Package javax.el

Class ELContext

java.lang.Object
javax.el.ELContext
Direct Known Subclasses:
FaceletContext, StandardELContext
public abstract class ELContext extends Object
Context information for expression parsing and evaluation.

To parse or evaluate an Expression, an ELContext must be provided. The ELContext holds:

  • a reference to FunctionMapper that will be used to resolve EL Functions. This is used only in parsing.
  • a reference to VariableMapper that will be used to resolve EL Variables. This is used only in parsing.
  • a reference to the base ELResolver that will be consulted to resolve model objects and their properties
  • a collection of all the relevant context objects for use by ELResolvers
  • state information during the evaluation of an expression, such as whether a property has been resolved yet
  • a reference to ImportHandler that will be consulted to resolve classes that have been imported
  • a reference to the arguments for the active LambdaExpressions
  • a reference to the list of registered evaluation listeners

The collection of context objects is necessary because each ELResolver may need access to a different context object. For example, JSP and Faces resolvers need access to a JspContext and a FacesContext, respectively.

When used in a web container, the creation of ELContext objects is controlled through the underlying technology. For example, in JSP the JspContext.getELContext() factory method is used. Some technologies provide the ability to add an ELContextListener so that applications and frameworks can ensure their own context objects are attached to any newly created ELContext.

When used in a stand-alone environment, StandardELContext provides a default ELContext, which is managed and modified by ELManager.

Because it stores state during expression evaluation, an ELContext object is not thread-safe. Care should be taken to never share an ELContext instance between two or more threads.

Since:
EL 2.1 and EL 3.0
See Also:

  • Constructor Details

    • ELContext

      public ELContext()

  • Method Details

    • setPropertyResolved

      public void setPropertyResolved(boolean resolved)
      Called to indicate that a ELResolver has successfully resolved a given (base, property) pair. Use setPropertyResolved(Object, Object) if resolved is true and to notify EvaluationListeners.

      The CompositeELResolver checks this property to determine whether it should consider or skip other component resolvers.

      Parameters:
      resolved - true if the property has been resolved, or false if not.
      See Also:

    • setPropertyResolved

      public void setPropertyResolved(Object base, Object property)
      Called to indicate that a ELResolver has successfully resolved a given (base, property) pair and to notify the EvaluationListeners.

      The CompositeELResolver checks this property to determine whether it should consider or skip other component resolvers.

      Parameters:
      base - The base object
      property - The property object
      Since:
      EL 3.0
      See Also:

    • isPropertyResolved

      public boolean isPropertyResolved()
      Returns whether an ELResolver has successfully resolved a given (base, property) pair.

      The CompositeELResolver checks this property to determine whether it should consider or skip other component resolvers.

      Returns:
      true if the property has been resolved, or false if not.
      See Also:

    • putContext

      public void putContext(Class key, Object contextObject)
      Associates a context object with this ELContext.

      The ELContext maintains a collection of context objects relevant to the evaluation of an expression. These context objects are used by ELResolvers. This method is used to add a context object to that collection.

      By convention, the contextObject will be of the type specified by the key. However, this is not required and the key is used strictly as a unique identifier.

      Parameters:
      key - The key used by an @{link ELResolver} to identify this context object.
      contextObject - The context object to add to the collection.
      Throws:
      NullPointerException - if key is null or contextObject is null.

    • getContext

      public Object getContext(Class key)
      Returns the context object associated with the given key.

      The ELContext maintains a collection of context objects relevant to the evaluation of an expression. These context objects are used by ELResolvers. This method is used to retrieve the context with the given key from the collection.

      By convention, the object returned will be of the type specified by the key. However, this is not required and the key is used strictly as a unique identifier.

      Parameters:
      key - The unique identifier that was used to associate the context object with this ELContext.
      Returns:
      The context object associated with the given key, or null if no such context was found.
      Throws:
      NullPointerException - if key is null.

    • getELResolver

      public abstract ELResolver getELResolver()
      Retrieves the ELResolver associated with this context.

      The ELContext maintains a reference to the ELResolver that will be consulted to resolve variables and properties during an expression evaluation. This method retrieves the reference to the resolver.

      Once an ELContext is constructed, the reference to the ELResolver associated with the context cannot be changed.

      Returns:
      The resolver to be consulted for variable and property resolution during expression evaluation.

    • getImportHandler

      public ImportHandler getImportHandler()
      Retrieves the ImportHandler associated with this ELContext.
      Returns:
      The import handler to manage imports of classes and packages.
      Since:
      EL 3.0

    • getFunctionMapper

      public abstract FunctionMapper getFunctionMapper()
      Retrieves the FunctionMapper associated with this ELContext.
      Returns:
      The function mapper to be consulted for the resolution of EL functions.

    • getLocale

      public Locale getLocale()
      Get the Locale stored by a previous invocation to setLocale(java.util.Locale). If this method returns non null, this Locale must be used for all localization needs in the implementation. The Locale must not be cached to allow for applications that change Locale dynamically.
      Returns:
      The Locale in which this instance is operating. Used primarily for message localization.

    • setLocale

      public void setLocale(Locale locale)
      Sets the Locale for this instance. This method may be called by the party creating the instance, such as JavaServer Faces or JSP, to enable the EL implementation to provide localized messages to the user. If no Locale is set, the implementation must use the locale returned by Locale.getDefault( ).

    • getVariableMapper

      public abstract VariableMapper getVariableMapper()
      Retrieves the VariableMapper associated with this ELContext.
      Returns:
      The variable mapper to be consulted for the resolution of EL variables.

    • addEvaluationListener

      public void addEvaluationListener(EvaluationListener listener)
      Registers an evaluation listener to the ELContext.
      Parameters:
      listener - The listener to be added.
      Since:
      EL 3.0

    • getEvaluationListeners

      public List<EvaluationListener> getEvaluationListeners()
      Returns the list of registered evaluation listeners.
      Returns:
      The list of registered evaluation listeners.
      Since:
      EL 3.0

    • notifyBeforeEvaluation

      public void notifyBeforeEvaluation(String expr)
      Notifies the listeners before an EL expression is evaluated
      Parameters:
      expr - The EL expression string to be evaluated

    • notifyAfterEvaluation

      public void notifyAfterEvaluation(String expr)
      Notifies the listeners after an EL expression is evaluated
      Parameters:
      expr - The EL expression string that has been evaluated

    • notifyPropertyResolved

      public void notifyPropertyResolved(Object base, Object property)
      Notifies the listeners when the (base, property) pair is resolved
      Parameters:
      base - The base object
      property - The property Object

    • isLambdaArgument

      public boolean isLambdaArgument(String arg)
      Inquires if the name is a LambdaArgument
      Parameters:
      arg - A possible Lambda formal parameter name
      Returns:
      true if arg is a LambdaArgument, false otherwise.

    • getLambdaArgument

      public Object getLambdaArgument(String arg)
      Retrieves the Lambda argument associated with a formal parameter. If the Lambda expression is nested within other Lambda expressions, the arguments for the current Lambda expression is first searched, and if not found, the arguments for the immediate nesting Lambda expression then searched, and so on.
      Parameters:
      arg - The formal parameter for the Lambda argument
      Returns:
      The object associated with formal parameter. Null if no object has been associated with the parameter.
      Since:
      EL 3.0

    • enterLambdaScope

      public void enterLambdaScope(Map<String,Object> args)
      Installs a Lambda argument map, in preparation for the evaluation of a Lambda expression. The arguments in the map will be in scope during the evaluation of the Lambda expression.
      Parameters:
      args - The Lambda arguments map
      Since:
      EL 3.0

    • exitLambdaScope

      public void exitLambdaScope()
      Exits the Lambda expression evaluation. The Lambda argument map that was previously installed is removed.
      Since:
      EL 3.0

    • convertToType

      public Object convertToType(Object obj, Class<?> targetType)
      Converts an object to a specific type. If a custom converter in the ELResolver handles this conversion, it is used. Otherwise the standard coercions is applied.

      An ELException is thrown if an error occurs during the conversion.

      Parameters:
      obj - The object to convert.
      targetType - The target type for the conversion.
      Throws:
      ELException - thrown if errors occur.
      Since:
      EL 3.0