do not try to load unexisting class multiple times

src/play/classloading/RebelClassloader.java

@@ -4,10 +4,29 @@
 import play.Play;
 import play.exceptions.RestartNeededException;
 
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.atomic.AtomicInteger;
+
 public class RebelClassloader extends ApplicationClassloader {
+  private static final Map<String, Class<?>> cache = new ConcurrentHashMap<>();
+  private static final Map<String, Boolean> unexistingClasses = new ConcurrentHashMap<>();
+
   @Override
   protected Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException {
-    return super.loadClass(name, resolve);
+    Class<?> aClass = cache.get(name);
+    if (aClass == null) {
+      if (unexistingClasses.get(name) != null) return null;
+
+      try {
+        aClass = super.loadClass(name, resolve);
+        cache.put(name, aClass);
+      }
+      catch (ClassNotFoundException e) {
+        unexistingClasses.put(name, true);
+      }
+    }
+    return aClass;
   }
 
   @Override public Class<?> loadApplicationClass(String name) {

test/play/classloading/RebelClassloaderTest.java

@@ -0,0 +1,68 @@
+package play.classloading;
+
+import org.junit.Before;
+import org.junit.Test;
+import play.Play;
+import play.classloading.ApplicationClasses.ApplicationClass;
+import play.exceptions.RestartNeededException;
+
+import static org.hamcrest.Matchers.equalTo;
+import static org.junit.Assert.assertThat;
+import static org.mockito.ArgumentMatchers.anyString;
+import static org.mockito.Mockito.*;
+
+public class RebelClassloaderTest {
+  RebelClassloader cl;
+
+  @Before
+  public void setUp() {
+    Play.classes = new ApplicationClasses();
+    cl = new RebelClassloader();
+  }
+
+  @Test
+  public void returnsNullForUnexistingClass() throws ClassNotFoundException {
+    assertThat(cl.loadClass("Script1BeanInfo", true), equalTo(null));
+  }
+
+  @Test
+  public void doesNotTryToLoadUnexistingClassMultipleTimes() throws ClassNotFoundException {
+    cl.loadClass("Script1BeanInfo", true);
+    cl = spy(cl);
+
+    assertThat(cl.loadClass("Script1BeanInfo", true), equalTo(null));
+    verify(cl, never()).loadApplicationClass(anyString());
+  }
+
+  @Test
+  public void loadsClassForApplicationClasses() throws ClassNotFoundException {
+    ApplicationClass applicationClass = new ApplicationClass("com.my.User");
+    applicationClass.javaClass = User.class;
+    Play.classes.add(applicationClass);
+
+    assertThat(cl.loadClass("com.my.User", true), equalTo(User.class));
+  }
+
+  @Test
+  public void cachesLoadedClasses() throws ClassNotFoundException {
+    ApplicationClass applicationClass = new ApplicationClass("com.my.User");
+    applicationClass.javaClass = User.class;
+    Play.classes.add(applicationClass);
+    cl.loadClass("com.my.User", true);
+
+    cl = spy(cl);
+    assertThat(cl.loadClass("com.my.User", true), equalTo(User.class));
+    verify(cl, never()).loadApplicationClass(anyString());
+  }
+
+  @Test
+  public void doesNotDetectChanges() throws RestartNeededException {
+    Play.classes = mock(ApplicationClasses.class);
+
+    cl.detectChanges();
+
+    verify(Play.classes, never()).all();
+  }
+
+  private static class User {}
+}