closes #3400

jooby/src/main/java/io/jooby/internal/RouterImpl.java

@@ -908,8 +908,7 @@ private void copy(Route src, Route it) {
     it.setExecutorKey(src.getExecutorKey());
     it.setTags(src.getTags());
     it.setDescription(src.getDescription());
-    it.setDecoders(src.getDecoders());
-    it.setMvcMethod(it.getMvcMethod());
+    it.setMvcMethod(src.getMvcMethod());
     it.setNonBlocking(src.isNonBlocking());
     it.setSummary(src.getSummary());
   }

tests/src/test/java/io/jooby/i3400/Issue3400.java

@@ -0,0 +1,39 @@
+package io.jooby.i3400;
+
+import io.jooby.Jooby;
+import io.jooby.jackson.JacksonModule;
+import io.jooby.junit.ServerTest;
+import io.jooby.junit.ServerTestRunner;
+import okhttp3.MediaType;
+import okhttp3.RequestBody;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class Issue3400 {
+
+  static class AppA extends Jooby {
+    {
+        post("/pets", ctx -> ctx.body(Pet.class));
+    }
+  }
+
+  @ServerTest
+  public void shouldShareDecodersOnMountedResources(ServerTestRunner runner) {
+    runner
+        .define(
+            app -> {
+              app.install(new JacksonModule());
+              app.mount(new AppA());
+            })
+        .ready(
+            http -> {
+                http.post(
+                "/pets",
+                  RequestBody.create("{\"id\": 1, \"name\": \"Cheddar\"}", MediaType.parse("application/json")),
+                  rsp -> {
+                    assertEquals("{\"id\":1,\"name\":\"Cheddar\"}", rsp.body().string());
+                    assertEquals("application/json;charset=UTF-8", rsp.header("Content-Type"));
+                  });
+            });
+  }
+}

tests/src/test/java/io/jooby/i3400/Pet.java

@@ -0,0 +1,27 @@
+package io.jooby.i3400;
+
+class Pet {
+    private int id;
+    private String name;
+
+    public Pet(int id, String name) {
+        this.id = id;
+        this.name = name;
+    }
+
+    public int getId() {
+        return id;
+    }
+
+    public void setId(int id) {
+        this.id = id;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+}