Ignore temporaryFileName when FileExistsMode is APPEND

Improve runtime behavior by ignoring temporary filename settings when file exists mode is APPEND. Now, in FileExistsMode.APPEND mode, content is always appended directly to the original file regardless of useTemporaryFileName setting.

In RemoteFileTemplate:
- Remove exception validation when APPEND mode is used with temporary filenames
- Modify logic to skip applying temporaryFileSuffix in APPEND mode

In AbstractRemoteFileOutboundGateway:
- Remove logic that disabled temporary filenames when setting APPEND mode

Signed-off-by: Jooyoung Pyoung <[email protected]>

Author: anthologia

spring-integration-file/src/main/java/org/springframework/integration/file/remote/RemoteFileTemplate.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2013-2024 the original author or authors.
+ * Copyright 2013-2025 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -63,6 +63,7 @@
  * @author Gary Russell
  * @author Artem Bilan
  * @author Alen Turkovic
+ * @author Jooyoung Pyoung
  *
  * @since 3.0
  *
@@ -303,8 +304,6 @@ public String send(Message<?> message, String subDirectory, FileExistsMode... mo
 
 	private String send(Message<?> message, String subDirectory, FileExistsMode mode) {
 		Assert.notNull(this.directoryExpressionProcessor, "'remoteDirectoryExpression' is required");
-		Assert.isTrue(!FileExistsMode.APPEND.equals(mode) || !this.useTemporaryFileName,
-				"Cannot append when using a temporary file name");
 		Assert.isTrue(!FileExistsMode.REPLACE_IF_MODIFIED.equals(mode),
 				"FilExistsMode.REPLACE_IF_MODIFIED can only be used for local files");
 		final StreamHolder inputStreamHolder = payloadToInputStream(message);
@@ -565,7 +564,10 @@ private void sendFileToRemoteDirectory(InputStream inputStream, String temporary
 		String tempRemoteFilePath = temporaryRemoteDirectory + fileName;
 		// write remote file first with temporary file extension if enabled
 
-		String tempFilePath = tempRemoteFilePath + (this.useTemporaryFileName ? this.temporaryFileSuffix : "");
+		String tempFilePath = tempRemoteFilePath;
+		if (!FileExistsMode.APPEND.equals(mode)) {
+			tempFilePath += this.useTemporaryFileName ? this.temporaryFileSuffix : "";
+		}
 
 		if (this.autoCreateDirectory) {
 			try {

spring-integration-file/src/main/java/org/springframework/integration/file/remote/gateway/AbstractRemoteFileOutboundGateway.java

@@ -524,9 +524,6 @@ public void setFileExistsModeExpression(String fileExistsModeExpression) {
 	 */
 	public void setFileExistsMode(FileExistsMode fileExistsMode) {
 		this.fileExistsMode = fileExistsMode;
-		if (FileExistsMode.APPEND.equals(fileExistsMode)) {
-			this.remoteFileTemplate.setUseTemporaryFileName(false);
-		}
 	}
 
 	/**

spring-integration-file/src/test/java/org/springframework/integration/file/remote/gateway/RemoteFileOutboundGatewayTests.java

@@ -968,18 +968,19 @@ public void testPutExistsExpression() throws Exception {
 
 		Message<String> appendMessage = requestMessageBuilder.setHeader("file.exists.mode", FileExistsMode.APPEND)
 				.build();
-
-		assertThatExceptionOfType(IllegalArgumentException.class)
-				.isThrownBy(() -> gw.handleRequestMessage(appendMessage))
-				.withStackTraceContaining("Cannot append when using a temporary file name");
+		path = (String) gw.handleRequestMessage(appendMessage);
+		assertThat(path).isEqualTo("foo/bar.txt");
+		captor = ArgumentCaptor.forClass(String.class);
+		verify(session).append(any(InputStream.class), captor.capture());
+		assertThat(captor.getValue()).isEqualTo("foo/bar.txt");
 
 		Message<String> ignoreMessage = requestMessageBuilder.setHeader("file.exists.mode", FileExistsMode.IGNORE)
 				.build();
 		path = (String) gw.handleRequestMessage(ignoreMessage);
 		assertThat(path).isEqualTo("foo/bar.txt");
 		// no more writes/appends
 		verify(session, times(2)).write(any(InputStream.class), anyString());
-		verify(session, times(0)).append(any(InputStream.class), anyString());
+		verify(session, times(1)).append(any(InputStream.class), anyString());
 	}
 
 	@Test