Merge pull request #350 from code-dot-org/sanchit/main-method

Validate full main method signature

Author: sanchitmalhotra126

org-code-javabuilder/lib/src/main/java/org/code/javabuilder/UserInitiatedExceptionKey.java

@@ -10,6 +10,8 @@ public enum UserInitiatedExceptionKey {
   TWO_MAIN_METHODS,
   // The user's code does not contain a main method.
   NO_MAIN_METHOD,
+  // The user's main method has an invalid signature.
+  INVALID_MAIN_METHOD,
   // The user's code has a compiler error.
   COMPILER_ERROR,
   // The user tried to include a source file that did not end in .java

org-code-javabuilder/lib/src/main/java/org/code/javabuilder/util/ProjectLoadUtils.java

@@ -1,6 +1,7 @@
 package org.code.javabuilder.util;
 
 import java.lang.reflect.Method;
+import java.lang.reflect.Modifier;
 import java.net.URLClassLoader;
 import java.util.List;
 import org.code.javabuilder.JavaProjectFile;
@@ -18,8 +19,8 @@ private ProjectLoadUtils() {
    * @param classLoader class loader pointing to location of compiled classes
    * @param javaFiles a list of JavaProjectFiles
    * @return the main method if it is found
-   * @throws UserInitiatedException if there is more than one main method or no main method, or if
-   *     the class definition is empty
+   * @throws UserInitiatedException if there is more than one main method, no main method, an error
+   *     with the main method signature, or if the class definition is empty
    */
   public static Method findMainMethod(URLClassLoader classLoader, List<JavaProjectFile> javaFiles)
       throws UserInitiatedException {
@@ -28,10 +29,7 @@ public static Method findMainMethod(URLClassLoader classLoader, List<JavaProject
       try {
         Method[] declaredMethods = classLoader.loadClass(file.getClassName()).getDeclaredMethods();
         for (Method method : declaredMethods) {
-          Class[] parameterTypes = method.getParameterTypes();
-          if (method.getName().equals("main")
-              && parameterTypes.length == 1
-              && parameterTypes[0].equals(String[].class)) {
+          if (method.getName().equals("main")) {
             if (mainMethod != null) {
               throw new UserInitiatedException(UserInitiatedExceptionKey.TWO_MAIN_METHODS);
             }
@@ -46,6 +44,20 @@ public static Method findMainMethod(URLClassLoader classLoader, List<JavaProject
       }
     }
 
+    // If we found a main method, make sure the method signature is valid
+    // (public, static, void return type, one argument which should be a String[]).
+    if (mainMethod != null) {
+      final Class<?>[] parameterTypes = mainMethod.getParameterTypes();
+      final int modifiers = mainMethod.getModifiers();
+      if (!Modifier.isPublic(modifiers)
+          || !Modifier.isStatic(modifiers)
+          || mainMethod.getGenericReturnType() != Void.TYPE
+          || parameterTypes.length != 1
+          || !parameterTypes[0].equals(String[].class)) {
+        throw new UserInitiatedException(UserInitiatedExceptionKey.INVALID_MAIN_METHOD);
+      }
+    }
+
     return mainMethod;
   }