org.ekrich.config

An immutable map from config paths to config values. Paths are dot-separated expressions such as foo.bar.baz. Values are as in JSON (booleans, strings, numbers, lists, or objects), represented by [[ConfigValue]] instances. Values accessed through the Config interface are never null.

Config is an immutable object and thus safe to use from multiple threads. There's never a need for "defensive copies."

Fundamental operations on a Config include getting configuration values, resolving substitutions with resolve(), and merging configs using withFallback(ConfigMergeable).

All operations return a new immutable Config rather than modifying the original instance.

Examples

You can find an example app and library on GitHub. Also be sure to read the package-summary.html#package_description package overview]] which describes the big picture as shown in those examples.

Paths, keys, and Config vs. ConfigObject

Config is a view onto a tree of [[ConfigObject]]; the corresponding object tree can be found through [[Config#root]]. ConfigObject is a map from config keys, rather than paths, to config values. Think of ConfigObject as a JSON object and Config as a configuration API.

The API tries to consistently use the terms "key" and "path." A key is a key in a JSON object; it's just a string that's the key in a map. A "path" is a parseable expression with a syntax and it refers to a series of keys. Path expressions are described in the spec for Human-Optimized Config Object Notation. In brief, a path is period-separated so "a.b.c" looks for key c in object b in object a in the root object. Sometimes double quotes are needed around special characters in path expressions.

The API for a Config is in terms of path expressions, while the API for a ConfigObject is in terms of keys. Conceptually, Config is a one-level map from paths to values, while a ConfigObject is a tree of nested maps from keys to values.

Use ConfigUtil.joinPath(String*) and ConfigUtil.splitPath(String) to convert between path expressions and individual path elements (keys).

Another difference between Config and ConfigObject is that conceptually, ConfigValues with a [[ConfigValue#valueType valueType]] of [[ConfigValueType#NULL NULL]] exist in a ConfigObject, while a Config treats null values as if they were missing. (With the exception of two methods: [[Config#hasPathOrNull]] and [[Config#getIsNull]] let you detect null values.)

Getting configuration values

The "getters" on a Config all work in the same way. They never return null, nor do they return a ConfigValue with [[ConfigValue#valueType valueType]] of [[ConfigValueType#NULL NULL]]. Instead, they throw [[ConfigException.Missing]] if the value is completely absent or set to null. If the value is set to null, a subtype of ConfigException.Missing called [[ConfigException.Null]] will be thrown. [[ConfigException.WrongType]] will be thrown anytime you ask for a type and the value has an incompatible type. Reasonable type conversions are performed for you though.

Iteration

If you want to iterate over the contents of a Config, you can get its ConfigObject with [[#root]], and then iterate over the ConfigObject (which implements java.util.Map). Or, you can use [[#entrySet]] which recurses the object tree for you and builds up a Set of all path-value pairs where the value is not null.

'''Resolving substitutions'''

''Substitutions'' are the ${foo.bar} syntax in config files, described in the <a href= "https://github.com/lightbend/config/blob/master/HOCON.md#substitutions"

specification. Resolving substitutions replaces these references with real values.

Before using a Config it's necessary to call resolve() to handle substitutions (though ConfigFactory.load() and similar methods will do the resolve for you already).

Merging

The full Config for your application can be constructed using the associative operation withFallback(ConfigMergeable). If you use ConfigFactory.load() (recommended), it merges system properties over the top of application.conf over the top of reference.conf, using withFallback. You can add in additional sources of configuration in the same way (usually, custom layers should go either just above or just below application.conf, keeping reference.conf at the bottom and system properties at the top).

Serialization

Convert a Config to a JSON or HOCON string by calling root to get the ConfigObject and then call render on the root object, myConfig.root.render. There's also a variant render(ConfigRenderOptions) inherited from ConfigValue which allows you to control the format of the rendered string. (See [[ConfigRenderOptions]].) Note that Config does not remember the formatting of the original file, so if you load, modify, and re-save a config file, it will be substantially reformatted.

As an alternative to render, the toString method produces a debug-output-oriented representation (which is not valid JSON).

Java serialization is supported as well for Config and all subtypes of ConfigValue.

This is an interface but don't implement it yourself

Do not implement Config; it should only be implemented by the config library. Arbitrary implementations will not work because the library internals assume a specific concrete implementation. Also, this interface is likely to grow new methods over time, so third-party implementations will break.

All exceptions thrown by the library are subclasses of ConfigException.

Contains static methods for creating Config instances.

See also ConfigValueFactory which contains static methods for converting Java values into a ConfigObject. You can then convert a ConfigObject into a Config with ConfigObject.toConfig().

The static methods with "load" in the name do some sort of higher-level operation potentially parsing multiple resources and resolving substitutions, while the ones with "parse" in the name just create a ConfigValue from a resource and nothing else.

You can find an example app and library <a on GitHub. Also be sure to read the package overview which describes the big picture as shown in those examples.

Context provided to a [[ConfigIncluder]]; this interface is only useful inside a ConfigIncluder implementation, and is not intended for apps to implement.

Do not implement this interface; it should only be implemented by the config library. Arbitrary implementations will not work because the library internals assume a specific concrete implementation. Also, this interface is likely to grow new methods over time, so third-party implementations will break.

Implement this interface and provide an instance to [[ConfigParseOptions#setIncluder ConfigParseOptions.setIncluder()]] to customize handling of include statements in config files. You may also want to implement [[ConfigIncluderClasspath]], [[ConfigIncluderFile]], and [[ConfigIncluderURL]], or not.

Implement this in addition to [[ConfigIncluder]] if you want to support inclusion of files with the include classpath("resource") syntax. If you do not implement this but do implement [[ConfigIncluder]], attempts to load classpath resources will use the default includer.

Implement this in addition to [[ConfigIncluder]] if you want to support inclusion of files with the include file("filename") syntax. If you do not implement this but do implement [[ConfigIncluder]], attempts to load files will use the default includer.

Implement this in addition to [[ConfigIncluder]] if you want to support inclusion of files with the include url("http://example.com") syntax. If you do not implement this but do implement [[ConfigIncluder]], attempts to load URLs will use the default includer.

Subtype of [[ConfigValue]] representing a list value, as in JSON's [1,2,3] syntax.

ConfigList implements java.util.List so you can use it like a regular Java list. Or call [[#unwrapped]] to unwrap the list elements into plain Java values.

Like all [[ConfigValue]] subtypes, ConfigList is immutable. This makes it threadsafe and you never have to create "defensive copies." The mutator methods from java.util.List all throw java.lang.UnsupportedOperationException.

The [[ConfigValue#valueType]] method on a list returns [[ConfigValueType#LIST]].

Do not implement ConfigList; it should only be implemented by the config library. Arbitrary implementations will not work because the library internals assume a specific concrete implementation. Also, this interface is likely to grow new methods over time, so third-party implementations will break.

This method allows you to alter default config loading strategy for all the code which calls one of the methods, e.g. ConfigFactory.load(String)

Usually you don't have to implement this interface but it may be required when you fixing a improperly implemented library with unavailable source code.

You have to define VM property config.strategy to replace default strategy with your own.

An immutable class representing an amount of memory. Use static factory methods such as [[ConfigMemorySize#ofBytes]] to create instances.

Marker for types whose instances can be merged, that is Config and ConfigValue. Instances of Config and ConfigValue can be combined into a single new instance using the withFallback() method.

''Do not implement this interface''; it should only be implemented by the config library. Arbitrary implementations will not work because the library internals assume a specific concrete implementation. Also, this interface is likely to grow new methods over time, so third-party implementations will break.

Subtype of [[ConfigValue]] representing an object (AKA dictionary or map) value, as in JSON's curly brace { "a" : 42 } syntax.

An object may also be viewed as a [[Config]] by calling [[ConfigObject#toConfig]].

ConfigObject implements java.util.Map<String, ConfigValue> so you can use it like a regular Java map. Or call [[#unwrapped]] to unwrap the map to a map with plain Java values rather than ConfigValue.

Like all [[ConfigValue]] subtypes, ConfigObject is immutable. This makes it threadsafe and you never have to create "defensive copies." The mutator methods from java.util.Map all throw java.lang.UnsupportedOperationException.

The [[ConfigValue#valueType]] method on an object returns [[ConfigValueType#OBJECT]].

In most cases you want to use the [[Config]] interface rather than this one. Call [[#toConfig]] to convert a ConfigObject to a Config.

The API for a ConfigObject is in terms of keys, while the API for a [[Config]] is in terms of path expressions. Conceptually, ConfigObject is a tree of maps from keys to values, while a Config is a one-level map from paths to values.

Use ConfigUtil.joinPath(String*) and ConfigUtil.splitPath(String) to convert between path expressions and individual path elements (keys).

A ConfigObject may contain null values, which will have [[ConfigValue#valueType]] equal to [[ConfigValueType#NULL]]. If [[ConfigObject#get]] returns Java's null then the key was not present in the parsed file (or wherever this value tree came from). If get("key") returns a [[ConfigValue]] with type ConfigValueType#NULL then the key was set to null explicitly in the config file.

Do not implement interface ConfigObject; it should only be implemented by the config library. Arbitrary implementations will not work because the library internals assume a specific concrete implementation. Also, this interface is likely to grow new methods over time, so third-party implementations will break.

Represents the origin (such as filename and line number) of a [[ConfigValue]] for use in error messages. Obtain the origin of a value with [[ConfigValue#origin]]. Exceptions may have an origin, see [[ConfigException#origin]], but be careful because ConfigException.origin() may return null.

It's best to use this interface only for debugging; its accuracy is "best effort" rather than guaranteed, and a potentially-noticeable amount of memory could probably be saved if origins were not kept around, so in the future there might be some option to discard origins.

Do not implement this interface; it should only be implemented by the config library. Arbitrary implementations will not work because the library internals assume a specific concrete implementation. Also, this interface is likely to grow new methods over time, so third-party implementations will break.

This class contains some static factory methods for building a ConfigOrigin. ConfigOrigins are automatically created when you call other API methods to get a ConfigValue or Config. But you can also set the origin of an existing ConfigValue, using ConfigValue.withOrigin(ConfigOrigin).

A set of options related to parsing.

This object is immutable, so the "setters" return a new object.

Here is an example of creating a custom ConfigParseOptions:

   ConfigParseOptions options = ConfigParseOptions.defaults()
       .setSyntax(ConfigSyntax.JSON)
       .setAllowMissing(false)

An opaque handle to something that can be parsed, obtained from [[ConfigIncludeContext]].

Do not implement this interface; it should only be implemented by the config library. Arbitrary implementations will not work because the library internals assume a specific concrete implementation. Also, this interface is likely to grow new methods over time, so third-party implementations will break.

A set of options related to rendering a [[ConfigValue]]. Passed to ConfigValue.render(ConfigRenderOptions).

Here is an example of creating a ConfigRenderOptions:

   ConfigRenderOptions options =
       ConfigRenderOptions.defaults().setComments(false)

A set of options related to resolving substitutions. Substitutions use the ${foo.bar syntax and are documented in the HOCON">spec.

Typically this class would be used with the method Config.resolve(ConfigResolveOptions).

This object is immutable, so the "setters" return a new object.

Here is an example of creating a custom ConfigResolveOptions:

   ConfigResolveOptions options = ConfigResolveOptions.defaults()
       .setUseSystemEnvironment(false)

In addition to [[ConfigResolveOptions#defaults]], there's a prebuilt [[ConfigResolveOptions#noSystem]] which avoids looking at any system environment variables or other external system information. (Right now, environment variables are the only example.)

Implement this interface and provide an instance to [[ConfigResolveOptions#appendResolver ConfigResolveOptions.appendResolver()]] to provide custom behavior when unresolved substitutions are encountered during resolution.

The syntax of a character stream (JSON, HOCON aka ".conf", or <a href= "http://download.oracle.com/javase/7/docs/api/java/util/Properties.html#load%28java.io.Reader%29"

Java properties).

Contains static utility methods.

An immutable value, following the JSON type schema.

Because this object is immutable, it is safe to use from multiple threads and there's no need for "defensive copies."

Do not implement interface ConfigValue; it should only be implemented by the config library. Arbitrary implementations will not work because the library internals assume a specific concrete implementation. Also, this interface is likely to grow new methods over time, so third-party implementations will break.

This class holds some static factory methods for building [[ConfigValue]] instances. See also [[ConfigFactory]] which has methods for parsing files and certain in-memory data structures.

The type of a configuration value (following the JSON type schema).

Default config loading strategy. Able to load resource, file or URL. Behavior may be altered by defining one of VM properties config.resource, config.file or config.url