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Jetty example source code file (JspContext.java)

This example Jetty source code file (JspContext.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Jetty tags/keywords

enumeration, expressionevaluator, jsp, jspcontext, jspcontext, jspwriter, jspwriter, object, object, servlet, util, variableresolver, xxx, xxx

The Jetty JspContext.java source code

/**
 *
 * 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.jsp;

import java.util.Enumeration;

import javax.servlet.jsp.el.ExpressionEvaluator;
import javax.servlet.jsp.el.VariableResolver;

/**
 * <p>
 * <code>JspContext 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>Methods Intended for Container Generated Code
 * <p>
 * The following methods enable the <B>management of nested JspWriter 
 * streams to implement Tag Extensions: <code>pushBody() and
 * <code>popBody()
 *
 * <p>Methods Intended for JSP authors
 * <p>
 * Some methods provide <B>uniform access 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(),  getAttribute(),
 * <code>findAttribute(),  removeAttribute(),
 * <code>getAttributesScope() and 
 * <code>getAttributeNamesInScope().
 * 
 * <p>
 * The following methods provide <B>convenient access to implicit objects:
 * <code>getOut()
 *
 * <p>
 * The following methods provide <B>programmatic access to the 
 * Expression Language evaluator:
 * <code>getExpressionEvaluator(), getVariableResolver()
 *
 * @since 2.0
 */

public abstract class JspContext {

    /**
     * Sole constructor. (For invocation by subclass constructors, 
     * typically implicit.)
     */
    public JspContext() {
    }
    
    /** 
     * Register the name and value specified with page scope semantics.
     * If the value passed in is <code>null, this has the same 
     * effect as calling 
     * <code>removeAttribute( name, PageContext.PAGE_SCOPE ).
     *
     * @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
     */

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

    /**
     * Register the name and value specified with appropriate 
     * scope semantics.  If the value passed in is <code>null, 
     * this has the same effect as calling
     * <code>removeAttribute( name, scope ).
     * 
     * @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.
     */

    abstract public 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
     */

    abstract public 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.
     */

    abstract public 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
     */

    abstract public 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
     */

    abstract public 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
     */

    abstract public 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
     */

    abstract public 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 (java.lang.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.
     */

    abstract public Enumeration getAttributeNamesInScope(int scope);

    /**
     * The current value of the out object (a JspWriter).
     *
     * @return the current JspWriter stream being used for client response
     */
    abstract public JspWriter getOut();
    
    /**
     * Provides programmatic access to the ExpressionEvaluator.
     * The JSP Container must return a valid instance of an 
     * ExpressionEvaluator that can parse EL expressions.
     *
     * @return A valid instance of an ExpressionEvaluator.
     * @since 2.0
     */
    public abstract ExpressionEvaluator getExpressionEvaluator();
    
    /**
     * Returns an instance of a VariableResolver that provides access to the
     * implicit objects specified in the JSP specification using this JspContext
     * as the context object.
     *
     * @return A valid instance of a VariableResolver.
     * @since 2.0
     */
    public abstract VariableResolver getVariableResolver();
    
    /**
     * 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:
     * <ul>
     *   <li>clear() must throw an IOException
     *   <li>clearBuffer() does nothing
     *   <li>getBufferSize() always returns 0
     *   <li>getRemaining() always returns 0
     * </ul>
     * </p>
     *
     * @param writer The Writer for the returned JspWriter to send
     *     output to.
     * @return a new JspWriter that writes to the given Writer.
     * @since 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
    }
}

Other Jetty examples (source code examples)

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