001/**
002 *   Copyright (C) 2011-2012 Typesafe Inc. <http://typesafe.com>
003 */
004package com.typesafe.config;
005
006import java.time.Duration;
007import java.time.Period;
008import java.time.temporal.TemporalAmount;
009import java.util.List;
010import java.util.Map;
011import java.util.Set;
012import java.util.concurrent.TimeUnit;
013
014/**
015 * An immutable map from config paths to config values. Paths are dot-separated
016 * expressions such as <code>foo.bar.baz</code>. Values are as in JSON
017 * (booleans, strings, numbers, lists, or objects), represented by
018 * {@link ConfigValue} instances. Values accessed through the
019 * <code>Config</code> interface are never null.
020 * 
021 * <p>
022 * {@code Config} is an immutable object and thus safe to use from multiple
023 * threads. There's never a need for "defensive copies."
024 * 
025 * <p>
026 * Fundamental operations on a {@code Config} include getting configuration
027 * values, <em>resolving</em> substitutions with {@link Config#resolve()}, and
028 * merging configs using {@link Config#withFallback(ConfigMergeable)}.
029 * 
030 * <p>
031 * All operations return a new immutable {@code Config} rather than modifying
032 * the original instance.
033 * 
034 * <p>
035 * <strong>Examples</strong>
036 * 
037 * <p>
038 * You can find an example app and library <a
039 * href="https://github.com/lightbend/config/tree/main/examples">on
040 * GitHub</a>. Also be sure to read the <a
041 * href="package-summary.html#package_description">package overview</a> which
042 * describes the big picture as shown in those examples.
043 * 
044 * <p>
045 * <strong>Paths, keys, and Config vs. ConfigObject</strong>
046 * 
047 * <p>
048 * <code>Config</code> is a view onto a tree of {@link ConfigObject}; the
049 * corresponding object tree can be found through {@link Config#root()}.
050 * <code>ConfigObject</code> is a map from config <em>keys</em>, rather than
051 * paths, to config values. Think of <code>ConfigObject</code> as a JSON object
052 * and <code>Config</code> as a configuration API.
053 * 
054 * <p>
055 * The API tries to consistently use the terms "key" and "path." A key is a key
056 * in a JSON object; it's just a string that's the key in a map. A "path" is a
057 * parseable expression with a syntax and it refers to a series of keys. Path
058 * expressions are described in the <a
059 * href="https://github.com/lightbend/config/blob/main/HOCON.md">spec for
060 * Human-Optimized Config Object Notation</a>. In brief, a path is
061 * period-separated so "a.b.c" looks for key c in object b in object a in the
062 * root object. Sometimes double quotes are needed around special characters in
063 * path expressions.
064 * 
065 * <p>
066 * The API for a {@code Config} is in terms of path expressions, while the API
067 * for a {@code ConfigObject} is in terms of keys. Conceptually, {@code Config}
068 * is a one-level map from <em>paths</em> to values, while a
069 * {@code ConfigObject} is a tree of nested maps from <em>keys</em> to values.
070 * 
071 * <p>
072 * Use {@link ConfigUtil#joinPath} and {@link ConfigUtil#splitPath} to convert
073 * between path expressions and individual path elements (keys).
074 * 
075 * <p>
076 * Another difference between {@code Config} and {@code ConfigObject} is that
077 * conceptually, {@code ConfigValue}s with a {@link ConfigValue#valueType()
078 * valueType()} of {@link ConfigValueType#NULL NULL} exist in a
079 * {@code ConfigObject}, while a {@code Config} treats null values as if they
080 * were missing. (With the exception of two methods: {@link Config#hasPathOrNull}
081 * and {@link Config#getIsNull} let you detect <code>null</code> values.)
082 *
083 * <p>
084 * <strong>Getting configuration values</strong>
085 * 
086 * <p>
087 * The "getters" on a {@code Config} all work in the same way. They never return
088 * null, nor do they return a {@code ConfigValue} with
089 * {@link ConfigValue#valueType() valueType()} of {@link ConfigValueType#NULL
090 * NULL}. Instead, they throw {@link ConfigException.Missing} if the value is
091 * completely absent or set to null. If the value is set to null, a subtype of
092 * {@code ConfigException.Missing} called {@link ConfigException.Null} will be
093 * thrown. {@link ConfigException.WrongType} will be thrown anytime you ask for
094 * a type and the value has an incompatible type. Reasonable type conversions
095 * are performed for you though.
096 * 
097 * <p>
098 * <strong>Iteration</strong>
099 * 
100 * <p>
101 * If you want to iterate over the contents of a {@code Config}, you can get its
102 * {@code ConfigObject} with {@link #root()}, and then iterate over the
103 * {@code ConfigObject} (which implements <code>java.util.Map</code>). Or, you
104 * can use {@link #entrySet()} which recurses the object tree for you and builds
105 * up a <code>Set</code> of all path-value pairs where the value is not null.
106 * 
107 * <p>
108 * <strong>Resolving substitutions</strong>
109 * 
110 * <p>
111 * <em>Substitutions</em> are the <code>${foo.bar}</code> syntax in config
112 * files, described in the <a href=
113 * "https://github.com/lightbend/config/blob/main/HOCON.md#substitutions"
114 * >specification</a>. Resolving substitutions replaces these references with real
115 * values.
116 * 
117 * <p>
118 * Before using a {@code Config} it's necessary to call {@link Config#resolve()}
119 * to handle substitutions (though {@link ConfigFactory#load()} and similar
120 * methods will do the resolve for you already).
121 * 
122 * <p>
123 * <strong>Merging</strong>
124 * 
125 * <p>
126 * The full <code>Config</code> for your application can be constructed using
127 * the associative operation {@link Config#withFallback(ConfigMergeable)}. If
128 * you use {@link ConfigFactory#load()} (recommended), it merges system
129 * properties over the top of <code>application.conf</code> over the top of
130 * <code>reference.conf</code>, using <code>withFallback</code>. You can add in
131 * additional sources of configuration in the same way (usually, custom layers
132 * should go either just above or just below <code>application.conf</code>,
133 * keeping <code>reference.conf</code> at the bottom and system properties at
134 * the top).
135 * 
136 * <p>
137 * <strong>Serialization</strong>
138 * 
139 * <p>
140 * Convert a <code>Config</code> to a JSON or HOCON string by calling
141 * {@link ConfigObject#render()} on the root object,
142 * <code>myConfig.root().render()</code>. There's also a variant
143 * {@link ConfigObject#render(ConfigRenderOptions)} which allows you to control
144 * the format of the rendered string. (See {@link ConfigRenderOptions}.) Note
145 * that <code>Config</code> does not remember the formatting of the original
146 * file, so if you load, modify, and re-save a config file, it will be
147 * substantially reformatted.
148 * 
149 * <p>
150 * As an alternative to {@link ConfigObject#render()}, the
151 * <code>toString()</code> method produces a debug-output-oriented
152 * representation (which is not valid JSON).
153 * 
154 * <p>
155 * Java serialization is supported as well for <code>Config</code> and all
156 * subtypes of <code>ConfigValue</code>.
157 * 
158 * <p>
159 * <strong>This is an interface but don't implement it yourself</strong>
160 * 
161 * <p>
162 * <em>Do not implement {@code Config}</em>; it should only be implemented by
163 * the config library. Arbitrary implementations will not work because the
164 * library internals assume a specific concrete implementation. Also, this
165 * interface is likely to grow new methods over time, so third-party
166 * implementations will break.
167 */
168public interface Config extends ConfigMergeable {
169    /**
170     * Gets the {@code Config} as a tree of {@link ConfigObject}. This is a
171     * constant-time operation (it is not proportional to the number of values
172     * in the {@code Config}).
173     *
174     * @return the root object in the configuration
175     */
176    ConfigObject root();
177
178    /**
179     * Gets the origin of the {@code Config}, which may be a file, or a file
180     * with a line number, or just a descriptive phrase.
181     *
182     * @return the origin of the {@code Config} for use in error messages
183     */
184    ConfigOrigin origin();
185
186    @Override
187    Config withFallback(ConfigMergeable other);
188
189    /**
190     * Returns a replacement config with all substitutions (the
191     * <code>${foo.bar}</code> syntax, see <a
192     * href="https://github.com/lightbend/config/blob/main/HOCON.md">the
193     * spec</a>) resolved. Substitutions are looked up using this
194     * <code>Config</code> as the root object, that is, a substitution
195     * <code>${foo.bar}</code> will be replaced with the result of
196     * <code>getValue("foo.bar")</code>.
197     * 
198     * <p>
199     * This method uses {@link ConfigResolveOptions#defaults()}, there is
200     * another variant {@link Config#resolve(ConfigResolveOptions)} which lets
201     * you specify non-default options.
202     * 
203     * <p>
204     * A given {@link Config} must be resolved before using it to retrieve
205     * config values, but ideally should be resolved one time for your entire
206     * stack of fallbacks (see {@link Config#withFallback}). Otherwise, some
207     * substitutions that could have resolved with all fallbacks available may
208     * not resolve, which will be potentially confusing for your application's
209     * users.
210     * 
211     * <p>
212     * <code>resolve()</code> should be invoked on root config objects, rather
213     * than on a subtree (a subtree is the result of something like
214     * <code>config.getConfig("foo")</code>). The problem with
215     * <code>resolve()</code> on a subtree is that substitutions are relative to
216     * the root of the config and the subtree will have no way to get values
217     * from the root. For example, if you did
218     * <code>config.getConfig("foo").resolve()</code> on the below config file,
219     * it would not work:
220     * 
221     * <pre>
222     *   common-value = 10
223     *   foo {
224     *      whatever = ${common-value}
225     *   }
226     * </pre>
227     * 
228     * <p>
229     * Many methods on {@link ConfigFactory} such as
230     * {@link ConfigFactory#load()} automatically resolve the loaded
231     * <code>Config</code> on the loaded stack of config files.
232     * 
233     * <p>
234     * Resolving an already-resolved config is a harmless no-op, but again, it
235     * is best to resolve an entire stack of fallbacks (such as all your config
236     * files combined) rather than resolving each one individually.
237     * 
238     * @return an immutable object with substitutions resolved
239     * @throws ConfigException.UnresolvedSubstitution
240     *             if any substitutions refer to nonexistent paths
241     * @throws ConfigException
242     *             some other config exception if there are other problems
243     */
244    Config resolve();
245
246    /**
247     * Like {@link Config#resolve()} but allows you to specify non-default
248     * options.
249     *
250     * @param options
251     *            resolve options
252     * @return the resolved <code>Config</code> (may be only partially resolved if options are set to allow unresolved)
253     */
254    Config resolve(ConfigResolveOptions options);
255
256    /**
257     * Checks whether the config is completely resolved. After a successful call
258     * to {@link Config#resolve()} it will be completely resolved, but after
259     * calling {@link Config#resolve(ConfigResolveOptions)} with
260     * <code>allowUnresolved</code> set in the options, it may or may not be
261     * completely resolved. A newly-loaded config may or may not be completely
262     * resolved depending on whether there were substitutions present in the
263     * file.
264     * 
265     * @return true if there are no unresolved substitutions remaining in this
266     *         configuration.
267     * @since 1.2.0
268     */
269    boolean isResolved();
270
271    /**
272     * Like {@link Config#resolve()} except that substitution values are looked
273     * up in the given source, rather than in this instance. This is a
274     * special-purpose method which doesn't make sense to use in most cases;
275     * it's only needed if you're constructing some sort of app-specific custom
276     * approach to configuration. The more usual approach if you have a source
277     * of substitution values would be to merge that source into your config
278     * stack using {@link Config#withFallback} and then resolve.
279     * <p>
280     * Note that this method does NOT look in this instance for substitution
281     * values. If you want to do that, you could either merge this instance into
282     * your value source using {@link Config#withFallback}, or you could resolve
283     * multiple times with multiple sources (using
284     * {@link ConfigResolveOptions#setAllowUnresolved(boolean)} so the partial
285     * resolves don't fail).
286     * 
287     * @param source
288     *            configuration to pull values from
289     * @return an immutable object with substitutions resolved
290     * @throws ConfigException.UnresolvedSubstitution
291     *             if any substitutions refer to paths which are not in the
292     *             source
293     * @throws ConfigException
294     *             some other config exception if there are other problems
295     * @since 1.2.0
296     */
297    Config resolveWith(Config source);
298
299    /**
300     * Like {@link Config#resolveWith(Config)} but allows you to specify
301     * non-default options.
302     * 
303     * @param source
304     *            source configuration to pull values from
305     * @param options
306     *            resolve options
307     * @return the resolved <code>Config</code> (may be only partially resolved
308     *         if options are set to allow unresolved)
309     * @since 1.2.0
310     */
311    Config resolveWith(Config source, ConfigResolveOptions options);
312
313    /**
314     * Validates this config against a reference config, throwing an exception
315     * if it is invalid. The purpose of this method is to "fail early" with a
316     * comprehensive list of problems; in general, anything this method can find
317     * would be detected later when trying to use the config, but it's often
318     * more user-friendly to fail right away when loading the config.
319     *
320     * <p>
321     * Using this method is always optional, since you can "fail late" instead.
322     *
323     * <p>
324     * You must restrict validation to paths you "own" (those whose meaning are
325     * defined by your code module). If you validate globally, you may trigger
326     * errors about paths that happen to be in the config but have nothing to do
327     * with your module. It's best to allow the modules owning those paths to
328     * validate them. Also, if every module validates only its own stuff, there
329     * isn't as much redundant work being done.
330     *
331     * <p>
332     * If no paths are specified in <code>checkValid()</code>'s parameter list,
333     * validation is for the entire config.
334     *
335     * <p>
336     * If you specify paths that are not in the reference config, those paths
337     * are ignored. (There's nothing to validate.)
338     *
339     * <p>
340     * Here's what validation involves:
341     *
342     * <ul>
343     * <li>All paths found in the reference config must be present in this
344     * config or an exception will be thrown.
345     * <li>
346     * Some changes in type from the reference config to this config will cause
347     * an exception to be thrown. Not all potential type problems are detected,
348     * in particular it's assumed that strings are compatible with everything
349     * except objects and lists. This is because string types are often "really"
350     * some other type (system properties always start out as strings, or a
351     * string like "5ms" could be used with {@link #getMilliseconds}). Also,
352     * it's allowed to set any type to null or override null with any type.
353     * <li>
354     * Any unresolved substitutions in this config will cause a validation
355     * failure; both the reference config and this config should be resolved
356     * before validation. If the reference config is unresolved, it's a bug in
357     * the caller of this method.
358     * </ul>
359     *
360     * <p>
361     * If you want to allow a certain setting to have a flexible type (or
362     * otherwise want validation to be looser for some settings), you could
363     * either remove the problematic setting from the reference config provided
364     * to this method, or you could intercept the validation exception and
365     * screen out certain problems. Of course, this will only work if all other
366     * callers of this method are careful to restrict validation to their own
367     * paths, as they should be.
368     *
369     * <p>
370     * If validation fails, the thrown exception contains a list of all problems
371     * found. See {@link ConfigException.ValidationFailed#problems}. The
372     * exception's <code>getMessage()</code> will have all the problems
373     * concatenated into one huge string, as well.
374     *
375     * <p>
376     * Again, <code>checkValid()</code> can't guess every domain-specific way a
377     * setting can be invalid, so some problems may arise later when attempting
378     * to use the config. <code>checkValid()</code> is limited to reporting
379     * generic, but common, problems such as missing settings and blatant type
380     * incompatibilities.
381     *
382     * @param reference
383     *            a reference configuration
384     * @param restrictToPaths
385     *            only validate values underneath these paths that your code
386     *            module owns and understands
387     * @throws ConfigException.ValidationFailed
388     *             if there are any validation issues
389     * @throws ConfigException.NotResolved
390     *             if this config is not resolved
391     * @throws ConfigException.BugOrBroken
392     *             if the reference config is unresolved or caller otherwise
393     *             misuses the API
394     */
395    void checkValid(Config reference, String... restrictToPaths);
396
397    /**
398     * Checks whether a value is present and non-null at the given path. This
399     * differs in two ways from {@code Map.containsKey()} as implemented by
400     * {@link ConfigObject}: it looks for a path expression, not a key; and it
401     * returns false for null values, while {@code containsKey()} returns true
402     * indicating that the object contains a null value for the key.
403     * 
404     * <p>
405     * If a path exists according to {@link #hasPath(String)}, then
406     * {@link #getValue(String)} will never throw an exception. However, the
407     * typed getters, such as {@link #getInt(String)}, will still throw if the
408     * value is not convertible to the requested type.
409     * 
410     * <p>
411     * Note that path expressions have a syntax and sometimes require quoting
412     * (see {@link ConfigUtil#joinPath} and {@link ConfigUtil#splitPath}).
413     * 
414     * @param path
415     *            the path expression
416     * @return true if a non-null value is present at the path
417     * @throws ConfigException.BadPath
418     *             if the path expression is invalid
419     */
420    boolean hasPath(String path);
421
422    /**
423     * Checks whether a value is present at the given path, even
424     * if the value is null. Most of the getters on
425     * <code>Config</code> will throw if you try to get a null
426     * value, so if you plan to call {@link #getValue(String)},
427     * {@link #getInt(String)}, or another getter you may want to
428     * use plain {@link #hasPath(String)} rather than this method.
429     *
430     * <p>
431     * To handle all three cases (unset, null, and a non-null value)
432     * the code might look like:
433     * <pre><code>
434     * if (config.hasPathOrNull(path)) {
435     *     if (config.getIsNull(path)) {
436     *        // handle null setting
437     *     } else {
438     *        // get and use non-null setting
439     *     }
440     * } else {
441     *     // handle entirely unset path
442     * }
443     * </code></pre>
444     *
445     * <p> However, the usual thing is to allow entirely unset
446     * paths to be a bug that throws an exception (because you set
447     * a default in your <code>reference.conf</code>), so in that
448     * case it's OK to call {@link #getIsNull(String)} without
449     * checking <code>hasPathOrNull</code> first.
450     *
451     * <p>
452     * Note that path expressions have a syntax and sometimes require quoting
453     * (see {@link ConfigUtil#joinPath} and {@link ConfigUtil#splitPath}).
454     *
455     * @param path
456     *            the path expression
457     * @return true if a value is present at the path, even if the value is null
458     * @throws ConfigException.BadPath
459     *             if the path expression is invalid
460     */
461    boolean hasPathOrNull(String path);
462
463    /**
464     * Returns true if the {@code Config}'s root object contains no key-value
465     * pairs.
466     *
467     * @return true if the configuration is empty
468     */
469    boolean isEmpty();
470
471    /**
472     * Returns the set of path-value pairs, excluding any null values, found by
473     * recursing {@link #root() the root object}. Note that this is very
474     * different from <code>root().entrySet()</code> which returns the set of
475     * immediate-child keys in the root object and includes null values.
476     * <p>
477     * Entries contain <em>path expressions</em> meaning there may be quoting
478     * and escaping involved. Parse path expressions with
479     * {@link ConfigUtil#splitPath}.
480     * <p>
481     * Because a <code>Config</code> is conceptually a single-level map from
482     * paths to values, there will not be any {@link ConfigObject} values in the
483     * entries (that is, all entries represent leaf nodes). Use
484     * {@link ConfigObject} rather than <code>Config</code> if you want a tree.
485     * (OK, this is a slight lie: <code>Config</code> entries may contain
486     * {@link ConfigList} and the lists may contain objects. But no objects are
487     * directly included as entry values.)
488     * 
489     * @return set of paths with non-null values, built up by recursing the
490     *         entire tree of {@link ConfigObject} and creating an entry for
491     *         each leaf value.
492     */
493    Set<Map.Entry<String, ConfigValue>> entrySet();
494
495    /**
496     * Checks whether a value is set to null at the given path,
497     * but throws an exception if the value is entirely
498     * unset. This method will not throw if {@link
499     * #hasPathOrNull(String)} returned true for the same path, so
500     * to avoid any possible exception check
501     * <code>hasPathOrNull()</code> first.  However, an exception
502     * for unset paths will usually be the right thing (because a
503     * <code>reference.conf</code> should exist that has the path
504     * set, the path should never be unset unless something is
505     * broken).
506     *
507     * <p>
508     * Note that path expressions have a syntax and sometimes require quoting
509     * (see {@link ConfigUtil#joinPath} and {@link ConfigUtil#splitPath}).
510     *
511     * @param path
512     *            the path expression
513     * @return true if the value exists and is null, false if it
514     * exists and is not null
515     * @throws ConfigException.BadPath
516     *             if the path expression is invalid
517     * @throws ConfigException.Missing
518     *             if value is not set at all
519     */
520    boolean getIsNull(String path);
521
522    /**
523     *
524     * @param path
525     *            path expression
526     * @return the boolean value at the requested path
527     * @throws ConfigException.Missing
528     *             if value is absent or null
529     * @throws ConfigException.WrongType
530     *             if value is not convertible to boolean
531     */
532    boolean getBoolean(String path);
533
534    /**
535     * @param path
536     *            path expression
537     * @return the numeric value at the requested path
538     * @throws ConfigException.Missing
539     *             if value is absent or null
540     * @throws ConfigException.WrongType
541     *             if value is not convertible to a number
542     */
543    Number getNumber(String path);
544
545    /**
546     * Gets the integer at the given path. If the value at the
547     * path has a fractional (floating point) component, it
548     * will be discarded and only the integer part will be
549     * returned (it works like a "narrowing primitive conversion"
550     * in the Java language specification).
551     *
552     * @param path
553     *            path expression
554     * @return the 32-bit integer value at the requested path
555     * @throws ConfigException.Missing
556     *             if value is absent or null
557     * @throws ConfigException.WrongType
558     *             if value is not convertible to an int (for example it is out
559     *             of range, or it's a boolean value)
560     */
561    int getInt(String path);
562
563    /**
564     * Gets the long integer at the given path.  If the value at
565     * the path has a fractional (floating point) component, it
566     * will be discarded and only the integer part will be
567     * returned (it works like a "narrowing primitive conversion"
568     * in the Java language specification).
569     *
570     * @param path
571     *            path expression
572     * @return the 64-bit long value at the requested path
573     * @throws ConfigException.Missing
574     *             if value is absent or null
575     * @throws ConfigException.WrongType
576     *             if value is not convertible to a long
577     */
578    long getLong(String path);
579
580    /**
581     * @param path
582     *            path expression
583     * @return the floating-point value at the requested path
584     * @throws ConfigException.Missing
585     *             if value is absent or null
586     * @throws ConfigException.WrongType
587     *             if value is not convertible to a double
588     */
589    double getDouble(String path);
590
591    /**
592     * @param path
593     *            path expression
594     * @return the string value at the requested path
595     * @throws ConfigException.Missing
596     *             if value is absent or null
597     * @throws ConfigException.WrongType
598     *             if value is not convertible to a string
599     */
600    String getString(String path);
601
602    /**
603     * @param enumClass
604     *            an enum class
605     * @param <T>
606     *            a generic denoting a specific type of enum
607     * @param path
608     *            path expression
609     * @return the {@code Enum} value at the requested path
610     *              of the requested enum class
611     * @throws ConfigException.Missing
612     *             if value is absent or null
613     * @throws ConfigException.WrongType
614     *             if value is not convertible to an Enum
615     */
616    public <T extends Enum<T>> T getEnum(Class<T> enumClass, String path);
617
618    /**
619     * @param path
620     *            path expression
621     * @return the {@link ConfigObject} value at the requested path
622     * @throws ConfigException.Missing
623     *             if value is absent or null
624     * @throws ConfigException.WrongType
625     *             if value is not convertible to an object
626     */
627    ConfigObject getObject(String path);
628
629    /**
630     * @param path
631     *            path expression
632     * @return the nested {@code Config} value at the requested path
633     * @throws ConfigException.Missing
634     *             if value is absent or null
635     * @throws ConfigException.WrongType
636     *             if value is not convertible to a Config
637     */
638    Config getConfig(String path);
639
640    /**
641     * Gets the value at the path as an unwrapped Java boxed value (
642     * {@link java.lang.Boolean Boolean}, {@link java.lang.Integer Integer}, and
643     * so on - see {@link ConfigValue#unwrapped()}).
644     *
645     * @param path
646     *            path expression
647     * @return the unwrapped value at the requested path
648     * @throws ConfigException.Missing
649     *             if value is absent or null
650     */
651    Object getAnyRef(String path);
652
653    /**
654     * Gets the value at the given path, unless the value is a
655     * null value or missing, in which case it throws just like
656     * the other getters. Use {@code get()} on the {@link
657     * Config#root()} object (or other object in the tree) if you
658     * want an unprocessed value.
659     *
660     * @param path
661     *            path expression
662     * @return the value at the requested path
663     * @throws ConfigException.Missing
664     *             if value is absent or null
665     */
666    ConfigValue getValue(String path);
667
668    /**
669     * Gets a value as a size in bytes (parses special strings like "128M"). If
670     * the value is already a number, then it's left alone; if it's a string,
671     * it's parsed understanding unit suffixes such as "128K", as documented in
672     * <a href="https://github.com/lightbend/config/blob/main/HOCON.md">the
673     * spec</a>.
674     *
675     * @param path
676     *            path expression
677     * @return the value at the requested path, in bytes
678     * @throws ConfigException.Missing
679     *             if value is absent or null
680     * @throws ConfigException.WrongType
681     *             if value is not convertible to Long or String
682     * @throws ConfigException.BadValue
683     *             if value cannot be parsed as a size in bytes
684     */
685    Long getBytes(String path);
686
687    /**
688     * Gets a value as an amount of memory (parses special strings like "128M"). If
689     * the value is already a number, then it's left alone; if it's a string,
690     * it's parsed understanding unit suffixes such as "128K", as documented in
691     * <a href="https://github.com/lightbend/config/blob/main/HOCON.md">the
692     * spec</a>.
693     *
694     * @since 1.3.0
695     *
696     * @param path
697     *            path expression
698     * @return the value at the requested path, in bytes
699     * @throws ConfigException.Missing
700     *             if value is absent or null
701     * @throws ConfigException.WrongType
702     *             if value is not convertible to Long or String
703     * @throws ConfigException.BadValue
704     *             if value cannot be parsed as a size in bytes
705     */
706    ConfigMemorySize getMemorySize(String path);
707
708    /**
709     * Get value as a duration in milliseconds. If the value is already a
710     * number, then it's left alone; if it's a string, it's parsed understanding
711     * units suffixes like "10m" or "5ns" as documented in
712     * <a href="https://github.com/lightbend/config/blob/main/HOCON.md">the spec</a>.
713     *
714     * @deprecated  As of release 1.1, replaced by {@link #getDuration(String, TimeUnit)}
715     *
716     * @param path
717     *            path expression
718     * @return the duration value at the requested path, in milliseconds
719     * @throws ConfigException.Missing
720     *             if value is absent or null
721     * @throws ConfigException.WrongType
722     *             if value is not convertible to Long or String
723     * @throws ConfigException.BadValue
724     *             if value cannot be parsed as a number of milliseconds
725     */
726    @Deprecated Long getMilliseconds(String path);
727
728    /**
729     * Get value as a duration in nanoseconds. If the value is already a number
730     * it's taken as milliseconds and converted to nanoseconds. If it's a
731     * string, it's parsed understanding unit suffixes, as for
732     * {@link #getDuration(String, TimeUnit)}.
733     *
734     * @deprecated  As of release 1.1, replaced by {@link #getDuration(String, TimeUnit)}
735     *
736     * @param path
737     *            path expression
738     * @return the duration value at the requested path, in nanoseconds
739     * @throws ConfigException.Missing
740     *             if value is absent or null
741     * @throws ConfigException.WrongType
742     *             if value is not convertible to Long or String
743     * @throws ConfigException.BadValue
744     *             if value cannot be parsed as a number of nanoseconds
745     */
746    @Deprecated Long getNanoseconds(String path);
747
748    /**
749     * Gets a value as a duration in a specified
750     * {@link java.util.concurrent.TimeUnit TimeUnit}. If the value is already a
751     * number, then it's taken as milliseconds and then converted to the
752     * requested TimeUnit; if it's a string, it's parsed understanding units
753     * suffixes like "10m" or "5ns" as documented in
754     * <a href="https://github.com/lightbend/config/blob/main/HOCON.md">the spec</a>.
755     * 
756     * @since 1.2.0
757     * 
758     * @param path
759     *            path expression
760     * @param unit
761     *            convert the return value to this time unit
762     * @return the duration value at the requested path, in the given TimeUnit
763     * @throws ConfigException.Missing
764     *             if value is absent or null
765     * @throws ConfigException.WrongType
766     *             if value is not convertible to Long or String
767     * @throws ConfigException.BadValue
768     *             if value cannot be parsed as a number of the given TimeUnit
769     */
770    long getDuration(String path, TimeUnit unit);
771
772    /**
773     * Gets a value as a java.time.Duration. If the value is
774     * already a number, then it's taken as milliseconds; if it's
775     * a string, it's parsed understanding units suffixes like
776     * "10m" or "5ns" as documented in
777     * <a href="https://github.com/lightbend/config/blob/main/HOCON.md">the spec</a>.
778     * This method never returns null.
779     *
780     * @since 1.3.0
781     *
782     * @param path
783     *            path expression
784     * @return the duration value at the requested path
785     * @throws ConfigException.Missing
786     *             if value is absent or null
787     * @throws ConfigException.WrongType
788     *             if value is not convertible to Long or String
789     * @throws ConfigException.BadValue
790     *             if value cannot be parsed as a number of the given TimeUnit
791     */
792    Duration getDuration(String path);
793
794    /**
795     * Gets a value as a java.time.Period. If the value is
796     * already a number, then it's taken as days; if it's
797     * a string, it's parsed understanding units suffixes like
798     * "10d" or "5w" as documented in
799     * <a href="https://github.com/lightbend/config/blob/main/HOCON.md">the spec</a>.
800     * This method never returns null.
801     *
802     * @since 1.3.0
803     *
804     * @param path
805     *            path expression
806     * @return the period value at the requested path
807     * @throws ConfigException.Missing
808     *             if value is absent or null
809     * @throws ConfigException.WrongType
810     *             if value is not convertible to Long or String
811     * @throws ConfigException.BadValue
812     *             if value cannot be parsed as a number of the given TimeUnit
813     */
814    Period getPeriod(String path);
815
816    /**
817     * Gets a value as a java.time.temporal.TemporalAmount.
818     * This method will first try to get the value as a java.time.Duration, and if unsuccessful,
819     * then as a java.time.Period.
820     * This means that values like "5m" will be parsed as 5 minutes rather than 5 months
821     * @param path path expression
822     * @return the temporal value at the requested path
823     * @throws ConfigException.Missing
824     *             if value is absent or null
825     * @throws ConfigException.WrongType
826     *             if value is not convertible to Long or String
827     * @throws ConfigException.BadValue
828     *             if value cannot be parsed as a TemporalAmount
829     */
830    TemporalAmount getTemporal(String path);
831
832    /**
833     * Gets a list value (with any element type) as a {@link ConfigList}, which
834     * implements {@code java.util.List<ConfigValue>}. Throws if the path is
835     * unset or null.
836     *
837     * @param path
838     *            the path to the list value.
839     * @return the {@link ConfigList} at the path
840     * @throws ConfigException.Missing
841     *             if value is absent or null
842     * @throws ConfigException.WrongType
843     *             if value is not convertible to a ConfigList
844     */
845    ConfigList getList(String path);
846
847    /**
848     * Gets a list value with boolean elements.  Throws if the
849     * path is unset or null or not a list or contains values not
850     * convertible to boolean.
851     *
852     * @param path
853     *            the path to the list value.
854     * @return the list at the path
855     * @throws ConfigException.Missing
856     *             if value is absent or null
857     * @throws ConfigException.WrongType
858     *             if value is not convertible to a list of booleans
859     */
860    List<Boolean> getBooleanList(String path);
861
862    /**
863     * Gets a list value with number elements.  Throws if the
864     * path is unset or null or not a list or contains values not
865     * convertible to number.
866     *
867     * @param path
868     *            the path to the list value.
869     * @return the list at the path
870     * @throws ConfigException.Missing
871     *             if value is absent or null
872     * @throws ConfigException.WrongType
873     *             if value is not convertible to a list of numbers
874     */
875    List<Number> getNumberList(String path);
876
877    /**
878     * Gets a list value with int elements.  Throws if the
879     * path is unset or null or not a list or contains values not
880     * convertible to int.
881     *
882     * @param path
883     *            the path to the list value.
884     * @return the list at the path
885     * @throws ConfigException.Missing
886     *             if value is absent or null
887     * @throws ConfigException.WrongType
888     *             if value is not convertible to a list of ints
889     */
890    List<Integer> getIntList(String path);
891
892    /**
893     * Gets a list value with long elements.  Throws if the
894     * path is unset or null or not a list or contains values not
895     * convertible to long.
896     *
897     * @param path
898     *            the path to the list value.
899     * @return the list at the path
900     * @throws ConfigException.Missing
901     *             if value is absent or null
902     * @throws ConfigException.WrongType
903     *             if value is not convertible to a list of longs
904     */
905    List<Long> getLongList(String path);
906
907    /**
908     * Gets a list value with double elements.  Throws if the
909     * path is unset or null or not a list or contains values not
910     * convertible to double.
911     *
912     * @param path
913     *            the path to the list value.
914     * @return the list at the path
915     * @throws ConfigException.Missing
916     *             if value is absent or null
917     * @throws ConfigException.WrongType
918     *             if value is not convertible to a list of doubles
919     */
920    List<Double> getDoubleList(String path);
921
922    /**
923     * Gets a list value with string elements.  Throws if the
924     * path is unset or null or not a list or contains values not
925     * convertible to string.
926     *
927     * @param path
928     *            the path to the list value.
929     * @return the list at the path
930     * @throws ConfigException.Missing
931     *             if value is absent or null
932     * @throws ConfigException.WrongType
933     *             if value is not convertible to a list of strings
934     */
935    List<String> getStringList(String path);
936
937    /**
938     * Gets a list value with {@code Enum} elements.  Throws if the
939     * path is unset or null or not a list or contains values not
940     * convertible to {@code Enum}.
941     *
942     * @param enumClass
943     *            the enum class
944     * @param <T>
945     *            a generic denoting a specific type of enum
946     * @param path
947     *            the path to the list value.
948     * @return the list at the path
949     * @throws ConfigException.Missing
950     *             if value is absent or null
951     * @throws ConfigException.WrongType
952     *             if value is not convertible to a list of {@code Enum}
953     */
954    <T extends Enum<T>> List<T> getEnumList(Class<T> enumClass, String path);
955
956    /**
957     * Gets a list value with object elements.  Throws if the
958     * path is unset or null or not a list or contains values not
959     * convertible to <code>ConfigObject</code>.
960     *
961     * @param path
962     *            the path to the list value.
963     * @return the list at the path
964     * @throws ConfigException.Missing
965     *             if value is absent or null
966     * @throws ConfigException.WrongType
967     *             if value is not convertible to a list of objects
968     */
969    List<? extends ConfigObject> getObjectList(String path);
970
971    /**
972     * Gets a list value with <code>Config</code> elements.
973     * Throws if the path is unset or null or not a list or
974     * contains values not convertible to <code>Config</code>.
975     *
976     * @param path
977     *            the path to the list value.
978     * @return the list at the path
979     * @throws ConfigException.Missing
980     *             if value is absent or null
981     * @throws ConfigException.WrongType
982     *             if value is not convertible to a list of configs
983     */
984    List<? extends Config> getConfigList(String path);
985
986    /**
987     * Gets a list value with any kind of elements.  Throws if the
988     * path is unset or null or not a list. Each element is
989     * "unwrapped" (see {@link ConfigValue#unwrapped()}).
990     *
991     * @param path
992     *            the path to the list value.
993     * @return the list at the path
994     * @throws ConfigException.Missing
995     *             if value is absent or null
996     * @throws ConfigException.WrongType
997     *             if value is not convertible to a list
998     */
999    List<? extends Object> getAnyRefList(String path);
1000
1001    /**
1002     * Gets a list value with elements representing a size in
1003     * bytes.  Throws if the path is unset or null or not a list
1004     * or contains values not convertible to memory sizes.
1005     *
1006     * @param path
1007     *            the path to the list value.
1008     * @return the list at the path
1009     * @throws ConfigException.Missing
1010     *             if value is absent or null
1011     * @throws ConfigException.WrongType
1012     *             if value is not convertible to a list of memory sizes
1013     */
1014    List<Long> getBytesList(String path);
1015
1016    /**
1017     * Gets a list, converting each value in the list to a memory size, using the
1018     * same rules as {@link #getMemorySize(String)}.
1019     *
1020     * @since 1.3.0
1021     * @param path
1022     *            a path expression
1023     * @return list of memory sizes
1024     * @throws ConfigException.Missing
1025     *             if value is absent or null
1026     * @throws ConfigException.WrongType
1027     *             if value is not convertible to a list of memory sizes
1028     */
1029    List<ConfigMemorySize> getMemorySizeList(String path);
1030
1031    /**
1032     * @deprecated  As of release 1.1, replaced by {@link #getDurationList(String, TimeUnit)}
1033     * @param path the path
1034     * @return list of millisecond values
1035     */
1036    @Deprecated List<Long> getMillisecondsList(String path);
1037
1038    /**
1039     * @deprecated  As of release 1.1, replaced by {@link #getDurationList(String, TimeUnit)}
1040     * @param path the path
1041     * @return list of nanosecond values
1042     */
1043    @Deprecated List<Long> getNanosecondsList(String path);
1044
1045    /**
1046     * Gets a list, converting each value in the list to a duration, using the
1047     * same rules as {@link #getDuration(String, TimeUnit)}.
1048     *
1049     * @since 1.2.0
1050     * @param path
1051     *            a path expression
1052     * @param unit
1053     *            time units of the returned values
1054     * @return list of durations, in the requested units
1055     */
1056    List<Long> getDurationList(String path, TimeUnit unit);
1057
1058    /**
1059     * Gets a list, converting each value in the list to a duration, using the
1060     * same rules as {@link #getDuration(String)}.
1061     *
1062     * @since 1.3.0
1063     * @param path
1064     *            a path expression
1065     * @return list of durations
1066     */
1067    List<Duration> getDurationList(String path);
1068
1069    /**
1070     * Clone the config with only the given path (and its children) retained;
1071     * all sibling paths are removed.
1072     * <p>
1073     * Note that path expressions have a syntax and sometimes require quoting
1074     * (see {@link ConfigUtil#joinPath} and {@link ConfigUtil#splitPath}).
1075     * 
1076     * @param path
1077     *            path to keep
1078     * @return a copy of the config minus all paths except the one specified
1079     */
1080    Config withOnlyPath(String path);
1081
1082    /**
1083     * Clone the config with the given path removed.
1084     * <p>
1085     * Note that path expressions have a syntax and sometimes require quoting
1086     * (see {@link ConfigUtil#joinPath} and {@link ConfigUtil#splitPath}).
1087     * 
1088     * @param path
1089     *            path expression to remove
1090     * @return a copy of the config minus the specified path
1091     */
1092    Config withoutPath(String path);
1093
1094    /**
1095     * Places the config inside another {@code Config} at the given path.
1096     * <p>
1097     * Note that path expressions have a syntax and sometimes require quoting
1098     * (see {@link ConfigUtil#joinPath} and {@link ConfigUtil#splitPath}).
1099     * 
1100     * @param path
1101     *            path expression to store this config at.
1102     * @return a {@code Config} instance containing this config at the given
1103     *         path.
1104     */
1105    Config atPath(String path);
1106
1107    /**
1108     * Places the config inside a {@code Config} at the given key. See also
1109     * atPath(). Note that a key is NOT a path expression (see
1110     * {@link ConfigUtil#joinPath} and {@link ConfigUtil#splitPath}).
1111     * 
1112     * @param key
1113     *            key to store this config at.
1114     * @return a {@code Config} instance containing this config at the given
1115     *         key.
1116     */
1117    Config atKey(String key);
1118
1119    /**
1120     * Returns a {@code Config} based on this one, but with the given path set
1121     * to the given value. Does not modify this instance (since it's immutable).
1122     * If the path already has a value, that value is replaced. To remove a
1123     * value, use withoutPath().
1124     * <p>
1125     * Note that path expressions have a syntax and sometimes require quoting
1126     * (see {@link ConfigUtil#joinPath} and {@link ConfigUtil#splitPath}).
1127     * 
1128     * @param path
1129     *            path expression for the value's new location
1130     * @param value
1131     *            value at the new path
1132     * @return the new instance with the new map entry
1133     */
1134    Config withValue(String path, ConfigValue value);
1135}