java/jakarta/servlet/jsp/JspContext.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 jakarta.servlet.jsp;

import java.util.Enumeration;

import jakarta.el.ELContext;

/**
 * <p>
 * <code>JspContext</code> serves as the base class for the PageContext class and abstracts all information that is not
 * specific to servlets. This allows for Simple Tag Extensions to be used outside of the context of a request/response
 * Servlet.
 * <p>
 * The JspContext provides a number of facilities to the page/component author and page implementor, including:
 * <ul>
 * <li>a single API to manage the various scoped namespaces
 * <li>a mechanism to obtain the JspWriter for output
 * <li>a mechanism to expose page directive attributes to the scripting environment
 * </ul>
 * <p>
 * <B>Methods Intended for Container Generated Code</B>
 * <p>
 * The following methods enable the <B>management of nested</B> JspWriter streams to implement Tag Extensions:
 * <code>pushBody()</code> and <code>popBody()</code>
 * <p>
 * <B>Methods Intended for JSP authors</B>
 * <p>
 * Some methods provide <B>uniform access</B> to the diverse objects representing scopes. The implementation must use
 * the underlying machinery corresponding to that scope, so information can be passed back and forth between the
 * underlying environment (e.g. Servlets) and JSP pages. The methods are: <code>setAttribute()</code>,
 * <code>getAttribute()</code>, <code>findAttribute()</code>, <code>removeAttribute()</code>,
 * <code>getAttributesScope()</code> and <code>getAttributeNamesInScope()</code>.
 * <p>
 * The following methods provide <B>convenient access</B> to implicit objects: <code>getOut()</code>
 *
 * @since JSP 2.0
 */

public abstract class JspContext {

    /**
     * Sole constructor. (For invocation by subclass constructors, typically implicit.)
     */
    public JspContext() {
        // NOOP by default
    }

    /**
     * Register the name and value specified with page scope semantics. If the value passed in is <code>null</code>,
     * this has the same effect as calling <code>removeAttribute( name, PageContext.PAGE_SCOPE )</code>.
     *
     * @param name  the name of the attribute to set
     * @param value the value to associate with the name, or null if the attribute is to be removed from the page scope.
     *
     * @throws NullPointerException if the name is null
     */

    public abstract void setAttribute(String name, Object value);

    /**
     * Register the name and value specified with appropriate scope semantics. If the value passed in is
     * <code>null</code>, this has the same effect as calling <code>removeAttribute( name, scope )</code>.
     *
     * @param name  the name of the attribute to set
     * @param value the object to associate with the name, or null if the attribute is to be removed from the specified
     *                  scope.
     * @param scope the scope with which to associate the name/object
     *
     * @throws NullPointerException     if the name is null
     * @throws IllegalArgumentException if the scope is invalid
     * @throws IllegalStateException    if the scope is PageContext.SESSION_SCOPE but the page that was requested does
     *                                      not participate in a session or the session has been invalidated.
     */

    public abstract void setAttribute(String name, Object value, int scope);

    /**
     * Returns the object associated with the name in the page scope or null if not found.
     *
     * @param name the name of the attribute to get
     *
     * @return the object associated with the name in the page scope or null if not found.
     *
     * @throws NullPointerException if the name is null
     */

    public abstract Object getAttribute(String name);

    /**
     * Return the object associated with the name in the specified scope or null if not found.
     *
     * @param name  the name of the attribute to set
     * @param scope the scope with which to associate the name/object
     *
     * @return the object associated with the name in the specified scope or null if not found.
     *
     * @throws NullPointerException     if the name is null
     * @throws IllegalArgumentException if the scope is invalid
     * @throws IllegalStateException    if the scope is PageContext.SESSION_SCOPE but the page that was requested does
     *                                      not participate in a session or the session has been invalidated.
     */

    public abstract Object getAttribute(String name, int scope);

    /**
     * Searches for the named attribute in page, request, session (if valid), and application scope(s) in order and
     * returns the value associated or null.
     *
     * @param name the name of the attribute to search for
     *
     * @return the value associated or null
     *
     * @throws NullPointerException if the name is null
     */

    public abstract Object findAttribute(String name);

    /**
     * Remove the object reference associated with the given name from all scopes. Does nothing if there is no such
     * object.
     *
     * @param name The name of the object to remove.
     *
     * @throws NullPointerException if the name is null
     */

    public abstract void removeAttribute(String name);

    /**
     * Remove the object reference associated with the specified name in the given scope. Does nothing if there is no
     * such object.
     *
     * @param name  The name of the object to remove.
     * @param scope The scope where to look.
     *
     * @throws IllegalArgumentException if the scope is invalid
     * @throws IllegalStateException    if the scope is PageContext.SESSION_SCOPE but the page that was requested does
     *                                      not participate in a session or the session has been invalidated.
     * @throws NullPointerException     if the name is null
     */

    public abstract void removeAttribute(String name, int scope);

    /**
     * Get the scope where a given attribute is defined.
     *
     * @param name the name of the attribute to return the scope for
     *
     * @return the scope of the object associated with the name specified or 0
     *
     * @throws NullPointerException if the name is null
     */

    public abstract int getAttributesScope(String name);

    /**
     * Enumerate all the attributes in a given scope.
     *
     * @param scope the scope to enumerate all the attributes for
     *
     * @return an enumeration of names ({@link String}) of all the attributes the specified scope
     *
     * @throws IllegalArgumentException if the scope is invalid
     * @throws IllegalStateException    if the scope is PageContext.SESSION_SCOPE but the page that was requested does
     *                                      not participate in a session or the session has been invalidated.
     */

    public abstract Enumeration<String> getAttributeNamesInScope(int scope);

    /**
     * The current value of the out object (a JspWriter).
     *
     * @return the current JspWriter stream being used for client response
     */
    public abstract JspWriter getOut();

    /**
     * Obtain the ELContext for this JSPContext. Each JSPContext has a dedicated ELContext.
     *
     * @return the ELContext for this JSPContext
     */
    public abstract ELContext getELContext();

    /**
     * Return a new JspWriter object that sends output to the provided Writer. Saves the current "out" JspWriter, and
     * updates the value of the "out" attribute in the page scope attribute namespace of the JspContext.
     * <p>
     * The returned JspWriter must implement all methods and behave as though it were unbuffered. More specifically:
     * </p>
     * <ul>
     * <li>clear() must throw an IOException</li>
     * <li>clearBuffer() does nothing</li>
     * <li>getBufferSize() always returns 0</li>
     * <li>getRemaining() always returns 0</li>
     * </ul>
     *
     * @param writer The Writer for the returned JspWriter to send output to.
     *
     * @return a new JspWriter that writes to the given Writer.
     *
     * @since JSP 2.0
     */
    public JspWriter pushBody(java.io.Writer writer) {
        return null; // XXX to implement
    }

    /**
     * Return the previous JspWriter "out" saved by the matching pushBody(), and update the value of the "out" attribute
     * in the page scope attribute namespace of the JspContext.
     *
     * @return the saved JspWriter.
     */
    public JspWriter popBody() {
        return null; // XXX to implement
    }
}