Add basic from/to String type adapter

This adapter does not use type information and is intended
to be extended for simple string types.

Author: Spottedleaf

src/main/java/ca/spottedleaf/yamlconfig/adapter/generic/StringFormTypeAdapter.java

@@ -0,0 +1,25 @@
+package ca.spottedleaf.yamlconfig.adapter.generic;
+
+import ca.spottedleaf.yamlconfig.adapter.TypeAdapter;
+import ca.spottedleaf.yamlconfig.adapter.TypeAdapterRegistry;
+import java.lang.reflect.Type;
+
+public abstract class StringFormTypeAdapter<T> extends TypeAdapter<T, String> {
+    @Override
+    public final T deserialize(TypeAdapterRegistry registry, Object input, Type type) {
+        final TypeAdapter<String, String> forString = (TypeAdapter<String, String>)registry.getAdapter(String.class);
+
+        return this.fromString(forString.deserialize(registry, input, type));
+    }
+
+    @Override
+    public final String serialize(final TypeAdapterRegistry registry, final T value, final Type type) {
+        final TypeAdapter<String, String> forString = (TypeAdapter<String, String>)registry.getAdapter(String.class);
+
+        return forString.serialize(registry, this.toString(value), type);
+    }
+
+    public abstract T fromString(final String value);
+
+    public abstract String toString(final T value);
+}

src/main/java/ca/spottedleaf/yamlconfig/adapter/type/DurationTypeAdapter.java

@@ -1,24 +1,19 @@
 package ca.spottedleaf.yamlconfig.adapter.type;
 
-import ca.spottedleaf.yamlconfig.adapter.TypeAdapter;
-import ca.spottedleaf.yamlconfig.adapter.TypeAdapterRegistry;
+import ca.spottedleaf.yamlconfig.adapter.generic.StringFormTypeAdapter;
 import ca.spottedleaf.yamlconfig.type.Duration;
-import java.lang.reflect.Type;
 
-public final class DurationTypeAdapter extends TypeAdapter<Duration, String> {
+public final class DurationTypeAdapter extends StringFormTypeAdapter<Duration> {
 
     public static final DurationTypeAdapter INSTANCE = new DurationTypeAdapter();
 
     @Override
-    public Duration deserialize(final TypeAdapterRegistry registry, final Object input, final Type type) {
-        if (!(input instanceof String string)) {
-            throw new IllegalArgumentException("Not a string: " + input.getClass());
-        }
-        return Duration.parse(string);
+    public Duration fromString(final String value) {
+        return Duration.parse(value);
     }
 
     @Override
-    public String serialize(final TypeAdapterRegistry registry, final Duration value, final Type type) {
+    public String toString(final Duration value) {
         return value.toString();
     }
 }