    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017
    018package org.apache.commons.jexl3;
    019
    020import java.util.concurrent.Callable;
    021import java.util.concurrent.atomic.AtomicBoolean;
    022
    023/**
    024 * Manages variables which can be referenced in a JEXL expression.
    025 *
    026 * <p>JEXL variable names in their simplest form are 'java-like' identifiers.
    027 * JEXL also considers 'ant' inspired variables expressions as valid.
    028 * For instance, the expression 'x.y.z' is an 'antish' variable and will be resolved as a whole by the context,
    029 * i.e. using the key "x.y.z". This proves to be useful to solve "fully qualified class names".</p>
    030 *
    031 * <p>The interpreter variable resolution algorithm will try the different sequences of identifiers till it finds
    032 * one that exists in the context; if "x" is an object known in the context (JexlContext.has("x") returns true),
    033 * "x.y" will <em>not</em> be looked up in the context but will most likely refer to "x.getY()".</p>
    034 *
    035 * <p>Note that JEXL may use '$jexl' and '$ujexl' variables for internal purpose; setting or getting those
    036 * variables may lead to unexpected results unless specified otherwise.</p>
    037 *
    038 * @since 1.0
    039 */
    040public interface JexlContext {
    041
    042    /**
    043     * A marker interface of the JexlContext that processes annotations.
    044     * It is used by the interpreter during evaluation to execute annotation evaluations.
    045     * <p>If the JexlContext is not an instance of an AnnotationProcessor, encountering an annotation will generate
    046     * an error or a warning depending on the engine strictness.
    047     * @since 3.1
    048     */
    049    interface AnnotationProcessor {
    050        /**
    051         * Processes an annotation.
    052         * <p>All annotations are processed through this method; the statement 'call' is to be performed within
    053         * the processAnnotation method. The implementation <em>must</em> perform the call explicitly.
    054         * <p>The arguments and the statement <em>must not</em> be referenced or cached for longer than the duration
    055         * of the processAnnotation call.
    056         *
    057         * @param name the annotation name
    058         * @param args the arguments of the annotation, evaluated as arguments of this call
    059         * @param statement the statement that was annotated; the processor should invoke this statement 'call' method
    060         * @return the result of statement.call()
    061         * @throws Exception if annotation processing fails
    062         */
    063        Object processAnnotation(String name, Object[] args, Callable<Object> statement) throws Exception;
    064    }
    065
    066    /**
    067     * A marker interface of the JexlContext sharing a cancelling flag.
    068     * <p>A script running in a thread can thus be notified through this reference
    069     * of its cancellation through the context. It uses the same interpreter logic
    070     * that reacts to cancellation and is an alternative to using callable() and/or
    071     * interrupting script interpreter threads.
    072     * @since 3.2
    073     */
    074    interface CancellationHandle {
    075        /**
    076         * @return a cancelable boolean used by the interpreter
    077         */
    078        AtomicBoolean getCancellation();
    079    }
    080
    081    /**
    082     * A marker interface that solves a simple class name into a fully-qualified one.
    083     * @since 3.3
    084     */
    085    interface ClassNameResolver {
    086        /**
    087         * Resolves a class name.
    088         * @param name the simple class name
    089         * @return the fully qualified class name
    090         */
    091        String resolveClassName(String name);
    092    }
    093
    094    /**
    095     * A marker interface of the JexlContext that processes module definitions.
    096     * It is used by the interpreter during evaluation of the pragma module definitions.
    097     * @since 3.3
    098     */
    099    interface ModuleProcessor {
    100        /**
    101         * Defines a module.
    102         * The module name will be the namespace mapped to the object returned by the evaluation
    103         * of its body.
    104         * @param engine the engine evaluating this module pragma
    105         * @param info the info at the pragma location
    106         * @param name the module name
    107         * @param body the module definition which can be its location or source
    108         * @return the module object
    109         */
    110        Object processModule(JexlEngine engine, JexlInfo info, String name, String body);
    111    }
    112
    113    /**
    114     * A marker interface of the JexlContext, NamespaceFunctor allows creating an instance
    115     * to delegate namespace methods calls to.
    116     *
    117     * <p>The functor is created once during the lifetime of a script evaluation.</p>
    118     */
    119    interface NamespaceFunctor {
    120        /**
    121         * Creates the functor object that will be used instead of the namespace.
    122         * @param context the context
    123         * @return the namespace functor instance
    124         */
    125        Object createFunctor(JexlContext context);
    126    }
    127
    128    /**
    129     * A marker interface of the JexlContext that declares how to resolve a namespace from its name;
    130     * it is used by the interpreter during evaluation.
    131     *
    132     * <p>In JEXL, a namespace is an object that serves the purpose of encapsulating functions; for instance,
    133     * the "math" namespace would be the proper object to expose functions like "log(...)", "sinus(...)", etc.</p>
    134     *
    135     * In expressions like "ns:function(...)", the resolver is called with resolveNamespace("ns").
    136     *
    137     * <p>JEXL itself reserves 'jexl' and 'ujexl' as namespaces for internal purpose; resolving those may lead to
    138     * unexpected results.</p>
    139     *
    140     * @since 3.0
    141     */
    142    interface NamespaceResolver {
    143
    144        /**
    145         * Resolves a namespace by its name.
    146         * @param name the name
    147         * @return the namespace object
    148         */
    149        Object resolveNamespace(String name);
    150    }
    151
    152    /**
    153     * A marker interface of the JexlContext that exposes runtime evaluation options.
    154     * @since 3.2
    155     */
    156    interface OptionsHandle {
    157        /**
    158         * Retrieves the current set of options though the context.
    159         * <p>
    160         * This method will be called once at beginning of evaluation and an interpreter private copy
    161         * of the context handled JexlOptions instance used for the duration of the execution;
    162         * the context handled JexlOptions instance being only used as the source of that copy,
    163         * it can safely alter its boolean flags during execution with no effect, avoiding any behavior ambiguity.
    164         * @return the engine options
    165         */
    166        JexlOptions getEngineOptions();
    167    }
    168
    169    /**
    170     * A marker interface of the JexlContext that processes pragmas.
    171     * It is called by the engine before interpreter creation; as a marker of
    172     * JexlContext, it is expected to have access and interact with the context
    173     * instance.
    174     * @since 3.2
    175     */
    176    interface PragmaProcessor {
    177        /**
    178         * Process one pragma.
    179         * @param opts the current evaluator options
    180         * @param key the key
    181         * @param value the value
    182         * @since 3.3
    183         */
    184        default void processPragma(final JexlOptions opts, final String key, final Object value) {
    185            processPragma(key, value);
    186        }
    187
    188        /**
    189         * Process one pragma.
    190         * <p>Never called in 3.3, must be implemented for 3.2 binary compatibility reasons.</p>
    191         * <p>Typical implementation in 3.3:</p>
    192         * <code>
    193         *         &#64;Override
    194         *         public void processPragma(String key, Object value) {
    195         *             processPragma(null, key, value);
    196         *         }
    197         * </code>
    198         * @param key the key
    199         * @param value the value
    200         * @deprecated 3.3
    201         */
    202        @Deprecated
    203        void processPragma(String key, Object value);
    204    }
    205
    206    /**
    207     * A marker interface  of the JexlContext that indicates the interpreter to put this context
    208     * in the JexlEngine thread local context instance during evaluation.
    209     * This allows user functions or methods to access the context during a call.
    210     * Note that the usual caveats wrt using thread local apply (caching/leaking references, etc.); in particular,
    211     * keeping a reference to such a context is to be considered with great care and caution.
    212     * It should also be noted that sharing such a context between threads should implicate synchronizing variable
    213     * accessing the implementation class.
    214     *
    215     * @see JexlEngine#setThreadContext(JexlContext.ThreadLocal)
    216     * @see JexlEngine#getThreadContext()
    217     */
    218    interface ThreadLocal extends JexlContext {
    219        // no specific method
    220    }
    221
    222    /**
    223     * Gets the value of a variable.
    224     *
    225     * @param name the variable's name
    226     * @return the value
    227     */
    228    Object get(String name);
    229
    230    /**
    231     * Checks whether a variable is defined in this context.
    232     *
    233     * <p>A variable may be defined with a null value; this method checks whether the
    234     * value is null or if the variable is undefined.</p>
    235     *
    236     * @param name the variable's name
    237     * @return true if it exists, false otherwise
    238     */
    239    boolean has(String name);
    240
    241    /**
    242     * Sets the value of a variable.
    243     *
    244     * @param name the variable's name
    245     * @param value the variable's value
    246     */
    247    void set(String name, Object value);
    248}