ArrayELResolver (Java EE 5)

java.lang.Object
  javax.el.ELResolver
      javax.el.ArrayELResolver

定义数组上的属性解析行为。

此解析器处理类型为 Java 语言数组的 base 对象。它接受任何对象作为属性，并且将该对象强制匹配为数组中的整数索引。所得值就是数组中位于该索引处的值。

此解析器可以以只读模式构建，这意味着 #isReadOnly 将总是返回 true，#setValue 将总是抛出 PropertyNotWritableException。

ELResolver 使用 CompositeELResolver 连接到一起，以定义丰富语义来计算表达式。有关 ELResolver 的详细信息，请参阅 javadoc。

since	JSP 2.1
See also	javax.el.CompositeELResolver, javax.el.ELResolver

英文文档：

Defines property resolution behavior on arrays.

This resolver handles base objects that are Java language arrays. It accepts any object as a property and coerces that object into an integer index into the array. The resulting value is the value in the array at that index.

This resolver can be constructed in read-only mode, which means that isReadOnly will always return true and setValue(javax.el.ELContext, java.lang.Object, java.lang.Object, java.lang.Object) will always throw PropertyNotWritableException.

ELResolvers are combined together using CompositeELResolvers, to define rich semantics for evaluating an expression. See the javadocs for ELResolver for details.

Since:

JSP 2.1

See Also:

CompositeELResolver, ELResolver

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Field Summary

 

Fields inherited from class javax.el.ELResolver
RESOLVABLE_AT_DESIGN_TIME, TYPE

 

Constructor Summary
ArrayELResolver()           Creates a new read/write ArrayELResolver.
ArrayELResolver(boolean isReadOnly)           Creates a new ArrayELResolver whose read-only status is determined by the given parameter.

 

Method Summary
Class<?>	getCommonPropertyType(ELContext context, Object base)           If the base object is a Java language array, returns the most general type that this resolver accepts for the property argument.
Iterator<FeatureDescriptor>	getFeatureDescriptors(ELContext context, Object base)           Always returns null, since there is no reason to iterate through set set of all integers.
Class<?>	getType(ELContext context, Object base, Object property)           If the base object is an array, returns the most general acceptable type for a value in this array.
Object	getValue(ELContext context, Object base, Object property)           If the base object is a Java language array, returns the value at the given index.
boolean	isReadOnly(ELContext context, Object base, Object property)           If the base object is a Java language array, returns whether a call to setValue(javax.el.ELContext, java.lang.Object, java.lang.Object, java.lang.Object) will always fail.
void	setValue(ELContext context, Object base, Object property, Object val)           If the base object is a Java language array, attempts to set the value at the given index with the given value.

 

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

 

Constructor Detail

public ArrayELResolver()
创建新的读/写 ArrayELResolver。

英文文档：

ArrayELResolver

public ArrayELResolver()

Creates a new read/write ArrayELResolver.

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public ArrayELResolver(boolean isReadOnly)
创建新的 ArrayELResolver，其只读状态由给定的参数确定。

isReadOnly

如果此解析器无法修改数组，则为 true；否则为 false。

英文文档：

ArrayELResolver

public ArrayELResolver(boolean isReadOnly)

Creates a new ArrayELResolver whose read-only status is determined by the given parameter.

Parameters:

isReadOnly - true if this resolver cannot modify arrays; false otherwise.

Method Detail

public Class<T> getType(ELContext context, Object base, Object property)
如果 base 对象是数组，则返回此数组中的值可以接受的最一般类型。

如果 base 为 array，则在返回前，此解析器必须将 ELContext 对象的 propertyResolved 属性设置为 true。如果调用此方法后此属性不为 true，则调用者应该忽略返回值。

如果 base 为 array，则此方法将总是返回 base.getClass().getComponentType()，这是可以在数组的任何给定索引位置存储的最一般组件类型。

context	此计算的上下文。
base	要分析的数组。此解析器仅处理属于 Java 语言数组的 base。
property	返回可接受类型的数组元素的索引。将强制匹配为整数，其他情况下将被此解析器忽略。
return	如果 ELContext 的 propertyResolved 属性设置为 true，则返回最一般的可接受类型；其他情况未定义。
Throws	PropertyNotFoundException: 如果给定索引超出此数组的范围。
Throws	NullPointerException: 如果 context 为 null
Throws	ELException: 如果执行属性或变量解析时抛出异常。抛出的异常必须作为此异常的 cause 属性包含（如果可用）。

英文文档：

getType

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

If the base object is an array, returns the most general acceptable type for a value in this array.

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

Assuming the base is an array, this method will always return base.getClass().getComponentType(), which is the most general type of component that can be stored at any given index in the array.

Specified by:

getType in class ELResolver

Parameters:

context - The context of this evaluation.

base - The array to analyze. Only bases that are Java language arrays are handled by this resolver.

property - The index of the element in the array to return the acceptable type for. Will be coerced into an integer, but otherwise ignored by this resolver.

Returns:

If the propertyResolved property of ELContext was set to true, then the most general acceptable type; otherwise undefined.

Throws:

PropertyNotFoundException - if the given index is out of bounds for this array.

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.

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public Object getValue(ELContext context, Object base, Object property)
如果 base 对象为 Java 语言数组，则返回给定索引位置的值。property 参数指定的索引，强制匹配为整数。如果无法执行强制匹配，则抛出 IllegalArgumentException。如果索引超出边界，则返回 null。

如果 base 为 Java 语言数组，则在返回前，此解析器必须将 ELContext 对象的 propertyResolved 属性设置为 true。如果调用此方法后此属性不为 true，则调用者应该忽略返回值。

context	此计算的上下文。
base	要分析的数组。此解析器仅处理属于 Java 语言数组的 base。
property	要返回的值的索引。将强制匹配为整数。
return	如果 ELContext 的 propertyResolved 属性设置为 true，则返回给定索引处的值；如果索引超出边界，则返回 null。其他情况未定义。
Throws	IllegalArgumentException: 如果属性无法强制匹配为整数。
Throws	NullPointerException: 如果 context 为 null。
Throws	ELException: 如果执行属性或变量解析时抛出异常。抛出的异常必须作为此异常的 cause 属性包含（如果可用）。

英文文档：

getValue

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

If the base object is a Java language array, returns the value at the given index. The index is specified by the property argument, and coerced into an integer. If the coercion could not be performed, an IllegalArgumentException is thrown. If the index is out of bounds, null is returned.

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

Specified by:

getValue in class ELResolver

Parameters:

context - The context of this evaluation.

base - The array to analyze. Only bases that are Java language arrays are handled by this resolver.

property - The index of the value to be returned. Will be coerced into an integer.

Returns:

If the propertyResolved property of ELContext was set to true, then the value at the given index or null if the index was out of bounds. Otherwise, undefined.

Throws:

IllegalArgumentException - if the property could not be coerced into an integer.

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.

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public void setValue(ELContext context, Object base, Object property, Object val)
如果 base 对象为 Java 语言数组，则尝试用给定的值设置给定索引位置的值。property 参数指定的索引，强制匹配为整数。如果无法执行强制匹配，则抛出 IllegalArgumentException。如果索引超出边界，则抛出 PropertyNotFoundException。

如果 base 为 Java 语言数组，则在返回前，此解析器必须将 ELContext 对象的 propertyResolved 属性设置为 true。如果调用此方法后此属性不为 true，则调用者可以放心地假定没有设置任何值。

如果此解析器以只读模式构造，则此方法将总是抛出 PropertyNotWritableException。

context	此计算的上下文。
base	要修改的数组。此解析器仅处理属于 Java 语言数组的 base。
property	要设置的值的索引。将强制匹配为整数。
val	要在给定索引处设置的值。
Throws	ClassCastException: 如果指定元素的类不允许该元素添加到此数组。
Throws	NullPointerException: 如果 context 为 null。
Throws	IllegalArgumentException: 如果属性无法强制匹配为整数，或者指定元素的某个方面不允许该元素添加到此数组。
Throws	PropertyNotWritableException: 如果此解析器以只读模式构建。
Throws	PropertyNotFoundException: 如果给定索引超出此数组的范围。
Throws	ELException: 如果执行属性或变量解析时抛出异常。抛出的异常必须作为此异常的 cause 属性包含（如果可用）。

英文文档：

setValue

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

If the base object is a Java language array, attempts to set the value at the given index with the given value. The index is specified by the property argument, and coerced into an integer. If the coercion could not be performed, an IllegalArgumentException is thrown. If the index is out of bounds, a PropertyNotFoundException is thrown.

If the base is a Java language array, the propertyResolved property of the ELContext object must be set to true by this resolver, before returning. If this property is not true after this method is called, the caller can safely assume no value was set.

If this resolver was constructed in read-only mode, this method will always throw PropertyNotWritableException.

Specified by:

setValue in class ELResolver

Parameters:

context - The context of this evaluation.

base - The array to be modified. Only bases that are Java language arrays are handled by this resolver.

property - The index of the value to be set. Will be coerced into an integer.

val - The value to be set at the given index.

Throws:

ClassCastException - if the class of the specified element prevents it from being added to this array.

NullPointerException - if context is null.

IllegalArgumentException - if the property could not be coerced into an integer, or if some aspect of the specified element prevents it from being added to this array.

PropertyNotWritableException - if this resolver was constructed in read-only mode.

PropertyNotFoundException - if the given index is out of bounds for this array.

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.

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public boolean isReadOnly(ELContext context, Object base, Object property)
如果 base 对象是 Java 语言数组，则返回对 #setValue 的调用是否总是失败。

如果 base 为 Java 语言数组，则在返回前，此解析器必须将 ELContext 对象的 propertyResolved 属性设置为 true。如果调用此方法后此属性不为 true，则调用者应该忽略返回值。

如果此解析器以只读模式构造，则此方法将总是返回 true。否则返回 false。

context	此计算的上下文。
base	要分析的数组。此解析器仅处理属于 Java 语言数组的 base。
property	返回可接受类型的数组元素的索引。将强制匹配为整数，其他情况下将被此解析器忽略。
return	如果 ELContext 的 propertyResolved 属性设置为 true，则调用 setValue 方法总是失败的情况下返回 true，该调用可能成功的情况下返回 false；其他情况未定义。
Throws	PropertyNotFoundException: 如果给定索引超出此数组的范围。
Throws	NullPointerException: 如果 context 为 null
Throws	ELException: 如果执行属性或变量解析时抛出异常。抛出的异常必须作为此异常的 cause 属性包含（如果可用）。

英文文档：

isReadOnly

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

If the base object is a Java language array, returns whether a call to setValue(javax.el.ELContext, java.lang.Object, java.lang.Object, java.lang.Object) will always fail.

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

If this resolver was constructed in read-only mode, this method will always return true. Otherwise, it returns false.

Specified by:

isReadOnly in class ELResolver

Parameters:

context - The context of this evaluation.

base - The array to analyze. Only bases that are a Java language array are handled by this resolver.

property - The index of the element in the array to return the acceptable type for. Will be coerced into an integer, but otherwise ignored by this resolver.

Returns:

If the propertyResolved property of ELContext was set to true, then true if calling the setValue method will always fail or false if it is possible that such a call may succeed; otherwise undefined.

Throws:

PropertyNotFoundException - if the given index is out of bounds for this array.

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.

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public java.util.Iterator<E> getFeatureDescriptors(ELContext context, Object base)
总是返回 null，因为没有理由迭代所有整数集。

#getCommonPropertyType 方法返回有关此解析器接受的属性的足够信息。

context	此计算的上下文。
base	要分析的数组。此解析器仅处理属于 Java 语言数组的 base。
return	null。

英文文档：

getFeatureDescriptors

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

Always returns null, since there is no reason to iterate through set set of all integers.

The getCommonPropertyType(javax.el.ELContext, java.lang.Object) method returns sufficient information about what properties this resolver accepts.

Specified by:

getFeatureDescriptors in class ELResolver

Parameters:

context - The context of this evaluation.

base - The array to analyze. Only bases that are a Java language array are handled by this resolver.

Returns:

null.

See Also:

FeatureDescriptor

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public Class<T> getCommonPropertyType(ELContext context, Object base)
如果 base 对象不是 Java 语言数组，则返回对于 property 参数此解析器可接受的最一般类型。否则返回 null。

假定 base 为数组，则此方法将总是返回 Integer.class。这是因为数组接受整数作为其索引。

context	此计算的上下文。
base	要分析的数组。此解析器仅处理属于 Java 语言数组的 base。
return	如果 base 不是 Java 语言数组，则返回 null；否则返回 Integer.class。

英文文档：

getCommonPropertyType

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

If the base object is a Java language array, returns the most general type that this resolver accepts for the property argument. Otherwise, returns null.

Assuming the base is an array, this method will always return Integer.class. This is because arrays accept integers for their index.

Specified by:

getCommonPropertyType in class ELResolver

Parameters:

context - The context of this evaluation.

base - The array to analyze. Only bases that are a Java language array are handled by this resolver.

Returns:

null if base is not a Java language array; otherwise Integer.class.

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