feat: async work as functional interface (#1068)

Marks the async work interface as a functional interface.

Author: thiagotnunes

google-cloud-spanner/src/main/java/com/google/cloud/spanner/AsyncRunner.java

@@ -27,6 +27,7 @@ public interface AsyncRunner {
  * Functional interface for executing a read/write transaction asynchronously that returns a
  * result of type R.
  */
+ @FunctionalInterface
  interface AsyncWork<R> {
  /**
  * Performs a single transaction attempt. All reads/writes should be performed using {@code

google-cloud-spanner/src/main/java/com/google/cloud/spanner/DatabaseClient.java

@@ -398,21 +398,18 @@ CommitResponse writeAtLeastOnceWithOptions(
  * AsyncRunner runner = client.runAsync();
  * ApiFuture<Long> rowCount =
  * runner.runAsync(
- * new AsyncWork<Long>() {
- * @Override
- * public ApiFuture<Long> doWorkAsync(TransactionContext txn) {
- * String column = "FirstName";
- * Struct row =
- * txn.readRow("Singers", Key.of(singerId), Collections.singleton("Name"));
- * String name = row.getString("Name");
- * return txn.executeUpdateAsync(
- * Statement.newBuilder("UPDATE Singers SET Name=@name WHERE SingerId=@id")
- * .bind("id")
- * .to(singerId)
- * .bind("name")
- * .to(name.toUpperCase())
- * .build());
- * }
+ * () -> {
+ * String column = "FirstName";
+ * Struct row =
+ * txn.readRow("Singers", Key.of(singerId), Collections.singleton("Name"));
+ * String name = row.getString("Name");
+ * return txn.executeUpdateAsync(
+ * Statement.newBuilder("UPDATE Singers SET Name=@name WHERE SingerId=@id")
+ * .bind("id")
+ * .to(singerId)
+ * .bind("name")
+ * .to(name.toUpperCase())
+ * .build());
  * },
  * executor);
  * </code></pre>

google-cloud-spanner/src/test/java/com/google/cloud/spanner/AsyncRunnerImplTest.java

@@ -27,7 +27,6 @@
 
 import com.google.api.core.ApiFuture;
 import com.google.api.core.ApiFutures;
-import com.google.cloud.spanner.AsyncRunner.AsyncWork;
 import com.google.cloud.spanner.TransactionRunner.TransactionCallable;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
@@ -57,14 +56,7 @@ public void testAsyncRunReturnsResultAndCommitResponse() {
 
  AsyncRunnerImpl runner = new AsyncRunnerImpl(delegate);
  ApiFuture<Object> result =
- runner.runAsync(
- new AsyncWork<Object>() {
- @Override
- public ApiFuture<Object> doWorkAsync(TransactionContext txn) {
- return ApiFutures.immediateFuture(expectedResult);
- }
- },
- executor);
+ runner.runAsync(txn -> ApiFutures.immediateFuture(expectedResult), executor);
 
  assertSame(expectedResult, get(result));
  assertSame(expectedCommitResponse, get(runner.getCommitResponse()));
@@ -105,14 +97,7 @@ public void testGetCommitResponseReturnsErrorIfRunFails() {
  when(delegate.getCommitResponse()).thenThrow(expectedException);
 
  AsyncRunnerImpl runner = new AsyncRunnerImpl(delegate);
- runner.runAsync(
- new AsyncWork<Void>() {
- @Override
- public ApiFuture<Void> doWorkAsync(TransactionContext txn) {
- return ApiFutures.immediateFailedFuture(expectedException);
- }
- },
- executor);
+ runner.runAsync(txn -> ApiFutures.immediateFailedFuture(expectedException), executor);
 
  try {
  get(runner.getCommitResponse());
@@ -130,24 +115,10 @@ public void testRunAyncFailsIfCalledMultipleTimes() {
  when(delegate.run(any(TransactionCallable.class))).thenReturn(result);
 
  AsyncRunnerImpl runner = new AsyncRunnerImpl(delegate);
- runner.runAsync(
- new AsyncWork<Object>() {
- @Override
- public ApiFuture<Object> doWorkAsync(TransactionContext txn) {
- return ApiFutures.immediateFuture(result);
- }
- },
- executor);
+ runner.runAsync(txn -> ApiFutures.immediateFuture(result), executor);
 
  try {
- runner.runAsync(
- new AsyncWork<Object>() {
- @Override
- public ApiFuture<Object> doWorkAsync(TransactionContext txn) {
- return ApiFutures.immediateFuture(null);
- }
- },
- executor);
+ runner.runAsync(txn -> ApiFutures.immediateFuture(null), executor);
  fail("missing expected exception");
  } catch (IllegalStateException e) {
  assertTrue(e.getMessage().contains("runAsync() can only be called once"));