      • setRequestCharacterEncoding

        void setRequestCharacterEncoding​(java.lang.String encoding)
        Set the default character encoding to use for reading request bodies. Calling this method will over-ride any value set in the deployment descriptor.
        Parameters:
        encoding - The name of the character encoding to use
        Throws:
        java.lang.UnsupportedOperationException - If called from a ServletContextListener.contextInitialized(ServletContextEvent) method of a ServletContextListener that was not defined in a web.xml file, a web-fragment.xml file nor annotated with WebListener. For example, a ServletContextListener defined in a TLD would not be able to use this method.
        java.lang.IllegalStateException - If the ServletContext has already been initialised
        Since:
        Servlet 4.0
      • getResponseCharacterEncoding

        java.lang.String getResponseCharacterEncoding()
        Get the default character encoding for writing response bodies.
        Returns:
        The character encoding name or null if no default has been specified
        Throws:
        java.lang.UnsupportedOperationException - If called from a ServletContextListener.contextInitialized(ServletContextEvent) method of a ServletContextListener that was not defined in a web.xml file, a web-fragment.xml file nor annotated with WebListener. For example, a ServletContextListener defined in a TLD would not be able to use this method.
        Since:
        Servlet 4.0
      • setResponseCharacterEncoding

        void setResponseCharacterEncoding​(java.lang.String encoding)
        Set the default character encoding to use for writing response bodies. Calling this method will over-ride any value set in the deployment descriptor.
        Parameters:
        encoding - The name of the character encoding to use
        Throws:
        java.lang.UnsupportedOperationException - If called from a ServletContextListener.contextInitialized(ServletContextEvent) method of a ServletContextListener that was not defined in a web.xml file, a web-fragment.xml file nor annotated with WebListener. For example, a ServletContextListener defined in a TLD would not be able to use this method.
        java.lang.IllegalStateException - If the ServletContext has already been initialised
        Since:
        Servlet 4.0