javax.el.ELContext Maven / Gradle / Ivy
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package javax.el;
import java.util.Map;
import java.util.Stack;
import java.util.HashMap;
import java.util.List;
import java.util.ArrayList;
import java.util.Locale;
/**
* Context information for expression parsing and evaluation.
*
* To parse or evaluate an {@link Expression}, an ELContext
* must be provided. The ELContext holds:
*
* - a reference to {@link FunctionMapper} that will be used
* to resolve EL Functions. This is used only in parsing.
* - a reference to {@link VariableMapper} that will be used
* to resolve EL Variables. This is used only in parsing.
* - a reference to the base {@link 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 {@link ImportHandler} that will be consulted to
* resolve classes that have been imported
* - a reference to the arguments for the active {@link LambdaExpression}s
* - 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
* {@link javax.servlet.jsp.JspContext} and a
* {@link javax.faces.context.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 {@link 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, {@link StandardELContext}
* provides a default ELContext, which is managed and modified
* by {@link 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.
*
* @see ELContextListener
* @see ELContextEvent
* @see ELResolver
* @see FunctionMapper
* @see VariableMapper
* @see ImportHandler
* @see LambdaExpression
* @see StandardELContext
* @see javax.servlet.jsp.JspContext
* @since EL 2.1 and EL 3.0
*/
public abstract class ELContext {
/**
* Called to indicate that a ELResolver has successfully
* resolved a given (base, property) pair.
* Use {@link #setPropertyResolved(Object, Object)} if
* resolved is true and to notify {@link EvaluationListener}s.
*
* The {@link CompositeELResolver} checks this property to determine
* whether it should consider or skip other component resolvers.
*
* @see CompositeELResolver
* @param resolved true if the property has been resolved, or false if
* not.
*/
public void setPropertyResolved(boolean resolved) {
this.resolved = resolved;
}
/**
* Called to indicate that a ELResolver has successfully
* resolved a given (base, property) pair and to notify the
* {@link EvaluationListener}s.
*
* The {@link CompositeELResolver} checks this property to determine
* whether it should consider or skip other component resolvers.
*
* @see CompositeELResolver
* @param base The base object
* @param property The property object
*
* @since EL 3.0
*/
public void setPropertyResolved(Object base, Object property) {
setPropertyResolved(true); // Don't set the variable here, for 2.2 users
// ELContext may be overridden or delegated.
notifyPropertyResolved(base, property);
}
/**
* Returns whether an {@link ELResolver} has successfully resolved a
* given (base, property) pair.
*
* The {@link CompositeELResolver} checks this property to determine
* whether it should consider or skip other component resolvers.
*
* @see CompositeELResolver
* @return true if the property has been resolved, or false if not.
*/
public boolean isPropertyResolved() {
return resolved;
}
/**
* 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.
*
* @param key The key used by an @{link ELResolver} to identify this
* context object.
* @param contextObject The context object to add to the collection.
* @throws NullPointerException if key is null or contextObject is null.
*/
public void putContext(Class key, Object contextObject) {
if((key == null) || (contextObject == null)) {
throw new NullPointerException();
}
map.put(key, contextObject);
}
/**
* 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.
*
* @param key The unique identifier that was used to associate the
* context object with this ELContext.
* @return The context object associated with the given key, or null
* if no such context was found.
* @throws NullPointerException if key is null.
*/
public Object getContext(Class key) {
if(key == null) {
throw new NullPointerException();
}
return map.get(key);
}
/**
* 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.
*
* @return The resolver to be consulted for variable and
* property resolution during expression evaluation.
*/
public abstract ELResolver getELResolver();
/**
* Retrieves the ImportHandler associated with this
* ELContext.
*
* @return The import handler to manage imports of classes and packages.
* @since EL 3.0
*/
public ImportHandler getImportHandler() {
if (importHandler == null) {
importHandler = new ImportHandler();
}
return importHandler;
}
/**
* Retrieves the FunctionMapper associated with this
* ELContext.
*
* @return The function mapper to be consulted for the resolution of
* EL functions.
*/
public abstract FunctionMapper getFunctionMapper();
/**
* Holds value of property locale.
*/
private Locale locale;
/**
* Get the Locale stored by a previous invocation to
* {@link #setLocale}. 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.
*
* @return The Locale in which this instance is operating.
* Used primarily for message localization.
*/
public Locale getLocale() {
return this.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( ).
*/
public void setLocale(Locale locale) {
this.locale = locale;
}
/**
* Retrieves the VariableMapper associated with this
* ELContext.
*
* @return The variable mapper to be consulted for the resolution of
* EL variables.
*/
public abstract VariableMapper getVariableMapper();
/**
* Registers an evaluation listener to the ELContext.
*
* @param listener The listener to be added.
*
* @since EL 3.0
*/
public void addEvaluationListener(EvaluationListener listener) {
if (listeners == null) {
listeners = new ArrayList();
}
listeners.add(listener);
}
/**
* Returns the list of registered evaluation listeners.
* @return The list of registered evaluation listeners.
*
* @since EL 3.0
*/
public List getEvaluationListeners() {
return listeners;
}
/**
* Notifies the listeners before an EL expression is evaluated
* @param expr The EL expression string to be evaluated
*/
public void notifyBeforeEvaluation(String expr) {
if (getEvaluationListeners() == null)
return;
for (EvaluationListener listener: getEvaluationListeners()) {
listener.beforeEvaluation(this, expr);
}
}
/**
* Notifies the listeners after an EL expression is evaluated
* @param expr The EL expression string that has been evaluated
*/
public void notifyAfterEvaluation(String expr) {
if (getEvaluationListeners() == null)
return;
for (EvaluationListener listener: getEvaluationListeners()) {
listener.afterEvaluation(this, expr);
}
}
/**
* Notifies the listeners when the (base, property) pair is resolved
* @param base The base object
* @param property The property Object
*/
public void notifyPropertyResolved(Object base, Object property) {
if (getEvaluationListeners() == null)
return;
for (EvaluationListener listener: getEvaluationListeners()) {
listener.propertyResolved(this, base, property);
}
}
/**
* Inquires if the name is a LambdaArgument
* @param arg A possible Lambda formal parameter name
* @return true if arg is a LambdaArgument, false otherwise.
*/
public boolean isLambdaArgument(String arg) {
if (lambdaArgs == null) {
return false;
}
for (int i = lambdaArgs.size() - 1; i >= 0; i--) {
Map lmap = lambdaArgs.elementAt(i);
if (lmap.containsKey(arg)) {
return true;
}
}
return false;
}
/**
* 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.
*
* @param arg The formal parameter for the Lambda argument
* @return The object associated with formal parameter. Null if
* no object has been associated with the parameter.
* @since EL 3.0
*/
public Object getLambdaArgument(String arg) {
if (lambdaArgs == null) {
return null;
}
for (int i = lambdaArgs.size() - 1; i >= 0; i--) {
Map lmap = lambdaArgs.elementAt(i);
Object v = lmap.get(arg);
if (v != null) {
return v;
}
}
return null;
}
/**
* 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.
* @param args The Lambda arguments map
* @since EL 3.0
*/
public void enterLambdaScope(Map args) {
if (lambdaArgs == null) {
lambdaArgs = new Stack>();
}
lambdaArgs.push(args);
}
/**
* Exits the Lambda expression evaluation. The Lambda argument map that
* was previously installed is removed.
* @since EL 3.0
*/
public void exitLambdaScope() {
if (lambdaArgs != null) {
lambdaArgs.pop();
}
}
/**
* 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.
*
* @param obj The object to convert.
* @param targetType The target type for the conversion.
* @throws ELException thrown if errors occur.
*
* @since EL 3.0
*/
public Object convertToType(Object obj,
Class targetType) {
boolean propertyResolvedSave = isPropertyResolved();
try {
setPropertyResolved(false);
ELResolver elResolver = getELResolver();
if (elResolver != null) {
Object res = elResolver.convertToType(this, obj, targetType);
if (isPropertyResolved()) {
return res;
}
}
} catch (ELException ex) {
throw ex;
} catch (Exception ex) {
throw new ELException(ex);
} finally {
setPropertyResolved(propertyResolvedSave);
}
ExpressionFactory exprFactory = (ExpressionFactory)getContext(ExpressionFactory.class);
if (exprFactory == null) {
exprFactory = ELUtil.getExpressionFactory();
}
return exprFactory.coerceToType(obj, targetType);
}
private boolean resolved;
private HashMap, Object> map = new HashMap, Object>();
private transient List listeners = null;
private Stack> lambdaArgs;
private ImportHandler importHandler;
}