javax.xml.bind.JAXBContext string xml to object

I'm trying to cast an xml to an object and print idObject but always getting null value.

text.xml

<startProcessInstanceResponse xmlns="urn:wf">
    <idObject>ff8081814b34a0fc014b8975ef6b10c0</idObject>
    <idProcess>005486</idProcess>
</startProcessInstanceResponse>

StartProcessInstanceResponse.class

import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement(namespace="urn:wf")
public class StartProcessInstanceResponse {

    private String idObject;
    private String idProcess;

    public String getIdObject() {
        return idObject;
    }

    @XmlElement
    public void setIdObject(String idObject) {
        this.idObject = idObject;
    }

    public String getIdProcess() {
        return idProcess;
    }

    @XmlElement
    public void setIdProcess(String idProcess) {
        this.idProcess = idProcess;
    }

}

my test function

StartProcessInstanceResponse resp =null;
    try {
        String respStr = "";
        BufferedReader br = new BufferedReader(new FileReader("C:\\Users\\ismail\\Desktop\\test.xml"));

        String sCurrentLine;
        while ((sCurrentLine = br.readLine()) != null) {
            respStr+=sCurrentLine;
        }

        JAXBContext jaxbContext = JAXBContext.newInstance(StartProcessInstanceResponse.class);
        Unmarshaller jaxbUnmarshaller = jaxbContext.createUnmarshaller();
        resp = (StartProcessInstanceResponse) jaxbUnmarshaller.unmarshal(new ByteArrayInputStream(respStr.getBytes()));

        //the output is null
        System.out.print(resp.getIdProcess());
    } catch (Exception e) {
        e.printStackTrace();
    }