Update Injector and create injectable object factory

- Using e.g. Factory<Converter> instead of the injector directly makes its purpose more specific and disallows any future abuse of the injector's functions

src/main/java/fr/xephi/authme/AuthMe.java

@@ -14,6 +14,7 @@ import fr.xephi.authme.initialization.OnShutdownPlayerSaver;
 import fr.xephi.authme.initialization.OnStartupTasks;
 import fr.xephi.authme.initialization.SettingsProvider;
 import fr.xephi.authme.initialization.TaskCloser;
+import fr.xephi.authme.initialization.factory.FactoryDependencyHandler;
 import fr.xephi.authme.listener.BlockListener;
 import fr.xephi.authme.listener.EntityListener;
 import fr.xephi.authme.listener.PlayerListener;
@@ -196,7 +197,10 @@ public class AuthMe extends JavaPlugin {
         getDataFolder().mkdir();
 
         // Create injector, provide elements from the Bukkit environment and register providers
-        injector = new InjectorBuilder().addDefaultHandlers("fr.xephi.authme").create();
+        injector = new InjectorBuilder()
+            .addHandlers(new FactoryDependencyHandler())
+            .addDefaultHandlers("fr.xephi.authme")
+            .create();
         injector.register(AuthMe.class, this);
         injector.register(Server.class, getServer());
         injector.register(PluginManager.class, getServer().getPluginManager());

src/main/java/fr/xephi/authme/command/CommandHandler.java

@@ -1,8 +1,8 @@
 package fr.xephi.authme.command;
 
-import ch.jalu.injector.Injector;
 import fr.xephi.authme.AuthMe;
 import fr.xephi.authme.command.help.HelpProvider;
+import fr.xephi.authme.initialization.factory.Factory;
 import fr.xephi.authme.message.MessageKey;
 import fr.xephi.authme.message.Messages;
 import fr.xephi.authme.permission.PermissionsManager;
@@ -40,13 +40,13 @@ public class CommandHandler {
     private Map<Class<? extends ExecutableCommand>, ExecutableCommand> commands = new HashMap<>();
 
     @Inject
-    CommandHandler(Injector injector, CommandMapper commandMapper, PermissionsManager permissionsManager,
-                          Messages messages, HelpProvider helpProvider) {
+    CommandHandler(Factory<ExecutableCommand> commandFactory, CommandMapper commandMapper,
+                   PermissionsManager permissionsManager, Messages messages, HelpProvider helpProvider) {
         this.commandMapper = commandMapper;
         this.permissionsManager = permissionsManager;
         this.messages = messages;
         this.helpProvider = helpProvider;
-        initializeCommands(injector, commandMapper.getCommandClasses());
+        initializeCommands(commandFactory, commandMapper.getCommandClasses());
     }
 
     /**
@@ -94,13 +94,13 @@ public class CommandHandler {
     /**
      * Initialize all required ExecutableCommand objects.
      *
-     * @param injector the injector
+     * @param commandFactory factory to create command objects
      * @param commandClasses the classes to instantiate
      */
-    private void initializeCommands(Injector injector,
+    private void initializeCommands(Factory<ExecutableCommand> commandFactory,
                                     Set<Class<? extends ExecutableCommand>> commandClasses) {
         for (Class<? extends ExecutableCommand> clazz : commandClasses) {
-            commands.put(clazz, injector.newInstance(clazz));
+            commands.put(clazz, commandFactory.newInstance(clazz));
         }
     }
 

src/main/java/fr/xephi/authme/command/executable/authme/ConverterCommand.java

@@ -1,6 +1,5 @@
 package fr.xephi.authme.command.executable.authme;
 
-import ch.jalu.injector.Injector;
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.collect.ImmutableMap;
 import fr.xephi.authme.ConsoleLogger;
@@ -13,6 +12,7 @@ import fr.xephi.authme.datasource.converter.RoyalAuthConverter;
 import fr.xephi.authme.datasource.converter.SqliteToSql;
 import fr.xephi.authme.datasource.converter.vAuthConverter;
 import fr.xephi.authme.datasource.converter.xAuthConverter;
+import fr.xephi.authme.initialization.factory.Factory;
 import fr.xephi.authme.message.MessageKey;
 import fr.xephi.authme.service.BukkitService;
 import fr.xephi.authme.service.CommonService;
@@ -37,7 +37,7 @@ public class ConverterCommand implements ExecutableCommand {
     private BukkitService bukkitService;
 
     @Inject
-    private Injector injector;
+    private Factory<Converter> converterFactory;
 
     @Override
     public void executeCommand(final CommandSender sender, List<String> arguments) {
@@ -52,7 +52,7 @@ public class ConverterCommand implements ExecutableCommand {
         }
 
         // Get the proper converter instance
-        final Converter converter = injector.newInstance(converterClass);
+        final Converter converter = converterFactory.newInstance(converterClass);
 
         // Run the convert job
         bukkitService.runTaskAsynchronously(new Runnable() {

src/main/java/fr/xephi/authme/initialization/factory/Factory.java

@@ -0,0 +1,19 @@
+package fr.xephi.authme.initialization.factory;
+
+/**
+ * Injectable factory that creates new instances of a certain type.
+ *
+ * @param <P> the parent type to which the factory is limited to
+ */
+public interface Factory<P> {
+
+    /**
+     * Creates an instance of the given class.
+     *
+     * @param clazz the class to instantiate
+     * @param <C> the class type
+     * @return new instance of the class
+     */
+    <C extends P> C newInstance(Class<C> clazz);
+
+}

src/main/java/fr/xephi/authme/initialization/factory/FactoryDependencyHandler.java

@@ -0,0 +1,46 @@
+package fr.xephi.authme.initialization.factory;
+
+import ch.jalu.injector.Injector;
+import ch.jalu.injector.context.ResolvedInstantiationContext;
+import ch.jalu.injector.handlers.dependency.DependencyHandler;
+import ch.jalu.injector.handlers.instantiation.DependencyDescription;
+import ch.jalu.injector.utils.ReflectionUtils;
+
+/**
+ * Dependency handler that builds {@link Factory} objects.
+ */
+public class FactoryDependencyHandler implements DependencyHandler {
+
+    @Override
+    public Object resolveValue(ResolvedInstantiationContext<?> context, DependencyDescription dependencyDescription) {
+        if (dependencyDescription.getType() == Factory.class) {
+            Class<?> genericType = ReflectionUtils.getGenericType(dependencyDescription.getGenericType());
+            if (genericType == null) {
+                throw new IllegalStateException("Factory fields must have concrete generic type. " +
+                    "Cannot get generic type for field in '" + context.getMappedClass() + "'");
+            }
+
+            return new FactoryImpl<>(genericType, context.getInjector());
+        }
+        return null;
+    }
+
+    private static final class FactoryImpl<P> implements Factory<P> {
+
+        private final Injector injector;
+        private final Class<P> parentClass;
+
+        FactoryImpl(Class<P> parentClass, Injector injector) {
+            this.parentClass = parentClass;
+            this.injector = injector;
+        }
+
+        @Override
+        public <C extends P> C newInstance(Class<C> clazz) {
+            if (parentClass.isAssignableFrom(clazz)) {
+                return injector.newInstance(clazz);
+            }
+            throw new IllegalArgumentException(clazz + " not child of " + parentClass);
+        }
+    }
+}

src/main/java/fr/xephi/authme/security/PasswordSecurity.java

@@ -1,9 +1,9 @@
 package fr.xephi.authme.security;
 
-import ch.jalu.injector.Injector;
 import fr.xephi.authme.datasource.DataSource;
 import fr.xephi.authme.events.PasswordEncryptionEvent;
 import fr.xephi.authme.initialization.Reloadable;
+import fr.xephi.authme.initialization.factory.Factory;
 import fr.xephi.authme.security.crypts.EncryptionMethod;
 import fr.xephi.authme.security.crypts.HashedPassword;
 import fr.xephi.authme.settings.Settings;
@@ -29,7 +29,7 @@ public class PasswordSecurity implements Reloadable {
     private PluginManager pluginManager;
 
     @Inject
-    private Injector injector;
+    private Factory<EncryptionMethod> hashAlgorithmFactory;
 
     private HashAlgorithm algorithm;
     private Collection<HashAlgorithm> legacyAlgorithms;
@@ -154,7 +154,7 @@ public class PasswordSecurity implements Reloadable {
         if (HashAlgorithm.CUSTOM.equals(algorithm) || HashAlgorithm.PLAINTEXT.equals(algorithm)) {
             return null;
         }
-        return injector.newInstance(algorithm.getClazz());
+        return hashAlgorithmFactory.newInstance(algorithm.getClazz());
     }
 
     private void hashPasswordForNewAlgorithm(String password, String playerName) {