前言

　　開心一刻

　　　　過年女婿來岳父家走親戚，當時小舅子主就問：姐夫，你什麼時候能給我姐幸福，讓我姐好好享受生活的美好。你們這輩子不準備買一套大點的房子嗎？姐夫說：現在沒錢啊！不過我有一個美麗可愛的女兒，等長大後找個有錢的老公嫁了，那時我就能和你姐一起住大房子了。岳父不樂意的說了一句：當初我也是這麼認為的，可惜未能如願。

　　路漫漫其修遠兮，吾將上下而求索！

ServletContext

　　ServletContext介紹

　　　　定義了servlet與其servlet容器通訊的一些列方法，例如，獲取檔案的MIME型別，分派請求或寫入日誌檔案。

　　　　Servlet的執行模式是一個典型的“握手型的互動式”執行模式。所謂“握手型的互動式”就是兩個模組為了交換資料通常都會準備一個交易場景，這個場景一直跟隨這個交易過程直到這個交易完成為止。這個交易場景的初始化是根據這次交易物件指定的引數來定製的，這些制定引數通常就是一個配置類。所以對號入座，交易場景由ServletContext來描述，而定製的引數集合由ServletConfig來描述。而ServletRequest和ServletResponse就是要互動的具體物件，它們通常都作為運輸工具來傳遞互動結果。ServletContext，即servlet上下文，用於存放web應用資訊；每個Java虛擬機器每個Web專案只有一個ServletContext，它是由Web伺服器建立，代表當前web應用。

　　Servlet 3.0規範之前

　　　　我們採用2.5來看下原始碼

　　　　maven依賴

<dependency>
    <groupId>javax.servlet</groupId>
    <artifactId>servlet-api</artifactId>
    <version>2.5</version>
    <scope>provided</scope>
</dependency>

　　　　原始碼

/*
 

 * The contents of this file are subject to the terms
 * of the Common Development and Distribution License
 * (the "License").  You may not use this file except
 * in compliance with the License.
 *
 * You can obtain a copy of the license at
 * glassfish/bootstrap/legal/CDDLv1.0.txt or
 * https://glassfish.dev.java.net/public/CDDLv1.0.html.
 

 * See the License for the specific language governing
 * permissions and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL
 * HEADER in each file and include the License file at
 * glassfish/bootstrap/legal/CDDLv1.0.txt.  If applicable,
 * add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your
 * own identifying information: Portions Copyright [yyyy]
 * [name of copyright owner]
 *
 * Copyright 2005 Sun Microsystems, Inc. All rights reserved.
 *
 * Portions Copyright Apache Software Foundation.
 */

package javax.servlet;

import java.io.InputStream;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.Enumeration;
import java.util.Set;


/**
 * 
 * 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.
 *
 * <p>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 <code>/catalog</code>
 * and possibly installed via a <code>.war</code> file.) 
 *
 * <p>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.
 *
 * <p>The <code>ServletContext</code> object is contained within 
 * the {@link ServletConfig} object, which the Web server provides the
 * servlet when the servlet is initialized.
 *
 * @author     Various
 *
 * @see     Servlet#getServletConfig
 * @see     ServletConfig#getServletContext
 *
 */

public interface ServletContext {

    /**
     * Returns the context path of the web application.
     *
     * <p>The context path is the portion of the request URI that is used
     * to select the context of the request. The context path always comes
     * first in a request URI. The path starts with a "/" character but does
     * not end with a "/" character. For servlets in the default (root)
     * context, this method returns "".
     *
     * <p>It is possible that a servlet container may match a context by
     * more than one context path. In such cases the
     * {@link javax.servlet.http.HttpServletRequest#getContextPath()}
     * will return the actual context path used by the request and it may
     * differ from the path returned by this method.
     * The context path returned by this method should be considered as the
     * prime or preferred context path of the application.
     *
     * @return The context path of the web application, or "" for the
     * default (root) context
     *
     * @see javax.servlet.http.HttpServletRequest#getContextPath()
     *
     * @since Servlet 2.5
     */
    public String getContextPath();


    /**
     * Returns a <code>ServletContext</code> object that 
     * corresponds to a specified URL on the server.
     *
     * <p>This method allows servlets to gain
     * access to the context for various parts of the server, and as
     * needed obtain {@link 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.
     * 
     * <p>In a security conscious environment, the servlet container may
     * return <code>null</code> for a given URL.
     *       
     * @param uripath     a <code>String</code> specifying the context path of
     *            another web application in the container.
     * @return        the <code>ServletContext</code> object that
     *            corresponds to the named URL, or null if either
            none exists or the container wishes to restrict 
     *             this access.
     *
     * @see         RequestDispatcher
     *
     */

    public ServletContext getContext(String uripath);
    
    

    /**
     * Returns the major version of the Java Servlet API that this
     * servlet container supports. All implementations that comply
     * with Version 2.5 must have this method
     * return the integer 2.
     *
     * @return         2
     *
     */
    
    public int getMajorVersion();
    
    

    /**
     * Returns the minor version of the Servlet API that this
     * servlet container supports. All implementations that comply
     * with Version 2.5 must have this method
     * return the integer 5.
     *
     * @return         5
     *
     */

    public int getMinorVersion();
    
    

    /**
     * Returns the MIME type of the specified file, or <code>null</code> 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 <code>"text/html"</code> and <code>"image/gif"</code>.
     *
     *
     * @param   file    a <code>String</code> specifying the name
     *            of a file
     *
     * @return         a <code>String</code> specifying the file's MIME type
     *
     */

    public String getMimeType(String file);
    
    /**
    * 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<br><br>

    * /welcome.html<br>
    * /catalog/index.html<br>
    * /catalog/products.html<br>
    * /catalog/offers/books.html<br>
    * /catalog/offers/music.html<br>
    * /customer/login.jsp<br>
    * /WEB-INF/web.xml<br>
    * /WEB-INF/classes/com.acme.OrderServlet.class,<br><br>
    *
    * getResourcePaths("/") returns {"/welcome.html", "/catalog/", "/customer/", "/WEB-INF/"}<br>
    * getResourcePaths("/catalog/") returns {"/catalog/index.html", "/catalog/products.html", "/catalog/offers/"}.<br>
       


    *@param path        the partial path used to match the resources,
    *                which must start with a /
    *@return 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
    */
    
    public Set getResourcePaths(String path);
    
    

    /**
     * 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.
     *
     * <p>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 <code>.war</code> file. 
     *
     * <p>The servlet container must implement the URL handlers
     * and <code>URLConnection</code> objects that are necessary
     * to access the resource.
     *
     * <p>This method returns <code>null</code>
     * if no resource is mapped to the pathname.
     *
     * <p>Some containers may allow writing to the URL returned by
     * this method using the methods of the URL class.
     *
     * <p>The resource content is returned directly, so be aware that 
     * requesting a <code>.jsp</code> page returns the JSP source code.
     * Use a <code>RequestDispatcher</code> instead to include results of 
     * an execution.
     *
     * <p>This method has a different purpose than
     * <code>java.lang.Class.getResource</code>,
     * which looks up resources based on a class loader. This
     * method does not use class loaders.
     * 
     * @param path                 a <code>String</code> specifying
     *                        the path to the resource
     *
     * @return                     the resource located at the named path,
     *                         or <code>null</code> if there is no resource
     *                        at that path
     *
     * @exception MalformedURLException     if the pathname is not given in 
     *                         the correct form
     *
     */
    
    public URL getResource(String path) throws MalformedURLException;
    
    

    /**
     * Returns the resource located at the named path as
     * an <code>InputStream</code> object.
     *
     * <p>The data in the <code>InputStream</code> can be 
     * of any type or length. The path must be specified according
     * to the rules given in <code>getResource</code>.
     * This method returns <code>null</code> if no resource exists at
     * the specified path. 
     * 
     * <p>Meta-information such as content length and content type
     * that is available via <code>getResource</code>
     * method is lost when using this method.
     *
     * <p>The servlet container must implement the URL handlers
     * and <code>URLConnection</code> objects necessary to access
     * the resource.
     *
     * <p>This method is different from 
     * <code>java.lang.Class.getResourceAsStream</code>,
     * 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.
     * 
     *
     * @param path     a <code>String</code> specifying the path
     *            to the resource
     *
     * @return         the <code>InputStream</code> returned to the 
     *            servlet, or <code>null</code> if no resource
     *            exists at the specified path 
     *
     *
     */

    public InputStream getResourceAsStream(String path);
    



    /**
     * 
     * Returns a {@link RequestDispatcher} object that acts
     * as a wrapper for the resource located at the given path.
     * A <code>RequestDispatcher</code> 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.
     *
     * <p>The pathname must begin with a "/" and is interpreted as relative
     * to the current context root.  Use <code>getContext</code> to obtain
     * a <code>RequestDispatcher</code> for resources in foreign contexts.
     * This method returns <code>null</code> if the <code>ServletContext</code>
     * cannot return a <code>RequestDispatcher</code>.
     *
     * @param path     a <code>String</code> specifying the pathname
     *            to the resource
     *
     * @return         a <code>RequestDispatcher</code> object
     *            that acts as a wrapper for the resource
     *            at the specified path, or <code>null</code> if 
     *            the <code>ServletContext</code> cannot return
     *            a <code>RequestDispatcher</code>
     *
     * @see         RequestDispatcher
     * @see         ServletContext#getContext
     *
     */

    public RequestDispatcher getRequestDispatcher(String path);



    /**
     * Returns a {@link RequestDispatcher} object that acts
     * as a wrapper for the named servlet.
     *
     * <p>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 
     * {@link ServletConfig#getServletName}.
     *
     * <p>This method returns <code>null</code> if the 
     * <code>ServletContext</code>
     * cannot return a <code>RequestDispatcher</code> for any reason.
     *
     * @param name     a <code>String</code> specifying the name
     *            of a servlet to wrap
     *
     * @return         a <code>RequestDispatcher</code> object
     *            that acts as a wrapper for the named servlet,
     *            or <code>null</code> if the <code>ServletContext</code>
     *            cannot return a <code>RequestDispatcher</code>
     *
     * @see         RequestDispatcher
     * @see         ServletContext#getContext
     * @see         ServletConfig#getServletName
     *
     */

    public RequestDispatcher getNamedDispatcher(String name);
    
    
    
    
    /**
     *
     * @deprecated    As of Java Servlet API 2.1, with no direct replacement.
     *
     * <p>This method was originally defined to retrieve a servlet
     * from a <code>ServletContext</code>. In this version, this method 
     * always returns <code>null</code> and remains only to preserve 
     * binary compatibility. This method will be permanently removed 
     * in a future version of the Java Servlet API.
     *
     * <p>In lieu of this method, servlets can share information using the 
     * <code>ServletContext</code> class and can perform shared business logic
     * by invoking methods on common non-servlet classes.
     *
     */

    public Servlet getServlet(String name) throws ServletException;
    
  
  
  
    

    /**
     *
     * @deprecated    As of Java Servlet API 2.0, with no replacement.
     *
     * <p>This method was originally defined to return an <code>Enumeration</code>
     * 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.
     *
     */
    
    public Enumeration getServlets();
    
    
    
    
    

    /**
     * @deprecated    As of Java Servlet API 2.1, with no replacement.
     *
     * <p>This method was originally defined to return an 
     * <code>Enumeration</code>
     * of all the servlet names known to this context. In this version,
     * this method always returns an empty <code>Enumeration</code> and 
     * remains only to preserve binary compatibility. This method will 
     * be permanently removed in a future version of the Java Servlet API.
     *
     */
 
    public Enumeration getServletNames();
    
  
  
    
    
    /**
     *
     * 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.
     *
     *
     * @param msg     a <code>String</code> specifying the 
     *            message to be written to the log file
     *
     */
     
    public void log(String msg);
    
    
    
    

    /**
     * @deprecated    As of Java Servlet API 2.1, use
     *             {@link #log(String message, Throwable throwable)} 
     *            instead.
     *
     * <p>This method was originally defined to write an 
     * exception's stack trace and an explanatory error message
     * to the servlet log file.
     *
     */

    public void log(Exception exception, String msg);
    
    
    
    

    /**
     * Writes an explanatory message and a stack trace
     * for a given <code>Throwable</code> 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.
     *
     *
     * @param message         a <code>String</code> that 
     *                describes the error or exception
     *
     * @param throwable     the <code>Throwable</code> error 
     *                or exception
     *
     */
    
    public void log(String message, Throwable throwable);
    
    
    
    
    
    /**
     * Returns a <code>String</code> 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..
     *
     * <p>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 <code>null</code>
     * 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 <code>.war</code> archive).
     *
     *
     * @param path     a <code>String</code> specifying a virtual path
     *
     *
     * @return         a <code>String</code> specifying the real path,
     *                  or null if the translation cannot be performed
     *            
     *
     */

    public String getRealPath(String path);
    
    


    /**
     * Returns the name and version of the servlet container on which
     * the servlet is running. 
     *
     * <p>The form of the returned string is 
     * <i>servername</i>/<i>versionnumber</i>.
     * For example, the JavaServer Web Development Kit may return the string
     * <code>JavaServer Web Dev Kit/1.0</code>.
     *
     * <p>The servlet container may return other optional information 
     * after the primary string in parentheses, for example,
     * <code>JavaServer Web Dev Kit/1.0 (JDK 1.1.6; Windows NT 4.0 x86)</code>.
     *
     *
     * @return         a <code>String</code> containing at least the 
     *            servlet container name and version number
     *
     */

    public String getServerInfo();
    
    


    /**
     * Returns a <code>String</code> containing the value of the named
     * context-wide initialization parameter, or <code>null</code> if the 
     * parameter does not exist.
     *
     * <p>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.
     *
     * @param    name    a <code>String</code> containing the name of the
     *                  parameter whose value is requested
     * 
     * @return         a <code>String</code> containing at least the 
     *            servlet container name and version number
     *
     * @see ServletConfig#getInitParameter
     */

    public String getInitParameter(String name);
    
    


    /**
     * Returns the names of the context's initialization parameters as an
     * <code>Enumeration</code> of <code>String</code> objects, or an
     * empty <code>Enumeration</code> if the context has no initialization
     * parameters.
     *
     * @return         an <code>Enumeration</code> of <code>String</code> 
     *                  objects containing the names of the context's
     *                  initialization parameters
     *
     * @see ServletConfig#getInitParameter
     */

    public Enumeration getInitParameterNames();
    
    

    /**
     * Returns the servlet container attribute with the given name, 
     * or <code>null</code> 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
     * <code>getAttributeNames</code>.
     *
     * <p>The attribute is returned as a <code>java.lang.Object</code>
     * or some subclass.
     * Attribute names should follow the same convention as package
     * names. The Java Servlet API specification reserves names
     * matching <code>java.*</code>, <code>javax.*</code>,
     * and <code>sun.*</code>.
     *
     *
     * @param name     a <code>String</code> specifying the name 
     *            of the attribute
     *
     * @return         an <code>Object</code> containing the value 
     *            of the attribute, or <code>null</code>
     *            if no attribute exists matching the given
     *            name
     *
     * @see         ServletContext#getAttributeNames
     *
     */
  
    public Object getAttribute(String name);
    
    
    

    /**
     * Returns an <code>Enumeration</code> containing the 
     * attribute names available
     * within this servlet context. Use the
     * {@link #getAttribute} method with an attribute name
     * to get the value of an attribute.
     *
     * @return         an <code>Enumeration</code> of attribute 
     *            names
     *
     * @see        #getAttribute
     *
     */

    public Enumeration getAttributeNames();
    
    
    
    
    /**
     *
     * 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.
     * <p>If listeners are configured on the <code>ServletContext</code> the  
     * container notifies them accordingly.
     * <p>
     * If a null value is passed, the effect is the same as calling 
     * <code>removeAttribute()</code>.
     * 
     * <p>Attribute names should follow the same convention as package
     * names. The Java Servlet API specification reserves names
     * matching <code>java.*</code>, <code>javax.*</code>, and
     * <code>sun.*</code>.
     *
     *
     * @param name     a <code>String</code> specifying the name 
     *            of the attribute
     *
     * @param object     an <code>Object</code> representing the
     *            attribute to be bound
     *
     *
     *
     */
    
    public void setAttribute(String name, Object object);
    
    



    /**
     * Removes the attribute with the given name from 
     * the servlet context. After removal, subsequent calls to
     * {@link #getAttribute} to retrieve the attribute's value
     * will return <code>null</code>.

     * <p>If listeners are configured on the <code>ServletContext</code> the 
     * container notifies them accordingly.

     *
     *
     * @param name    a <code>String</code> specifying the name 
     *             of the attribute to be removed
     *
     */

    public void removeAttribute(String name);
    
    /**
     * 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.
     *
     *
     * @return        The name of the web application or null if no name has been declared in the deployment descriptor.
     * @since Servlet 2.3
     */
    
    public String getServletContextName();
}

　　　　定義了 一些列的方法，具體就不看了，有興趣的可以詳細看下

　　Servlet 3.0+ 規範

　　　　我們採用4.0.1來看下原始碼

　　　　maven依賴

<dependency>
    <groupId>javax.servlet</groupId>
    <artifactId>javax.servlet-api</artifactId>
    <version>4.0.1</version>
    <scope>provided</scope>
</dependency>

　　　　原始碼

/*
 * Copyright (c) 1997-2018 Oracle and/or its affiliates. All rights reserved.
 * Copyright 2004 The Apache Software Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package javax.servlet;

import java.io.InputStream;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.Enumeration;
import java.util.EnumSet;
import java.util.EventListener;
import java.util.Map;
import java.util.Set;
import javax.servlet.descriptor.JspConfigDescriptor;

/**
 * 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.
 *
 * <p>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 <code>/catalog</code>
 * and possibly installed via a <code>.war</code> file.)
 *
 * <p>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.
 *
 * <p>The <code>ServletContext</code> object is contained within
 * the {@link ServletConfig} object, which the Web server provides the
 * servlet when the servlet is initialized.
 *
 * @author     Various
 *
 * @see     Servlet#getServletConfig
 * @see     ServletConfig#getServletContext
 */

public interface ServletContext {

    /**
     * The name of the <tt>ServletContext</tt> attribute which stores
     * the private temporary directory (of type <tt>java.io.File</tt>)
     * provided by the servlet container for the <tt>ServletContext</tt>
     */
    public static final String TEMPDIR = "javax.servlet.context.tempdir";


    /**
     * The name of the <code>ServletContext</code> attribute whose value
     * (of type <code>java.util.List&lt;java.lang.String&gt;</code>) contains
     * the list of names of JAR files in <code>WEB-INF/lib</code> ordered by
     * their web fragment names (with possible exclusions if
     * <code>&lt;absolute-ordering&gt;</code> without any
     * <code>&lt;others/&gt;</code> is being used), or null if no
     * absolute or relative ordering has been specified
     */
    public static final String ORDERED_LIBS =
        "javax.servlet.context.orderedLibs";


    /**
     * Returns the context path of the web application.
     *
     * <p>The context path is the portion of the request URI that is used
     * to select the context of the request. The context path always comes
     * first in a request URI. If this context is the "root" context
     * rooted at the base of the Web server's URL name space, this path
     * will be an empty string. Otherwise, if the context is not rooted at
     * the root of the server's name space, the path starts with a /
     * character but does not end with a / character.
     *
     * <p>It is possible that a servlet container may match a context by
     * more than one context path. In such cases the
     * {@link javax.servlet.http.HttpServletRequest#getContextPath()}
     * will return the actual context path used by the request and it may
     * differ from the path returned by this method.
     * The context path returned by this method should be considered as the
     * prime or preferred context path of the application.
     *
     * @return The context path of the web application, or "" for the
     * root context
     *
     * @see javax.servlet.http.HttpServletRequest#getContextPath()
     *
     * @since Servlet 2.5
     */
    public String getContextPath();


    /**
     * Returns a <code>ServletContext</code> object that
     * corresponds to a specified URL on the server.
     *
     * <p>This method allows servlets to gain
     * access to the context for various parts of the server, and as
     * needed obtain {@link RequestDispatcher} objects from the context.
     * The given path must be begin with <tt>/</tt>, is interpreted relative
     * to the server's document root and is matched against the context
     * roots of other web applications hosted on this container.
     *
     * <p>In a security conscious environment, the servlet container may
     * return <code>null</code> for a given URL.
     *
     * @param uripath     a <code>String</code> specifying the context path of
     *            another web application in the container.
     * @return        the <code>ServletContext</code> object that
     *            corresponds to the named URL, or null if either
            none exists or the container wishes to restrict
     *             this access.
     *
     * @see         RequestDispatcher
     */
    public ServletContext getContext(String uripath);


    /**
     * Returns the major version of the Servlet API that this
     * servlet container supports. All implementations that comply
     * with Version 4.0 must have this method return the integer 4.
     *
     * @return 4
     */
    public int getMajorVersion();


    /**
     * Returns the minor version of the Servlet API that this
     * servlet container supports. All implementations that comply
     * with Version 4.0 must have this method return the integer 0.
     *
     * @return 0
     */
    public int getMinorVersion();


    /**
     * Gets the major version of the Servlet specification that the
     * application represented by this ServletContext is based on.
     *
     * <p>The value returned may be different from {@link #getMajorVersion},
     * which returns the major version of the Servlet specification
     * supported by the Servlet container.
     *
     * @return the major version of the Servlet specification that the
     * application represented by this ServletContext is based on
     *
     * @throws UnsupportedOperationException if this ServletContext was
     * passed to the {@link ServletContextListener#contextInitialized} method
     * of a {@link ServletContextListener} that was neither declared in
     * <code>web.xml</code> or <code>web-fragment.xml</code>, nor annotated
     * with {@link javax.servlet.annotation.WebListener}
     *
     * @since Servlet 3.0
     */
    public int getEffectiveMajorVersion();


    /**
     * Gets the minor version of the Servlet specification that the
     * application represented by this ServletContext is based on.
     *
     * <p>The value returned may be different from {@link #getMinorVersion},
     * which returns the minor version of the Servlet specification
     * supported by the Servlet container.
     *
     * @return the minor version of the Servlet specification that the
     * application represented by this ServletContext is based on
     *
     * @throws UnsupportedOperationException if this ServletContext was
     * passed to the {@link ServletContextListener#contextInitialized} method
     * of a {@link ServletContextListener} that was neither declared in
     * <code>web.xml</code> or <code>web-fragment.xml</code>, nor annotated
     * with {@link javax.servlet.annotation.WebListener}
     *
     * @since Servlet 3.0
     */
    public int getEffectiveMinorVersion();


    /**
     * Returns the MIME type of the specified file, or <code>null</code> 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 include <code>text/html</code> and <code>image/gif</code>.
     *
     * @param file a <code>String</code> specifying the name of a file
     *
     * @return a <code>String</code> specifying the file's MIME type
     */
    public String getMimeType(String file);


    /**
     * Returns a directory-like listing of all the paths to resources
     * within the web application whose longest sub-path matches the
     * supplied path argument.
     *
     * <p>Paths indicating subdirectory paths end with a <tt>/</tt>.
     *
     * <p>The returned paths are all relative to the root of the web
     * application, or relative to the <tt>/META-INF/resources</tt>
     * directory of a JAR file inside the web application's
     * <tt>/WEB-INF/lib</tt> directory, and have a leading <tt>/</tt>.
     *
     * <p>The returned set is not backed by the {@code ServletContext} object,
     * so changes in the returned set are not reflected in the
     * {@code ServletContext} object, and vice-versa.</p>
     *
     * <p>For example, for a web application containing:
     *
     * <pre>{@code
     *   /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
     *   /WEB-INF/lib/catalog.jar!/META-INF/resources/catalog/moreOffers/books.html
     * }</pre>
     *
     * <tt>getResourcePaths("/")</tt> would return
     * <tt>{"/welcome.html", "/catalog/", "/customer/", "/WEB-INF/"}</tt>,
     * and <tt>getResourcePaths("/catalog/")</tt> would return
     * <tt>{"/catalog/index.html", "/catalog/products.html",
     * "/catalog/offers/", "/catalog/moreOffers/"}</tt>.
     *
     * @param path the partial path used to match the resources,
     * which must start with a <tt>/</tt>
     * @return 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
     */
    public Set<String> getResourcePaths(String path);


    /**
     * Returns a URL to the resource that is mapped to the given path.
     *
     * <p>The path must begin with a <tt>/</tt> and is interpreted
     * as relative to the current context root,
     * or relative to the <tt>/META-INF/resources</tt> directory
     * of a JAR file inside the web application's <tt>/WEB-INF/lib</tt>
     * directory.
     * This method will first search the document root of the
     * web application for the requested resource, before searching
     * any of the JAR files inside <tt>/WEB-INF/lib</tt>.
     * The order in which the JAR files inside <tt>/WEB-INF/lib</tt>
     * are searched is undefined.
     *
     * <p>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 <code>.war</code> file.
     *
     * <p>The servlet container must implement the URL handlers
     * and <code>URLConnection</code> objects that are necessary
     * to access the resource.
     *
     * <p>This method returns <code>null</code>
     * if no resource is mapped to the pathname.
     *
     * <p>Some containers may allow writing to the URL returned by
     * this method using the methods of the URL class.
     *
     * <p>The resource content is returned directly, so be aware that
     * requesting a <code>.jsp</code> page returns the JSP source code.
     * Use a <code>RequestDispatcher</code> instead to include results of
     * an execution.
     *
     * <p>This method has a different purpose than
     * <code>java.lang.Class.getResource</code>,
     * which looks up resources based on a class loader. This
     * method does not use class loaders.
     *
     * @param path a <code>String</code> specifying
     * the path to the resource
     *
     * @return the resource located at the named path,
     * or <code>null</code> if there is no resource at that path
     *
     * @exception MalformedURLException if the pathname is not given in
     * the correct form
     */
    public URL getResource(String path) throws MalformedURLException;


    /**
     * Returns the resource located at the named path as
     * an <code>InputStream</code> object.
     *
     * <p>The data in the <code>InputStream</code> can be
     * of any type or length. The path must be specified according
     * to the rules given in <code>getResource</code>.
     * This method returns <code>null</code> if no resource exists at
     * the specified path.
     *
     * <p>Meta-information such as content length and content type
     * that is available via <code>getResource</code>
     * method is lost when using this method.
     *
     * <p>The servlet container must implement the URL handlers
     * and <code>URLConnection</code> objects necessary to access
     * the resource.
     *
     * <p>This method is different from
     * <code>java.lang.Class.getResourceAsStream</code>,
     * 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.
     *
     *
     * @param path     a <code>String</code> specifying the path
     *            to the resource
     *
     * @return         the <code>InputStream</code> returned to the
     *            servlet, or <code>null</code> if no resource
     *            exists at the specified path
     */
    public InputStream getResourceAsStream(String path);


    /**
     *
     * Returns a {@link RequestDispatcher} object that acts
     * as a wrapper for the resource located at the given path.
     * A <code>RequestDispatcher</code> 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.
     *
     * <p>The pathname must begin with a <tt>/</tt> and is interpreted as
     * relative to the current context root.  Use <code>getContext</code>
     * to obtain a <code>RequestDispatcher</code> for resources in foreign
     * contexts.
     *
     * <p>This method returns <code>null</code> if the
     * <code>ServletContext</code> cannot return a
     * <code>RequestDispatcher</code>.
     *
     * @param path     a <code>String</code> specifying the pathname
     *            to the resource
     *
     * @return         a <code>RequestDispatcher</code> object
     *            that acts as a wrapper for the resource
     *            at the specified path, or <code>null</code> if
     *            the <code>ServletContext</code> cannot return
     *            a <code>RequestDispatcher</code>
     *
     * @see         RequestDispatcher
     * @see         ServletContext#getContext
     */
    public RequestDispatcher getRequestDispatcher(String path);


    /**
     * Returns a {@link RequestDispatcher} object that acts
     * as a wrapper for the named servlet.