Interface IExpressionEvaluator

All Superinterfaces:
ICookable, IMultiCookable
All Known Implementing Classes:
ExpressionEvaluator, ExpressionEvaluator
public interface IExpressionEvaluator extends ICookable, IMultiCookable
An engine that evaluates expressions in JVM 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 ClassLoader 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, Object.equals(java.lang.Object) 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 Java Language Specification, Java SE 7 Edition.

  • Field Details

    • DEFAULT_CLASS_NAME

      static final String DEFAULT_CLASS_NAME
      The fully qualified name of the generated class, iff not reconfigured by setClassName(String).
      See Also:

    • DEFAULT_EXPRESSION_TYPE

      static final Class<?> DEFAULT_EXPRESSION_TYPE
      The type of all expressions that were not reconfigured with setExpressionTypes(Class[]).

    • ANY_TYPE

      @Deprecated static final Class<?> ANY_TYPE
      Deprecated.
      Since autoboxing was introduced in JANINO, this feature is no longer necessary because you can use expression type Object.class
      Special value for setExpressionType(Class) that indicates that the expression may have any type.

  • Method Details

    • setParentClassLoader

      void setParentClassLoader(@Nullable ClassLoader parentClassLoader)
      The "parent class loader" is used to load referenced classes. Useful values are:
      System.getSystemClassLoader() The running JVM's class path
      Thread.currentThread().getContextClassLoader() or null The class loader effective for the invoking thread
      ClassLoaders.BOOTCLASSPATH_CLASS_LOADER The running JVM's boot class path

      The parent class loader defaults to the current thread's context class loader.

    • setDebuggingInformation

      void setDebuggingInformation(boolean debugSource, boolean debugLines, boolean debugVars)
      Determines what kind of debugging information is included in the generates classes. The default is typically "-g:none".

    • setCompileErrorHandler

      void setCompileErrorHandler(@Nullable ErrorHandler compileErrorHandler)
      Installs an ErrorHandler which is invoked during compilation on each error. (By default, the compilation throws a CompileException on the first error and terminates.)

      If the given ErrorHandler throws a CompileException, then the compilation terminates and the exception is propagated.

      If the given ErrorHandler does not throw a CompileException but completes normally, then the compilation may or may not continue, depending on the error. Iff the compilation completes normally but errors were reported, then it will throw a CompileException indicating the number of errors.

      In other words: The ErrorHandler may throw a CompileException or not, but the compilation will definitely throw a CompileException if one or more compile errors have occurred.

      Parameters:
      compileErrorHandler - null to restore the default behavior (throwing a CompileException)

    • setWarningHandler

      void setWarningHandler(@Nullable WarningHandler warningHandler)
      By default, warnings are discarded, but an application my install a custom WarningHandler.
      Parameters:
      warningHandler - null to indicate that no warnings be issued

    • evaluate

      @Nullable Object evaluate() throws InvocationTargetException
      Shorthand for evaluate(new Object[0]).
      Throws:
      InvocationTargetException

    • evaluate

      @Nullable Object evaluate(@Nullable Object[] arguments) throws InvocationTargetException
      Evaluates the expression with concrete parameter values.

      Each argument value must have the same type as specified through the "parameterTypes" parameter of 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.

      Null arguments is equivalent with new Object[0].

      Notice: In version 3.1.8, the arguments parameter was changed from Object[] to Object..., which turned out to be a really bad decision because it caused a very ugly invocation ambiguity with evaluate(int, Object[]). Thus, with version 3.1.10, the parameter was changed back to Object[].

      Parameters:
      arguments - The actual parameter values
      Throws:
      InvocationTargetException

    • setDefaultExpressionType

      void setDefaultExpressionType(Class<?> defaultExpressionType)
      Reconfigures the "default expression type"; if no expression type is configured for an expression, then, when cooking this IExpressionEvaluator, the "default expression type" is used for the expression

    • getDefaultExpressionType

      Class<?> getDefaultExpressionType()
      Returns:
      The currently configured "default expression type"
      See Also:

    • setImplementedInterfaces

      void setImplementedInterfaces(Class<?>[] implementedTypes)
      Configures the interfaces that the generated class implements.

    • setReturnType

      @Deprecated void setReturnType(@Deprecated Class<?> returnType)
      Deprecated.
      Use setExpressionType(Class) instead

    • setExpressionType

      void setExpressionType(Class<?> expressionType)
      Defines the type of the expression.

      Defaults to Object.class, which, thanks to autoboxing, allows for any expression type (including primitive types).

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

    • setExpressionTypes

      void setExpressionTypes(Class<?>[] expressionTypes)
      Configures the types of the expressions.

      Unless this method is called, all expressions have type Object.class.

      If any expression has type void.class, then it must be an invocation of a void method.

    • setOverrideMethod

      void setOverrideMethod(boolean overrideMethod)
      Defines whether the generated method overrides a methods declared in a supertype.

    • setOverrideMethod

      void setOverrideMethod(boolean[] overrideMethod)
      Same as setOverrideMethod(boolean), but for multiple expressions.

    • setParameters

      void setParameters(String[] parameterNames, Class<?>[] parameterTypes)
      Defines the names and types of the parameters of the generated method.

      names.length and types.length must be equal. This invariant may be checked immediately, or later when the expression is cooked.

      The parameters can be of primitive type, e.g. double.class.

      The default is to have zero parameters.

    • setParameters

      void setParameters(String[][] parameterNames, Class<?>[][] parameterTypes)
      Same as setParameters(String[], Class[]), but for multiple expressions.

    • setClassName

      void setClassName(String className)
      Sets the name of the generated class. Defaults to DEFAULT_CLASS_NAME. In most cases, there is no need to set this name, because the generated class is loaded into its own ClassLoader where its name cannot collide with classes generated by other evaluators.

      One reason to use this function is to have a class name in a non-default package, which can be relevant when types and members with DEFAULT accessibility are accessed.

    • setExtendedClass

      void setExtendedClass(Class<?> extendedType)
      Sets a particular superclass that the generated class will extend. If extendedClass is null, the generated class will extend Object.

      The usual reason to set a base class for an evaluator is that the generated class can directly access the superclass's (non-private) members.

    • setDefaultImports

      void setDefaultImports(String... defaultImports)
      "Default imports" add to the system import "java.lang", i.e. the evaluator may refer to classes imported by default imports without having to explicitly declare IMPORT statements.

      Notice that JDK 5 "static imports" are also supported, as shown here: 

          sc.setDefaultImports(
        "java.util.Map",                          // Single type import
        "java.io.*",                              // Type-import-on-demand
        "static java.util.Collections.EMPTY_MAP", // Single static import
        "static java.util.Collections.*",         // Static-import-on-demand
    );

    • getDefaultImports

      String[] getDefaultImports()
      Returns:
      The default imports that were previously configured with setDefaultImports(String...)

    • setStaticMethod

      void setStaticMethod(boolean staticMethod)
      Defines whether the generated method should be STATIC or not. Defaults to true.

    • setStaticMethod

      void setStaticMethod(boolean[] staticMethod)
      Same as setStaticMethod(boolean), but for multiple expressions.

    • setMethodName

      void setMethodName(String methodName)
      Defines the name of the generated method. Initially, the method name is "eval*".
      Parameters:
      methodName - null means reset to default name
      See Also:

    • setMethodNames

      void setMethodNames(String[] methodNames)
      Same as setMethodName(String), but for multiple expressions.

      Define the names of the generated methods. By default the methods have distinct and implementation-specific names.

      If two expressions have the same name, then they must have different parameter types (see setParameters(String[][], Class[][])).

    • setThrownExceptions

      void setThrownExceptions(Class<?>[] thrownExceptions)
      Defines the exceptions that the generated method may throw.

    • setThrownExceptions

      void setThrownExceptions(Class<?>[][] thrownExceptions)
      Same as setThrownExceptions(Class[]), but for multiple expressions.

    • evaluate

      @Nullable Object evaluate(int idx, @Nullable Object[] arguments) throws InvocationTargetException
      Same as evaluate(Object[]), but for multiple expressions.

      Notice: In version 3.1.8, the arguments parameter was changed from Object[] to Object..., which turned out to be a really bad decision because it caused a very ugly invocation ambiguity with evaluate(int, Object[]). Thus, with version 3.1.10, the parameter was changed back to Object[].

      Throws:
      InvocationTargetException

    • createFastEvaluator

      <T> T createFastEvaluator(String expression, Class<? extends T> interfaceToImplement, String... 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 setClassName(String).

      Throws:
      CompileException

    • createFastEvaluator

      <T> T createFastEvaluator(Reader reader, Class<? extends T> interfaceToImplement, String... parameterNames) throws CompileException, IOException
      Throws:
      CompileException
      IOException
      See Also:

    • getMethod

      Method getMethod()
      Returns:
      The generated and loaded Method
      Throws:
      IllegalStateException - This IExpressionEvaluator is not yet cooked

    • getMethod

      Method getMethod(int idx)
      Same as getMethod(), but for multiple expressions.

    • getClazz

      Class<?> getClazz()
      Returns:
      The generated Class
      Throws:
      IllegalStateException - This IClassBodyEvaluator is not yet cooked

    • getResult

      Method[] getResult()
      Returns:
      The generated and loaded methods that implement the cooked expressions
      Throws:
      IllegalStateException - This IScriptEvaluator is not yet cooked