javax.servlet.jsp

Class JspContext

Known Direct 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:

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

Object
findAttribute(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.
Object
getAttribute(String name)
Returns the object associated with the name in the page scope or null if not found.
Object
getAttribute(String name, int scope)
Return the object associated with the name in the specified scope or null if not found.
Enumeration
getAttributeNamesInScope(int scope)
Enumerate all the attributes in a given scope.
int
getAttributesScope(String name)
Get the scope where a given attribute is defined.
ExpressionEvaluator
getExpressionEvaluator()
Provides programmatic access to the ExpressionEvaluator.
JspWriter
getOut()
The current value of the out object (a JspWriter).
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.
void
removeAttribute(String name)
Remove the object reference associated with the given name from all scopes.
void
removeAttribute(String name, int scope)
Remove the object reference associated with the specified name in the given scope.
void
setAttribute(String name, Object value)
Register the name and value specified with page scope semantics.
void
setAttribute(String name, Object value, int scope)
Register the name and value specified with appropriate scope semantics.

Constructor Details

JspContext

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

Method Details

findAttribute

public Object findAttribute(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


getAttribute

public Object getAttribute(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.


getAttribute

public Object getAttribute(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.


getAttributeNamesInScope

public 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


getAttributesScope

public int getAttributesScope(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


getExpressionEvaluator

public 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


getOut

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

Returns:
the current JspWriter stream being used for client response


getVariableResolver

public 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


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.

Returns:
the saved JspWriter.


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


removeAttribute

public void removeAttribute(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.


removeAttribute

public void removeAttribute(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.


setAttribute

public void setAttribute(String name,
                         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.


setAttribute

public void setAttribute(String name,
                         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


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