Pierre De Rop | 1152750 | 2016-02-18 21:07:16 +0000 | [diff] [blame^] | 1 | package org.apache.felix.dm.lambda.callbacks; |
| 2 | |
| 3 | import java.util.Collection; |
| 4 | import java.util.Dictionary; |
| 5 | import java.util.Map; |
| 6 | import java.util.Objects; |
| 7 | |
| 8 | /** |
| 9 | * Represents a callback(Configuration) that is invoked on a Component implementation class. |
| 10 | * The callback which accepts a type-safe configuration class for wrapping properties behind a dynamic proxy interface. |
| 11 | * |
| 12 | * <p> The T generic parameter represents the type of the class on which the callback is invoked on. |
| 13 | * <p> The U generic parameter represents the type of the configuration class passed to the callback argument. |
| 14 | * |
| 15 | * <p> Using such callback provides a way for creating type-safe configurations from a actual {@link Map} or {@link Dictionary} that is |
| 16 | * normally injected by Dependency Manager. |
| 17 | * The callback accepts in argument an interface that you have to provide, and DM will inject a proxy that converts |
| 18 | * method calls from your configuration-type to lookups in the actual map or dictionary. The results of these lookups are then |
| 19 | * converted to the expected return type of the invoked configuration method.<br> |
| 20 | * As proxies are injected, no implementations of the desired configuration-type are necessary! |
| 21 | * </p> |
| 22 | * <p> |
| 23 | * The lookups performed are based on the name of the method called on the configuration type. The method names are |
| 24 | * "mangled" to the following form: <tt>[lower case letter] [any valid character]*</tt>. Method names starting with |
| 25 | * <tt>get</tt> or <tt>is</tt> (JavaBean convention) are stripped from these prefixes. For example: given a dictionary |
| 26 | * with the key <tt>"foo"</tt> can be accessed from a configuration-type using the following method names: |
| 27 | * <tt>foo()</tt>, <tt>getFoo()</tt> and <tt>isFoo()</tt>. |
| 28 | * </p> |
| 29 | * <p> |
| 30 | * The return values supported are: primitive types (or their object wrappers), strings, enums, arrays of |
| 31 | * primitives/strings, {@link Collection} types, {@link Map} types, {@link Class}es and interfaces. When an interface is |
| 32 | * returned, it is treated equally to a configuration type, that is, it is returned as a proxy. |
| 33 | * </p> |
| 34 | * <p> |
| 35 | * Arrays can be represented either as comma-separated values, optionally enclosed in square brackets. For example: |
| 36 | * <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". |
| 37 | * Alternatively, you can append the array index to the key in the dictionary to obtain the same: a dictionary with |
| 38 | * "arr.0" => "a", "arr.1" => "b", "arr.2" => "c" would result in the same array as the earlier examples. |
| 39 | * </p> |
| 40 | * <p> |
| 41 | * Maps can be represented as single string values similarly as arrays, each value consisting of both the key and value |
| 42 | * separated by a dot. Optionally, the value can be enclosed in curly brackets. Similar to array, you can use the same |
| 43 | * dot notation using the keys. For example, a dictionary with |
| 44 | * |
| 45 | * <pre>{@code "map" => "{key1.value1, key2.value2}"}</pre> |
| 46 | * |
| 47 | * and a dictionary with <p> |
| 48 | * |
| 49 | * <pre>{@code "map.key1" => "value1", "map2.key2" => "value2"}</pre> |
| 50 | * |
| 51 | * result in the same map being returned. |
| 52 | * Instead of a map, you could also define an interface with the methods <tt>getKey1()</tt> and <tt>getKey2</tt> and use |
| 53 | * that interface as return type instead of a {@link Map}. |
| 54 | * |
| 55 | * <p> |
| 56 | * In case a lookup does not yield a value from the underlying map or dictionary, the following rules are applied: |
| 57 | * <ol> |
| 58 | * <li>primitive types yield their default value, as defined by the Java Specification; |
| 59 | * <li>string, {@link Class}es and enum values yield <code>null</code>; |
| 60 | * <li>for arrays, collections and maps, an empty array/collection/map is returned; |
| 61 | * <li>for other interface types that are treated as configuration type a null-object is returned. |
| 62 | * </ol> |
| 63 | * </p> |
| 64 | * |
| 65 | * @author <a href="mailto:dev@felix.apache.org">Felix Project Team</a> |
| 66 | */ |
| 67 | @FunctionalInterface |
| 68 | public interface CbConfiguration<T, U> extends SerializableLambda { |
| 69 | /** |
| 70 | * Handles the given arguments |
| 71 | * @param instance the Component implementation instance on which the callback is invoked on. |
| 72 | * @param configuration the configuration proxy |
| 73 | */ |
| 74 | void accept(T instance, U configuration); |
| 75 | |
| 76 | default CbConfiguration<T, U> andThen(CbConfiguration<T, U> after) { |
| 77 | Objects.requireNonNull(after); |
| 78 | return (T instance, U configuration) -> { |
| 79 | accept(instance, configuration); |
| 80 | after.accept(instance, configuration); |
| 81 | }; |
| 82 | } |
| 83 | } |