Parse options from environment

[rhynodge.git] / src / main / java / net / pterodactylus / util / envopt / Parser.java

diff --git a/src/main/java/net/pterodactylus/util/envopt/Parser.java b/src/main/java/net/pterodactylus/util/envopt/Parser.java
new file mode 100644 (file)
index 0000000..208d6f4
--- /dev/null
+++ b/src/main/java/net/pterodactylus/util/envopt/Parser.java
@@ -0,0 +1,51 @@
+package net.pterodactylus.util.envopt;
+
+import java.lang.reflect.Field;
+import java.util.Optional;
+import java.util.function.Supplier;
+
+/**
+ * Parses values from an {@link Environment} into {@link Option}-annotated fields of an object.
+ *
+ * @author <a href="mailto:bombe@pterodactylus.net">David ‘Bombe’ Roden</a>
+ */
+public class Parser {
+
+       private final Environment environment;
+
+       public Parser(Environment environment) {
+               this.environment = environment;
+       }
+
+       public <T> T parseEnvironment(Supplier<T> optionsObjectSupplier) {
+               T optionsObject = optionsObjectSupplier.get();
+               Class<?> optionsClass = optionsObject.getClass();
+               for (Field field : optionsClass.getDeclaredFields()) {
+                       Option[] options = field.getAnnotationsByType(Option.class);
+                       if (options.length == 0) {
+                               continue;
+                       }
+                       for (Option option : options) {
+                               String variableName = option.name();
+                               Optional<String> value = environment.getValue(variableName);
+                               if (option.required() && !value.isPresent()) {
+                                       throw new RequiredOptionIsMissing();
+                               }
+                               field.setAccessible(true);
+                               try {
+                                       field.set(optionsObject, value.orElse(null));
+                               } catch (IllegalAccessException iae1) {
+                                       /* swallow. */
+                               }
+                       }
+               }
+               return optionsObject;
+       }
+
+       public static Parser fromSystemEnvironment() {
+               return new Parser(new SystemEnvironment());
+       }
+
+       public static class RequiredOptionIsMissing extends RuntimeException { }
+
+}