ValueExpressionImpl (Apache Tomcat 8.0.53 API Documentation)

java.lang.Object
- javax.el.Expression
- - javax.el.ValueExpression
  - - org.apache.el.ValueExpressionImpl

All Implemented Interfaces:

java.io.Externalizable, java.io.Serializable
```
public final class ValueExpressionImpl
extends 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

Constructors
Constructor and Description
`ValueExpressionImpl()`
`ValueExpressionImpl(java.lang.String expr, Node node, FunctionMapper fnMapper, VariableMapper varMapper, java.lang.Class<?> expectedType)`

Method Summary

Methods
Modifier and Type	Method and Description
`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(ELContext context)`
`java.lang.Object`	`getValue(ELContext context)`
`ValueReference`	`getValueReference(ELContext context)`
`int`	`hashCode()`
`boolean`	`isLiteralText()`
`boolean`	`isReadOnly(ELContext context)`
`void`	`readExternal(java.io.ObjectInput in)`
`void`	`setValue(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,
                   FunctionMapper fnMapper,
                   VariableMapper varMapper,
                   java.lang.Class<?> expectedType)
```
- Method Detail
  - equals
```
public boolean equals(java.lang.Object obj)
```
    Specified by:
    
    equals in class Expression
  - getExpectedType
```
public java.lang.Class<?> getExpectedType()
```
    Specified by:
    
    getExpectedType in class 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 Expression
    
    Returns:
    the expectedType passed to the ExpressionFactory.createValueExpression method that created this ValueExpression.
    See Also:
    Expression.getExpressionString()
  - getType
```
public java.lang.Class<?> getType(ELContext context)
                           throws PropertyNotFoundException,
                                  ELException
```
    Specified by:
    
    getType in class ValueExpression
    
    Parameters:
    context - The EL context for this evaluation
    
    Returns:
    The type of the result of this value expression
    
    Throws:
    
    PropertyNotFoundException - If a property/variable resolution failed because no match was found or a match was found but was not readable
    
    ELException - Wraps any exception throw whilst resolving a property or variable
  - getValue
```
public java.lang.Object getValue(ELContext context)
                          throws PropertyNotFoundException,
                                 ELException
```
    Specified by:
    
    getValue in class ValueExpression
    
    Parameters:
    context - The EL context for this evaluation
    
    Returns:
    The result of evaluating this value expression
    
    Throws:
    
    PropertyNotFoundException - If a property/variable resolution failed because no match was found or a match was found but was not readable
    
    ELException - Wraps any exception throw whilst resolving a property or variable
  - hashCode
```
public int hashCode()
```
    Specified by:
    
    hashCode in class Expression
  - isLiteralText
```
public boolean isLiteralText()
```
    Specified by:
    
    isLiteralText in class Expression
  - isReadOnly
```
public boolean isReadOnly(ELContext context)
                   throws PropertyNotFoundException,
                          ELException
```
    Specified by:
    
    isReadOnly in class ValueExpression
    
    Parameters:
    context - The EL context for this evaluation
    
    Returns:
    true if this expression is read only otherwise false
    
    Throws:
    
    PropertyNotFoundException - If a property/variable resolution failed because no match was found or a match was found but was not readable
    
    ELException - Wraps any exception throw whilst resolving a property or variable
  - 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(ELContext context,
            java.lang.Object value)
              throws PropertyNotFoundException,
                     PropertyNotWritableException,
                     ELException
```
    Specified by:
    
    setValue in class ValueExpression
    
    Parameters:
    context - The EL context for this evaluation
    value - The value to set the property to which this value expression refers
    
    Throws:
    
    PropertyNotFoundException - If a property/variable resolution failed because no match was found
    
    PropertyNotWritableException - If a property/variable resolution failed because a match was found but was not writable
    
    ELException - Wraps any exception throw whilst resolving a property or variable
  - 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
  - getValueReference
```
public ValueReference getValueReference(ELContext context)
```
    Overrides:
    
    getValueReference in class ValueExpression
    
    Parameters:
    context - The EL context for this evaluation
    
    Returns:
    This default implementation always returns null
    Since:
    
    EL 2.2

Class ValueExpressionImpl

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Constructor Detail

ValueExpressionImpl

ValueExpressionImpl

Method Detail

equals

getExpectedType

getExpressionString

getType

getValue

hashCode

isLiteralText

isReadOnly

readExternal

setValue

writeExternal

toString

getValueReference