# ConfigLib **A Minecraft library for saving, loading, updating, and commenting YAML configuration files.** This library facilitates creating, saving, loading, updating, and commenting YAML configuration files. It does so by automatically mapping instances of configuration classes to serializable maps which are first transformed into YAML and then saved to some specified file. Information on how to [import](#import) this library can be found at the end of this documentation. For a step-by-step tutorial that shows most features of this library in action check out the [Tutorial](https://github.com/Exlll/ConfigLib/wiki/Tutorial) page on the wiki! ## Features * Automatic creation, saving, loading, and updating of configuration files * Support for comments through annotations * Support for all primitive types, their wrapper types, and strings * Support for all Java enums, records, and POJOs (+ inheritance!) * Support for (nested) lists, sets, arrays, and maps * Support for `BigInteger` and `BigDecimal` * Support for `LocalDate`, `LocalTime`, `LocalDateTime`, and `Instant` * Support for `UUID`, `File`, `Path`, `URL`, and `URI` * Support for Bukkit's `ConfigurationSerializable` types (e.g. `ItemStack`) * Option to format the names of configuration elements * Option to exclude fields from being converted * Option to customize null handling * Option to customize serialization by providing your own serializers * Option to add headers and footers to configuration files * Option to overwrite configuration values with environment variables * ...and a few more! ## Usage example This section contains a short usage example to get you started. The whole range of features is discussed in the following sections. Information on how to [import](#import) this library is located at the end of this documentation. For a step-by-step tutorial with a more advanced example check out the [Tutorial](https://github.com/Exlll/ConfigLib/wiki/Tutorial) page on the wiki. If you want support for Bukkit classes like `ItemStack`, check out the [Configuration properties](#configuration-properties) section. ```java public final class Example { // * To create a configuration annotate a class with @Configuration and make sure that // it has a no-args constructor. // * Now add fields to that class and assign them default values. // * That's it! Fields can be private; setters are not required. @Configuration public static class BaseConfiguration { private String host = "127.0.0.1"; private int port = 1234; // The library supports lists, sets, and maps. private Set blockedAddresses = Set.of("8.8.8.8"); // Fields can be ignored by making them final, transient, static or by // annotating them with @Ignore. private final double ignoreMe = 3.14; } // This library supports records; no @Configuration annotation required public record User( String username, @Comment("Please choose a strong password.") String password ) {} // Subclassing of configurations and nesting of configurations in other configurations // is also supported. Subclasses don't need to be annotated again. public static final class UserConfiguration extends BaseConfiguration { // You can add comments with the @Comment annotation. Each string in the comment // array is written (as a comment) on a new line. @Comment({"The admin user has full access.", "Choose a proper password!"}) User admin = new User("root", "toor"); // The User class is a record! List blockedUsers = List.of( new User("user1", null), // null values are supported new User("user2", null) ); } public static void main(String[] args) { var configFile = Paths.get("/tmp/config.yml"); var config = new UserConfiguration(); // Save an instance to the configuration file YamlConfigurations.save(configFile, UserConfiguration.class, config); // Load a new instance from the configuration file config = YamlConfigurations.load(configFile, UserConfiguration.class); System.out.println(config.admin.username); System.out.println(config.blockedUsers); // Modify the configuration and save it again config.blockedUsers.add(new User("user3", "pass3")); YamlConfigurations.save(configFile, UserConfiguration.class, config); } } ``` By running the above code, a new YAML configuration is created at `/tmp/config.yml`. Its content looks like this: ```yaml host: 127.0.0.1 port: 1234 blockedAddresses: - 8.8.8.8 # The admin user has full access. # Choose a proper password! admin: username: root # Please choose a strong password. password: toor blockedUsers: - username: user1 - username: user2 - username: user3 password: pass3 ``` Two things are noticeable here: 1. Not every user in the `blockedUsers` list has a `password` mapping. This is because null values are not output by default. That behavior can be changed by the builder. 2. The password of the user with username `user3` has no comment. This is due to limitations of the YAML library. Configurations in lists, sets, or maps cannot have their comments printed. ## General information In the following sections the term _configuration type_ refers to any Java record type or to any non-generic class that is directly or indirectly (i.e. through subclassing) annotated with`@de.exlll.configlib.Configuration`. Accordingly, the term _configuration_ refers to an instance of such a type. A _configuration element_ is either a class field or a record component of a configuration type. ### Declaring configuration types To declare a configuration type, either define a Java record or annotate a class with `@Configuration` and make sure that it has a no-args constructor. The no-args constructor can be `private`. Inner classes (i.e. the ones that are nested but not `static`) have an implicit synthetic constructor with at least one argument and are, therefore, not supported. Now simply add components to your record or fields to your class whose type is any of the supported types listed in the next section. You can (and should) initialize all fields of a configuration class with non-null default values. ### Supported types A configuration type may only contain configuration elements of the following types: | Type class | Types | |-----------------------------|--------------------------------------------------------------------| | Boolean types | `boolean`, and `Boolean` | | Integer types | `byte`, `short`, `int`, `long`, and their respective wrapper types | | Floating point types | `float`, `double`, and their respective wrapper types | | Characters and strings | `char`, `Character`, `String` | | Big numeric types | `BigInteger`, `BigDecimal` | | Time related types | `LocalTime`, `LocalDate`, `LocalDateTime`, `Instant` | | Utility types | `UUID`, `File`, `Path`, `URL`, `URI` | | Enums | Any Java enum | | Configurations | Any Java record or any class annotated with `@Configuration` | | `ConfigurationSerializable` | All Bukkit classes that implement this interface, like `ItemStack` | | Collections | (Nested) Lists, sets, maps*, or arrays of previously listed types | (*) Map keys can only be of simple or enum type, i.e. they cannot be in the `Collections`, `Configurations`, or `ConfigurationSerializable` type class. For all types that are not listed in the table above, you can provide your own [custom serializer](#custom-serializers). #### Examples of supported types The following class contains examples of types that this library supports: ```java public final class SupportedTypes { boolean supported; Character supported; String supported; LocalTime supported; UUID supported; ExampleEnum supported; // where 'ExampleEnum' is some Java enum type ExampleConfig supported; // where 'ExampleConfig' is a class annotated with @Configuration ExampleRecord supported; // where 'ExampleRecord' is a Java record /* collection types */ List supported; Set supported; LocalDate[] supported; Map supported; /* nested collection types */ List> supported; int[][] supported; Map>>> supported; // supported if a custom serializer is registered java.awt.Point supported; // supported when a special properties object is used (explained further below) org.bukkit.inventory.ItemStack supported; } ```

Examples of unsupported types

The following class contains examples of types that this library does (and will) not support: ```java public final class UnsupportedTypes { Map unsupported; // invalid map key Map, String> unsupported; // invalid map key Box unsupported; // custom parameterized type List unsupported; // wildcard type List unsupported; // wildcard type List[] unsupported; // wildcard type T unsupported; // type variable List unsupported; // raw type List[] unsupported; // raw type List[] unsupported; // generic array type Set[] unsupported; // generic array type Map[] unsupported; // generic array type } ``` **NOTE:** Even though this library does not support these types, it is still possible to serialize them by providing a custom serializer via the [`@SerializeWith`](#the-serializewith-annotation) annotation. That serializer then has to be applied to top-level type (i.e. `nesting` must be set to `0`, which is the default).

### Loading and saving configurations There are two ways to load and save configurations. Which way you choose depends on your liking. Both ways have five methods in common: * The `save` method converts a configuration to a string in YAML format and saves that string to a file. The file is created if it does not exist and is overwritten otherwise. * The `load` method creates a new configuration instance and populates it with values taken from a file. For classes, the no-args constructor is used to create a new instance. For records, the canonical constructor is called. * The `update` method is a combination of `load` and `save` and the method you'd usually want to use: it takes care of creating the configuration file if it does not exist and otherwise updates it to reflect changes to (the configuration elements of) the configuration type. * The `write` method works the same way as the `save` method but writes the string to a `java.io.OutputStream`. * The `read` method works the same way as the `load` method but reads the values from a `java.io.InputStream`.

Example of update behavior when configuration file exists

Let's say you have the following configuration type ```java @Configuration public final class C { int i = 10; int j = 11; } ``` ... and a YAML configuration file that contains: ```yaml i: 20 k: 30 ``` Now, when you call the `update` method for that configuration type and file using any of the two options listed below, the configuration instance that `update` returns will have its `i` variable initialized to `20` and its `j` variable will have its default of `11`. After the operation, the configuration file will contain the following content (note that `k` has been dropped): ```yaml i: 20 j: 11 ```

To exemplify the usage of these five methods we assume for the following sections that you have implemented the configuration type below and have access to some regular `java.nio.file.Path` object `configurationFile`. ```java @Configuration public final class Config { /* some fields */ } ``` #### Option 1 The first option is to create a `YamlConfigurationStore` instance and use it to save, load, or update configurations. ```java YamlConfigurationProperties properties = YamlConfigurationProperties.newBuilder().build(); YamlConfigurationStore store = new YamlConfigurationStore<>(Config.class, properties); Config config1 = store.load(configurationFile); store.save(config1, configurationFile); Config config2 = store.update(configurationFile); ``` Using a `YamlConfigurationStore` directly is always more efficient than the second option show below, especially if you are calling any of its method multiple times. #### Option 2 The second option is to use the static methods from the `YamlConfigurations` class. ```java Config config1 = YamlConfigurations.load(configurationFile, Config.class); YamlConfigurations.save(configurationFile, Config.class, config1); Config config2 = YamlConfigurations.update(configurationFile, Config.class); ``` Each of these methods has two additional overloads: One that takes a properties object and another that lets you configure a properties object builder. For example, the overloads of the `load` method are: ```java // overload 1 YamlConfigurationProperties properties = YamlConfigurationProperties.newBuilder().build(); Config config1 = YamlConfigurations.load(configurationFile, Config.class, properties); // overload 2 Config config2 = YamlConfigurations.load( configurationFile, Config.class, builder -> builder.inputNulls(true).outputNulls(false) ); ```

All five methods can also be passed a Java record instead of a class. To provide default values for records when calling the `update` method, you can add a constructor with no parameters that initializes its components. This constructor is only called if the configuration file does not exist. ```java record User(String name, String email) { User() { this("John Doe", "john@doe.com"); } } User user = YamlConfigurations.update(configurationFile, User.class); ``` ### Configuration properties Instances of the `ConfigurationProperties` class allow customization of how configurations are stored and loaded. To create such an instance, instantiate a new builder using the `YamlConfigurationProperties.newBuilder()` method, configure it, and finally call its `build()` method. Alternatively, you can use the `toBuilder()` method of an existing `YamlConfigurationProperties` to create a new builder that is initialized with values takes from the properties object. Check out the methods of the builder class to see which configuration options are available. #### Support for Bukkit classes like `ItemStack` There is a special `YamlConfigurationProperties` object with name `BUKKIT_DEFAULT_PROPERTIES` that adds support for Bukkit's `ConfigurationSerializable` types. If you want to use any of these types in your configuration, you have to use that object as a starting point: ```java YamlConfigurationProperties properties = ConfigLib.BUKKIT_DEFAULT_PROPERTIES.toBuilder() // ...further configure the builder... .build(); ``` To get access to this object, you have to import `configlib-paper` instead of `configlib-yaml` as described in the [Import](#import) section. ### Comments The configuration elements of a configuration type can be annotated with the `@Comment` annotation. This annotation takes an array of strings. Each of these strings is written onto a new line as a comment. The strings can contain `\n` characters. Empty strings are written as newlines (not as comments). If a configuration type _C_ that defines comments is used (as a configuration element) within another configuration type, the comments of _C_ are written with the proper indentation. However, if instances of _C_ are stored inside a collection, their comments are not printed when the collection is written. Serializing the following configuration as YAML ... ```java @Configuration public final class ExampleConfiguration { @Comment({"Hello", "", " ", "World"}) private String commentedField = "commented field"; } ``` ... results in the YAML file shown below: ```yaml # Hello # # World commentedField: commented field ``` Similarly, if you define the following record configuration and save it ... ```java record Address(@Comment("The street") String street) {} record User(@Comment("The name") String name, @Comment("The address") Address address) {} User user = new User("John Doe", new Address("10 Downing St")); ``` ... you get: ```yaml # The name name: John Doe # The address address: # The street street: 10 Downing St ``` ### Subclassing Subclassing of configurations types is supported. Subclasses of configuration types don't need to be annotated with `@Configuration`. When a configuration is written, the fields of parent classes are written before the fields of the child in a top to bottom manner. Parent configurations can be `abstract`. #### Shadowing of fields Shadowing of fields refers to the situation where a subclass of configuration has a field that has the same name as a field in one of its super classes. Shadowing of fields is currently not supported. (This restriction might easily be lifted. If you need this feature, please open an issue and describe how to handle name clashes.) ### Ignoring and filtering fields Fields that are `final`, `static`, `transient` or annotated with `@Ignore` are neither serialized nor updated during deserialization. You can filter out additional fields by providing an instance of `FieldFilter` to the configuration properties. Record components cannot be filtered. ### Handling of missing and `null` values #### Missing values When a configuration file is read, values that correspond to a configuration element might be missing. That can happen, for example, when somebody deleted that value from the configuration file, when you add configuration elements to your configuration type, or when the `NameFormatter` that was used to create that file is replaced. In such cases, fields of configuration classes keep the default value you assigned to them and record components are initialized with the default value of their corresponding type. #### Null values **NOTE:** Null values written to a configuration file generally don't give any indication about which kinds of values the configuration expects. Therefore, they not only make it harder for the users of that configuration file to properly configure it, but they might also prevent loading a configuration if the values the users set are of the wrong type. Although strongly discouraged, null values are supported and `ConfigurationProperties` let you configure how they are handled when serializing and deserializing a configuration: * By setting `outputNulls` to false, configuration elements, and collection elements that are null are not output. Any comments that belong to such fields are also not written. * By setting `inputNulls` to false, null values read from the configuration file are treated as missing and are, therefore, handled as described in the section above. * By setting `inputNulls` to true, null values read from the configuration file overwrite the corresponding default values of a configuration class with null or set the component value of a record type to null. If the configuration element type is primitive, an exception is thrown. The following code forbids null values to be output but allows null values to be input. By default, both are forbidden which makes the call to `outputNulls` in this case redundant. ```java YamlConfigurationProperties.newBuilder() .outputNulls(false) .inputNulls(true) .build(); ``` ### Formatting the names of configuration elements You can define how the names of configuration elements are formatted by configuring the configuration properties with a custom formatter. Formatters are implementations of the `NameFormatter` interface. You can implement this interface yourself or use one of the several formatters this library provides. These pre-defined formatters can be found in the `NameFormatters` class. The following code formats fields using the `IDENTITY` formatter (which is the default). ```java YamlConfigurationProperties.newBuilder() .setNameFormatter(NameFormatters.IDENTITY) .build(); ``` ### Type conversion and serializer selection Before instances of the types listed in the [supported types](#supported-types) section can be stored, they need to be converted into serializable types (i.e. into types the underlying YAML library knows how to handle). The conversion happens according to the following table: | Source type | Target type | |-----------------------------|------------------| | Boolean types | `Boolean` | | Integer types | `Long` | | Floating point types | `Double` | | Characters and strings | `String` | | Big numeric types | `String` | | Time related types | `String` | | Utility types | `String` | | Enums | `String` | | Configurations | `Map` | | `Set` | `List` | | `List` | `List` | | `S[]` | `List` | | `Map` | `Map` | | `ConfigurationSerializable` | `String` | #### Serializer selection To convert the value of a configuration element `E` with (source) type `S` into a serializable value of some target type, a serializer has to be selected. Serializers are instances of the `de.exlll.configlib.Serializer` interface and are selected based on `S`. Put differently, serializers are, by default, always selected based on the compile-time type of `E` and never on the runtime type of its value.

Why should I care about this?
This distinction makes a difference (and might lead to confusion) when you have configuration elements that are configuration classes, and you extend those classes. Concretely, assume you have written two configuration classes `A` and `B` where `B extends A`. Then, if you use `A a = new B()` in your main configuration, only the fields of a `A` will be stored when you save your main configuration. That is because the serializer of field `a` was selected based on the compile-time type of `a` which is `A` and not `B`. The same happens if you have a `List` and put instances of `B` (or some other subclass of `A`) in it. If you need such behavior, have a look at the [`@Polymorphic`](#the-polymorphic-annotation) annotation.

Order of serializer selection
You can override the default selection by annotating a configuration element with [`@SerializeWith`](#the-serializewith-annotation), by annotating a type with `@SerializeWith`, or by adding your own serializer for `S` to the configuration properties. When you do so, it can happen that there multiple serializers available for a particular configuration element and its type. In that case, one of them chosen according to the following precedence rules: 1. If the element is annotated with `@SerializeWith` and the `nesting` matches, the serializer referenced by the annotation is selected. 2. Otherwise, if the `ConfigurationProperties` contain a serializer for the type in question, that serializer is returned. * Serializers created by factories that were added through `addSerializerFactory` for some type take precedence over serializers added by `addSerializer` for the same type. 3. If the type is annotated `@SerializeWith`, the serializer referenced by the annotation is selected. 4. If the type is annotated with an annotation which is annotated with `@SerializeWith`, the serializer referenced by `@SerializeWith` is returned. 5. If this library defines a serializer for that type, that serializer is selected. 6. Ultimately, if no serializer can be found, an exception is thrown. For lists, sets, and maps, the algorithm is applied to their generic type arguments recursively first.
##### The `@SerializeWith` annotation The `@SerializeWith` annotation enforces the use of the specified serializer for a configuration element or type. It can be applied to configuration elements (i.e. class fields and record components), to types, and to other annotations. ```java @SerializeWith(serializer = MyPointSerializer.class) Point point; ``` ```java @SerializeWith(serializer = SomeClassSerializer.class) public final class SomeClass {/* ... */} ``` The serializer referenced by this annotation is selected regardless of whether the annotated type or type of configuration element matches the type the serializer expects. If the annotation is applied to a configuration element and that element is an array, list, set, or map, a nesting level can be set to apply the serializer not to the top-level type but to its elements. For maps, the serializer is applied to the values and not the keys. ```java @SerializeWith(serializer = MySetSerializer.class, nesting = 1) List> list; ``` Setting `nesting` to an invalid value, i.e. a negative one or one that is greater than the number of levels the element actually has, results in the serializer not being selected. For type annotations, the `nesting` has no effect.

More nesting examples
In this example... ```java @SerializeWith(serializer = MySetSerializer.class, nesting = 1) List> list; ``` * a nesting of `0` would apply the serializer to `list` (which is of type `List>`), * a nesting of `1` would apply it to the `Set` elements within `list`, and * a nesting of `2` would apply it to the strings within the sets of `list`. However, since the referenced serializer `MySetSerializer` most likely expects `Set`s as input, setting `nesting` to `0` or `2` would result in an exception being thrown when the configuration is serialized. Some more examples: ```java // MyListSerializer is applied to 'list' @SerializeWith(serializer = MyListSerializer.class) List> list; // MySetSerializer is applied to the Set elements of 'list' @SerializeWith(serializer = MySetSerializer.class, nesting = 1) List> list; // MyStringSerializer is applied to the strings within the set elements of 'list' @SerializeWith(serializer = MyStringSerializer.class, nesting = 2) List> list; // MyMap0Serializer is applied to 'map' @SerializeWith(serializer = MyMap0Serializer.class) Map> map; // MyMap1Serializer is applied to the Map values of 'map' @SerializeWith(serializer = MyMap1Serializer.class, nesting = 1) Map> map; // MyDoubleSerializer is applied to the doubles within the nested values of 'map' @SerializeWith(serializer = MyDoubleSerializer.class, nesting = 2) Map> map; ```
#### The `@Polymorphic` annotation The `@Polymorphic` annotation indicates that the annotated type is polymorphic. Serializers for polymorphic types are not selected based on the compile-time types of configuration elements, but instead are chosen at runtime based on the actual types of their values. This enables adding instances of subclasses / implementations of a polymorphic type to collections. The subtypes must be valid configurations. ```java @Polymorphic @Configuration static abstract class A { ... } static final class Impl1 extends A { ... } static final class Impl2 extends A { ... } List as = List.of(new Impl1(...), new Impl2(...), ...); ``` For correct deserialization, if an instance of polymorphic type (or one of its implementations / subclasses) is serialized, an additional property that holds type information is added to its serialization. By default, that type information is the Java class name of the actual type. It is possible to provide type aliases by using the `PolymorphicTypes` annotation. ```java @Polymorphic @PolymorphicTypes({ @PolymorphicTypes.Type(type = Impl1.class, alias = "IMPL_1"), @PolymorphicTypes.Type(type = Impl2.class, alias = "IMPL_2") }) interface B { ... } record Impl1(...) implements B { ... } record Impl2(...) implements B { ... } ``` ### Custom serializers If you want to add support for a type that is not a Java record or whose class is not annotated with `@Configuration`, or if you don't like how one of the supported types is serialized by default, you can write your own custom serializer. Serializers are instances of the `de.exlll.configlib.Serializer` interface. When implementing that interface you have to make sure that you convert your source type into one of the valid target types listed in [type conversion](#type-conversion-and-serializer-selection) section. The serializer then has to be registered through a `ConfigurationProperties` object or alternatively be applied to a configuration element or type with [`@SerializeWith`](#the-serializewith-annotation). If you want to use the `@SerializeWith` annotation, your serializer class must either have a constructor with no parameters or one with exactly one parameter of type [`SerializerContext`](#the-serializercontext-interface). The following `Serializer` serializes instances of `java.awt.Point` into strings and vice versa. ```java public final class PointSerializer implements Serializer { @Override public String serialize(Point element) { return element.x + ":" + element.y; } @Override public Point deserialize(String element) { String[] parts = element.split(":"); int x = Integer.parseInt(parts[0]); int y = Integer.parseInt(parts[1]); return new Point(x, y); } } ``` ```java YamlConfigurationProperties properties = YamlConfigurationProperties.newBuilder() .addSerializer(Point.class, new PointSerializer()) .build(); ``` ##### The `SerializerContext` interface Instances of the `SerializerContext` interface contain contextual information for custom serializers. A context object gives access to the configuration properties, configuration element, and the annotated type for which the serializer was selected. Context objects can be obtained when adding serializer factories through the `addSerializerFactory` method: ```java public final class PointSerializer implements Serializer { private final SerializerContext context; public PointSerializer(SerializerContext context) { this.context = context; } // implementation ... } ``` ```java YamlConfigurationProperties properties = YamlConfigurationProperties.newBuilder() .addSerializerFactory(Point.class, PointSerializer::new) .build(); ``` Custom serializers used with `@SerializeWith` are allowed to declare a constructor with one parameter of type `SerializerContext`. If such a constructor exists, a context object is passed to it when the serializer is instantiated by this library. ### Post-processing There are two ways to apply some post-processing to your configurations: - The first is to annotate a method in your configuration type with the `@PostProcess` annotation. - The second is to add post-processor functions to a `ConfigurationProperties` object. These functions are then applied to some set of configuration elements that is defined by a `ConfigurationElementFilter`. Both ways of post-processing can be applied at the same time. In this case, the post-processor functions added to a `ConfigurationProperties` object run first. #### Post-process configurations via annotated method One way to apply post-processing to your configuration is to annotate some method of your configuration type with the `@PostProcess` annotation. ```java @Configuration public final class Config { private int i = 10; private String s = "abc"; @PostProcess private void postProcess() { this.i = this.i * 2; this.s = this.s.repeat(2); } } ``` The return type of the `@PostProcess` method must either be `void` or the same type as the type in which that method is defined. In the first case, the method is simply executed. In the latter case, the return value of the method replaces the current instance when initializing a configuration. This is, in particular, useful for Java records whose fields are final and cannot be modified. ```java public record Config(int i, String s) { @PostProcess private Config postProcess() { return new Config(i * 2, s.repeat(2)); } } ``` The name of the `@PostProcess` method can be any valid Java method name. However, your configuration type is allowed to define at most one such method and `@PostProcess` methods of parent classes are _not_ executed. #### Post-process configuration elements by condition The second way to apply post-processing to your configuration is to define a `ConfigurationElementFilter`. Such a filter implicitly defines a set of configuration elements to which some post-processing function should be applied. Both, filters and post-processing functions, can be added via the `ConfigurationProperties#addPostProcessor` method at the same time and the function is then applied to all configuration elements that are defined by the filter. For example, to double the values of _all_ configuration elements of type `int`, you would add the following filter and post-processing function: ```java ConfigurationProperties.newBuilder() .addPostProcessor( // Predicate> filter element -> element.type().equals(int.class), // UnaryOperator postProcessor (Integer value) -> value * 2 ) .build(); ``` Note that it is your responsibility to make sure that the filter only selects configuration elements whose type matches the type the post-processing function expects. Also note, that the post-processing function will be applied regardless of whether a configuration file contained a value for some specific element. This means that your post-processing function should properly handle `null` input values if, for example, you allow the input of such values. The `ConfigurationElementFilter` interface defines static factories to facilitate the creation of common filters: ```java ConfigurationElementFilter.byType(Class type) ConfigurationElementFilter.byPostProcessKey(String key) ``` The second factory creates a filter that selects all configuration elements that are annotated with `@PostProcess` and where the `key()` method of that annotation returns the given `key`. In the following example, the values of `a` and `b` are doubled, the value of `c` is tripled, `d` is set to zero, and no post-processing is applied to `e` and `f`. ```java record Config( @PostProcess(key = "double") int a, @PostProcess(key = "double") int b, @PostProcess(key = "tripple") int c, @PostProcess int d, @PostProcess(key = "missing processor") int e, int f ) {} ConfigurationProperties.newBuilder() .addPostProcessor( ConfigurationElementFilter.byPostProcessKey("double"), (Integer value) -> value * 2 ) .addPostProcessor( ConfigurationElementFilter.byPostProcessKey("tripple"), (Integer value) -> value * 3 ) .addPostProcessor( ConfigurationElementFilter.byPostProcessKey(""), (Integer value) -> 0 ) .build(); ``` ### Overwriting configuration values with environment variables You can allow users of your configuration to overwrite values that come from configuration files with values that are provided by environment variables. When a configuration is loaded, boolean values, numbers, and strings that appear in that configuration files can be overwritten with values that come from environment variables. To enable support for overwriting config values with environment variables first create a `ConfigurationProperties.EnvVarResolutionConfiguration` object and then configure your `ConfigurationProperties` instance with it: ```java final var envVarConf = ConfigurationProperties.EnvVarResolutionConfiguration .resolveEnvVarsWithPrefix(prefix, caseSensitiveResolution); final var properties = ConfigurationProperties.newBuilder() .setEnvVarResolutionConfiguration(envVarConf) // ... build ``` The `resolveEnvVarsWithPrefix` method returns a configuration object that resolves environment variables that start with the given prefix. If you specify a non-empty prefix, then only variables that start with that prefix will be resolved when loading your configuration. For example, if you choose `MY_PREFIX_` as your prefix, only environment variables that start with `MY_PREFIX_` will be able to overwrite configuration values. Specifying a non-empty prefix that is specific to your project is highly recommended. #### Environment variable names To be able to overwrite configuration values, you need to name your environment variables in a specific way (see example below): - To overwrite a boolean, number, or string value of a field, use an environment variable whose name matches the name of the field. The environment variable must be uppercase if case-sensitive resolution is disabled. - You can target nested elements by joining all field names that lead to that element with an underscore `_`. - You can target list elements by using the index of an element as the field name. For example, in the following configuration file ```yaml a: 0 b: c: 1 d: - 2 - 3 e: - f: 4 g: 5 ``` `a` is a simple value, `b` is a map, `d` is a list, and `e` is a list of maps. Then, under the assumption that you aren't using a prefix and that case-sensitive resolution is disabled, you can overwrite the values from 0 to 5 using the following environment variables, respectively: `A`, `B_C`, `D_0`, `D_1`, `E_0_F`, and `E_0_G`. #### Case-sensitivity **NOTE:** Environment variables are case-sensitive on UNIX systems and case-insensitive on Windows. If you want to (or have to, because you are on Windows) target the values of your configuration using uppercase environment variables (irrespective of the actual casing of the name of the fields), then you have to disable case-sensitive resolution. For example, if you have a configuration file with the following content ```yaml alPHA: be_ta: 1 ga_mma: dELTa: 2 ``` then, with `caseSensitiveResolution` set to `false`, you can overwrite the values `1` and `2` using the environment variables `ALPHA_BE_TA` and `GA_MMA_DELTA`, respectively. If your configuration contains paths that differ only in their case but are otherwise the same, and if you want to target these paths individually, then you have to enable case-sensitive resolution. For example, if you have a configuration file with the following content ```yaml alpha: beta: 1 ALPHA: BETA: 2 ``` and you want to target the values of `beta` and `BETA` individually, then you have to set `caseSensitiveResolution` to `true`. After doing so you can overwrite the values `1` and `2` by using the environment variables `alpha_beta` and `ALPHA_BETA`, respectively. #### Restrictions The values provided by environment variables come as strings and need to be converted to the correct target type. Because the resolution of environment variables happens very early in the process (before the type information of the configuration type is available) there are a few restrictions on how environment variables are resolved and which values can be overwritten: - Environment variables can only be used to overwrite simple values. Trying to overwrite a collection or map will cause an exception. - Environment variables cannot be used to insert new values into collections or maps. - Overwriting `null` values is not possible because `null`s don't carry any type information. - To overwrite a boolean value, an environment variable must be assigned the string `true` or `false` (using any casing). - Numbers that, when a configuration file is read, are interpreted as integers (because they don't contain a decimal point), (currently) cannot be overwritten by floating point numbers. This applies even if the configuration type actually expects a floating point number. ### Changing the type of configuration elements Changing the type of configuration elements is not supported. If you change the type of one of these but your configuration file still contains a value of the old type, a type mismatch will occur when loading a configuration from that file. Instead, remove the old element and add a new one with a different name. ### Recursive type definitions Recursive type definitions are currently not allowed but might be supported in a future version if this feature is requested.

Examples of recursive type definitions
Neither direct nor indirect recursive type definitions are supported. ```java public final class RecursiveTypDefinitions { // Direct recursive definition @Configuration static final class R { R r; } // Indirect recursive definition @Configuration static final class R1 { R2 r2; } @Configuration static final class R2 { R1 r1; } } ```
## Project and repository structure This project contains three classes of modules: * The `configlib-core` module contains most of the logic of this library. In it, you can find (among other things), the object mapper that converts configuration instances to maps (and vice versa), most serializers, and the classes responsible for the extraction of comments. It does not contain anything Minecraft related. * The `configlib-yaml` module contains the classes that can save configuration instances as YAML files and instantiate new instances from such files. This module does not contain anything Minecraft related, either. * The `configlib-paper`, `configlib-velocity`, and `configlib-waterfall` modules contain basic plugins that are used to conveniently load this library. These three modules shade the `-core` module, the `-yaml` module, and the YAML parser when the `shadowJar` task is executed. The shaded jar files are released on the [releases page](https://github.com/Exlll/ConfigLib/releases). * The `configlib-paper` module additionally contains the `ConfigLib.BUKKIT_DEFAULT_PROPERTIES` object which adds support for the serialization of Bukkit classes like `ItemStack` as described [here](#support-for-bukkit-classes-like-itemstack). The GitHub repository of this project uses two branches: * The `master` branch contains the functionality of the latest release version. * The `dev` branch contains the newest, possibly unstable features and refactorings. **If you plan to contribute to this project, please base your commits on the `dev` branch.** ## Import To use this library, import it into your project with Maven or Gradle. Examples of how to do that are at the end of this section within the spoilers. Currently, there are three repositories from which you can choose: - [Maven Central](https://central.sonatype.com/search?q=de.exlll) (recommended), - [jitpack.io](https://jitpack.io/#Exlll/ConfigLib), and - GitHub (which [requires authentication](https://github.com/Exlll/ConfigLib/issues/12)) This library has additional dependencies (namely, a YAML parser) which are not exposed by the artifact you import. You can download _plugin versions_ of this library that bundle all its dependencies. The artifacts of these versions can be found on the [releases page](https://github.com/Exlll/ConfigLib/releases) where you can identify them by their `-paper-`, `-waterfall-`, and `-velocity-` infix and `-all` suffix. Except for the `-paper-` version, the other plugin versions currently do not add any additional features. A benefit of these versions is that they make it easier for you to update this library if you have written multiple plugins that use it. If you plan to use these versions, don't forget to add the plugin as a dependency to the `plugin.yml` (for Paper and Waterfall) or to the dependencies array (for Velocity) of your own plugin. Alternatively, if you don't want to use an extra plugin, you can shade the `-yaml` version with its YAML parser yourself. ### Import examples If you want serialization support for Bukkit classes like `ItemStack`, replace `configlib-yaml` with `configlib-paper` (see [here](#support-for-bukkit-classes-like-itemstack)). #### Import via Maven Central **Maven** ```xml de.exlll configlib-yaml 4.6.0 ``` **Gradle** ```kotlin repositories { mavenCentral() } dependencies { implementation("de.exlll:configlib-yaml:4.6.0") } ```

Import via jitpack.io
**Maven** ```xml jitpack.io https://jitpack.io com.github.Exlll.ConfigLib configlib-yaml v4.6.0 ``` **Gradle** ```groovy repositories { maven { url 'https://jitpack.io' } } dependencies { implementation 'com.github.Exlll.ConfigLib:configlib-yaml:v4.6.0' } ``` ```kotlin repositories { maven { url = uri("https://jitpack.io") } } dependencies { implementation("com.github.Exlll.ConfigLib:configlib-yaml:v4.6.0") } ```

Import via GitHub
Importing via GitHub requires authentication. Check this [issue](https://github.com/Exlll/ConfigLib/issues/12) if you have any trouble with that. **Maven** ```xml de.exlll https://maven.pkg.github.com/Exlll/ConfigLib de.exlll configlib-yaml 4.6.0 ``` **Gradle** ```groovy repositories { maven { url 'https://maven.pkg.github.com/Exlll/ConfigLib' } } dependencies { implementation 'de.exlll:configlib-yaml:4.6.0' } ``` ```kotlin repositories { maven { url = uri("https://maven.pkg.github.com/Exlll/ConfigLib") } } dependencies { implementation("de.exlll:configlib-yaml:4.6.0") } ```
## Future work This section contains ideas for upcoming features. If you want any of these to happen any time soon, please [open an issue](https://github.com/Exlll/ConfigLib/issues/new) where we can discuss the details. - JSON, TOML, XML support - More features and control over updating/versioning - More control over the ordering of fields, especially in parent/child class scenarios - Recursive definitions - Shadowing of fields

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