[Bug bash] Allow ResponseBody.toFile option to override file

.changes/next-release/bugfix-AWSSDKforJavav2-c980953.json

@@ -0,0 +1,6 @@
+{
+    "type": "bugfix",
+    "category": "AWS SDK for Java v2",
+    "contributor": "",
+    "description": "Allow ResponseBody.toFile option to override file"
+}

core/sdk-core/src/main/java/software/amazon/awssdk/core/sync/ResponseTransformer.java

@@ -24,6 +24,7 @@
 import java.nio.file.FileAlreadyExistsException;
 import java.nio.file.Files;
 import java.nio.file.Path;
+import java.nio.file.StandardCopyOption;
 import software.amazon.awssdk.annotations.SdkPublicApi;
 import software.amazon.awssdk.core.ResponseBytes;
 import software.amazon.awssdk.core.ResponseInputStream;
@@ -100,10 +101,24 @@ default boolean needsConnectionLeftOpen() {
      * @return ResponseTransformer instance.
      */
     static <ResponseT> ResponseTransformer<ResponseT, ResponseT> toFile(Path path) {
+        return toFile(path, new StandardCopyOption[0]);
+    }
+
+    /**
+     * Creates a response transformer that writes all response content to the specified file. Passing
+     * {@link StandardCopyOption#REPLACE_EXISTING} will prevent a a {@link java.nio.file.FileAlreadyExistsException} to be thrown
+     * if the file already exists.
+     *
+     * @param path        Path to file to write to.
+     * @param <ResponseT> Type of unmarshalled response POJO.
+     * @param copyOptions options to be passed to the file copy
+     * @return ResponseTransformer instance.
+     */
+    static <ResponseT> ResponseTransformer<ResponseT, ResponseT> toFile(Path path, StandardCopyOption... copyOptions) {
         return (resp, in) -> {
             try {
                 InterruptMonitor.checkInterrupted();
-                Files.copy(in, path);
+                Files.copy(in, path, copyOptions);
                 return resp;
             } catch (IOException copyException) {
                 String copyError = "Failed to read response into file: " + path;

test/protocol-tests/src/test/java/software/amazon/awssdk/protocol/tests/ResponseTransformerTest.java

@@ -33,6 +33,7 @@
 import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
 import java.nio.file.Path;
+import java.nio.file.StandardCopyOption;
 import java.time.Duration;
 import java.util.UUID;
 import org.junit.Rule;
@@ -122,6 +123,19 @@ public void downloadToOutputStreamDoesNotRetry() throws IOException {
             .isInstanceOf(SdkClientException.class);
     }
 
+    @Test
+    public void downloadToExistingFileWithOverwriteSucceeds() throws IOException {
+        stubForSuccess();
+
+        Path tmpFile = Files.createTempFile("overwrite-test.", ".tmp");
+        tmpFile.toFile().deleteOnExit();
+
+        testClient().streamingOutputOperation(StreamingOutputOperationRequest.builder().build(),
+                                              ResponseTransformer.toFile(tmpFile, StandardCopyOption.REPLACE_EXISTING));
+
+        assertThat(Files.readAllLines(tmpFile)).containsExactly("test \uD83D\uDE02");
+    }
+
     @Test
     public void streamingCloseActuallyCloses() throws IOException {
         stubForSuccess();