ELContext (Java EE 5 SDK)

javax.el Class ELContext

java.lang.Object
  javax.el.ELContext

public abstract class ELContext

extends Object

Context information for expression evaluation.

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

• a reference to the base ELResolver that will be consulted to resolve model objects and their properties
• a reference to FunctionMapper that will be used to resolve EL Functions.
• a reference to VariableMapper that will be used to resolve EL Variables.
• 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

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.

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.

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.

从以下版本开始:

JSP 2.1

另请参见:

ELContextListener, ELContextEvent, ELResolver, FunctionMapper, VariableMapper, JspContext

ELContext

public ELContext()

setPropertyResolved

public void setPropertyResolved(boolean resolved)

Called to indicate that a 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.

参数:

resolved - true if the property has been resolved, or false if not.

另请参见:

CompositeELResolver

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.

返回:

true if the property has been resolved, or false if not.

另请参见:

CompositeELResolver

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.

参数:

key - The key used by an @{link ELResolver} to identify this context object.

contextObject - The context object to add to the collection.

抛出异常:

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.

参数:

key - The unique identifier that was used to associate the context object with this ELContext.

返回:

The context object associated with the given key, or null if no such context was found.

抛出异常:

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.

返回:

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

getFunctionMapper

public abstract FunctionMapper getFunctionMapper()

Retrieves the FunctionMapper associated with this ELContext.

返回:

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.

返回:

The Locale in which this instance is operating. Used primarily for message localization.

setLocale

public void setLocale(Locale locale)

Set 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.

返回:

The variable mapper to be consulted for the resolution of EL variables.

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