Camel Spring DSL - FTP consumerTemplate.receive gives null Exchange

[hardikdesai81]

Hi folks,

I am using Camel with Spring DSL. I have implemented the FTP producer
correctly and I am able to generated a JSON object at runtime and send it to
an FTP Endpoint. However, when trying to consume that same JSON using
Consumer Template, I am facing a sporadic problem.

Following is my Spring context XML:
        <bean id="propertyConfigurer"
        
class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
                <property name="locations">
                        <list>
                                <value>classpath:ftp.properties</value>
                                <value>classpath:jdbc.properties</value>
                        </list>
                </property>
                <property name="ignoreUnresolvablePlaceholders" value="true" />
        </bean>

        <camel:camelContext id="camelContext">
                <camel:template id="camelTemplate" />
                <camel:consumerTemplate id="consumerTemplate" />
                <camel:endpoint id="myFTPEndpoint"
                
uri="${ftp.protocol}://${ftp.userName}@${ftp.host}${ftp.remoteDirectory}?password=${ftp.password}&amp;passiveMode=${ftp.passiveMode}&amp;download=${ftp.download}&amp;localWorkDirectory=${ftp.localWorkDirectory}"
/>
        </camel:camelContext>

Following is my Producer code which is working fine:
@Service
public class FtpSenderServiceImpl implements FtpSenderService {

        private final ProducerTemplate producerTemplate;
        private final Endpoint ftpEndpoint;
        
        @Autowired
        FtpSenderServiceImpl(ProducerTemplate producerTemplate, Endpoint
ftpEndpoint) {
                this.producerTemplate = producerTemplate;
                this.ftpEndpoint = ftpEndpoint;
        }

        @Override
        public void sendFile(File file) throws CamelExecutionException,
UnsupportedEncodingException {
                producerTemplate.sendBodyAndHeader(ftpEndpoint, file,
                                Exchange.FILE_NAME, file.getName());
        }
}

Following is my Consumer code:
@Service
public class FtpReceiverServiceImpl implements FtpReceiverService {

        private final ConsumerTemplate consumerTemplate;
        private final Endpoint ftpEndpoint;
        
        @Autowired
        FtpReceiverServiceImpl(ConsumerTemplate consumerTemplate, Endpoint
ftpEndpoint) {
                this.consumerTemplate = consumerTemplate;
                this.ftpEndpoint = ftpEndpoint;
        }

        @Override
        public List<String> receiveFiles() throws InterruptedException {
                List<String> files = new ArrayList<String>();
                Exchange ex = consumerTemplate.receive(ftpEndpoint, 5000);
                while(ex!=null) {
                        files.add((String) 
ex.getIn().getHeader("CamelFileName"));
                        ex = consumerTemplate.receive(ftpEndpoint, 5000);
                }
                return files;
        }
}

Basically, the receiveFiles() method should create a list of all files on
the FTP site. When I start my server, and immediately invoke my Service to
call receiveFiles(), then consumerTemplate.receive(ftpEndpoint, 5000)
returns a 'null' Exchange. 

But, if I wait for few seconds, and then execute the same
consumerTemplate.receive(ftpEndpoint, 5000), I am successfully able to fetch
the DefaultExchange object.

Why doesn't the consumerTemplate.receive(ftpEndpoint, 5000) return the valid
Exchange object in first attempt? Is there some configuration that I can set
in my FTP URI that can force it to invoke receive() only after a valid FTP
connection has been established?





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