Add try/catch abstraction for RestAction operators (discord-jda#2044)

Author: MinnDevelopment

src/main/java/net/dv8tion/jda/internal/requests/restaction/operator/DelayRestAction.java

@@ -43,11 +43,11 @@ public DelayRestAction(RestAction<T> action, TimeUnit unit, long delay, Schedule
     @Override
     public void queue(@Nullable Consumer<? super T> success, @Nullable Consumer<? super Throwable> failure)
     {
-        action.queue((result) ->
+        handle(action, failure, (result) ->
             scheduler.schedule(() ->
                 doSuccess(success, result),
-            delay, unit),
-        contextWrap(failure));
+            delay, unit)
+        );
     }
 
     @Override

src/main/java/net/dv8tion/jda/internal/requests/restaction/operator/FlatMapRestAction.java

@@ -47,16 +47,15 @@ private RestAction<O> supply(I input)
     @Override
     public void queue(@Nullable Consumer<? super O> success, @Nullable Consumer<? super Throwable> failure)
     {
-        Consumer<? super Throwable> contextFailure = contextWrap(failure);
-        action.queue((result) -> {
+        Consumer<? super Throwable> catcher = contextWrap(failure);
+        handle(action, catcher, (result) -> {
             if (condition != null && !condition.test(result))
                 return;
             RestAction<O> then = supply(result);
-            if (then == null)
-                doFailure(contextFailure, new IllegalStateException("FlatMap operand is null"));
-            else
-                then.queue(success, contextFailure);
-        }, contextFailure);
+            if (then == null) // caught by handle try/catch abstraction
+                throw new IllegalStateException("FlatMap operand is null");
+            then.queue(success, catcher);
+        });
     }
 
     @Override

src/main/java/net/dv8tion/jda/internal/requests/restaction/operator/MapRestAction.java

@@ -38,7 +38,9 @@ public MapRestAction(RestAction<I> action, Function<? super I, ? extends O> func
     @Override
     public void queue(@Nullable Consumer<? super O> success, @Nullable Consumer<? super Throwable> failure)
     {
-        action.queue((result) -> doSuccess(success, function.apply(result)), contextWrap(failure));
+        handle(action, failure,
+            (result) -> doSuccess(success, function.apply(result))
+        );
     }
 
     @Override

src/main/java/net/dv8tion/jda/internal/requests/restaction/operator/RestActionOperator.java

@@ -54,6 +54,22 @@ protected static void doFailure(Consumer<? super Throwable> callback, Throwable
             throw (Error) throwable;
     }
 
+    protected void handle(RestAction<I> action, Consumer<? super Throwable> failure, Consumer<? super I> success)
+    {
+        Consumer<? super Throwable> catcher = contextWrap(failure);
+        action.queue((result) -> {
+            try
+            {
+                if (success != null)
+                    success.accept(result);
+            }
+            catch (Throwable ex)
+            {
+                doFailure(catcher, ex);
+            }
+        }, catcher);
+    }
+
     @Nonnull
     @Override
     public JDA getJDA()
@@ -86,6 +102,7 @@ public RestAction<O> deadline(long timestamp)
         return this;
     }
 
+    @Nullable
     protected <T> RestAction<T> applyContext(RestAction<T> action)
     {
         if (action == null)
@@ -97,6 +114,7 @@ protected <T> RestAction<T> applyContext(RestAction<T> action)
         return action;
     }
 
+    @Nullable
     protected Consumer<? super Throwable> contextWrap(@Nullable Consumer<? super Throwable> callback)
     {
         if (callback instanceof ContextException.ContextConsumer)