Class JspContext

java.lang.Object
jakarta.servlet.jsp.JspContext
Direct Known Subclasses:
PageContext
public abstract class JspContext extends 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()

Since:
JSP 2.0

  • Constructor Summary

    Constructors
    Constructor
    Description
    JspContext()
    Sole constructor.

  • Method Summary

    Modifier and Type
    Method
    Description
    abstract 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.
    abstract Object
    getAttribute(String name)
    Returns the object associated with the name in the page scope or null if not found.
    abstract Object
    getAttribute(String name, int scope)
    Return the object associated with the name in the specified scope or null if not found.
    abstract Enumeration<String>
    getAttributeNamesInScope(int scope)
    Enumerate all the attributes in a given scope.
    abstract int
    getAttributesScope(String name)
    Get the scope where a given attribute is defined.
    abstract jakarta.el.ELContext
    getELContext()
    Obtain the ELContext for this JSPContext.
    abstract JspWriter
    getOut()
    The current value of the out object (a JspWriter).
    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(Writer writer)
    Return a new JspWriter object that sends output to the provided Writer.
    abstract void
    removeAttribute(String name)
    Remove the object reference associated with the given name from all scopes.
    abstract void
    removeAttribute(String name, int scope)
    Remove the object reference associated with the specified name in the given scope.
    abstract void
    setAttribute(String name, Object value)
    Register the name and value specified with page scope semantics.
    abstract void
    setAttribute(String name, 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 Details

    • JspContext

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

  • Method Details

    • setAttribute

      public abstract 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.
      Throws:
      NullPointerException - if the name is null

    • setAttribute

      public abstract 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
      Throws:
      NullPointerException - if the name is null
      IllegalArgumentException - if the scope is invalid
      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 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.
      Throws:
      NullPointerException - if the name is null

    • getAttribute

      public abstract 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.
      Throws:
      NullPointerException - if the name is null
      IllegalArgumentException - if the scope is invalid
      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 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
      Throws:
      NullPointerException - if the name is null

    • removeAttribute

      public abstract 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.
      Throws:
      NullPointerException - if the name is null

    • removeAttribute

      public abstract 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.
      Throws:
      IllegalArgumentException - if the scope is invalid
      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.
      NullPointerException - if the name is null

    • getAttributesScope

      public abstract 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
      Throws:
      NullPointerException - if the name is null

    • getAttributeNamesInScope

      public abstract Enumeration<String> 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 (String) of all the attributes the specified scope
      Throws:
      IllegalArgumentException - if the scope is invalid
      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

    • getELContext

      public abstract jakarta.el.ELContext getELContext()
      Obtain the ELContext for this JSPContext. Each JSPContext has a dedicated ELContext.
      Returns:
      the ELContext for this JSPContext

    • pushBody

      public JspWriter pushBody(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:
      JSP 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.