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}