Gson转换返回空Java对象

我正在尝试使用Gson在Java bean中转换json字符串，但它是returnig null值。

public static void convert(String args) {
    String json =
                "{"body":{"response":{"total":"294","num":"294","filelist":[{"id":"56712","camname":"Camera1","camid":"514","start":"2016-07-08 12:00:38","end":"2016-07-08 12:03:00","stream":"3","recReason":"Activity","filename":"fs/514/2016-07-08/AD_1_1_3_2016_07_08_12_00_57.mrv","snapshot":"fs-1/514/2016-07-08/AD_1_1_3_2016_07_08_12_00_57.jpg","nvrip":"192.168.0.200:8095"},{"id":"56708","camname":"Camera1","camid":"514","start":"2016-07-08 11:58:14","end":"2016-07-08 12:00:36","stream":"3","recReason":"Activity","filename":"fs-1/514/2016-07-08/AD_1_1_3_2016_07_08_11_58_33.mrv","snapshot":"fs-1/514/2016-07-08/AD_1_1_3_2016_07_08_11_58_33.jpg","nvrip":"192.168.0.200:8095"},{"id":"56705","camname":"Camera1","camid":"514","start":"2016-07-08 11:55:49","end":"2016-07-08 11:58:11","stream":"3","recReason":"Activity","filename":"fs-1/514/2016-07-08/AD_1_1_3_2016_07_08_11_56_08.mrv","snapshot":"fs-1/514/2016-07-08/AD_1_1_3_2016_07_08_11_56_08.jpg","nvrip":"192.168.0.200:8095"},{"id":"56702","camname":"Camera1","camid":"514","start":"2016-07-08 11:53:25","end":"2016-07-08 11:55:47","stream":"3","recReason":"Activity","filename":"fs-1/514/2016-07-08/AD_1_1_3_2016_07_08_11_53_44.mrv","snapshot":"fs-/514/2016-07-08/AD_1_1_3_2016_07_08_11_53_44.jpg","nvrip":"192.168.0.200:8095"},{"id":"56699","camname":"Camera1","camid":"514","start":"2016-07-08 11:51:00","end":"2016-07-08 11:53:22","stream":"3","recReason":"Activity","filename":"fs/514/2016-07-08/AD_1_1_3_2016_07_08_11_51_19.mrv","snapshot":"fs-/514/2016-07-08/AD_1_1_3_2016_07_08_11_51_19.jpg","nvrip":"192.168.0.200:8095"}],"status":"OK"}}}";

    // Now do the magic.
    RecordingListResponseDTO data = new Gson().fromJson(json, RecordingListResponseDTO .class);

    // Show it.
    System.out.println("converted data :"+data);
}

我的Bean类正在关注。RecordingListResponseDTO

   public class RecordingListResponseDTO implements Serializable {
    private String status;
    private int total;
    private int num;
    List<FileListDTO> fileList;

    public RecordingListResponseDTO(){

    }
    public RecordingListResponseDTO(String status, int total, int num, List<FileListDTO> fileList) {
        this.status = status;
        this.total = total;
        this.num = num;
        this.fileList = fileList;
    }

    public String getStatus() {
        return status;
    }

    public void setStatus(String status) {
        this.status = status;
    }

    public int getTotal() {
        return total;
    }

    public void setTotal(int total) {
        this.total = total;
    }

    public int getNum() {
        return num;
    }

    public void setNum(int num) {
        this.num = num;
    }

    public List<FileListDTO> getFileList() {
        return fileList;
    }

    public void setFileList(List<FileListDTO> fileList) {
        this.fileList = fileList;
    }

    @Override
    public String toString() {
        return "RecordingListResponseDTO{" +
                "status='" + status + '\'' +
                ", total=" + total +
                ", num=" + num +

                ", fileList=" + fileList +
                '}';
    }}

FileListDTO.java

public class FileListDTO {
private int id;
private String camname;
private int camid;
private Date start;
private Date end;
private int stream;
private String recReason;
private String filename;
private String snapshot;
private String nvrip;

public FileListDTO(int id, String camname, Date start, int camid, Date end, int stream, String recReason, String filename, String snapshot, String nvrip) {
    this.id = id;
    this.camname = camname;
    this.start = start;
    this.camid = camid;
    this.end = end;
    this.stream = stream;
    this.recReason = recReason;
    this.filename = filename;
    this.snapshot = snapshot;
    this.nvrip = nvrip;
}

public int getId() {
    return id;
}

public void setId(int id) {
    this.id = id;
}

public String getCamname() {
    return camname;
}

public void setCamname(String camname) {
    this.camname = camname;
}

public int getCamid() {
    return camid;
}

public void setCamid(int camid) {
    this.camid = camid;
}

public Date getStart() {
    return start;
}

public void setStart(Date start) {
    this.start = start;
}

public Date getEnd() {
    return end;
}

public void setEnd(Date end) {
    this.end = end;
}

public int getStream() {
    return stream;
}

public void setStream(int stream) {
    this.stream = stream;
}

public String getRecReason() {
    return recReason;
}

public void setRecReason(String recReason) {
    this.recReason = recReason;
}

public String getFilename() {
    return filename;
}

public void setFilename(String filename) {
    this.filename = filename;
}

public String getSnapshot() {
    return snapshot;
}

public void setSnapshot(String snapshot) {
    this.snapshot = snapshot;
}

public String getNvrip() {
    return nvrip;
}

public void setNvrip(String nvrip) {
    this.nvrip = nvrip;
}

@Override
public String toString() {
    return "FileListDTO{" +
            "id=" + id +
            ", camname='" + camname + '\'' +
            ", camid=" + camid +
            ", start=" + start +
            ", end=" + end +
            ", stream=" + stream +
            ", recReason='" + recReason + '\'' +
            ", filename='" + filename + '\'' +
            ", snapshot='" + snapshot + '\'' +
            ", nvrip='" + nvrip + '\'' +
            '}';
}}

将Json字符串转换为Java对象后，我得到了空值。我做错了，请建议我。预先感谢。