The configuration for file reading can be simplified using the file specific namespace. To do this use the following template.

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns:int="http://www.springframework.org/schema/integration"
  xmlns:int-file="http://www.springframework.org/schema/integration/file"
  xsi:schemaLocation="http://www.springframework.org/schema/beans
    https://www.springframework.org/schema/beans/spring-beans.xsd
    http://www.springframework.org/schema/integration
    https://www.springframework.org/schema/integration/spring-integration.xsd
    http://www.springframework.org/schema/integration/file
    https://www.springframework.org/schema/integration/file/spring-integration-file.xsd">
</beans>

Within this namespace you can reduce the FileReadingMessageSource and wrap it in an inbound Channel Adapter like this:

<int-file:inbound-channel-adapter id="filesIn1"
    directory="file:${input.directory}" prevent-duplicates="true" ignore-hidden="true"/>

<int-file:inbound-channel-adapter id="filesIn2"
    directory="file:${input.directory}"
    filter="customFilterBean" />

<int-file:inbound-channel-adapter id="filesIn3"
    directory="file:${input.directory}"
    filename-pattern="test*" />

<int-file:inbound-channel-adapter id="filesIn4"
    directory="file:${input.directory}"
    filename-regex="test[0-9]+\.txt" />

The first channel adapter example is relying on the default FileListFilter s:

Therefore, you can also leave off the 2 attributes prevent-duplicates and ignore-hidden as they are true by default.

	Important
	The ignore-hidden attribute was introduced with Spring Integration 4.2. In prior versions hidden files were included.

The second channel adapter example is using a custom filter, the third is using the filename-pattern attribute to add an AntPathMatcher based filter, and the fourth is using the filename-regex attribute to add a regular expression Pattern based filter to the FileReadingMessageSource. The filename-pattern and filename-regex attributes are each mutually exclusive with the regular filter reference attribute. However, you can use the filter attribute to reference an instance of CompositeFileListFilter that combines any number of filters, including one or more pattern based filters to fit your particular needs.

When multiple processes are reading from the same directory it can be desirable to lock files to prevent them from being picked up concurrently. To do this you can use a FileLocker. There is a java.nio based implementation available out of the box, but it is also possible to implement your own locking scheme. The nio locker can be injected as follows

<int-file:inbound-channel-adapter id="filesIn"
    directory="file:${input.directory}" prevent-duplicates="true">
    <int-file:nio-locker/>
</int-file:inbound-channel-adapter>

A custom locker you can configure like this:

<int-file:inbound-channel-adapter id="filesIn"
    directory="file:${input.directory}" prevent-duplicates="true">
    <int-file:locker ref="customLocker"/>
</int-file:inbound-channel-adapter>

Note

When a file inbound adapter is configured with a locker, it will take the responsibility to acquire a lock before the file is allowed to be received. It will not assume the responsibility to unlock the file. If you have processed the file and keeping the locks hanging around you have a memory leak. If this is a problem in your case you should call FileLocker.unlock(File file) yourself at the appropriate time.

When filtering and locking files is not enough it might be needed to control the way files are listed entirely. To implement this type of requirement you can use an implementation of DirectoryScanner. This scanner allows you to determine entirely what files are listed each poll. This is also the interface that Spring Integration uses internally to wire FileListFilter s and FileLocker to the FileReadingMessageSource. A custom DirectoryScanner can be injected into the <int-file:inbound-channel-adapter/> on the scanner attribute.

<int-file:inbound-channel-adapter id="filesIn" directory="file:${input.directory}"
     scanner="customDirectoryScanner"/>

This gives you full freedom to choose the ordering, listing and locking strategies.

It is also important to understand that filters (including patterns, regex, prevent-duplicates etc) and locker s, are actually used by the scanner. Any of these attributes set on the adapter are subsequently injected into the internal scanner. For the case of an external scanner, all filter and locker attributes are prohibited on the FileReadingMessageSource; they must be specified (if required) on that custom DirectoryScanner. In other words, if you inject a scanner into the FileReadingMessageSource, you should supply filter and locker on that scanner not on the FileReadingMessageSource.

	Note
	The DefaultDirectoryScanner uses a IgnoreHiddenFileListFilter and AcceptOnceFileListFilter by default. To prevent their use, you should configure your own filter (e.g. AcceptAllFileListFilter) or even set it to null.

This scanner was added in version 4.2. It replaces the existing RecursiveLeafOnlyDirectoryScanner which is inefficient for large directory trees. The FileReadingMessageSource.WatchServiceDirectoryScanner requires Java 7 or above.

This scanner relies on file system events when new files are added to the directory. During initialization, the directory is registered to generate events; the initial file list is also built. While walking the directory tree, any subdirectories encountered are also registered to generate events. On the first poll, the initial file list from walking the directory is returned. On subsequent polls, files from new creation events are returned. If a new subdirectory is added, its creation event is used to walk the new subtree to find existing files, as well as registering any new subdirectories found.

Note

There is a case with WatchKey, when its internal events queue isn’t drained by the program as quickly as the directory modification events occur. If the queue size is exceeded, a StandardWatchEventKinds.OVERFLOW is emitted to indicate that some file system events may be lost. In this case, the root directory is re-scanned completely. To avoid duplicates consider using an appropriate FileListFilter such as the AcceptOnceFileListFilter and/or remove files when processing is completed.

Since version 4.3, the top level WatchServiceDirectoryScanner has been deprecated in favor of FileReadingMessageSource internal logic for the WatchService. Now this can be enable via use-watch-service option, which is mutually exclusive with the scanner option. An internal FileReadingMessageSource.WatchServiceDirectoryScanner instance is populated for the provided directory.

In addition, now the WatchService polling logic can track the StandardWatchEventKinds.ENTRY_MODIFY and StandardWatchEventKinds.ENTRY_DELETE, too.

The ENTRY_MODIFY events logic should be implemented properly in the FileListFilter to track not only new files but also the modification, if that is requirement. Otherwise the files from those events are treated the same way.

The ENTRY_DELETE events have effect for the ResettableFileListFilter implementations and, therefore, their files are provided for the remove() operation. This means that (when this event is enabled), filters such as the AcceptOnceFileListFilter will have the file removed, meaning that, if a file with the same name appears, it will pass the filter and be sent as a message.

For this purpose the watch-events (FileReadingMessageSource.setWatchEvents(WatchEventType... watchEvents)) has been introduced (WatchEventType is a public inner enum in FileReadingMessageSource). With such an option we can implement some scenarios, when we would like to do one downstream flow logic for new files, and other for modified. We can achieve that with different <int-file:inbound-channel-adapter> definitions, but for the same directory:

<int-file:inbound-channel-adapter id="newFiles"
     directory="${input.directory}"
     use-watch-service="true"/>

<int-file:inbound-channel-adapter id="modifiedFiles"
     directory="${input.directory}"
     use-watch-service="true"
     filter="acceptAllFilter"
     watch-events="MODIFY"/> <!-- CREATE by default -->

A HeadDirectoryScanner can be used to limit the number of files retained in memory. This can be useful when scanning large directories. With XML configuration, this is enabled using the queue-size property on the inbound channel adapter.

Prior to version 4.2, this setting was incompatible with the use of any other filters. Any other filters (including prevent-duplicates="true") overwrote the filter used to limit the size.

Note

The use of a HeadDirectoryScanner is incompatible with an AcceptOnceFileListFilter. Since all filters are consulted during the poll decision, the AcceptOnceFileListFilter does not know that other filters might be temporarily filtering files. Even if files that were previously filtered by the HeadDirectoryScanner.HeadFilter are now available, the AcceptOnceFileListFilter will filter them. Generally, instead of using an AcceptOnceFileListFilter in this case, one would simply remove the processed files so that the previously filtered files will be available on a future poll.

The following Spring Boot application provides an example of configuring the inbound adapter using Java configuration:

@SpringBootApplication
public class FileReadingJavaApplication {

    public static void main(String[] args) {
        new SpringApplicationBuilder(FileReadingJavaApplication.class)
            .web(false)
            .run(args);
    }

    @Bean
    public MessageChannel fileInputChannel() {
        return new DirectChannel();
    }

    @Bean
    @InboundChannelAdapter(value = "fileInputChannel", poller = @Poller(fixedDelay = "1000"))
    public MessageSource<File> fileReadingMessageSource() {
         FileReadingMessageSource source = new FileReadingMessageSource();
         source.setDirectory(new File(INBOUND_PATH));
         source.setFilter(new SimplePatternFileListFilter("*.txt"));
         return source;
    }

    @Bean
    @Transformer(inputChannel = "fileInputChannel", outputChannel = "processFileChannel")
    public FileToStringTransformer fileToStringTransformer() {
        return new FileToStringTransformer();
    }

}

The following Spring Boot application provides an example of configuring the inbound adapter using the Java DSL:

@SpringBootApplication
public class FileReadingJavaApplication {

    public static void main(String[] args) {
        new SpringApplicationBuilder(FileReadingJavaApplication.class)
            .web(false)
            .run(args);
    }

    @Bean
    public IntegrationFlow fileReadingFlow() {
         return IntegrationFlows
                  .from(s -> s.file(new File(INBOUND_PATH))
                              .patternFilter("*.txt"),
                          e -> e.poller(Pollers.fixedDelay(1000)))
                  .transform(Transformers.fileToString())
                  .channel("processFileChannel")
                  .get();
        }

}

Another popular use case is to get lines from the end (or tail) of a file, capturing new lines when they are added. Two implementations are provided; the first, OSDelegatingFileTailingMessageProducer, uses the native tail command (on operating systems that have one). This is likely the most efficient implementation on those platforms. For operating systems that do not have a tail command, the second implementation ApacheCommonsFileTailingMessageProducer which uses the Apache commons-io Tailer class.

In both cases, file system events, such as files being unavailable etc, are published as ApplicationEvent s using the normal Spring event publishing mechanism. Examples of such events are:

[message=tail: cannot open `/tmp/foo' for reading: No such file or directory, file=/tmp/foo]

[message=tail: `/tmp/foo' has become accessible, file=/tmp/foo]

[message=tail: `/tmp/foo' has become inaccessible: No such file or directory, file=/tmp/foo]

[message=tail: `/tmp/foo' has appeared; following end of new file, file=/tmp/foo]

This sequence of events might occur, for example, when a file is rotated.

	Note
	Not all platforms supporting a tail command provide these status messages.

Example configurations:

<int-file:tail-inbound-channel-adapter id="native"
	channel="input"
	task-executor="exec"
	file="/tmp/foo"/>

This creates a native adapter with default -F -n 0 options (follow the file name from the current end).

<int-file:tail-inbound-channel-adapter id="native"
	channel="input"
	native-options="-F -n +0"
	task-executor="exec"
	file-delay=10000
	file="/tmp/foo"/>

This creates a native adapter with -F -n +0 options (follow the file name, emitting all existing lines). If the tail command fails (on some platforms, a missing file causes the tail to fail, even with -F specified), the command will be retried every 10 seconds.

<int-file:tail-inbound-channel-adapter id="native"
	channel="input"
	enable-status-reader="false"
	task-executor="exec"
	file="/tmp/foo"/>

By default native adapter capture from standard output and send them as messages and from standard error to raise events. Starting with version 4.3.6, you can discard the standard error events by setting the enable-status-reader to false.

<int-file:tail-inbound-channel-adapter id="apache"
	channel="input"
	task-executor="exec"
	file="/tmp/bar"
	delay="2000"
	end="false"
	reopen="true"
	file-delay="10000"/>

This creates an Apache commons-io Tailer adapter that examines the file for new lines every 2 seconds, and checks for existence of a missing file every 10 seconds. The file will be tailed from the beginning (end="false") instead of the end (which is the default). The file will be reopened for each chunk (the default is to keep the file open).

	Important
	Specifying the delay, end or reopen attributes, forces the use of the Apache commons-io adapter and the native-options attribute is not allowed.

In its simplest form, the FileWritingMessageHandler only requires a destination directory for writing the files. The name of the file to be written is determined by the handler’s FileNameGenerator. The default implementation looks for a Message header whose key matches the constant defined as FileHeaders.FILENAME.

Alternatively, you can specify an expression to be evaluated against the Message in order to generate a file name, e.g. headers[myCustomHeader] + '.foo'. The expression must evaluate to a String. For convenience, the DefaultFileNameGenerator also provides the setHeaderName method, allowing you to explicitly specify the Message header whose value shall be used as the filename.

Once setup, the DefaultFileNameGenerator will employ the following resolution steps to determine the filename for a given Message payload:

When using the XML namespace support, both, the File Outbound Channel Adapter and the File Outbound Gateway support the following two mutually exclusive configuration attributes:

While writing files, a temporary file suffix will be used (default: .writing). It is appended to the filename while the file is being written. To customize the suffix, you can set the temporary-file-suffix attribute on both the File Outbound Channel Adapter and the File Outbound Gateway.

	Note
	When using the APPEND file mode, the temporary-file-suffix attribute is ignored, since the data is appended to the file directly.

Starting with version 4.2.5 the generated file name (as a result of filename-generator/filename-generator-expression evaluation) can represent a sub-path together with the target file name. It is used as a second constructor argument for File(File parent, String child) as before, but in the past we didn’t created (mkdirs()) directories for sub-path assuming only the file name. This approach is useful for cases when we need to restore the file system tree according the source directory. For example we unzipping the archive and want to save all file in the target directory at the same order.

Both, the File Outbound Channel Adapter and the File Outbound Gateway provide two configuration attributes for specifying the output directory:

	Note
	The directory-expression attribute is available since Spring Integration 2.2.

Using the directory attribute

When using the directory attribute, the output directory will be set to a fixed value, that is set at initialization time of the FileWritingMessageHandler. If you don’t specify this attribute, then you must use the directory-expression attribute.

Using the directory-expression attribute

If you want to have full SpEL support you would choose the directory-expression attribute. This attribute accepts a SpEL expression that is evaluated for each message being processed. Thus, you have full access to a Message’s payload and its headers to dynamically specify the output file directory.

The SpEL expression must resolve to either a String or to java.io.File. Furthermore the resulting String or File must point to a directory. If you don’t specify the directory-expression attribute, then you must set the directory attribute.

Using the auto-create-directory attribute

If the destination directory does not exists, yet, by default the respective destination directory and any non-existing parent directories are being created automatically. You can set the auto-create-directory attribute to false in order to prevent that. This attribute applies to both, the directory and the directory-expression attribute.

Note

When using the directory attribute and auto-create-directory is false, the following change was made starting with Spring Integration 2.2: Instead of checking for the existence of the destination directory at initialization time of the adapter, this check is now performed for each message being processed. Furthermore, if auto-create-directory is true and the directory was deleted between the processing of messages, the directory will be re-created for each message being processed.

When writing files and the destination file already exists, the default behavior is to overwrite that target file. This behavior, though, can be changed by setting the mode attribute on the respective File Outbound components. The following options exist:

	Note
	The mode attribute and the options APPEND, FAIL and IGNORE, are available since Spring Integration 2.2.

REPLACE

If the target file already exists, it will be overwritten. If the mode attribute is not specified, then this is the default behavior when writing files.

APPEND

This mode allows you to append Message content to the existing file instead of creating a new file each time. Note that this attribute is mutually exclusive with temporary-file-suffix attribute since when appending content to the existing file, the adapter no longer uses a temporary file. The file is closed after each message.

APPEND_NO_FLUSH

This has the same semantics as APPEND but the data is not flushed and the file is not closed after each message. This can provide a significant performance at the risk of data loss in the case of a failure. See Section 14.3.4, “Flushing Files When using APPEND_NO_FLUSH” for more information.

FAIL

If the target file exists, a MessageHandlingException is thrown.

IGNORE

If the target file exists, the message payload is silently ignored.

	Note
	When using a temporary file suffix (default: .writing), the IGNORE mode will apply if the final file name exists, or the temporary file name exists.

The APPEND_NO_FLUSH mode was added in version 4.3. This can improve performance because the file is not closed after each message. However, this can cause data loss in the event of a failure.

Several flushing strategies, to mitigate this data loss, are provided:

The predicates are called for each open file. See the java docs for these interfaces for more information.

When using flushInterval, the interval starts at the last write - the file is flushed only if it is idle for the interval. Starting with version 4.3.7, and additional property flushWhenIdle can be set to false, meaning that the interval starts with the first write to a previously flushed (or new) file.

By default, the destination file lastModified timestamp will be the time the file was created (except a rename in-place will retain the current timestamp). Starting with version 4.3, you can now configure preserve-timestamp (or setPreserveTimestamp(true) when using Java configuration). For File payloads, this will transfer the timestamp from the inbound file to the outbound (regardless of whether a copy was required). For other payloads, if the FileHeaders.SET_MODIFIED header (file_setModified) is present, it will be used to set the destination file’s lastModified timestamp, as long as the header is a Number.

<int-file:outbound-channel-adapter id="filesOut" directory="${input.directory.property}"/>

The namespace based configuration also supports a delete-source-files attribute. If set to true, it will trigger the deletion of the original source files after writing to a destination. The default value for that flag is false.

<int-file:outbound-channel-adapter id="filesOut"
    directory="${output.directory}"
    delete-source-files="true"/>

	Note
	The delete-source-files attribute will only have an effect if the inbound Message has a File payload or if the FileHeaders.ORIGINAL_FILE header value contains either the source File instance or a String representing the original file path.

Starting with version 4.2 The FileWritingMessageHandler supports an append-new-line option. If set to true, a new line is appended to the file after a message is written. The default attribute value is false.

<int-file:outbound-channel-adapter id="newlineAdapter"
	append-new-line="true"
    directory="${output.directory}"/>

In cases where you want to continue processing messages based on the written file, you can use the outbound-gateway instead. It plays a very similar role as the outbound-channel-adapter. However, after writing the file, it will also send it to the reply channel as the payload of a Message.

<int-file:outbound-gateway id="mover" request-channel="moveInput"
    reply-channel="output"
    directory="${output.directory}"
    mode="REPLACE" delete-source-files="true"/>

As mentioned earlier, you can also specify the mode attribute, which defines the behavior of how to deal with situations where the destination file already exists. Please see Section 14.3.3, “Dealing with Existing Destination Files” for further details. Generally, when using the File Outbound Gateway, the result file is returned as the Message payload on the reply channel.

This also applies when specifying the IGNORE mode. In that case the pre-existing destination file is returned. If the payload of the request message was a file, you still have access to that original file through the Message Header FileHeaders.ORIGINAL_FILE.

	Note
	The outbound-gateway works well in cases where you want to first move a file and then send it through a processing pipeline. In such cases, you may connect the file namespace’s inbound-channel-adapter element to the outbound-gateway and then connect that gateway’s reply-channel to the beginning of the pipeline.

If you have more elaborate requirements or need to support additional payload types as input to be converted to file content you could extend the FileWritingMessageHandler, but a much better option is to rely on a Transformer.

The following Spring Boot application provides an example of configuring the inbound adapter using Java configuration:

@SpringBootApplication
@IntegrationComponentScan
public class FileWritingJavaApplication {

    public static void main(String[] args) {
        ConfigurableApplicationContext context =
                      new SpringApplicationBuilder(FileWritingJavaApplication.class)
                              .web(false)
                              .run(args);
             MyGateway gateway = context.getBean(MyGateway.class);
             gateway.writeToFile("foo.txt", new File(tmpDir.getRoot(), "fileWritingFlow"), "foo");
    }

    @Bean
    @ServiceActivator(inputChannel = "writeToFileChannel")
    public MessageHandler fileWritingMessageHandler() {
         Expression directoryExpression = new SpelExpressionParser().parseExpression("headers.directory");
         FileWritingMessageHandler handler = new FileWritingMessageHandler(directoryExpression);
         handler.setFileExistsMode(FileExistsMode.APPEND);
         return handler;
    }

    @MessagingGateway(defaultRequestChannel = "writeToFileChannel")
    public interface MyGateway {

        void writeToFile(@Header(FileHeaders.FILENAME) String fileName,
                       @Header(FileHeaders.FILENAME) File directory, String data);

    }
}

The following Spring Boot application provides an example of configuring the inbound adapter using the Java DSL:

@SpringBootApplication
public class FileWritingJavaApplication {

    public static void main(String[] args) {
        ConfigurableApplicationContext context =
                 new SpringApplicationBuilder(FileWritingJavaApplication.class)
                         .web(false)
                         .run(args);
        MessageChannel fileWritingInput = context.getBean("fileWritingInput", MessageChannel.class);
        fileWritingInput.send(new GenericMessage<>("foo"));
    }

    @Bean
   	public IntegrationFlow fileWritingFlow() {
   	    return IntegrationFlows.from("fileWritingInput")
   		        .enrichHeaders(h -> h.header(FileHeaders.FILENAME, "foo.txt")
   		                  .header("directory", new File(tmpDir.getRoot(), "fileWritingFlow")))
   	            .handleWithAdapter(a -> a.fileGateway(m -> m.getHeaders().get("directory")))
   	            .channel(MessageChannels.queue("fileWritingResultChannel"))
   	            .get();
    }

}