com.sun.el
类 ValueExpressionImpl

java.lang.Object
  javax.el.Expression
      javax.el.ValueExpression
          com.sun.el.ValueExpressionImpl

所有已实现的接口：

Externalizable, Serializable

public final class ValueExpressionImpl
extends ValueExpression
implements Externalizable

An Expression that can get or set a value.

In previous incarnations of this API, expressions could only be read. ValueExpression objects can now be used both to retrieve a value and to set a value. Expressions that can have a value set on them are referred to as l-value expressions. Those that cannot are referred to as r-value expressions. Not all r-value expressions can be used as l-value expressions (e.g. "${1+1}" or "${firstName} ${lastName}"). See the EL Specification for details. Expressions that cannot be used as l-values must always return true from isReadOnly().

The ExpressionFactory.createValueExpression(javax.el.ELContext, java.lang.String, java.lang.Class) method can be used to parse an expression string and return a concrete instance of ValueExpression that encapsulates the parsed expression. The FunctionMapper is used at parse time, not evaluation time, so one is not needed to evaluate an expression using this class. However, the ELContext is needed at evaluation time.

The getValue(javax.el.ELContext), setValue(javax.el.ELContext, java.lang.Object), isReadOnly(javax.el.ELContext) and getType(javax.el.ELContext) methods will evaluate the expression each time they are called. The ELResolver in the ELContext is used to resolve the top-level variables and to determine the behavior of the . and [] operators. For any of the four methods, the ELResolver.getValue(javax.el.ELContext, java.lang.Object, java.lang.Object) method is used to resolve all properties up to but excluding the last one. This provides the base object. At the last resolution, the ValueExpression will call the corresponding ELResolver.getValue(javax.el.ELContext, java.lang.Object, java.lang.Object), ELResolver.setValue(javax.el.ELContext, java.lang.Object, java.lang.Object, java.lang.Object), ELResolver.isReadOnly(javax.el.ELContext, java.lang.Object, java.lang.Object) or ELResolver.getType(javax.el.ELContext, java.lang.Object, java.lang.Object) method, depending on which was called on the ValueExpression.

See the notes about comparison, serialization and immutability in the Expression javadocs.

版本：

$Change: 181177 $$DateTime: 2001/06/26 08:45:09 $$Author: hmalphett $

作者：

Jacob Hookom [jacob@hookom.net]

另请参见：

ELResolver, Expression, ExpressionFactory, ValueExpression, 序列化表格

构造方法摘要

ValueExpressionImpl()

ValueExpressionImpl(String expr, Node node, FunctionMapper fnMapper, VariableMapper varMapper, Class expectedType)

方法摘要

boolean	equals(Object obj) Determines whether the specified object is equal to this Expression.
Class	getExpectedType() Returns the type the result of the expression will be coerced to after evaluation.
String	getExpressionString() Returns the type the result of the expression will be coerced to after evaluation.
Class	getType(ELContext context) Evaluates the expression relative to the provided context, and returns the most general type that is acceptable for an object to be passed as the value parameter in a future call to the ValueExpression.setValue(javax.el.ELContext, java.lang.Object) method.
Object	getValue(ELContext context) Evaluates the expression relative to the provided context, and returns the resulting value.
ValueReference	getValueReference(ELContext context) Returns a ValueReference for this expression instance.
int	hashCode() Returns the hash code for this Expression.
boolean	isLiteralText() Returns whether this expression was created from only literal text.
boolean	isReadOnly(ELContext context) Evaluates the expression relative to the provided context, and returns true if a call to ValueExpression.setValue(javax.el.ELContext, java.lang.Object) will always fail.
void	readExternal(ObjectInput in)
void	setValue(ELContext context, Object value) Evaluates the expression relative to the provided context, and sets the result to the provided value.
String	toString()
void	writeExternal(ObjectOutput out)

从类 java.lang.Object 继承的方法

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

构造方法详细信息

ValueExpressionImpl

public ValueExpressionImpl()

ValueExpressionImpl

public ValueExpressionImpl(String expr,
                           Node node,
                           FunctionMapper fnMapper,
                           VariableMapper varMapper,
                           Class expectedType)

方法详细信息

equals

public boolean equals(Object obj)

从类 Expression 复制的描述

Determines whether the specified object is equal to this Expression.

The result is true if and only if the argument is not null, is an Expression object that is the of the same type (ValueExpression or MethodExpression), and has an identical parsed representation.

Note that two expressions can be equal if their expression Strings are different. For example, ${fn1:foo()} and ${fn2:foo()} are equal if their corresponding FunctionMappers mapped fn1:foo and fn2:foo to the same method.

指定者：

类 Expression 中的 equals

参数：

obj - the Object to test for equality.

返回：

true if obj equals this Expression; false otherwise.

另请参见：

Hashtable, Object.equals(java.lang.Object)

getExpectedType

public Class getExpectedType()

从类 ValueExpression 复制的描述

Returns the type the result of the expression will be coerced to after evaluation.

指定者：

类 ValueExpression 中的 getExpectedType

返回：

the expectedType passed to the ExpressionFactory.createValueExpression method that created this ValueExpression.

getExpressionString

public String getExpressionString()

Returns the type the result of the expression will be coerced to after evaluation.

指定者：

类 Expression 中的 getExpressionString

返回：

the expectedType passed to the ExpressionFactory.createValueExpression method that created this ValueExpression.

另请参见：

Expression.getExpressionString()

getType

public Class getType(ELContext context)
              throws PropertyNotFoundException,
                     ELException

从类 ValueExpression 复制的描述

Evaluates the expression relative to the provided context, and returns the most general type that is acceptable for an object to be passed as the value parameter in a future call to the ValueExpression.setValue(javax.el.ELContext, java.lang.Object) method.

This is not always the same as getValue().getClass(). For example, in the case of an expression that references an array element, the getType method will return the element type of the array, which might be a superclass of the type of the actual element that is currently in the specified array element.

指定者：

类 ValueExpression 中的 getType

参数：

context - The context of this evaluation.

返回：

the most general acceptable type; otherwise undefined.

抛出：

PropertyNotFoundException - if one of the property resolutions failed because a specified variable or property does not exist or is not readable.

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

getValueReference

public ValueReference getValueReference(ELContext context)
                                 throws PropertyNotFoundException,
                                        ELException

从类 ValueExpression 复制的描述

Returns a ValueReference for this expression instance.

覆盖：

类 ValueExpression 中的 getValueReference

参数：

context - the context of this evaluation

返回：

the ValueReference for this ValueExpression, or null if this ValueExpression is not a reference to a base (null or non-null) and a property. If the base is null, and the property is a EL variable, return the ValueReference for the ValueExpression associated with this EL variable.

抛出：

PropertyNotFoundException

ELException

getValue

public Object getValue(ELContext context)
                throws PropertyNotFoundException,
                       ELException

从类 ValueExpression 复制的描述

Evaluates the expression relative to the provided context, and returns the resulting value.

The resulting value is automatically coerced to the type returned by getExpectedType(), which was provided to the ExpressionFactory when this expression was created.

指定者：

类 ValueExpression 中的 getValue

参数：

context - The context of this evaluation.

返回：

The result of the expression evaluation.

抛出：

PropertyNotFoundException - if one of the property resolutions failed because a specified variable or property does not exist or is not readable.

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

hashCode

public int hashCode()

从类 Expression 复制的描述

Returns the hash code for this Expression.

See the note in the Expression.equals(java.lang.Object) method on how two expressions can be equal if their expression Strings are different. Recall that if two objects are equal according to the equals(Object) method, then calling the hashCode method on each of the two objects must produce the same integer result. Implementations must take special note and implement hashCode correctly.

指定者：

类 Expression 中的 hashCode

返回：

The hash code for this Expression.

另请参见：

Expression.equals(java.lang.Object), Hashtable, Object.hashCode()

isLiteralText

public boolean isLiteralText()

从类 Expression 复制的描述

Returns whether this expression was created from only literal text.

This method must return true if and only if the expression string this expression was created from contained no unescaped EL delimeters (${...} or #{...}).

指定者：

类 Expression 中的 isLiteralText

返回：

true if this expression was created from only literal text; false otherwise.

isReadOnly

public boolean isReadOnly(ELContext context)
                   throws PropertyNotFoundException,
                          ELException

从类 ValueExpression 复制的描述

Evaluates the expression relative to the provided context, and returns true if a call to ValueExpression.setValue(javax.el.ELContext, java.lang.Object) will always fail.

指定者：

类 ValueExpression 中的 isReadOnly

参数：

context - The context of this evaluation.

返回：

true if the expression is read-only or false if not.

抛出：

PropertyNotFoundException - if one of the property resolutions failed because a specified variable or property does not exist or is not readable.

ELException - if an exception was thrown while performing property or variable resolution. The thrown exception must be included as the cause property of this exception, if available. * @throws NullPointerException if context is null

readExternal

public void readExternal(ObjectInput in)
                  throws IOException,
                         ClassNotFoundException

指定者：

接口 Externalizable 中的 readExternal

抛出：

IOException

ClassNotFoundException

setValue

public void setValue(ELContext context,
                     Object value)
              throws PropertyNotFoundException,
                     PropertyNotWritableException,
                     ELException

从类 ValueExpression 复制的描述

Evaluates the expression relative to the provided context, and sets the result to the provided value.

指定者：

类 ValueExpression 中的 setValue

参数：

context - The context of this evaluation.

value - The new value to be set.

抛出：

PropertyNotFoundException - if one of the property resolutions failed because a specified variable or property does not exist or is not readable.

PropertyNotWritableException - if the final variable or property resolution failed because the specified variable or property is not writable.

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

writeExternal

public void writeExternal(ObjectOutput out)
                   throws IOException

指定者：

接口 Externalizable 中的 writeExternal

抛出：

IOException

toString

public String toString()

覆盖：

类 Object 中的 toString