src/main/java/net/pterodactylus/util/envopt/Parser.java

   1 package net.pterodactylus.util.envopt;
   2
   3 import java.lang.reflect.Field;
   4 import java.util.Optional;
   5 import java.util.function.Supplier;
   6
   7 /**
   8  * Parses values from an {@link Environment} into {@link Option}-annotated fields of an object.
   9  *
  10  * @author <a href="mailto:bombe@pterodactylus.net">David ‘Bombe’ Roden</a>
  11  */
  12 public class Parser {
  13
  14         private final Environment environment;
  15
  16         public Parser(Environment environment) {
  17                 this.environment = environment;
  18         }
  19
  20         public <T> T parseEnvironment(Supplier<T> optionsObjectSupplier) {
  21                 T optionsObject = optionsObjectSupplier.get();
  22                 Class<?> optionsClass = optionsObject.getClass();
  23                 for (Field field : optionsClass.getDeclaredFields()) {
  24                         Option[] options = field.getAnnotationsByType(Option.class);
  25                         if (options.length == 0) {
  26                                 continue;
  27                         }
  28                         for (Option option : options) {
  29                                 String variableName = option.name();
  30                                 Optional<String> value = environment.getValue(variableName);
  31                                 if (option.required() && !value.isPresent()) {
  32                                         throw new RequiredOptionIsMissing(option.name());
  33                                 }
  34                                 field.setAccessible(true);
  35                                 try {
  36                                         field.set(optionsObject, value.orElse(null));
  37                                 } catch (IllegalAccessException iae1) {
  38                                         /* swallow. */
  39                                 }
  40                         }
  41                 }
  42                 return optionsObject;
  43         }
  44
  45         public static Parser fromSystemEnvironment() {
  46                 return new Parser(new SystemEnvironment());
  47         }
  48
  49         public static class RequiredOptionIsMissing extends RuntimeException {
  50
  51                 public RequiredOptionIsMissing(String message) {
  52                         super(message);
  53                 }
  54
  55         }
  56
  57 }