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org.apache.el
Class ValueExpressionImpl

java.lang.Object
  extended by javax.el.Expression
      extended by javax.el.ValueExpression
          extended by org.apache.el.ValueExpressionImpl
All Implemented Interfaces:
java.io.Externalizable, java.io.Serializable
public final class ValueExpressionImpl
extends javax.el.ValueExpression
implements java.io.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.

Author:
Jacob Hookom [jacob@hookom.net]
See Also:
ELResolver, Expression, ExpressionFactory, ValueExpression, Serialized Form

Constructor Summary
ValueExpressionImpl()
           
ValueExpressionImpl(java.lang.String expr, Node node, javax.el.FunctionMapper fnMapper, javax.el.VariableMapper varMapper, java.lang.Class expectedType)
           
 
Method Summary
 boolean equals(java.lang.Object obj)
           
 java.lang.Class getExpectedType()
           
 java.lang.String getExpressionString()
          Returns the type the result of the expression will be coerced to after evaluation.
 java.lang.Class getType(javax.el.ELContext context)
           
 java.lang.Object getValue(javax.el.ELContext context)
           
 int hashCode()
           
 boolean isLiteralText()
           
 boolean isReadOnly(javax.el.ELContext context)
           
 void readExternal(java.io.ObjectInput in)
           
 void setValue(javax.el.ELContext context, java.lang.Object value)
           
 java.lang.String toString()
           
 void writeExternal(java.io.ObjectOutput out)
           
 
Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait
 

Constructor Detail

ValueExpressionImpl

public ValueExpressionImpl()

ValueExpressionImpl

public ValueExpressionImpl(java.lang.String expr,
                           Node node,
                           javax.el.FunctionMapper fnMapper,
                           javax.el.VariableMapper varMapper,
                           java.lang.Class expectedType)
Method Detail

equals

public boolean equals(java.lang.Object obj)
Specified by:
equals in class javax.el.Expression

getExpectedType

public java.lang.Class getExpectedType()
Specified by:
getExpectedType in class javax.el.ValueExpression

getExpressionString

public java.lang.String getExpressionString()
Returns the type the result of the expression will be coerced to after evaluation.

Specified by:
getExpressionString in class javax.el.Expression
Returns:
the expectedType passed to the ExpressionFactory.createValueExpression method that created this ValueExpression.
See Also:
Expression.getExpressionString()

getType

public java.lang.Class getType(javax.el.ELContext context)
                        throws javax.el.PropertyNotFoundException,
                               javax.el.ELException
Specified by:
getType in class javax.el.ValueExpression
Throws:
javax.el.PropertyNotFoundException
javax.el.ELException

getValue

public java.lang.Object getValue(javax.el.ELContext context)
                          throws javax.el.PropertyNotFoundException,
                                 javax.el.ELException
Specified by:
getValue in class javax.el.ValueExpression
Throws:
javax.el.PropertyNotFoundException
javax.el.ELException

hashCode

public int hashCode()
Specified by:
hashCode in class javax.el.Expression

isLiteralText

public boolean isLiteralText()
Specified by:
isLiteralText in class javax.el.Expression

isReadOnly

public boolean isReadOnly(javax.el.ELContext context)
                   throws javax.el.PropertyNotFoundException,
                          javax.el.ELException
Specified by:
isReadOnly in class javax.el.ValueExpression
Throws:
javax.el.PropertyNotFoundException
javax.el.ELException

readExternal

public void readExternal(java.io.ObjectInput in)
                  throws java.io.IOException,
                         java.lang.ClassNotFoundException
Specified by:
readExternal in interface java.io.Externalizable
Throws:
java.io.IOException
java.lang.ClassNotFoundException

setValue

public void setValue(javax.el.ELContext context,
                     java.lang.Object value)
              throws javax.el.PropertyNotFoundException,
                     javax.el.PropertyNotWritableException,
                     javax.el.ELException
Specified by:
setValue in class javax.el.ValueExpression
Throws:
javax.el.PropertyNotFoundException
javax.el.PropertyNotWritableException
javax.el.ELException

writeExternal

public void writeExternal(java.io.ObjectOutput out)
                   throws java.io.IOException
Specified by:
writeExternal in interface java.io.Externalizable
Throws:
java.io.IOException

toString

public java.lang.String toString()
Overrides:
toString in class java.lang.Object
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