Package edu.internet2.middleware.grouperClientExt.org.apache.commons.jexl2

Class JexlEngine

java.lang.Object
edu.internet2.middleware.grouperClientExt.org.apache.commons.jexl2.JexlEngine
public class JexlEngine extends Object

Creates and evaluates Expression and Script objects. Determines the behavior of Expressions & Scripts during their evaluation with respect to:

The setSilent and setLenient methods allow to fine-tune an engine instance behavior according to various error control needs. The lenient/strict flag tells the engine when and if null as operand is considered an error, the silent/verbose flag tells the engine what to do with the error (log as warning or throw exception).

  • When "silent" & "lenient":

    0 & null should be indicators of "default" values so that even in an case of error, something meaningfull can still be inferred; may be convenient for configurations.

  • When "silent" & "strict":

    One should probably consider using null as an error case - ie, every object manipulated by JEXL should be valued; the ternary operator, especially the '?:' form can be used to workaround exceptional cases. Use case could be configuration with no implicit values or defaults.

  • When "verbose" & "lenient":

    The error control grain is roughly on par with JEXL 1.0

  • When "verbose" & "strict":

    The finest error control grain is obtained; it is the closest to Java code - still augmented by "script" capabilities regarding automated conversions & type matching.

Note that methods that evaluate expressions may throw unchecked exceptions; The JexlException are thrown in "non-silent" mode but since these are RuntimeException, user-code should catch them wherever most appropriate.

Since:
2.0

  • Field Details

    • EMPTY_CONTEXT

      public static final JexlContext EMPTY_CONTEXT
      An empty/static/non-mutable JexlContext used instead of null context.

    • uberspect

      protected final Uberspect uberspect
      The Uberspect instance.

    • arithmetic

      protected final JexlArithmetic arithmetic
      The JexlArithmetic instance.

    • logger

      protected final Log logger
      The Log to which all JexlEngine messages will be logged.

    • parser

      protected final Parser parser
      The singleton ExpressionFactory also holds a single instance of Parser. When parsing expressions, ExpressionFactory synchronizes on Parser.

    • silent

      protected volatile boolean silent
      Whether expressions evaluated by this engine will throw exceptions (false) or return null (true) on errors. Default is false.

    • debug

      protected volatile boolean debug
      Whether error messages will carry debugging information.

    • functions

      protected Map<String,Object> functions
      The map of 'prefix:function' to object implementing the functions.

    • cache

      protected JexlEngine.SoftCache<String,ASTJexlScript> cache
      The expression cache.

  • Constructor Details

    • JexlEngine

      public JexlEngine()
      Creates an engine with default arguments.

    • JexlEngine

      public JexlEngine(Uberspect anUberspect, JexlArithmetic anArithmetic, Map<String,Object> theFunctions, Log log)
      Creates a JEXL engine using the provided Uberspect, (@link JexlArithmetic), a function map and logger.
      Parameters:
      anUberspect - to allow different introspection behaviour
      anArithmetic - to allow different arithmetic behaviour
      theFunctions - an optional map of functions (@link setFunctions)
      log - the logger for various messages

  • Method Details

    • getUberspect

      public static Uberspect getUberspect(Log logger)
      Gets the default instance of Uberspect.

      This is lazily initialized to avoid building a default instance if there is no use for it. The main reason for not using the default Uberspect instance is to be able to use a (low level) introspector created with a given logger instead of the default one.

      Parameters:
      logger - the logger to use for the underlying Uberspect
      Returns:
      Uberspect the default uberspector instance.

    • getUberspect

      public Uberspect getUberspect()
      Gets this engine underlying uberspect.
      Returns:
      the uberspect

    • getArithmetic

      public JexlArithmetic getArithmetic()
      Gets this engine underlying arithmetic.
      Returns:
      the arithmetic
      Since:
      2.1

    • setDebug

      public void setDebug(boolean flag)
      Sets whether this engine reports debugging information when error occurs.

      This method is not thread safe; it should be called as an optional step of the JexlEngine initialization code before expression creation & evaluation.

      Parameters:
      flag - true implies debug is on, false implies debug is off.
      See Also:

    • isDebug

      public boolean isDebug()
      Checks whether this engine is in debug mode.
      Returns:
      true if debug is on, false otherwise

    • setSilent

      public void setSilent(boolean flag)
      Sets whether this engine throws JexlException during evaluation when an error is triggered.

      This method is not thread safe; it should be called as an optional step of the JexlEngine initialization code before expression creation & evaluation.

      Parameters:
      flag - true means no JexlException will occur, false allows them
      See Also:

    • isSilent

      public boolean isSilent()
      Checks whether this engine throws JexlException during evaluation.
      Returns:
      true if silent, false (default) otherwise

    • setLenient

      public void setLenient(boolean flag)
      Sets whether this engine considers unknown variables, methods and constructors as errors or evaluates them as null or zero.

      This method is not thread safe; it should be called as an optional step of the JexlEngine initialization code before expression creation & evaluation.

      As of 2.1, you can use a JexlThreadedArithmetic instance to allow the JexlArithmetic leniency behavior to be independently specified per thread, whilst still using a single engine.

      Parameters:
      flag - true means no JexlException will occur, false allows them
      See Also:

    • isLenient

      public boolean isLenient()
      Checks whether this engine considers unknown variables, methods and constructors as errors.
      Returns:
      true if lenient, false if strict

    • setStrict

      public final void setStrict(boolean flag)
      Sets whether this engine behaves in strict or lenient mode. Equivalent to setLenient(!flag).

      This method is not thread safe; it should be called as an optional step of the JexlEngine initialization code before expression creation & evaluation.

      Parameters:
      flag - true for strict, false for lenient
      Since:
      2.1

    • isStrict

      public final boolean isStrict()
      Checks whether this engine behaves in strict or lenient mode. Equivalent to !isLenient().
      Returns:
      true for strict, false for lenient
      Since:
      2.1

    • setClassLoader

      public void setClassLoader(ClassLoader loader)
      Sets the class loader used to discover classes in 'new' expressions.

      This method should be called as an optional step of the JexlEngine initialization code before expression creation & evaluation.

      Parameters:
      loader - the class loader to use

    • setCache

      public void setCache(int size)
      Sets a cache for expressions of the defined size.

      The cache will contain at most size expressions. Note that all JEXL caches are held through SoftReferences and may be garbage-collected.

      Parameters:
      size - if not strictly positive, no cache is used.

    • setFunctions

      public void setFunctions(Map<String,Object> funcs)
      Sets the map of function namespaces.

      This method is not thread safe; it should be called as an optional step of the JexlEngine initialization code before expression creation & evaluation.

      Each entry key is used as a prefix, each entry value used as a bean implementing methods; an expression like 'nsx:method(123)' will thus be solved by looking at a registered bean named 'nsx' that implements method 'method' in that map. If all methods are static, you may use the bean class instead of an instance as value.

      If the entry value is a class that has one contructor taking a JexlContext as argument, an instance of the namespace will be created at evaluation time. It might be a good idea to derive a JexlContext to carry the information used by the namespace to avoid variable space pollution and strongly type the constructor with this specialized JexlContext.

      The key or prefix allows to retrieve the bean that plays the role of the namespace. If the prefix is null, the namespace is the top-level namespace allowing to define top-level user defined functions ( ie: myfunc(...) )

      Note that the JexlContext is also used to try to solve top-level functions. This allows ObjectContext derived instances to call methods on the wrapped object.

      Parameters:
      funcs - the map of functions that should not mutate after the call; if null is passed, the empty collection is used.

    • getFunctions

      public Map<String,Object> getFunctions()
      Retrieves the map of function namespaces.
      Returns:
      the map passed in setFunctions or the empty map if the original was null.

    • createExpression

      protected Expression createExpression(ASTJexlScript tree, String text)
      An overridable through covariant return Expression creator.
      Parameters:
      text - the script text
      tree - the parse AST tree
      Returns:
      the script instance

    • createExpression

      public Expression createExpression(String expression)
      Creates an Expression from a String containing valid JEXL syntax. This method parses the expression which must contain either a reference or an expression.
      Parameters:
      expression - A String containing valid JEXL syntax
      Returns:
      An Expression object which can be evaluated with a JexlContext
      Throws:
      JexlException - An exception can be thrown if there is a problem parsing this expression, or if the expression is neither an expression nor a reference.

    • createExpression

      public Expression createExpression(String expression, JexlInfo info)
      Creates an Expression from a String containing valid JEXL syntax. This method parses the expression which must contain either a reference or an expression.
      Parameters:
      expression - A String containing valid JEXL syntax
      info - An info structure to carry debugging information if needed
      Returns:
      An Expression object which can be evaluated with a JexlContext
      Throws:
      JexlException - An exception can be thrown if there is a problem parsing this expression, or if the expression is neither an expression or a reference.

    • createScript

      public Script createScript(String scriptText)
      Creates a Script from a String containing valid JEXL syntax. This method parses the script which validates the syntax.
      Parameters:
      scriptText - A String containing valid JEXL syntax
      Returns:
      A Script which can be executed using a JexlContext.
      Throws:
      JexlException - if there is a problem parsing the script.

    • createScript

      @Deprecated public Script createScript(String scriptText, JexlInfo info)
      Deprecated.
      Use createScript(String, JexlInfo, String[])
      Creates a Script from a String containing valid JEXL syntax. This method parses the script which validates the syntax.
      Parameters:
      scriptText - A String containing valid JEXL syntax
      info - An info structure to carry debugging information if needed
      Returns:
      A Script which can be executed using a JexlContext.
      Throws:
      JexlException - if there is a problem parsing the script.

    • createScript

      public Script createScript(String scriptText, String... names)
      Creates a Script from a String containing valid JEXL syntax. This method parses the script which validates the syntax.
      Parameters:
      scriptText - A String containing valid JEXL syntax
      names - the script parameter names
      Returns:
      A Script which can be executed using a JexlContext.
      Throws:
      JexlException - if there is a problem parsing the script.

    • createScript

      public Script createScript(String scriptText, JexlInfo info, String[] names)
      Creates a Script from a String containing valid JEXL syntax. This method parses the script which validates the syntax. It uses an array of parameter names that will be resolved during parsing; a corresponding array of arguments containing values should be used during evaluation.
      Parameters:
      scriptText - A String containing valid JEXL syntax
      info - An info structure to carry debugging information if needed
      names - the script parameter names
      Returns:
      A Script which can be executed using a JexlContext.
      Throws:
      JexlException - if there is a problem parsing the script.
      Since:
      2.1

    • createScript

      protected Script createScript(ASTJexlScript tree, String text)
      An overridable through covariant return Script creator.
      Parameters:
      text - the script text
      tree - the parse AST tree
      Returns:
      the script instance

    • createScript

      public Script createScript(File scriptFile) throws IOException
      Creates a Script from a File containing valid JEXL syntax. This method parses the script and validates the syntax.
      Parameters:
      scriptFile - A File containing valid JEXL syntax. Must not be null. Must be a readable file.
      Returns:
      A Script which can be executed with a JexlContext.
      Throws:
      IOException - if there is a problem reading the script.
      JexlException - if there is a problem parsing the script.

    • createScript

      public Script createScript(URL scriptUrl) throws IOException
      Creates a Script from a URL containing valid JEXL syntax. This method parses the script and validates the syntax.
      Parameters:
      scriptUrl - A URL containing valid JEXL syntax. Must not be null. Must be a readable file.
      Returns:
      A Script which can be executed with a JexlContext.
      Throws:
      IOException - if there is a problem reading the script.
      JexlException - if there is a problem parsing the script.

    • getProperty

      public Object getProperty(Object bean, String expr)
      Accesses properties of a bean using an expression.

      jexl.get(myobject, "foo.bar"); should equate to myobject.getFoo().getBar(); (or myobject.getFoo().get("bar"))

      If the JEXL engine is silent, errors will be logged through its logger as warning.

      Parameters:
      bean - the bean to get properties from
      expr - the property expression
      Returns:
      the value of the property
      Throws:
      JexlException - if there is an error parsing the expression or during evaluation

    • getProperty

      public Object getProperty(JexlContext context, Object bean, String expr)
      Accesses properties of a bean using an expression.

      If the JEXL engine is silent, errors will be logged through its logger as warning.

      Parameters:
      context - the evaluation context
      bean - the bean to get properties from
      expr - the property expression
      Returns:
      the value of the property
      Throws:
      JexlException - if there is an error parsing the expression or during evaluation

    • setProperty

      public void setProperty(Object bean, String expr, Object value)
      Assign properties of a bean using an expression.

      jexl.set(myobject, "foo.bar", 10); should equate to myobject.getFoo().setBar(10); (or myobject.getFoo().put("bar", 10) )

      If the JEXL engine is silent, errors will be logged through its logger as warning.

      Parameters:
      bean - the bean to set properties in
      expr - the property expression
      value - the value of the property
      Throws:
      JexlException - if there is an error parsing the expression or during evaluation

    • setProperty

      public void setProperty(JexlContext context, Object bean, String expr, Object value)
      Assign properties of a bean using an expression.

      If the JEXL engine is silent, errors will be logged through its logger as warning.

      Parameters:
      context - the evaluation context
      bean - the bean to set properties in
      expr - the property expression
      value - the value of the property
      Throws:
      JexlException - if there is an error parsing the expression or during evaluation

    • invokeMethod

      public Object invokeMethod(Object obj, String meth, Object... args)
      Invokes an object's method by name and arguments.
      Parameters:
      obj - the method's invoker object
      meth - the method's name
      args - the method's arguments
      Returns:
      the method returned value or null if it failed and engine is silent
      Throws:
      JexlException - if method could not be found or failed and engine is not silent

    • newInstance

      public <T> T newInstance(Class<? extends T> clazz, Object... args)
      Creates a new instance of an object using the most appropriate constructor based on the arguments.
      Type Parameters:
      T - the type of object
      Parameters:
      clazz - the class to instantiate
      args - the constructor arguments
      Returns:
      the created object instance or null on failure when silent

    • newInstance

      public Object newInstance(String clazz, Object... args)
      Creates a new instance of an object using the most appropriate constructor based on the arguments.
      Parameters:
      clazz - the name of the class to instantiate resolved through this engine's class loader
      args - the constructor arguments
      Returns:
      the created object instance or null on failure when silent

    • doCreateInstance

      protected Object doCreateInstance(Object clazz, Object... args)
      Creates a new instance of an object using the most appropriate constructor based on the arguments.
      Parameters:
      clazz - the class to instantiate
      args - the constructor arguments
      Returns:
      the created object instance or null on failure when silent

    • createInterpreter

      protected Interpreter createInterpreter(JexlContext context)
      Creates an interpreter.
      Parameters:
      context - a JexlContext; if null, the EMPTY_CONTEXT is used instead.
      Returns:
      an Interpreter

    • createInterpreter

      protected Interpreter createInterpreter(JexlContext context, boolean strictFlag, boolean silentFlag)
      Creates an interpreter.
      Parameters:
      context - a JexlContext; if null, the EMPTY_CONTEXT is used instead.
      strictFlag - whether the interpreter runs in strict mode
      silentFlag - whether the interpreter runs in silent mode
      Returns:
      an Interpreter
      Since:
      2.1

    • createCache

      protected <K, V> Map<K,V> createCache(int cacheSize)
      Creates a cache.
      Type Parameters:
      K - the key type
      V - the value type
      Parameters:
      cacheSize - the cache size, must be > 0
      Returns:
      a Map usable as a cache bounded to the given size

    • clearCache

      public void clearCache()
      Clears the expression cache.
      Since:
      2.1

    • getVariables

      public Set<List<String>> getVariables(Script script)
      Gets the list of variables accessed by a script.

      This method will visit all nodes of a script and extract all variables whether they are written in 'dot' or 'bracketed' notation. (a.b is equivalent to a['b']).

      Parameters:
      script - the script
      Returns:
      the set of variables, each as a list of strings (ant-ish variables use more than 1 string) or the empty set if no variables are used
      Since:
      2.1

    • getVariables

      protected void getVariables(JexlNode node, Set<List<String>> refs, List<String> ref)
      Fills up the list of variables accessed by a node.
      Parameters:
      node - the node
      refs - the set of variable being filled
      ref - the current variable being filled
      Since:
      2.1

    • getParameters

      protected String[] getParameters(Script script)
      Gets the array of parameters from a script.
      Parameters:
      script - the script
      Returns:
      the parameters which may be empty (but not null) if no parameters were defined
      Since:
      2.1

    • getLocalVariables

      protected String[] getLocalVariables(Script script)
      Gets the array of local variable from a script.
      Parameters:
      script - the script
      Returns:
      the local variables array which may be empty (but not null) if no local variables were defined
      Since:
      2.1

    • parse

      @Deprecated protected ASTJexlScript parse(CharSequence expression, JexlInfo info)
      Deprecated.
      Use parse(CharSequence, JexlInfo, Scope) instead
      Parses an expression.
      Parameters:
      expression - the expression to parse
      info - debug information structure
      Returns:
      the parsed tree
      Throws:
      JexlException - if any error occured during parsing

    • parse

      protected ASTJexlScript parse(CharSequence expression, JexlInfo info, JexlEngine.Scope frame)
      Parses an expression.
      Parameters:
      expression - the expression to parse
      info - debug information structure
      frame - the script frame to use
      Returns:
      the parsed tree
      Throws:
      JexlException - if any error occured during parsing

    • createInfo

      protected JexlInfo createInfo(String fn, int l, int c)
      Creates a JexlInfo instance.
      Parameters:
      fn - url/file name
      l - line number
      c - column number
      Returns:
      a JexlInfo instance

    • debugInfo

      protected JexlInfo debugInfo()
      Creates and fills up debugging information.

      This gathers the class, method and line number of the first calling method not owned by JexlEngine, UnifiedJEXL or {Script,Expression}Factory.

      Returns:
      an Info if debug is set, null otherwise

    • cleanExpression

      public static String cleanExpression(CharSequence str)
      Trims the expression from front & ending spaces.
      Parameters:
      str - expression to clean
      Returns:
      trimmed expression ending in a semi-colon

    • readerToString

      public static String readerToString(Reader scriptReader) throws IOException
      Read from a reader into a local buffer and return a String with the contents of the reader.
      Parameters:
      scriptReader - to be read.
      Returns:
      the contents of the reader as a String.
      Throws:
      IOException - on any error reading the reader.