org.activiti.engine.impl.juel

Class TreeValueExpression

java.lang.Object

org.activiti.engine.impl.javax.el.Expression

org.activiti.engine.impl.javax.el.ValueExpression

org.activiti.engine.impl.juel.TreeValueExpression

All Implemented Interfaces:

Serializable

public final class TreeValueExpression
extends ValueExpression

A value expression is ready to be evaluated (by calling either getType(ELContext), getValue(ELContext), isReadOnly(ELContext) or setValue(ELContext, Object). Instances of this class are usually created using an ExpressionFactoryImpl.

Author:

Christoph Beck

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
TreeValueExpression(TreeStore store, FunctionMapper functions, VariableMapper variables, TypeConverter converter, String expr, Class<?> type) Create a new value expression.

Method Summary

Methods

Modifier and Type	Method and Description
void	dump(PrintWriter writer) Print the parse tree.
boolean	equals(Object obj) Expressions are compared using the concept of a structural id: variable and function names are anonymized such that two expressions with same tree structure will also have the same structural id and vice versa.
Class<?>	getExpectedType() Returns the type the result of the expression will be coerced to after evaluation.
String	getExpressionString() Returns the original String used to create this Expression, unmodified.
Class<?>	getType(ELContext context) Evaluates the expression as an lvalue and answers the result type.
Object	getValue(ELContext context) Evaluates the expression as an rvalue and answers the result.
ValueReference	getValueReference(ELContext context) Returns a ValueReference for this expression instance.
int	hashCode() Returns the hash code for this Expression.
boolean	isDeferred() Answer true if this is a deferred expression (containing sub-expressions starting with #{)
boolean	isLeftValue() Answer true if this could be used as an lvalue.
boolean	isLiteralText() Returns whether this expression was created from only literal text.
boolean	isReadOnly(ELContext context) Evaluates the expression as an lvalue and determines if setValue(ELContext, Object) will always fail.
void	setValue(ELContext context, Object value) Evaluates the expression as an lvalue and assigns the given value.
String	toString()

Methods inherited from class java.lang.Object

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

Constructor Detail

TreeValueExpression

public TreeValueExpression(TreeStore store,
                   FunctionMapper functions,
                   VariableMapper variables,
                   TypeConverter converter,
                   String expr,
                   Class<?> type)

Create a new value expression.

Parameters:

store - used to get the parse tree from.

functions - the function mapper used to bind functions

variables - the variable mapper used to bind variables

expr - the expression string

type - the expected type (may be null)

Method Detail

getExpectedType

public Class<?> getExpectedType()

Description copied from class: ValueExpression

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

Specified by:

getExpectedType in class ValueExpression

Returns:

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

getExpressionString

public String getExpressionString()

Description copied from class: Expression

Returns the original String used to create this Expression, unmodified. This is used for debugging purposes but also for the purposes of comparison (e.g. to ensure the expression in a configuration file has not changed). This method does not provide sufficient information to re-create an expression. Two different expressions can have exactly the same expression string but different function mappings. Serialization should be used to save and restore the state of an Expression.

Specified by:

getExpressionString in class Expression

Returns:

The original expression String.

getType

public Class<?> getType(ELContext context)
                 throws ELException

Evaluates the expression as an lvalue and answers the result type.

Specified by:

getType in class ValueExpression

Parameters:

context - used to resolve properties (base.property and base[property]) and to determine the result from the last base/property pair

Returns:

lvalue evaluation type or null for rvalue expressions

Throws:

ELException - if evaluation fails (e.g. property not found, type conversion failed, ...)

getValue

public Object getValue(ELContext context)
                throws ELException

Evaluates the expression as an rvalue and answers the result.

Specified by:

getValue in class ValueExpression

Parameters:

context - used to resolve properties (base.property and base[property]) and to determine the result from the last base/property pair

Returns:

rvalue evaluation result

Throws:

ELException - if evaluation fails (e.g. property not found, type conversion failed, ...)

isReadOnly

public boolean isReadOnly(ELContext context)
                   throws ELException

Evaluates the expression as an lvalue and determines if setValue(ELContext, Object) will always fail.

Specified by:

isReadOnly in class ValueExpression

Parameters:

context - used to resolve properties (base.property and base[property]) and to determine the result from the last base/property pair

Returns:

true if setValue(ELContext, Object) always fails.

Throws:

ELException - if evaluation fails (e.g. property not found, type conversion failed, ...)

setValue

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

Evaluates the expression as an lvalue and assigns the given value.

Specified by:

setValue in class ValueExpression

Parameters:

context - used to resolve properties (base.property and base[property]) and to perform the assignment to the last base/property pair

value - The new value to be set.

Throws:

ELException - if evaluation fails (e.g. property not found, type conversion failed, assignment failed...)

isLiteralText

public boolean isLiteralText()

Description copied from class: Expression

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 #{...}).

Specified by:

isLiteralText in class Expression

Returns:

true if this is a literal text expression

getValueReference

public ValueReference getValueReference(ELContext context)

Description copied from class: ValueExpression

Returns a ValueReference for this expression instance.

Overrides:

getValueReference in class ValueExpression

Parameters:

context - the context of this evaluation

Returns:

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.

isLeftValue

public boolean isLeftValue()

Answer true if this could be used as an lvalue. This is the case for eval expressions consisting of a simple identifier or a nonliteral prefix, followed by a sequence of property operators (. or [])

isDeferred

public boolean isDeferred()

Answer true if this is a deferred expression (containing sub-expressions starting with #{)

equals

public boolean equals(Object obj)

Expressions are compared using the concept of a structural id: variable and function names are anonymized such that two expressions with same tree structure will also have the same structural id and vice versa. Two value expressions are equal if

1. their structural id's are equal
2. their bindings are equal
3. their expected types are equal

Specified by:

equals in class Expression

Parameters:

obj - the Object to test for equality.

Returns:

true if obj equals this Expression; false otherwise.

hashCode

public int hashCode()

Description copied from class: Expression

Returns the hash code for this Expression. See the note in the Expression.equals(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.

Specified by:

hashCode in class Expression

Returns:

The hash code for this Expression.

See Also:

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

toString

public String toString()

Overrides:

toString in class Object

dump

public void dump(PrintWriter writer)

Print the parse tree.

Parameters:

writer -