SyncClient: avoid credentials NPE, simplify constructors #252

Also link docs instead of duplicating them.

Author: greenrobot-team

objectbox-java/src/main/java/io/objectbox/sync/Sync.java

@@ -64,13 +64,9 @@ public static SyncBuilder client(BoxStore boxStore, String url, SyncCredentials
     }
 
     /**
-     * Starts building a {@link SyncClient}. Once done, complete with {@link SyncBuilder#build() build()}.
+     * Like {@link #client(BoxStore, String, SyncCredentials)}, but supports passing a set of authentication methods.
      *
-     * @param boxStore The {@link BoxStore} the client should use.
-     * @param url The URL of the Sync server on which the Sync protocol is exposed. This is typically a WebSockets URL
-     * starting with {@code ws://} or {@code wss://} (for encrypted connections), for example
-     * {@code ws://127.0.0.1:9999}.
-     * @param multipleCredentials An array of {@link SyncCredentials} to be used to authenticate the user.
+     * @param multipleCredentials An array of {@link SyncCredentials} to be used to authenticate with the server.
      */
     public static SyncBuilder client(BoxStore boxStore, String url, SyncCredentials[] multipleCredentials) {
         return new SyncBuilder(boxStore, url, multipleCredentials);

objectbox-java/src/main/java/io/objectbox/sync/SyncBuilder.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2019-2024 ObjectBox Ltd. All rights reserved.
+ * Copyright 2019-2025 ObjectBox Ltd. All rights reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -42,7 +42,7 @@ public final class SyncBuilder {
 
     final Platform platform;
     final BoxStore boxStore;
-    String url;
+    @Nullable private String url;
     final List<SyncCredentials> credentials;
 
     @Nullable SyncLoginListener loginListener;
@@ -94,41 +94,32 @@ private static void checkSyncFeatureAvailable() {
         }
     }
 
-
-    @Internal
-    public SyncBuilder(BoxStore boxStore, SyncCredentials credentials) {
+    private SyncBuilder(BoxStore boxStore, @Nullable String url, @Nullable List<SyncCredentials> credentials) {
         checkNotNull(boxStore, "BoxStore is required.");
         checkNotNull(credentials, "Sync credentials are required.");
-        checkSyncFeatureAvailable();
-        this.platform = Platform.findPlatform();
         this.boxStore = boxStore;
-        this.credentials = Collections.singletonList(credentials);
+        this.url = url;
+        this.credentials = credentials;
+        checkSyncFeatureAvailable();
+        this.platform = Platform.findPlatform(); // Requires APIs only present in Android Sync library
     }
 
     @Internal
-    public SyncBuilder(BoxStore boxStore, SyncCredentials[] multipleCredentials) {
-        checkNotNull(boxStore, "BoxStore is required.");
-        if (multipleCredentials.length == 0) {
-            throw new IllegalArgumentException("At least one Sync credential is required.");
-        }
-        checkSyncFeatureAvailable();
-        this.platform = Platform.findPlatform();
-        this.boxStore = boxStore;
-        this.credentials = Arrays.asList(multipleCredentials);
+    public SyncBuilder(BoxStore boxStore, String url, @Nullable SyncCredentials credentials) {
+        this(boxStore, url, credentials == null ? null : Collections.singletonList(credentials));
     }
 
     @Internal
-    public SyncBuilder(BoxStore boxStore, String url, SyncCredentials credentials) {
-        this(boxStore, credentials);
-        checkNotNull(url, "Sync server URL is required.");
-        this.url = url;
+    public SyncBuilder(BoxStore boxStore, String url, @Nullable SyncCredentials[] multipleCredentials) {
+        this(boxStore, url, multipleCredentials == null ? null : Arrays.asList(multipleCredentials));
     }
 
+    /**
+     * When using this constructor, make sure to set the server URL before starting.
+     */
     @Internal
-    public SyncBuilder(BoxStore boxStore, String url, SyncCredentials[] multipleCredentials) {
-        this(boxStore, multipleCredentials);
-        checkNotNull(url, "Sync server URL is required.");
-        this.url = url;
+    public SyncBuilder(BoxStore boxStore, @Nullable SyncCredentials credentials) {
+        this(boxStore, null, credentials == null ? null : Collections.singletonList(credentials));
     }
 
     /**
@@ -140,6 +131,12 @@ SyncBuilder serverUrl(String url) {
         return this;
     }
 
+    @Internal
+    String serverUrl() {
+        checkNotNull(url, "Sync Server URL is null.");
+        return url;
+    }
+
     /**
      * Configures a custom set of directory or file paths to search for trusted certificates in.
      * The first path that exists will be used.
@@ -261,7 +258,7 @@ public SyncClient buildAndStart() {
         return syncClient;
     }
 
-    private void checkNotNull(Object object, String message) {
+    private void checkNotNull(@Nullable Object object, String message) {
         //noinspection ConstantConditions Non-null annotation does not enforce, so check for null.
         if (object == null) {
             throw new IllegalArgumentException(message);

objectbox-java/src/main/java/io/objectbox/sync/SyncClient.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2019-2024 ObjectBox Ltd. All rights reserved.
+ * Copyright 2019-2025 ObjectBox Ltd. All rights reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -128,14 +128,13 @@ public interface SyncClient extends Closeable {
     void setSyncTimeListener(@Nullable SyncTimeListener timeListener);
 
     /**
-     * Updates the login credentials. This should not be required during regular use.
+     * Updates the credentials used to authenticate with the server. This should not be required during regular use.
      * The original credentials were passed when building sync client.
      */
     void setLoginCredentials(SyncCredentials credentials);
 
     /**
-     * Updates the login credentials. This should not be required during regular use.
-     * It allows passing login credentials that the client can use to authenticate with the server.
+     * Like {@link #setLoginCredentials(SyncCredentials)}, but allows setting multiple credentials.
      */
     void setLoginCredentials(SyncCredentials[] multipleCredentials);
 

objectbox-java/src/main/java/io/objectbox/sync/SyncClientImpl.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2019-2024 ObjectBox Ltd. All rights reserved.
+ * Copyright 2019-2025 ObjectBox Ltd. All rights reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -61,7 +61,7 @@ public final class SyncClientImpl implements SyncClient {
 
     SyncClientImpl(SyncBuilder builder) {
         this.boxStore = builder.boxStore;
-        this.serverUrl = builder.url;
+        this.serverUrl = builder.serverUrl();
         this.connectivityMonitor = builder.platform.getConnectivityMonitor();
 
         long boxStoreHandle = builder.boxStore.getNativeStore();
@@ -189,6 +189,9 @@ public void setSyncListener(@Nullable SyncListener listener) {
 
     @Override
     public void setLoginCredentials(SyncCredentials credentials) {
+        if (credentials == null) {
+            throw new IllegalArgumentException("credentials must not be null");
+        }
         if (credentials instanceof SyncCredentialsToken) {
             SyncCredentialsToken credToken = (SyncCredentialsToken) credentials;
             nativeSetLoginInfo(getHandle(), credToken.getTypeId(), credToken.getTokenBytes());
@@ -204,6 +207,9 @@ public void setLoginCredentials(SyncCredentials credentials) {
 
     @Override
     public void setLoginCredentials(SyncCredentials[] multipleCredentials) {
+        if (multipleCredentials == null) {
+            throw new IllegalArgumentException("credentials must not be null");
+        }
         for (int i = 0; i < multipleCredentials.length; i++) {
             SyncCredentials credentials = multipleCredentials[i];
             boolean isLast = i == (multipleCredentials.length - 1);

tests/objectbox-java-test/src/test/java/io/objectbox/sync/SyncTest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2020-2024 ObjectBox Ltd. All rights reserved.
+ * Copyright 2020-2025 ObjectBox Ltd. All rights reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,12 +16,13 @@
 
 package io.objectbox.sync;
 
-import io.objectbox.exception.FeatureNotAvailableException;
 import org.junit.Test;
 
+import java.nio.charset.StandardCharsets;
+
 import io.objectbox.AbstractObjectBoxTest;
+import io.objectbox.exception.FeatureNotAvailableException;
 
-import java.nio.charset.StandardCharsets;
 
 import static org.junit.Assert.assertArrayEquals;
 import static org.junit.Assert.assertFalse;
@@ -31,6 +32,8 @@
 
 public class SyncTest extends AbstractObjectBoxTest {
 
+    private static final String SERVER_URL = "wss://127.0.0.1";
+
     /**
      * Ensure that non-sync native library correctly reports sync client availability.
      * <p>
@@ -54,9 +57,14 @@ public void serverIsNotAvailable() {
 
     @Test
     public void creatingSyncClient_throws() {
+        // If no credentials are passed
+        assertThrows(IllegalArgumentException.class, () -> Sync.client(store, SERVER_URL, (SyncCredentials) null));
+        assertThrows(IllegalArgumentException.class, () -> Sync.client(store, SERVER_URL, (SyncCredentials[]) null));
+
+        // If no Sync feature is available
         FeatureNotAvailableException exception = assertThrows(
                 FeatureNotAvailableException.class,
-                () -> Sync.client(store, "wss://127.0.0.1", SyncCredentials.none())
+                () -> Sync.client(store, SERVER_URL, SyncCredentials.none())
         );
         String message = exception.getMessage();
         assertTrue(message, message.contains("does not include ObjectBox Sync") &&
@@ -67,7 +75,7 @@ public void creatingSyncClient_throws() {
     public void creatingSyncServer_throws() {
         FeatureNotAvailableException exception = assertThrows(
                 FeatureNotAvailableException.class,
-                () -> Sync.server(store, "wss://127.0.0.1", SyncCredentials.none())
+                () -> Sync.server(store, SERVER_URL, SyncCredentials.none())
         );
         String message = exception.getMessage();
         assertTrue(message, message.contains("does not include ObjectBox Sync Server") &&