ScopedAttributeELResolver (Java EE 5 SDK)

javax.servlet.jsp.el Class ScopedAttributeELResolver

java.lang.Object
  javax.el.ELResolver
      javax.servlet.jsp.el.ScopedAttributeELResolver

public class ScopedAttributeELResolver

extends ELResolver

Defines variable resolution behavior for scoped attributes.

This resolver handles all variable resolutions (where base is null. It searches PageContext.findAttribute() for a matching attribute. If not found, it will return null, or in the case of setValue it will create a new attribute in the page scope with the given name.

从以下版本开始:

JSP 2.1

另请参见:

ELResolver

ScopedAttributeELResolver

public ScopedAttributeELResolver()

getValue

public Object getValue(ELContext context,
                       Object base,
                       Object property)

If the base object is null, searches the page, request, session and application scopes for an attribute with the given name and returns it, or null if no attribute exists with the current name.

The propertyResolved property of the ELContext object must be set to true by this resolver before returning if base is null. If this property is not true after this method is called, the caller should ignore the return value.

规范说明:

getValue in class ELResolver

参数:

context - The context of this evaluation.

base - Only null is handled by this resolver. Other values will result in an immediate return.

property - The name of the scoped attribute to resolve.

返回:

If the propertyResolved property of ELContext was set to true, then the scoped attribute; otherwise undefined.

抛出异常:

NullPointerException - if context is null

ELException - if an exception was thrown while performing the property or variable resolution. The thrown exception must be included as the cause property of this exception, if available.

getType

public Class<Object> getType(ELContext context,
                             Object base,
                             Object property)

If the base object is null, returns Object.class to indicate that any type is valid to set for a scoped attribute.

The propertyResolved property of the ELContext object must be set to true by this resolver before returning if base is null. If this property is not true after this method is called, the caller should ignore the return value.

规范说明:

getType in class ELResolver

参数:

context - The context of this evaluation.

base - Only null is handled by this resolver. Other values will result in an immediate return.

property - The name of the scoped attribute to resolve.

返回:

If the propertyResolved property of ELContext was set to true, then Object.class; otherwise undefined.

抛出异常:

NullPointerException - if context is null

ELException - if an exception was thrown while performing the property or variable resolution. The thrown exception must be included as the cause property of this exception, if available.

setValue

public void setValue(ELContext context,
                     Object base,
                     Object property,
                     Object val)

If the base object is null, sets an existing scoped attribute to the new value, or creates a new scoped attribute if one does not exist by this name.

If the provided attribute name matches the key of an attribute in page scope, request scope, session scope, or application scope, the corresponding attribute value will be replaced by the provided value. Otherwise, a new page scope attribute will be created with the given name and value.

The propertyResolved property of the ELContext object must be set to true by this resolver before returning if base is null. If this property is not true after this method is called, the caller should ignore the return value.

规范说明:

setValue in class ELResolver

参数:

context - The context of this evaluation.

base - Only null is handled by this resolver. Other values will result in an immediate return.

property - The name of the scoped attribute to set.

val - The value for the scoped attribute.

抛出异常:

NullPointerException - if context is null.

ELException - if an exception was thrown while performing the property or variable resolution. The thrown exception must be included as the cause property of this exception, if available.

isReadOnly

public boolean isReadOnly(ELContext context,
                          Object base,
                          Object property)

If the base object is null, returns false to indicate that scoped attributes are never read-only.

The propertyResolved property of the ELContext object must be set to true by this resolver before returning if base is null. If this property is not true after this method is called, the caller should ignore the return value.

规范说明:

isReadOnly in class ELResolver

参数:

context - The context of this evaluation.

base - Only null is handled by this resolver. Other values will result in an immediate return.

property - The name of the scoped attribute.

返回:

If the propertyResolved property of ELContext was set to true, then false; otherwise undefined.

抛出异常:

NullPointerException - if context is null.

ELException - if an exception was thrown while performing the property or variable resolution. The thrown exception must be included as the cause property of this exception, if available.

getFeatureDescriptors

public Iterator<FeatureDescriptor> getFeatureDescriptors(ELContext context,
                                                         Object base)

If the base object is null, returns an Iterator containing FeatureDescriptor objects with information about each scoped attribute resolved by this resolver. Otherwise, returns null.

The Iterator returned must contain one instance of FeatureDescriptor for each scoped attribute found in any scope. Each info object contains information about a single scoped attribute, and is initialized as follows:

displayName - The name of the scoped attribute.

name - Same as displayName property.

shortDescription - A suitable description for the scoped attribute. Should include the attribute's current scope (page, request, session, application). Will vary by implementation.

expert - false

hidden - false

preferred - true

In addition, the following named attributes must be set in the returned FeatureDescriptors:

ELResolver.TYPE - The current runtime type of the scoped attribute.

ELResolver.RESOLVABLE_AT_DESIGN_TIME - true.

规范说明:

getFeatureDescriptors in class ELResolver

参数:

context - The context of this evaluation.

base - Only null is handled by this resolver. Other values will result in a null return value.

返回:

An Iterator containing one FeatureDescriptor object for each scoped attribute, or null if base is not null.

另请参见:

FeatureDescriptor

getCommonPropertyType

public Class<String> getCommonPropertyType(ELContext context,
                                           Object base)

If the base object is null, returns String.class. Otherwise, returns null.

规范说明:

getCommonPropertyType in class ELResolver

参数:

context - The context of this evaluation.

base - Only null is handled by this resolver. Other values will result in a null return value.

返回:

null if base is not null; otherwise String.class.

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