[Java] Fix loading driver resources issue. (#3046)

## What do these changes do?
Fix the issue how we load driver resources by a specified path.
Also this addressed the comments from the related PR [3044](https://github.com/ray-project/ray/pull/3044).

## Related PRs:
 [#3044](https://github.com/ray-project/ray/pull/3044) and [#3001](https://github.com/ray-project/ray/pull/3001).

java/runtime/src/main/java/org/ray/runtime/config/RayConfig.java

@@ -158,17 +158,12 @@ public class RayConfig {
     rayletExecutablePath = rayHome + "/build/src/ray/raylet/raylet";
 
     // driver resource path
-    String localDriverResourcePath;
     if (config.hasPath("ray.driver.resource-path")) {
-      localDriverResourcePath = config.getString("ray.driver.resource-path");
+      driverResourcePath = config.getString("ray.driver.resource-path");
     } else {
-      localDriverResourcePath = rayHome + "/driver/resource";
-      LOGGER.warn("Didn't configure ray.driver.resource-path, set it to default value: {}",
-          localDriverResourcePath);
+      driverResourcePath = null;
     }
 
-    driverResourcePath = localDriverResourcePath;
-
     // validate config
     validate();
     LOGGER.debug("Created config: {}", this);

java/runtime/src/main/java/org/ray/runtime/functionmanager/FunctionManager.java

@@ -89,13 +89,11 @@ public class FunctionManager {
       String resourcePath = driverResourcePath + "/" + driverId.toString() + "/";
       ClassLoader classLoader;
 
-      try {
+      if (driverResourcePath != null && !driverResourcePath.isEmpty()) {
         classLoader = JarLoader.loadJars(resourcePath, false);
         LOGGER.info("Succeeded to load driver({}) resource. Resource path is {}",
             driverId, resourcePath);
-      } catch (Exception e) {
-        LOGGER.error("Failed to load driver({}) resource. Resource path is {}",
-            driverId, resourcePath);
+      } else {
         classLoader = getClass().getClassLoader();
       }
 

java/runtime/src/main/resources/ray.default.conf

@@ -25,15 +25,16 @@ ray {
   // Available resources on this node, for example "CPU:4,GPU:0".
   resources: ""
 
-    // Configuration items about driver.
-    driver {
-      // If worker.mode is DRIVER, specify the driver id.
-      // If not provided, a random id will be used.
-      id: ""
-      // If worker.mode is WORKER, it means that worker will load
-      // the resources from this path to execute tasks.
-      resource-path: /tmp/ray/driver/resource
-    }
+  // Configuration items about driver.
+  driver {
+    // If worker.mode is DRIVER, specify the driver id.
+    // If not provided, a random id will be used.
+    id: ""
+    // If this config is set, worker will use different paths to loadresources when
+    // executing tasks from different drivers. E.g. if it's set to '/tm/driver_resources',
+    // the path for driver 123 will be '/tmp/driver_resources/123'.
+    resource-path: ""
+  }
 
   // Root dir of log files.
   log-dir: /tmp/ray/logs

java/runtime/src/test/java/org/ray/runtime/functionmanager/FunctionManagerTest.java

@@ -45,10 +45,6 @@ public class FunctionManagerTest {
   private static FunctionDescriptor barDescriptor;
   private static FunctionDescriptor barConstructorDescriptor;
 
-  private final static String resourcePath = "/tmp/ray/test/resource";
-
-  private FunctionManager functionManager;
-
   @BeforeClass
   public static void beforeClass() {
     fooFunc = FunctionManagerTest::foo;
@@ -63,13 +59,9 @@ public class FunctionManagerTest {
         "()V");
   }
 
-  @Before
-  public void before() {
-    functionManager = new FunctionManager(FunctionManagerTest.resourcePath);
-  }
-
   @Test
   public void testGetFunctionFromRayFunc() {
+    final FunctionManager functionManager = new FunctionManager(null);
     // Test normal function.
     RayFunction func = functionManager.getFunction(UniqueId.NIL, fooFunc);
     Assert.assertFalse(func.isConstructor());
@@ -91,6 +83,7 @@ public class FunctionManagerTest {
 
   @Test
   public void testGetFunctionFromFunctionDescriptor() {
+    final FunctionManager functionManager = new FunctionManager(null);
     // Test normal function.
     RayFunction func = functionManager.getFunction(UniqueId.NIL, fooDescriptor);
     Assert.assertFalse(func.isConstructor());
@@ -129,6 +122,7 @@ public class FunctionManagerTest {
     UniqueId driverId = UniqueId.fromHexString("0123456789012345678901234567890123456789");
 
     //TODO(qwang): We should use a independent app demo instead of `tutorial`.
+    final String resourcePath = "/tmp/ray/test/resource";
     final String srcJarPath = System.getProperty("user.dir") +
                                   "/../tutorial/target/ray-tutorial-0.1-SNAPSHOT.jar";
     final String destJarPath = resourcePath + "/" + driverId.toString() +
@@ -136,9 +130,9 @@ public class FunctionManagerTest {
 
     File file = new File(resourcePath + "/" + driverId.toString());
     file.mkdirs();
-
     Files.copy(Paths.get(srcJarPath), Paths.get(destJarPath), StandardCopyOption.REPLACE_EXISTING);
 
+    final FunctionManager functionManager = new FunctionManager(resourcePath);
     FunctionDescriptor sayHelloDescriptor = new FunctionDescriptor("org.ray.exercise.Exercise02",
         "sayHello", "()Ljava/lang/String;");
     RayFunction func = functionManager.getFunction(driverId, sayHelloDescriptor);