JexlEngine (Commons JEXL 2.0.1 API)
Keywords: org.apache.commons.jexl2.JexlEngine class

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## org.apache.commons.jexl2
Class JexlEngine

    java.lang.Object
      org.apache.commons.jexl2.JexlEngine

    public class JexlEngine

extends java.lang.Object

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

- Introspection, see `Uberspect`
- Arithmetic & comparison, see `JexlArithmetic`
- Error reporting
- Logging

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

Nested Class Summary
`protected class` | `JexlEngine.SoftCache<K,V>` A soft reference on cache.

Field Summary
`protected JexlArithmetic` | `arithmetic` The JexlArithmetic instance.
`protected JexlEngine.SoftCache<java.lang.String,ASTJexlScript>` | `cache` The expression cache.
`protected boolean` | `debug` Whether error messages will carry debugging information.
`static JexlContext` | `EMPTY_CONTEXT` An empty/static/non-mutable JexlContext used instead of null context.
`protected java.util.Map<java.lang.String,java.lang.Object>` | `functions` The map of 'prefix:function' to object implementing the function.
`protected org.apache.commons.logging.Log` | `logger` The Log to which all JexlEngine messages will be logged.
`protected Parser` | `parser` The singleton ExpressionFactory also holds a single instance of `Parser`.
`protected boolean` | `silent` Whether expressions evaluated by this engine will throw exceptions (false) or return null (true).
`protected Uberspect` | `uberspect` The Uberspect instance.

Constructor Summary
`JexlEngine()` Creates an engine with default arguments.
`JexlEngine(Uberspect anUberspect, JexlArithmetic anArithmetic, java.util.Map<java.lang.String,java.lang.Object> theFunctions, org.apache.commons.logging.Log log)` Creates a JEXL engine using the provided `Uberspect`, (@link JexlArithmetic), a function map and logger.

Method Summary
`static java.lang.String` | `cleanExpression(java.lang.CharSequence str)` Trims the expression from front & ending spaces.
`protected
`<K,V> java.util.Map<K,V>`
` | `createCache(int cacheSize)` Creates a cache.
`protected Expression` | `createExpression(ASTJexlScript tree, java.lang.String text)` An overridable through covariant return Expression creator.
`Expression` | `createExpression(java.lang.String expression)` Creates an Expression from a String containing valid JEXL syntax.
`Expression` | `createExpression(java.lang.String expression, JexlInfo info)` Creates an Expression from a String containing valid JEXL syntax.
`protected JexlInfo` | `createInfo(java.lang.String fn, int l, int c)` Creates a JexlInfo instance.
`protected Interpreter` | `createInterpreter(JexlContext context)` Creates an interpreter.
`protected Script` | `createScript(ASTJexlScript tree, java.lang.String text)` An overridable through covariant return Script creator.
`Script` | `createScript(java.io.File scriptFile)` Creates a Script from a `File` containing valid JEXL syntax.
`Script` | `createScript(java.lang.String scriptText)` Creates a Script from a String containing valid JEXL syntax.
`Script` | `createScript(java.lang.String scriptText, JexlInfo info)` Creates a Script from a String containing valid JEXL syntax.
`Script` | `createScript(java.net.URL scriptUrl)` Creates a Script from a `URL` containing valid JEXL syntax.
`protected JexlInfo` | `debugInfo()` Creates and fills up debugging information.
`protected java.lang.Object` | `doCreateInstance(java.lang.Object clazz, java.lang.Object... args)` Creates a new instance of an object using the most appropriate constructor based on the arguments.
`java.util.Map<java.lang.String,java.lang.Object>` | `getFunctions()` Retrieves the map of function namespaces.
`java.lang.Object` | `getProperty(JexlContext context, java.lang.Object bean, java.lang.String expr)` Accesses properties of a bean using an expression.
`java.lang.Object` | `getProperty(java.lang.Object bean, java.lang.String expr)` Accesses properties of a bean using an expression.
`Uberspect` | `getUberspect()` Gets this engine underlying uberspect.
`static Uberspect` | `getUberspect(org.apache.commons.logging.Log logger)` Gets the default instance of Uberspect.
`java.lang.Object` | `invokeMethod(java.lang.Object obj, java.lang.String meth, java.lang.Object... args)` Invokes an object's method by name and arguments.
`boolean` | `isDebug()` Checks whether this engine is in debug mode.
`boolean` | `isLenient()` Checks whether this engine triggers errors during evaluation when null is used as an operand.
`boolean` | `isSilent()` Checks whether this engine throws JexlException during evaluation.
`
`<T> T`
` | `newInstance(java.lang.Class<? extends T> clazz, java.lang.Object... args)` Creates a new instance of an object using the most appropriate constructor based on the arguments.
`java.lang.Object` | `newInstance(java.lang.String clazz, java.lang.Object... args)` Creates a new instance of an object using the most appropriate constructor based on the arguments.
`protected ASTJexlScript` | `parse(java.lang.CharSequence expression, JexlInfo info)` Parses an expression.
`static java.lang.String` | `readerToString(java.io.Reader scriptReader)` Read from a reader into a local buffer and return a String with the contents of the reader.
`void` | `setCache(int size)` Sets a cache for expressions of the defined size.
`void` | `setClassLoader(java.lang.ClassLoader loader)` Sets the class loader used to discover classes in 'new' expressions.
`void` | `setDebug(boolean flag)` Sets whether this engine reports debugging information when error occurs.
`void` | `setFunctions(java.util.Map<java.lang.String,java.lang.Object> funcs)` Sets the map of function namespaces.
`void` | `setLenient(boolean flag)` Sets whether this engine triggers errors during evaluation when null is used as an operand.
`void` | `setProperty(JexlContext context, java.lang.Object bean, java.lang.String expr, java.lang.Object value)` Assign properties of a bean using an expression.
`void` | `setProperty(java.lang.Object bean, java.lang.String expr, java.lang.Object value)` Assign properties of a bean using an expression.
`void` | `setSilent(boolean flag)` Sets whether this engine throws JexlException during evaluation when an error is triggered.

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Field Detail

### 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 org.apache.commons.logging.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 boolean silent

  Whether expressions evaluated by this engine will throw exceptions (false) or return null (true). Default is false.

### debug

    protected boolean debug

  Whether error messages will carry debugging information.

### functions

    protected java.util.Map<java.lang.String,java.lang.Object> functions

  The map of 'prefix:function' to object implementing the function.

### cache

    protected JexlEngine.SoftCache<java.lang.String,ASTJexlScript> cache

  The expression cache.

Constructor Detail

### JexlEngine

    public JexlEngine()

  Creates an engine with default arguments.

### JexlEngine

    public JexlEngine(Uberspect anUberspect,
                      JexlArithmetic anArithmetic,
                      java.util.Map<java.lang.String,java.lang.Object> theFunctions,
                      org.apache.commons.logging.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 Detail

### getUberspect

    public static Uberspect getUberspect(org.apache.commons.logging.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

### 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:
    `setSilent(boolean)`, `setLenient(boolean)`

### 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:
    `setDebug(boolean)`, `setLenient(boolean)`

### 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 triggers errors during evaluation when null is used as an operand.

  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:
    `setSilent(boolean)`, `setDebug(boolean)`

### isLenient

    public boolean isLenient()

  Checks whether this engine triggers errors during evaluation when null is used as an operand.

  Returns:
    true if lenient, false if strict

### setClassLoader

    public void setClassLoader(java.lang.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(java.util.Map<java.lang.String,java.lang.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(...) )

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

### getFunctions

    public java.util.Map<java.lang.String,java.lang.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,
                                          java.lang.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(java.lang.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(java.lang.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(java.lang.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

    public Script createScript(java.lang.String scriptText,
                               JexlInfo info)

  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

    protected Script createScript(ASTJexlScript tree,
                                  java.lang.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(java.io.File scriptFile)
                        throws java.io.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:
    `java.io.IOException` - if there is a problem reading the script.
    `JexlException` - if there is a problem parsing the script.

### createScript

    public Script createScript(java.net.URL scriptUrl)
                        throws java.io.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:
    `java.io.IOException` - if there is a problem reading the script.
    `JexlException` - if there is a problem parsing the script.

### getProperty

    public java.lang.Object getProperty(java.lang.Object bean,
                                        java.lang.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 java.lang.Object getProperty(JexlContext context,
                                        java.lang.Object bean,
                                        java.lang.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(java.lang.Object bean,
                            java.lang.String expr,
                            java.lang.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,
                            java.lang.Object bean,
                            java.lang.String expr,
                            java.lang.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 java.lang.Object invokeMethod(java.lang.Object obj,
                                         java.lang.String meth,
                                         java.lang.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(java.lang.Class<? extends T> clazz,
                             java.lang.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 java.lang.Object newInstance(java.lang.String clazz,
                                        java.lang.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 java.lang.Object doCreateInstance(java.lang.Object clazz,
                                                java.lang.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

### createCache

    protected <K,V> java.util.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

### parse

    protected ASTJexlScript parse(java.lang.CharSequence expression,
                                  JexlInfo info)

  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

### createInfo

    protected JexlInfo createInfo(java.lang.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 final java.lang.String cleanExpression(java.lang.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 final java.lang.String readerToString(java.io.Reader scriptReader)
                                                 throws java.io.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:
    `java.io.IOException` - on any error reading the reader.

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