springboot sftp integration unsatisfied dependency expressed through filed 'gateway' - spring-boot

Question

My spring-boot applications fails to start with the following exceptions:
Caused by: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'BatchConfiguration': Unsatisfied dependency expressed through field 'sftpProcessor'; nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'SFTPProcessor': Unsatisfied dependency expressed through field 'gateway'; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'com....SFTPProcessor$UploadGateway' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {#org.springframework.beans.factory.annotation.Autowired(required=true)}
...
Caused by: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'SFTPProcessor': Unsatisfied dependency expressed through field 'gateway'; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'com....SFTPProcessor$UploadGateway' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {#org.springframework.beans.factory.annotation.Autowired(required=true)}
And the class SFTPProcessor is a step of a spring boot batch application.
It complains that the gateway cannot be Autowired. However, I don't see any obvious problem with the code below.
I've searched on the internet some people talks about the messaginggateway and itemwriter are not in the same context.
How can I identify the root cause and fix this issue.
import com.jcraft.jsch.ChannelSftp.LsEntry;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Bean;
import org.springframework.core.io.Resource;
import org.springframework.expression.common.LiteralExpression;
import org.springframework.integration.annotation.Gateway;
import org.springframework.integration.annotation.MessagingGateway;
import org.springframework.integration.annotation.ServiceActivator;
import org.springframework.integration.file.FileNameGenerator;
import org.springframework.integration.file.remote.session.CachingSessionFactory;
import org.springframework.integration.file.remote.session.SessionFactory;
import org.springframework.integration.sftp.outbound.SftpMessageHandler;
import org.springframework.integration.sftp.session.DefaultSftpSessionFactory;
import org.springframework.messaging.Message;
import org.springframework.messaging.MessageHandler;
import org.springframework.stereotype.Component;
import java.io.File;
import java.io.IOException;
import java.nio.file.Path;
import java.nio.file.Paths;
#Component
public class SFTPProcessor {
#Value("${sftp.host}")
private String sftpHost;
#Value("${sftp.port:22}")
private int sftpPort;
#Value("${sftp.user}")
private String sftpUser;
#Value("${sftp.privateKey:#{null}}")
private Resource sftpPrivateKey;
#Value("${sftp.privateKeyPassphrase:}")
private String sftpPrivateKeyPassphrase;
#Value("${sftp.password:#{null}}")
private String sftpPasword;
#Value("${sftp.remote.directory:/}")
private String sftpRemoteDirectory;
#Autowired private UploadGateway gateway;
#Bean
public SessionFactory<LsEntry> sftpSessionFactory() {
DefaultSftpSessionFactory factory = new DefaultSftpSessionFactory(true);
factory.setHost(sftpHost);
factory.setPort(sftpPort);
factory.setUser(sftpUser);
if (sftpPrivateKey != null) {
factory.setPrivateKey(sftpPrivateKey);
factory.setPrivateKeyPassphrase(sftpPrivateKeyPassphrase);
} else if (sftpPasword != null) {
factory.setPassword(sftpPasword);
}
factory.setAllowUnknownKeys(true);
return new CachingSessionFactory<LsEntry>(factory);
}
#Bean
#ServiceActivator(inputChannel = "toSftpChannel")
public MessageHandler handler() {
SftpMessageHandler handler = new SftpMessageHandler(sftpSessionFactory());
handler.setRemoteDirectoryExpression(new LiteralExpression(sftpRemoteDirectory));
handler.setFileNameGenerator(
new FileNameGenerator() {
#Override
public String generateFileName(Message<?> message) {
if (message.getPayload() instanceof File) {
return ((File) message.getPayload()).getName();
} else {
throw new IllegalArgumentException("File expected as payload.");
}
}
});
return handler;
}
#MessagingGateway
public interface UploadGateway {
#Gateway(requestChannel = "toSftpChannel")
void upload(File file);
}
public void doSFTP(String fileName) throws IOException {
// Prepare phase
Path tempFile = Paths.get(fileName);
// Prerequisites
gateway.upload(tempFile.toFile());
}
}