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ServletContext.java

/**
 *
 * Copyright 2003-2004 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.
 */

//
// This source code implements specifications defined by the Java
// Community Process. In order to remain compliant with the specification
// DO NOT add / change / or delete method signatures!
//

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.
 *
 * @see Servlet#getServletConfig
 * @see ServletConfig#getServletContext
 *
 * @version $Rev: 46019 $ $Date: 2005/03/15 10:03:20 $
 */
00058 public interface ServletContext {
    /**
     * 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 2.4 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 2.4 must have this method
     * return the integer 4.
     *
     * @return 4
     */
    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 correponding 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();
}

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