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package javax.servlet.jsp;
import java.util.Enumeration;
import javax.servlet.jsp.el.ExpressionEvaluator;
import javax.servlet.jsp.el.VariableResolver;
import javax.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>
*
* <p>
* The following methods provide <B>programmatic access</b> to the
* Expression Language evaluator:
* <code>getExpressionEvaluator()</code>, <code>getVariableResolver()</code>
*
* @since JSP 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</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
*/
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</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.
*/
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<String> 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.
*
* @deprecated As of JSP 2.1, replaced by
* {@link JspApplicationContext#getExpressionFactory}
* @return A valid instance of an ExpressionEvaluator.
* @since JSP 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.
*
* @deprecated As of JSP 2.1, replaced by {@link ELContext#getELResolver},
* which can be obtained by
* <code>jspContext.getELContext().getELResolver()</code>.
* @return A valid instance of a VariableResolver.
* @since JSP 2.0
*/
public abstract VariableResolver getVariableResolver();
/**
* Returns the <code>ELContext</code> associated with this
* <code>JspContext</code>.
*
* <p>The <code>ELContext</code> is created lazily and is reused if
* it already exists. There is a new <code>ELContext</code> for each
* <code>JspContext</code>.</p>
*
* <p>The <code>ELContext</code> must contain the <code>ELResolver</code>
* described in the JSP specification (and in the javadocs for
* {@link JspApplicationContext#addELResolver}).</p>
*
* @return The <code>ELContext</code> associated with this
* <code>JspContext</code>.
* @since JSP 2.1
*/
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:
* <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>
* </p>
*
* @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
}
}
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