    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 */
    017package org.apache.commons.configuration2.interpol;
    018
    019import java.util.ArrayList;
    020import java.util.Objects;
    021
    022import org.apache.commons.configuration2.ex.ConfigurationRuntimeException;
    023import org.apache.commons.configuration2.io.ConfigurationLogger;
    024import org.apache.commons.jexl2.Expression;
    025import org.apache.commons.jexl2.JexlContext;
    026import org.apache.commons.jexl2.JexlEngine;
    027import org.apache.commons.jexl2.MapContext;
    028import org.apache.commons.lang3.ClassUtils;
    029import org.apache.commons.lang3.StringUtils;
    030import org.apache.commons.text.StringSubstitutor;
    031import org.apache.commons.text.lookup.StringLookup;
    032
    033/**
    034 * Lookup that allows expressions to be evaluated.
    035 *
    036 * <pre>
    037 * ExprLookup.Variables vars = new ExprLookup.Variables();
    038 * vars.add(new ExprLookup.Variable("String", org.apache.commons.lang.StringUtils.class));
    039 * vars.add(new ExprLookup.Variable("Util", new Utility("Hello")));
    040 * vars.add(new ExprLookup.Variable("System", "Class:java.lang.System"));
    041 * XMLConfiguration config = new XMLConfiguration(TEST_FILE);
    042 * config.setLogger(log);
    043 * ExprLookup lookup = new ExprLookup(vars);
    044 * lookup.setConfiguration(config);
    045 * String str = lookup.lookup("'$[element] ' + String.trimToEmpty('$[space.description]')");
    046 * </pre>
    047 *
    048 * In the example above TEST_FILE contains xml that looks like:
    049 *
    050 * <pre>
    051 * &lt;configuration&gt;
    052 *   &lt;element&gt;value&lt;/element&gt;
    053 *   &lt;space xml:space="preserve"&gt;
    054 *     &lt;description xml:space="default"&gt;     Some text      &lt;/description&gt;
    055 *   &lt;/space&gt;
    056 * &lt;/configuration&gt;
    057 * </pre>
    058 *
    059 * The result will be "value Some text".
    060 *
    061 * This lookup uses Apache Commons Jexl and requires that the dependency be added to any projects which use this.
    062 *
    063 * @since 1.7
    064 */
    065public class ExprLookup implements Lookup {
    066    /**
    067     * The key and corresponding object that will be made available to the JexlContext for use in expressions.
    068     */
    069    public static class Variable {
    070        /** The name to be used in expressions. */
    071        private String key;
    072
    073        /** The object to be accessed in expressions. */
    074        private Object value;
    075
    076        /**
    077         * Constructs a new instance.
    078         */
    079        public Variable() {
    080        }
    081
    082        /**
    083         * Constructs a new instance.
    084         *
    085         * @param name The name to be used in expressions.
    086         * @param value The object to be accessed in expressions.
    087         */
    088        public Variable(final String name, final Object value) {
    089            setName(name);
    090            setValue(value);
    091        }
    092
    093        /**
    094         * Gets the name to be used in expressions.
    095         *
    096         * @return the name to be used in expressions.
    097         */
    098        public String getName() {
    099            return key;
    100        }
    101
    102        /**
    103         * Sets the value to be used in expressions.
    104         *
    105         * @return the value to be used in expressions.
    106         */
    107        public Object getValue() {
    108            return value;
    109        }
    110
    111        /**
    112         * Sets the name to be used in expressions.
    113         *
    114         * @param name the name to be used in expressions.
    115         */
    116        public void setName(final String name) {
    117            this.key = name;
    118        }
    119
    120        /**
    121         * Sets the value to be used in expressions.
    122         *
    123         * @param value The object to be accessed in expressions.
    124         * @throws ConfigurationRuntimeException Wraps an exception creating the value.
    125         */
    126        public void setValue(final Object value) throws ConfigurationRuntimeException {
    127            try {
    128                if (!(value instanceof String)) {
    129                    this.value = value;
    130                    return;
    131                }
    132                final String val = (String) value;
    133                final String name = StringUtils.removeStartIgnoreCase(val, CLASS);
    134                final Class<?> clazz = ClassUtils.getClass(name);
    135                if (name.length() == val.length()) {
    136                    this.value = clazz.getConstructor().newInstance();
    137                } else {
    138                    this.value = clazz;
    139                }
    140            } catch (final Exception e) {
    141                throw new ConfigurationRuntimeException("Unable to create " + value, e);
    142            }
    143
    144        }
    145    }
    146
    147    /**
    148     * List wrapper used to allow the Variables list to be created as beans in DefaultConfigurationBuilder.
    149     */
    150    public static class Variables extends ArrayList<Variable> {
    151        /**
    152         * The serial version UID.
    153         */
    154        private static final long serialVersionUID = 20111205L;
    155
    156        /**
    157         * Creates a new empty instance of {@code Variables}.
    158         */
    159        public Variables() {
    160        }
    161
    162        /**
    163         * Creates a new instance of {@code Variables} and copies the content of the given object.
    164         *
    165         * @param vars the {@code Variables} object to be copied
    166         */
    167        public Variables(final Variables vars) {
    168            super(vars);
    169        }
    170
    171        /**
    172         * Gets the variable or null if empty.
    173         *
    174         * @return the variable or null if empty.
    175         */
    176        public Variable getVariable() {
    177            return !isEmpty() ? get(size() - 1) : null;
    178        }
    179
    180    }
    181
    182    /** Prefix to identify a Java Class object */
    183    private static final String CLASS = "Class:";
    184
    185    /** The default prefix for subordinate lookup expressions */
    186    private static final String DEFAULT_PREFIX = "$[";
    187
    188    /** The default suffix for subordinate lookup expressions */
    189    private static final String DEFAULT_SUFFIX = "]";
    190
    191    /** The ConfigurationInterpolator used by this object. */
    192    private ConfigurationInterpolator interpolator;
    193
    194    /** The StringSubstitutor for performing replace operations. */
    195    private StringSubstitutor substitutor;
    196
    197    /** The logger used by this instance. */
    198    private ConfigurationLogger logger;
    199
    200    /** The engine. */
    201    private final JexlEngine engine = new JexlEngine();
    202
    203    /** The variables maintained by this object. */
    204    private Variables variables;
    205
    206    /** The String to use to start subordinate lookup expressions */
    207    private String prefixMatcher = DEFAULT_PREFIX;
    208
    209    /** The String to use to terminate subordinate lookup expressions */
    210    private String suffixMatcher = DEFAULT_SUFFIX;
    211
    212    /**
    213     * Constructs a new instance. Will get used when the Lookup is constructed via configuration.
    214     */
    215    public ExprLookup() {
    216    }
    217
    218    /**
    219     * Constructor for use by applications.
    220     *
    221     * @param list The list of objects to be accessible in expressions.
    222     */
    223    public ExprLookup(final Variables list) {
    224        setVariables(list);
    225    }
    226
    227    /**
    228     * Constructor for use by applications.
    229     *
    230     * @param list The list of objects to be accessible in expressions.
    231     * @param prefix The prefix to use for subordinate lookups.
    232     * @param suffix The suffix to use for subordinate lookups.
    233     */
    234    public ExprLookup(final Variables list, final String prefix, final String suffix) {
    235        this(list);
    236        setVariablePrefixMatcher(prefix);
    237        setVariableSuffixMatcher(suffix);
    238    }
    239
    240    /**
    241     * Creates a new {@code JexlContext} and initializes it with the variables managed by this Lookup object.
    242     *
    243     * @return the newly created context
    244     */
    245    private JexlContext createContext() {
    246        final JexlContext ctx = new MapContext();
    247        initializeContext(ctx);
    248        return ctx;
    249    }
    250
    251    /**
    252     * Gets the {@code ConfigurationInterpolator} used by this object.
    253     *
    254     * @return the {@code ConfigurationInterpolator}
    255     * @since 2.0
    256     */
    257    public ConfigurationInterpolator getInterpolator() {
    258        return interpolator;
    259    }
    260
    261    /**
    262     * Gets the logger used by this object.
    263     *
    264     * @return the {@code Log}
    265     * @since 2.0
    266     */
    267    public ConfigurationLogger getLogger() {
    268        return logger;
    269    }
    270
    271    /**
    272     * Gets the list of Variables that are accessible within expressions. This method returns a copy of the variables
    273     * managed by this lookup; so modifying this object has no impact on this lookup.
    274     *
    275     * @return the List of Variables that are accessible within expressions.
    276     */
    277    public Variables getVariables() {
    278        return new Variables(variables);
    279    }
    280
    281    /**
    282     * Initializes the specified context with the variables managed by this Lookup object.
    283     *
    284     * @param ctx the context to be initialized
    285     */
    286    private void initializeContext(final JexlContext ctx) {
    287        variables.forEach(var -> ctx.set(var.getName(), var.getValue()));
    288    }
    289
    290    /**
    291     * Creates a {@code StringSubstitutor} object which uses the passed in {@code ConfigurationInterpolator} as lookup
    292     * object.
    293     *
    294     * @param ip the {@code ConfigurationInterpolator} to be used
    295     */
    296    private void installSubstitutor(final ConfigurationInterpolator ip) {
    297        if (ip == null) {
    298            substitutor = null;
    299        } else {
    300            final StringLookup variableResolver = key -> Objects.toString(ip.resolve(key), null);
    301            substitutor = new StringSubstitutor(variableResolver, prefixMatcher, suffixMatcher, StringSubstitutor.DEFAULT_ESCAPE);
    302        }
    303    }
    304
    305    /**
    306     * Evaluates the expression.
    307     *
    308     * @param var The expression.
    309     * @return The String result of the expression.
    310     */
    311    @Override
    312    public String lookup(final String var) {
    313        if (substitutor == null) {
    314            return var;
    315        }
    316
    317        String result = substitutor.replace(var);
    318        try {
    319            final Expression exp = engine.createExpression(result);
    320            final Object exprResult = exp.evaluate(createContext());
    321            result = exprResult != null ? String.valueOf(exprResult) : null;
    322        } catch (final Exception e) {
    323            final ConfigurationLogger l = getLogger();
    324            if (l != null) {
    325                l.debug("Error encountered evaluating " + result + ": " + e);
    326            }
    327        }
    328
    329        return result;
    330    }
    331
    332    /**
    333     * Sets the {@code ConfigurationInterpolator} to be used by this object.
    334     *
    335     * @param interpolator the {@code ConfigurationInterpolator} (may be <strong>null</strong>)
    336     * @since 2.0
    337     */
    338    public void setInterpolator(final ConfigurationInterpolator interpolator) {
    339        this.interpolator = interpolator;
    340        installSubstitutor(interpolator);
    341    }
    342
    343    /**
    344     * Sets the logger to be used by this object. If no logger is passed in, no log output is generated.
    345     *
    346     * @param logger the {@code Log}
    347     * @since 2.0
    348     */
    349    public void setLogger(final ConfigurationLogger logger) {
    350        this.logger = logger;
    351    }
    352
    353    /**
    354     * Sets the prefix to use to identify subordinate expressions. This cannot be the same as the prefix used for the primary
    355     * expression.
    356     *
    357     * @param prefix The String identifying the beginning of the expression.
    358     */
    359    public void setVariablePrefixMatcher(final String prefix) {
    360        prefixMatcher = prefix;
    361    }
    362
    363    /**
    364     * Add the Variables that will be accessible within expressions.
    365     *
    366     * @param list The list of Variables.
    367     */
    368    public void setVariables(final Variables list) {
    369        variables = new Variables(list);
    370    }
    371
    372    /**
    373     * Sets the suffix to use to identify subordinate expressions. This cannot be the same as the suffix used for the primary
    374     * expression.
    375     *
    376     * @param suffix The String identifying the end of the expression.
    377     */
    378    public void setVariableSuffixMatcher(final String suffix) {
    379        suffixMatcher = suffix;
    380    }
    381}