| java.lang.Object
 org.jbpm.jpdl.el.ExpressionEvaluator
org.jbpm.jpdl.el.impl.ExpressionEvaluatorImpl
| ExpressionEvaluatorImpl | | public class ExpressionEvaluatorImpl extends ExpressionEvaluator (Code) | | This is the main class for evaluating expression Strings. An
expression String is a String that may contain expressions of the
form ${...}. Multiple expressions may appear in the same
expression String. In such a case, the expression String's value
is computed by concatenating the String values of those evaluated
expressions and any intervening non-expression text, then
converting the resulting String to the expected type using the
PropertyEditor mechanism.
In the special case where the expression String is a single
expression, the value of the expression String is determined by
evaluating the expression, without any intervening conversion to a
String.
The evaluator maintains a cache mapping expression Strings to
their parsed results. For expression Strings containing no
expression elements, it maintains a cache mapping
ExpectedType/ExpressionString to parsed value, so that static
expression Strings won't have to go through a conversion step every
time they are used. All instances of the evaluator share the same
cache. The cache may be bypassed by setting a flag on the
evaluator's constructor.
The evaluator must be passed a VariableResolver in its
constructor. The VariableResolver is used to resolve variable
names encountered in expressions, and can also be used to implement
"implicit objects" that are always present in the namespace.
Different applications will have different policies for variable
lookups and implicit objects - these differences can be
encapsulated in the VariableResolver passed to the evaluator's
constructor.
Most VariableResolvers will need to perform their resolution
against some context. For example, a JSP environment needs a
PageContext to resolve variables. The evaluate() method takes a
generic Object context which is eventually passed to the
VariableResolver - the VariableResolver is responsible for casting
the context to the proper type.
Once an evaluator instance has been constructed, it may be used
multiple times, and may be used by multiple simultaneous Threads.
In other words, an evaluator instance is well-suited for use as a
singleton.
author:
Nathan Abramson - Art Technology Group
author:
Shawn Bayern
version:
$Change: 181177 $$DateTime: 2001/06/26 08:45:09 $$Author$ |
| Method Summary | |
| static String | addEscapes(String str)
Used to convert raw characters to their escaped version when
these raw version cannot be used as part of an ASCII string
literal. | | Object | convertStaticValueToExpectedType(String pValue, Class pExpectedType, Logger pLogger)
Converts the given String, specified as a static expression
string, to the given expected type. | | Object | convertToExpectedType(Object pValue, Class pExpectedType, Logger pLogger)
Converts the given value to the specified expected type. | | public Object | evaluate(String pExpressionString, Class pExpectedType, VariableResolver pResolver, FunctionMapper functions)
Evaluates the given expression String
Parameters:
pExpressionString - The expression to be evaluated.
Parameters:
pExpectedType - The expected type of the result of the evaluation
Parameters:
pResolver - A VariableResolver instance that can be used at runtime to resolve the name of implicit objects into Objects.
Parameters:
functions - A FunctionMapper to resolve functions found in the expression. | | Object | evaluate(String pExpressionString, Class pExpectedType, VariableResolver pResolver, FunctionMapper functions, Logger pLogger)
| | static String | formatParseException(String pExpressionString, ParseException pExc)
| | static Map | getOrCreateExpectedTypeMap(Class pExpectedType)
Creates or returns the Map that maps string literals to parsed
values for the specified expected type. | | public String | parseAndRender(String pExpressionString)
Parses the given expression string, then converts it back to a
String in its canonical form. | | public org.jbpm.jpdl.el.Expression | parseExpression(String expression, Class expectedType, FunctionMapper fMapper)
Prepare an expression for later evaluation. | | public Object | parseExpressionString(String pExpressionString)
Gets the parsed form of the given expression string. |
| mBypassCache | | boolean mBypassCache(Code) | | Flag if the cache should be bypassed *
|
| sCachedExpectedTypes | | static Map sCachedExpectedTypes(Code) | | The mapping from ExpectedType to Maps mapping literal String to
parsed value *
|
| sCachedExpressionStrings | | static Map sCachedExpressionStrings(Code) | | The mapping from expression String to its parsed form (String,
Expression, or ExpressionString) *
|
| ExpressionEvaluatorImpl | | public ExpressionEvaluatorImpl()(Code) | | Constructor
|
| ExpressionEvaluatorImpl | | public ExpressionEvaluatorImpl(boolean pBypassCache)(Code) | | Constructor
Parameters:
pBypassCache - flag indicating if the cache should bebypassed |
| addEscapes | | static String addEscapes(String str)(Code) | | Used to convert raw characters to their escaped version when
these raw version cannot be used as part of an ASCII string
literal.
|
| convertStaticValueToExpectedType | | Object convertStaticValueToExpectedType(String pValue, Class pExpectedType, Logger pLogger) throws ELException(Code) | | Converts the given String, specified as a static expression
string, to the given expected type. The conversion is cached.
|
| evaluate | | public Object evaluate(String pExpressionString, Class pExpectedType, VariableResolver pResolver, FunctionMapper functions) throws ELException(Code) | | Evaluates the given expression String
Parameters:
pExpressionString - The expression to be evaluated.
Parameters:
pExpectedType - The expected type of the result of the evaluation
Parameters:
pResolver - A VariableResolver instance that can be used at runtime to resolve the name of implicit objects into Objects.
Parameters:
functions - A FunctionMapper to resolve functions found in the expression. It can be null, in which case no functions are supported for this invocation. the expression String evaluated to the given expectedtype |
| formatParseException | | static String formatParseException(String pExpressionString, ParseException pExc)(Code) | | Formats a ParseException into an error message suitable for
displaying on a web page
|
| getOrCreateExpectedTypeMap | | static Map getOrCreateExpectedTypeMap(Class pExpectedType)(Code) | | Creates or returns the Map that maps string literals to parsed
values for the specified expected type.
|
| parseAndRender | | public String parseAndRender(String pExpressionString) throws ELException(Code) | | Parses the given expression string, then converts it back to a
String in its canonical form. This is used to test parsing.
|
| parseExpression | | public org.jbpm.jpdl.el.Expression parseExpression(String expression, Class expectedType, FunctionMapper fMapper) throws ELException(Code) | | Prepare an expression for later evaluation. This method should perform
syntactic validation of the expression; if in doing so it detects
errors, it should raise an ELParseException.
Parameters:
expression - The expression to be evaluated.
Parameters:
expectedType - The expected type of the result of the evaluation
Parameters:
fMapper - A FunctionMapper to resolve functions found inthe expression. It can be null, in which case no functionsare supported for this invocation. The ExpressionEvaluatormust not hold on to the FunctionMapper reference afterreturning from parseExpression(). TheExpression object returned must invoke the samefunctions regardless of whether the mappings in theprovided FunctionMapper instance change betweencalling ExpressionEvaluator.parseExpression()and Expression.evaluate(). The Expression object encapsulating the arguments.
exception:
ELException - Thrown if parsing errors were found. |
| parseExpressionString | | public Object parseExpressionString(String pExpressionString) throws ELException(Code) | | Gets the parsed form of the given expression string. If the
parsed form is cached (and caching is not bypassed), return the
cached form, otherwise parse and cache the value. Returns either
a String, Expression, or ExpressionString.
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