FTP Outbound Channel Adapter

The FTP outbound channel adapter relies on a MessageHandler implementation that connects to the FTP server and initiates an FTP transfer for every file it receives in the payload of incoming messages. It also supports several representations of a file, so you are not limited only to java.io.File-typed payloads. The FTP outbound channel adapter supports the following payloads:

  • java.io.File: The actual file object

  • byte[]: A byte array that represents the file contents

  • java.lang.String: Text that represents the file contents

  • java.io.InputStream: a stream of data to transfer to remote file

  • org.springframework.core.io.Resource: a resource for data to transfer to remote file

The following example shows how to configure an outbound-channel-adapter:

<int-ftp:outbound-channel-adapter id="ftpOutbound"
    channel="ftpChannel"
    session-factory="ftpSessionFactory"
    charset="UTF-8"
    remote-file-separator="/"
    auto-create-directory="true"
    remote-directory-expression="headers['remote_dir']"
    temporary-remote-directory-expression="headers['temp_remote_dir']"
    filename-generator="fileNameGenerator"
    use-temporary-filename="true"
    chmod="600"
    mode="REPLACE"/>

The preceding configuration shows how you can configure an FTP outbound channel adapter by using the outbound-channel-adapter element while also providing values for various attributes, such as filename-generator (an implementation of the o.s.i.file.FileNameGenerator strategy interface), a reference to a session-factory, and other attributes. You can also see some examples of *expression attributes that let you use SpEL to configure settings such as remote-directory-expression, temporary-remote-directory-expression, and remote-filename-generator-expression (a SpEL alternative to filename-generator, shown in the preceding example). As with any component that allows the usage of SpEL, access to the payload and the message Headers is available through the 'payload' and 'headers' variables. See the schema for more details on the available attributes.

By default, if no file name generator is specified, Spring Integration uses o.s.i.file.DefaultFileNameGenerator. DefaultFileNameGenerator determines the file name based on the value of the file_name header (if it exists) in the MessageHeaders, or, if the payload of the Message is already a java.io.File, it uses the original name of that file.
Defining certain values (such as remote-directory) might be platform- or FTP server-dependent. For example, as was reported on forum.spring.io/showthread.php?p=333478&posted=1#post333478, on some platforms, you must add a slash to the end of the directory definition (for example, remote-directory="/thing1/thing2/" instead of remote-directory="/thing1/thing2").

Starting with version 4.1, you can specify the mode when transferring the file. By default, an existing file is overwritten. The modes are defined by the FileExistsMode enumeration, which includes the following values:

  • REPLACE (default)

  • REPLACE_IF_MODIFIED

  • APPEND

  • APPEND_NO_FLUSH

  • IGNORE

  • FAIL

IGNORE and FAIL do not transfer the file. FAIL causes an exception to be thrown, while IGNORE silently ignores the transfer (although a DEBUG log entry is produced).

Version 5.2 introduced the chmod attribute, which you can use to change the remote file permissions after upload. You can use the conventional Unix octal format (for example, 600 allows read-write for the file owner only). When configuring the adapter using java, you can use setChmodOctal("600") or setChmod(0600). Only applies if your FTP server supports the SITE CHMOD subcommand.

Avoiding Partially Written Files

One of the common problems that arises when dealing with file transfers is the possibility of processing a partial file. That is, a file might appear in the file system before its transfer is actually complete.

To deal with this issue, Spring Integration FTP adapters use a common algorithm: Files are transferred under a temporary name and then renamed once they are fully transferred.

By default, every file that is in the process of being transferred appears in the file system with an additional suffix, which, by default, is .writing. You can change this suffix by setting the temporary-file-suffix attribute.

However, there may be situations where you do not want to use this technique (for example, if the server does not permit renaming files). For situations like this, you can disable this feature by setting use-temporary-file-name to false (the default is true). When this attribute is false, the file is written with its final name and the consuming application needs some other mechanism to detect that the file is completely uploaded before accessing it.

Configuring with Java Configuration

The following Spring Boot application shows an example of how to configure the outbound adapter with Java configuration:

@SpringBootApplication
@IntegrationComponentScan
public class FtpJavaApplication {

    public static void main(String[] args) {
        ConfigurableApplicationContext context =
                    new SpringApplicationBuilder(FtpJavaApplication.class)
                        .web(false)
                        .run(args);
        MyGateway gateway = context.getBean(MyGateway.class);
        gateway.sendToFtp(new File("/foo/bar.txt"));
    }

    @Bean
    public SessionFactory<FTPFile> ftpSessionFactory() {
        DefaultFtpSessionFactory sf = new DefaultFtpSessionFactory();
        sf.setHost("localhost");
        sf.setPort(port);
        sf.setUsername("foo");
        sf.setPassword("foo");
        sf.setTestSession(true);
        return new CachingSessionFactory<FTPFile>(sf);
    }

    @Bean
    @ServiceActivator(inputChannel = "ftpChannel")
    public MessageHandler handler() {
        FtpMessageHandler handler = new FtpMessageHandler(ftpSessionFactory());
        handler.setRemoteDirectoryExpressionString("headers['remote-target-dir']");
        handler.setFileNameGenerator(new FileNameGenerator() {

            @Override
            public String generateFileName(Message<?> message) {
                 return "handlerContent.test";
            }

        });
        return handler;
    }

    @MessagingGateway
    public interface MyGateway {

         @Gateway(requestChannel = "toFtpChannel")
         void sendToFtp(File file);

    }
}

Configuring with the Java DSL

The following Spring Boot application shows an example of how to configure the outbound adapter using the Java DSL:

@SpringBootApplication
@IntegrationComponentScan
public class FtpJavaApplication {

    public static void main(String[] args) {
        ConfigurableApplicationContext context =
            new SpringApplicationBuilder(FtpJavaApplication.class)
                .web(false)
                .run(args);
        MyGateway gateway = context.getBean(MyGateway.class);
        gateway.sendToFtp(new File("/foo/bar.txt"));
    }

    @Bean
    public SessionFactory<FTPFile> ftpSessionFactory() {
        DefaultFtpSessionFactory sf = new DefaultFtpSessionFactory();
        sf.setHost("localhost");
        sf.setPort(port);
        sf.setUsername("foo");
        sf.setPassword("foo");
        sf.setTestSession(true);
        return new CachingSessionFactory<FTPFile>(sf);
    }

    @Bean
    public IntegrationFlow ftpOutboundFlow() {
        return IntegrationFlow.from("toFtpChannel")
                .handle(Ftp.outboundAdapter(ftpSessionFactory(), FileExistsMode.FAIL)
                        .useTemporaryFileName(false)
                        .fileNameExpression("headers['" + FileHeaders.FILENAME + "']")
                        .remoteDirectory(this.ftpServer.getTargetFtpDirectory().getName())
                ).get();
    }

    @MessagingGateway
    public interface MyGateway {

         @Gateway(requestChannel = "toFtpChannel")
         void sendToFtp(File file);

    }

}