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org.codehaus.commons.compiler
Interface IExpressionEvaluator

All Superinterfaces:
IClassBodyEvaluator, ICookable, IScriptEvaluator
All Known Implementing Classes:
ExpressionEvaluator, ExpressionEvaluator
public interface IExpressionEvaluator
extends IScriptEvaluator

An engine that evaluates expressions in Java™ bytecode.

The syntax of the expression to compile is that of a Java™ expression, as defined in JLS7, section 15. Notice that a Java™ expression does not have a concluding semicolon.

Example:

   a + 7 * b
(Notice that this expression refers to two parameters "a" and "b", as explained below.)

The expression may optionally be preceeded with a sequence of import directives like 

   import java.text.*;
   new DecimalFormat("####,###.##").format(10200020.345345)
(Notice that the import directive is concluded with a semicolon, while the expression is not.) This feature is not available if you compile many expressions at a time (see below).

To set up an IExpressionEvaluator object, proceed as follows:

  1. Create an IExpressionEvaluator-derived class
  2. Configure the IExpressionEvaluator by calling any of the following methods:
  3. Call any of the ICookable.cook(String, java.io.Reader) methods to scan, parse, compile and load the expression into the JVM.
After the IExpressionEvaluator object is set up, the expression can be evaluated as often with different parameter values (see evaluate(Object[])). This evaluation is very fast, compared to the compilation.

Less common methods exist that allow for the specification of the name of the generated class, the class it extends, the interfaces it implements, the name of the method that executes the expression, the exceptions that this method (i.e. the expression) is allowed to throw, and the that is used to define the generated class and to load classes referenced by the expression.

If you want to compile many expressions at the same time, you have the option to cook an array of expressions in one IExpressionEvaluator by using the following methods:

Notice that these methods have array parameters in contrast to their one-expression brethren.

Notice that for functionally identical IExpressionEvaluators, will return true. E.g. "a+b" and "c + d" are functionally identical if "a" and "c" have the same type, and so do "b" and "d".

'JLS7' refers to the .

Field Summary
static  ANY_TYPE
          Special value for setExpressionType(Class) that indicates that the expression may have any type.
 
Fields inherited from interface org.codehaus.commons.compiler.IClassBodyEvaluator
DEFAULT_CLASS_NAME
 
Fields inherited from interface org.codehaus.commons.compiler.ICookable
BOOT_CLASS_LOADER, SYSTEM_PROPERTY_SOURCE_DEBUGGING_DIR, SYSTEM_PROPERTY_SOURCE_DEBUGGING_ENABLE
 
Method Summary
<T>
createFastEvaluator( reader, <T> interfaceToImplement, [] parameterNames)
          If the parameter and return types of the expression are known at compile time, then a "fast" script evaluator can be instantiated through this method.
<T>
createFastEvaluator( expression, <T> interfaceToImplement, [] parameterNames)
          If the parameter and return types of the expression are known at compile time, then a "fast" expression evaluator can be instantiated through createFastEvaluator(String, Class, String[]).
  evaluate([] arguments)
          Evaluates the expression with concrete parameter values.
 void setExpressionType( expressionType)
          Define the type of the expression.
 void setExpressionTypes([] expressionTypes)
          Same as setExpressionType(Class), but for multiple expressions.
 void setReturnType( returnType)
          Deprecated. Must not be used on an IExpressionEvaluator; use setExpressionType(Class) instead.
 void setReturnTypes([] returnTypes)
          Deprecated. Must not be used on an IExpressionEvaluator; use setExpressionTypes(Class[]) instead.
 
Methods inherited from interface org.codehaus.commons.compiler.IScriptEvaluator
cook, cook, cook, cook, evaluate, getMethod, getMethod, setMethodName, setMethodNames, setOverrideMethod, setOverrideMethod, setParameters, setParameters, setStaticMethod, setStaticMethod, setThrownExceptions, setThrownExceptions
 
Methods inherited from interface org.codehaus.commons.compiler.IClassBodyEvaluator
createInstance, getClazz, setClassName, setDefaultImports, setExtendedClass, setExtendedType, setImplementedInterfaces, setImplementedTypes
 
Methods inherited from interface org.codehaus.commons.compiler.ICookable
cook, cook, cook, cook, cook, cook, cook, cook, cookFile, cookFile, cookFile, cookFile, setCompileErrorHandler, setDebuggingInformation, setParentClassLoader, setWarningHandler
 

Field Detail

ANY_TYPE

static final  ANY_TYPE
Special value for setExpressionType(Class) that indicates that the expression may have any type.

Method Detail

setExpressionType

void setExpressionType( expressionType)
Define the type of the expression. The special type ANY_TYPE allows the expression to return any type (primitive or reference).

If expressionType is , then the expression must be an invocation of a void method.

Defaults to ANY_TYPE.

setExpressionTypes

void setExpressionTypes([] expressionTypes)
Same as setExpressionType(Class), but for multiple expressions.

setReturnType


void setReturnType( returnType)
Deprecated. Must not be used on an IExpressionEvaluator; use setExpressionType(Class) instead.

Description copied from interface: IScriptEvaluator
Defines the return type of the generated method. The meaning of a null value is implementation-dependent.

Specified by:
setReturnType in interface IScriptEvaluator

setReturnTypes


void setReturnTypes([] returnTypes)
Deprecated. Must not be used on an IExpressionEvaluator; use setExpressionTypes(Class[]) instead.

Description copied from interface: IScriptEvaluator
Defines the return types of the generated methods. The meaning of null elements is implementation-dependent.

Specified by:
setReturnTypes in interface IScriptEvaluator

evaluate

 evaluate([] arguments)
                throws
Evaluates the expression with concrete parameter values.

Each argument value must have the same type as specified through the "parameterTypes" parameter of IScriptEvaluator.setParameters(String[], Class[]).

Arguments of primitive type must passed with their wrapper class objects.

The object returned has the class as specified through setExpressionType(Class).

This method is thread-safe.

Specified by:
evaluate in interface IScriptEvaluator
Parameters:
arguments - The actual parameter values.
Throws:

createFastEvaluator

<T>  createFastEvaluator( expression,
                               <T> interfaceToImplement,
                               [] parameterNames)
                           throws CompileException
If the parameter and return types of the expression are known at compile time, then a "fast" expression evaluator can be instantiated through createFastEvaluator(String, Class, String[]). Expression evaluation is faster than through evaluate(Object[]), because it is not done through reflection but through direct method invocation.

Example: 

 public interface Foo {
     int bar(int a, int b);
 }
 ...
 ExpressionEvaluator ee = CompilerFactoryFactory.getDefaultCompilerFactory().newExpressionEvaluator();

 // Optionally configure the EE here...
 ee.setClassName("Bar");
 ee.setDefaultImports(new String[] { "java.util.*" });
 ee.setExtendedClass(SomeOtherClass.class);
 ee.setParentClassLoader(someClassLoader);

 // Optionally configure the EE here...
 Foo f = (Foo) ee.createFastEvaluator(
     "a + b",                    // expression to evaluate
     Foo.class,                  // interface that describes the expression's signature
     new String[] { "a", "b" }   // the parameters' names
 );
 System.out.println("1 + 2 = " + f.bar(1, 2)); // Evaluate the expression
All other configuration (implemented type, static method, return type, method name, parameter names and types, thrown exceptions) are predetermined by the interfaceToImplement. Notice: The interfaceToImplement must be accessible by the compiled class, i.e. either be declared public, or with protected or default access in the package of the compiled class (see IClassBodyEvaluator.setClassName(String).

Specified by:
createFastEvaluator in interface IScriptEvaluator
Parameters:
expression - Contains the sequence of script tokens
Throws:
CompileException
See Also:
IScriptEvaluator.createFastEvaluator(Reader, Class, String[])

createFastEvaluator

<T>  createFastEvaluator( reader,
                               <T> interfaceToImplement,
                               [] parameterNames)
                           throws CompileException,
Description copied from interface: IScriptEvaluator
If the parameter and return types of the expression are known at compile time, then a "fast" script evaluator can be instantiated through this method.

Script evaluation is faster than through IScriptEvaluator.evaluate(Object[]), because it is not done through reflection but through direct method invocation.

Example: 

 public interface Foo {
     int bar(int a, int b);
 }
 ...
 IScriptEvaluator se = CompilerFactoryFactory.getDefaultCompilerFactory().newScriptEvaluator();

 // Optionally configure the SE her:
 se.setClassName("Bar");
 se.setDefaultImports(new String[] { "java.util.*" });
 se.setExtendedClass(SomeOtherClass.class);
 se.setParentClassLoader(someClassLoader);

 Foo f = (Foo) se.createFastScriptEvaluator(
     "return a - b;",
     Foo.class,
     new String[] { "a", "b" }
 );
 System.out.println("1 - 2 = " + f.bar(1, 2));
All other configuration (implemented type, static method, return type, method name, parameter names and types, thrown exceptions) are predetermined by the interfaceToImplement. Notice: The interfaceToImplement must either be declared public, or with package scope in the same package as the generated class (see IClassBodyEvaluator.setClassName(String)).

Specified by:
createFastEvaluator in interface IScriptEvaluator
Parameters:
reader - Produces the stream of script tokens
interfaceToImplement - Must declare exactly one method
parameterNames - The names of the parameters of that method
Returns:
An object that implements the given interface
Throws:
CompileException
See Also:
createFastEvaluator(String, Class, String[])
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