string - PropertyNotFoundException：在类型 java.lang.String 上找不到属性“foo”

Question

我在这里看到了大量类似的问题，但他们没有给我答案，可能我错过了一个，这涵盖了我的情况。所以这是产生异常的代码部分：

<c:forEach var="srPeer" items="${preset_groups}">
    $("#preset_checkbox_" + "<c:out value='${srPeer.srPeerPK.peerGroupId}' />").attr("checked", true);
</c:forEach>

javax.el.PropertyNotFoundException: Property 'srPeerPK' not found on type java.lang.String

preset_groups会话中的变量存储。我是这样设置的：

Set<SrPeer> presetGroups = srPeerDao.findSelectedPresetPeerGroupsByFirm(intFirmID);
session.setAttribute(SessionAttributes.PRESET_GROUPS, presetGroups);

SrPeer班级：

@Entity
@Table(name = "SR_PEERS")
public class SrPeer implements Serializable {
    private static final long serialVersionUID = -6119498549478635542L;

    @EmbeddedId
    private SrPeerPK srPeerPK;

    @Column(name = "PEERGROUPNAME_UI")
    private String peerGroupNameUi;

    @Column(name = "PEER_FIRM_DATA_VALID")
    private String peerFirmDataValid;

    @Column(name = "PEER_FIRM_NAME")
    private String peerFirmName;

    @Column(name = "REPORT_VERSION")
    private String reportVersion;

    //Getters and Setters
}

SrPeerPK班级：

@Embeddable
public class SrPeerPK implements Serializable {
    private static final long serialVersionUID = -4539516420308504052L;

    @Column(name = "FIRM_ID")
    private Integer firmId;

    @Column(name = "PEERGROUP_ID")
    private Integer peerGroupId;

    @Column(name = "PEER_FIRM_ID")
    private Integer peerFirmId;

    //Getters and Setters
}

任何猜测是什么问题？