    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     * Gets the value of a variable.
    044     *
    045     * @param name the variable's name
    046     * @return the value
    047     */
    048    Object get(String name);
    049
    050    /**
    051     * Sets the value of a variable.
    052     *
    053     * @param name the variable's name
    054     * @param value the variable's value
    055     */
    056    void set(String name, Object value);
    057
    058    /**
    059     * Checks whether a variable is defined in this context.
    060     *
    061     * <p>A variable may be defined with a null value; this method checks whether the
    062     * value is null or if the variable is undefined.</p>
    063     *
    064     * @param name the variable's name
    065     * @return true if it exists, false otherwise
    066     */
    067    boolean has(String name);
    068
    069    /**
    070     * A marker interface of the JexlContext that declares how to resolve a namespace from its name;
    071     * it is used by the interpreter during evaluation.
    072     *
    073     * <p>In JEXL, a namespace is an object that serves the purpose of encapsulating functions; for instance,
    074     * the "math" namespace would be the proper object to expose functions like "log(...)", "sinus(...)", etc.</p>
    075     *
    076     * In expressions like "ns:function(...)", the resolver is called with resolveNamespace("ns").
    077     *
    078     * <p>JEXL itself reserves 'jexl' and 'ujexl' as namespaces for internal purpose; resolving those may lead to
    079     * unexpected results.</p>
    080     *
    081     * @since 3.0
    082     */
    083    interface NamespaceResolver {
    084
    085        /**
    086         * Resolves a namespace by its name.
    087         * @param name the name
    088         * @return the namespace object
    089         */
    090        Object resolveNamespace(String name);
    091    }
    092
    093    /**
    094     * A marker interface of the JexlContext, NamespaceFunctor allows creating an instance
    095     * to delegate namespace methods calls to.
    096     *
    097     * <p>The functor is created once during the lifetime of a script evaluation.</p>
    098     */
    099    interface NamespaceFunctor {
    100        /**
    101         * Creates the functor object that will be used instead of the namespace.
    102         * @param context the context
    103         * @return the namespace functor instance
    104         */
    105        Object createFunctor(JexlContext context);
    106    }
    107
    108    /**
    109     * A marker interface  of the JexlContext that indicates the interpreter to put this context
    110     * in the JexlEngine thread local context instance during evaluation.
    111     * This allows user functions or methods to access the context during a call.
    112     * Note that the usual caveats wrt using thread local apply (caching/leaking references, etc.); in particular,
    113     * keeping a reference to such a context is to be considered with great care and caution.
    114     * It should also be noted that sharing such a context between threads should implicate synchronizing variable
    115     * accessing the implementation class.
    116     *
    117     * @see JexlEngine#setThreadContext(JexlContext.ThreadLocal)
    118     * @see JexlEngine#getThreadContext()
    119     */
    120    interface ThreadLocal extends JexlContext {
    121        // no specific method
    122    }
    123
    124    /**
    125     * A marker interface of the JexlContext that processes annotations.
    126     * It is used by the interpreter during evaluation to execute annotation evaluations.
    127     * <p>If the JexlContext is not an instance of an AnnotationProcessor, encountering an annotation will generate
    128     * an error or a warning depending on the engine strictness.
    129     * @since 3.1
    130     */
    131    interface AnnotationProcessor {
    132        /**
    133         * Processes an annotation.
    134         * <p>All annotations are processed through this method; the statement 'call' is to be performed within
    135         * the processAnnotation method. The implementation <em>must</em> perform the call explicitly.
    136         * <p>The arguments and the statement <em>must not</em> be referenced or cached for longer than the duration
    137         * of the processAnnotation call.
    138         *
    139         * @param name the annotation name
    140         * @param args the arguments of the annotation, evaluated as arguments of this call
    141         * @param statement the statement that was annotated; the processor should invoke this statement 'call' method
    142         * @return the result of statement.call()
    143         * @throws Exception if annotation processing fails
    144         */
    145        Object processAnnotation(String name, Object[] args, Callable<Object> statement) throws Exception;
    146    }
    147
    148    /**
    149     * A marker interface of the JexlContext that exposes runtime evaluation options.
    150     * @since 3.2
    151     */
    152    interface OptionsHandle {
    153        /**
    154         * Retrieves the current set of options though the context.
    155         * <p>
    156         * This method will be called once at beginning of evaluation and an interpreter private copy
    157         * of the context handled JexlOptions instance used for the duration of the execution;
    158         * the context handled JexlOptions instance being only used as the source of that copy,
    159         * it can safely alter its boolean flags during execution with no effect, avoiding any behavior ambiguity.
    160         * @return the engine options
    161         */
    162        JexlOptions getEngineOptions();
    163    }
    164
    165    /**
    166     * A marker interface of the JexlContext that processes pragmas.
    167     * It is called by the engine before interpreter creation; as a marker of
    168     * JexlContext, it is expected to have access and interact with the context
    169     * instance.
    170     * @since 3.2
    171     */
    172    interface PragmaProcessor {
    173        /**
    174         * Process one pragma.
    175         * @param key the key
    176         * @param value the value
    177         */
    178        void processPragma(String key, Object value);
    179    }
    180
    181    /**
    182     * A marker interface of the JexlContext sharing a cancelling flag.
    183     * <p>A script running in a thread can thus be notified through this reference
    184     * of its cancellation through the context. It uses the same interpreter logic
    185     * that reacts to cancellation and is an alternative to using callable() and/or
    186     * interrupting script interpreter threads.
    187     * @since 3.2
    188     */
    189    interface CancellationHandle {
    190        /**
    191         * @return a cancelable boolean used by the interpreter
    192         */
    193        AtomicBoolean getCancellation();
    194    }
    195}