| package org.apache.felix.dm.lambda.callbacks; |
| |
| import java.util.Collection; |
| import java.util.Dictionary; |
| import java.util.Map; |
| import java.util.Objects; |
| |
| /** |
| * Represents a callback(Configuration) that is invoked on a Component implementation class. |
| * The callback which accepts a type-safe configuration class for wrapping properties behind a dynamic proxy interface. |
| * |
| * <p> The T generic parameter represents the type of the class on which the callback is invoked on. |
| * <p> The U generic parameter represents the type of the configuration class passed to the callback argument. |
| * |
| * <p> Using such callback provides a way for creating type-safe configurations from a actual {@link Map} or {@link Dictionary} that is |
| * normally injected by Dependency Manager. |
| * The callback accepts in argument an interface that you have to provide, and DM will inject a proxy that converts |
| * method calls from your configuration-type to lookups in the actual map or dictionary. The results of these lookups are then |
| * converted to the expected return type of the invoked configuration method.<br> |
| * As proxies are injected, no implementations of the desired configuration-type are necessary! |
| * </p> |
| * <p> |
| * The lookups performed are based on the name of the method called on the configuration type. The method names are |
| * "mangled" to the following form: <tt>[lower case letter] [any valid character]*</tt>. Method names starting with |
| * <tt>get</tt> or <tt>is</tt> (JavaBean convention) are stripped from these prefixes. For example: given a dictionary |
| * with the key <tt>"foo"</tt> can be accessed from a configuration-type using the following method names: |
| * <tt>foo()</tt>, <tt>getFoo()</tt> and <tt>isFoo()</tt>. |
| * </p> |
| * <p> |
| * The return values supported are: primitive types (or their object wrappers), strings, enums, arrays of |
| * primitives/strings, {@link Collection} types, {@link Map} types, {@link Class}es and interfaces. When an interface is |
| * returned, it is treated equally to a configuration type, that is, it is returned as a proxy. |
| * </p> |
| * <p> |
| * Arrays can be represented either as comma-separated values, optionally enclosed in square brackets. For example: |
| * <tt>[ a, b, c ]</tt> and <tt>a, b,c</tt> are both considered an array of length 3 with the values "a", "b" and "c". |
| * Alternatively, you can append the array index to the key in the dictionary to obtain the same: a dictionary with |
| * "arr.0" => "a", "arr.1" => "b", "arr.2" => "c" would result in the same array as the earlier examples. |
| * </p> |
| * <p> |
| * Maps can be represented as single string values similarly as arrays, each value consisting of both the key and value |
| * separated by a dot. Optionally, the value can be enclosed in curly brackets. Similar to array, you can use the same |
| * dot notation using the keys. For example, a dictionary with |
| * |
| * <pre>{@code "map" => "{key1.value1, key2.value2}"}</pre> |
| * |
| * and a dictionary with <p> |
| * |
| * <pre>{@code "map.key1" => "value1", "map2.key2" => "value2"}</pre> |
| * |
| * result in the same map being returned. |
| * Instead of a map, you could also define an interface with the methods <tt>getKey1()</tt> and <tt>getKey2</tt> and use |
| * that interface as return type instead of a {@link Map}. |
| * |
| * <p> |
| * In case a lookup does not yield a value from the underlying map or dictionary, the following rules are applied: |
| * <ol> |
| * <li>primitive types yield their default value, as defined by the Java Specification; |
| * <li>string, {@link Class}es and enum values yield <code>null</code>; |
| * <li>for arrays, collections and maps, an empty array/collection/map is returned; |
| * <li>for other interface types that are treated as configuration type a null-object is returned. |
| * </ol> |
| * </p> |
| * |
| * @author <a href="mailto:dev@felix.apache.org">Felix Project Team</a> |
| */ |
| @FunctionalInterface |
| public interface CbConfiguration<T, U> extends SerializableLambda { |
| /** |
| * Handles the given arguments |
| * @param instance the Component implementation instance on which the callback is invoked on. |
| * @param configuration the configuration proxy |
| */ |
| void accept(T instance, U configuration); |
| |
| default CbConfiguration<T, U> andThen(CbConfiguration<T, U> after) { |
| Objects.requireNonNull(after); |
| return (T instance, U configuration) -> { |
| accept(instance, configuration); |
| after.accept(instance, configuration); |
| }; |
| } |
| } |