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JspContext (JavaServer Pages API Documentation)

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javax.servlet.jsp
Class JspContext

java.lang.Object
  javax.servlet.jsp.JspContext

Direct Known Subclasses:: PageContext

public abstract class JspContext
extends java.lang.Object

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.

The JspContext provides a number of facilities to the page/component author and page implementor, including:

a single API to manage the various scoped namespaces
a mechanism to obtain the JspWriter for output
a mechanism to expose page directive attributes to the scripting environment

Methods Intended for Container Generated Code

The following methods enable the management of nested JspWriter streams to implement Tag Extensions: pushBody() and popBody()

Methods Intended for JSP authors

Some methods provide 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: setAttribute(), getAttribute(), findAttribute(), removeAttribute(), getAttributesScope() and getAttributeNamesInScope().

The following methods provide convenient access to implicit objects: getOut()

The following methods provide programmatic access to the Expression Language evaluator: getExpressionEvaluator(), getVariableResolver()

Since:: 2.0

Constructor Summary

JspContext()
          Sole constructor.

Method Summary

abstract java.lang.Object findAttribute(java.lang.String name)
          Searches for the named attribute in page, request, session (if valid), and application scope(s) in order and returns the value associated or null.

abstract java.lang.Object getAttribute(java.lang.String name)
          Returns the object associated with the name in the page scope or null if not found.

abstract java.lang.Object getAttribute(java.lang.String name, int scope)
          Return the object associated with the name in the specified scope or null if not found.

abstract java.util.Enumeration getAttributeNamesInScope(int scope)
          Enumerate all the attributes in a given scope.

abstract int getAttributesScope(java.lang.String name)
          Get the scope where a given attribute is defined.

abstract ExpressionEvaluator getExpressionEvaluator()
          Provides programmatic access to the ExpressionEvaluator.

abstract JspWriter getOut()
          The current value of the out object (a JspWriter).

abstract VariableResolver getVariableResolver()
          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.

JspWriter popBody()
          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.

JspWriter pushBody(java.io.Writer writer)
          Return a new JspWriter object that sends output to the provided Writer.

abstract void removeAttribute(java.lang.String name)
          Remove the object reference associated with the given name from all scopes.

abstract void removeAttribute(java.lang.String name, int scope)
          Remove the object reference associated with the specified name in the given scope.

abstract void setAttribute(java.lang.String name, java.lang.Object value)
          Register the name and value specified with page scope semantics.

abstract void setAttribute(java.lang.String name, java.lang.Object value, int scope)
          Register the name and value specified with appropriate scope semantics.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

JspContext

public JspContext()

Sole constructor. (For invocation by subclass constructors, typically implicit.)

Method Detail

setAttribute

public abstract void setAttribute(java.lang.String name,
                                  java.lang.Object value)

Register the name and value specified with page scope semantics. If the value passed in is null, this has the same effect as calling removeAttribute( name, PageContext.PAGE_SCOPE ).

Parameters:: name - the name of the attribute to set; value - the value to associate with the name, or null if the attribute is to be removed from the page scope.
Throws:: java.lang.NullPointerException - if the name is null

setAttribute

public abstract void setAttribute(java.lang.String name,
                                  java.lang.Object value,
                                  int scope)

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

Parameters:: name - the name of the attribute to set; value - the object to associate with the name, or null if the attribute is to be removed from the specified scope.; scope - the scope with which to associate the name/object
Throws:: java.lang.NullPointerException - if the name is null; java.lang.IllegalArgumentException - if the scope is invalid; java.lang.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.

getAttribute

public abstract java.lang.Object getAttribute(java.lang.String name)

Returns the object associated with the name in the page scope or null if not found.

Parameters:: name - the name of the attribute to get
Returns:: the object associated with the name in the page scope or null if not found.
Throws:: java.lang.NullPointerException - if the name is null

getAttribute

public abstract java.lang.Object getAttribute(java.lang.String name,
                                              int scope)

Return the object associated with the name in the specified scope or null if not found.

Parameters:: name - the name of the attribute to set; scope - the scope with which to associate the name/object
Returns:: the object associated with the name in the specified scope or null if not found.
Throws:: java.lang.NullPointerException - if the name is null; java.lang.IllegalArgumentException - if the scope is invalid; java.lang.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.

findAttribute

public abstract java.lang.Object findAttribute(java.lang.String name)

Searches for the named attribute in page, request, session (if valid), and application scope(s) in order and returns the value associated or null.

Parameters:: name - the name of the attribute to search for
Returns:: the value associated or null
Throws:: java.lang.NullPointerException - if the name is null

removeAttribute

public abstract void removeAttribute(java.lang.String name)

Remove the object reference associated with the given name from all scopes. Does nothing if there is no such object.

Parameters:: name - The name of the object to remove.
Throws:: java.lang.NullPointerException - if the name is null

removeAttribute

public abstract void removeAttribute(java.lang.String name,
                                     int scope)

Remove the object reference associated with the specified name in the given scope. Does nothing if there is no such object.

Parameters:: name - The name of the object to remove.; scope - The scope where to look.
Throws:: java.lang.IllegalArgumentException - if the scope is invalid; java.lang.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.; java.lang.NullPointerException - if the name is null

getAttributesScope

public abstract int getAttributesScope(java.lang.String name)

Get the scope where a given attribute is defined.

Parameters:: name - the name of the attribute to return the scope for
Returns:: the scope of the object associated with the name specified or 0
Throws:: java.lang.NullPointerException - if the name is null

getAttributeNamesInScope

public abstract java.util.Enumeration getAttributeNamesInScope(int scope)

Enumerate all the attributes in a given scope.

Parameters:: scope - the scope to enumerate all the attributes for
Returns:: an enumeration of names (java.lang.String) of all the attributes the specified scope
Throws:: java.lang.IllegalArgumentException - if the scope is invalid; java.lang.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.

getOut

public abstract JspWriter getOut()

The current value of the out object (a JspWriter).

Returns:: the current JspWriter stream being used for client response

getExpressionEvaluator

public abstract ExpressionEvaluator getExpressionEvaluator()

Provides programmatic access to the ExpressionEvaluator. The JSP Container must return a valid instance of an ExpressionEvaluator that can parse EL expressions.

Returns:: A valid instance of an ExpressionEvaluator.
Since:: 2.0

getVariableResolver

public abstract VariableResolver getVariableResolver()

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.

Returns:: A valid instance of a VariableResolver.
Since:: 2.0

pushBody

public JspWriter pushBody(java.io.Writer writer)

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.

The returned JspWriter must implement all methods and behave as though it were unbuffered. More specifically:

clear() must throw an IOException
clearBuffer() does nothing
getBufferSize() always returns 0
getRemaining() always returns 0

Parameters:: writer - The Writer for the returned JspWriter to send output to.
Returns:: a new JspWriter that writes to the given Writer.
Since:: 2.0

popBody

public JspWriter popBody()

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.