I am working on a Spring-MVC application in which I am trying to search for List of GroupNotes in database. The mapping in my project is GroupCanvas has one-to-many mapping with GroupSection and GroupSection has one-to-many mapping with GroupNotes. Because of these mappings, I was getting LazyInitializationException. As suggested on SO, I should be converting the objects to a DTO objects for transfer. I checked on net, but couldnt find a suitable way to translate those.
I have just created a new List to avoid the error, but one field is still giving me an error. I would appreciate if anyone tells me either how to fix this error or convert the objects to a DTO objects so they can be transferred.
Controller code :
@RequestMapping(value = "/findgroupnotes/{days}/{canvasid}")
public @ResponseBody List<GroupNotes> findGroupNotesByDays(@PathVariable("days")int days, @PathVariable("canvasid")int canvasid){
List<GroupNotes> groupNotesList = this.groupNotesService.findGroupNotesByDays(days,canvasid);
List<GroupNotes> toSendList = new ArrayList<>();
for(GroupNotes groupNotes : groupNotesList){
GroupNotes toSendNotes = new GroupNotes();
toSendNotes.setMnotecolor(groupNotes.getMnotecolor());
toSendNotes.setNoteCreationTime(groupNotes.getNoteCreationTime());
toSendNotes.setMnotetag(groupNotes.getMnotetag());
toSendNotes.setMnotetext(groupNotes.getMnotetext());
toSendNotes.setAttachCount(groupNotes.getAttachCount());
toSendNotes.setNoteDate(groupNotes.getNoteDate());
toSendList.add(toSendNotes);
}
return toSendList;
}
GroupNotesDAOImpl :
@Override
public List<GroupNotes> searchNotesByDays(int days, int mcanvasid) {
Session session = this.sessionFactory.getCurrentSession();
Calendar cal = Calendar.getInstance();
cal.add(Calendar.DAY_OF_YEAR, -days);
long daysAgo = cal.getTimeInMillis();
Timestamp nowMinusDaysAsTimestamp = new Timestamp(daysAgo);
GroupCanvas groupCanvas = (GroupCanvas) session.get(GroupCanvas.class,mcanvasid);
Query query = session.createQuery("from GroupSection as n where n.currentcanvas.mcanvasid=:mcanvasid");
query.setParameter("mcanvasid", mcanvasid);
List<GroupSection> sectionList = query.list();
List<GroupNotes> notesList = new ArrayList<GroupNotes>();
for (GroupSection e : sectionList) {
System.out.println("Section name is "+e.getMsectionname());
GroupSection groupSection = (GroupSection) session.get(GroupSection.class,e.getMsectionid());
Query query1 = session.createQuery("from GroupNotes as gn where gn.ownednotes.msectionid=:msectionid and gn.noteCreationTime >:limit");
query1.setParameter("limit", nowMinusDaysAsTimestamp);
query1.setParameter("msectionid",e.getMsectionid());
notesList.addAll(query1.list());
}
// I am getting the data below, but I get JSON errors.
for(GroupNotes groupNotes : notesList){
System.out.println("Group notes found are "+groupNotes.getMnotetext());
}
return notesList;
}
GroupCanvas model :
@Entity
@Table(name = "membercanvas")
public class GroupCanvas{
@OneToMany(mappedBy = "currentcanvas",fetch=FetchType.LAZY, cascade = CascadeType.REMOVE)
@JsonIgnore
private Set<GroupSection> ownedsection = new HashSet<>();
@JsonIgnore
public Set<GroupSection> getOwnedsection() {
return this.ownedsection;
}
public void setOwnedsection(Set<GroupSection> ownedsection) {
this.ownedsection = ownedsection;
}
}
GroupSection model :
@Entity
@Table(name = "membersection")
public class GroupSection{
@OneToMany(mappedBy = "ownednotes", fetch = FetchType.EAGER,cascade = CascadeType.REMOVE)
@JsonIgnore
private Set<GroupNotes> sectionsnotes = new HashSet<>();
public Set<GroupNotes> getSectionsnotes(){
return this.sectionsnotes;
}
public void setSectionsnotes(Set<GroupNotes> sectionsnotes){
this.sectionsnotes=sectionsnotes;
}
}
GroupNotes model :
@Entity
@Table(name="groupnotes")
public class GroupNotes{
@Id
@Column(name="mnoteid")
@GeneratedValue(strategy = GenerationType.SEQUENCE,generator = "mnote_gen")
@SequenceGenerator(name = "mnote_gen",sequenceName = "mnote_seq")
@org.hibernate.annotations.Index(name = "mnoticesidindex")
private int mnoticesid;
@Column(name = "mnotetext")
private String mnotetext;
@Column(name = "mnoteheadline")
private String mnotetag;
@Column(name = "mnotecolor")
private String mnotecolor;
@Column(name = "mnoteorder")
private double mnoteorder;
@Column(name = "attachmentcount")
private int attachCount;
@Column(name = "notedate")
private String noteDate;
@Column(name = "uploader")
private String uploader;
@Column(name = "activeedit")
private boolean activeEdit;
@Column(name = "notedisabled")
private boolean noteDisabled;
@Column(name = "noteinactive")
private boolean noteInActive;
@Column(name = "notecreatoremail")
private String noteCreatorEmail;
@Column(name = "prefix")
private String prefix;
@Column(name = "timestamp")
private Timestamp noteCreationTime;
@Transient
private boolean notRead;
@Transient
private String tempNote;
@Transient
private String canvasUrl;
@ManyToOne
@JoinColumn(name = "msectionid")
@JsonIgnore
private GroupSection ownednotes;
@JsonIgnore
public GroupSection getOwnednotes(){return this.ownednotes;}
public void setOwnednotes(GroupSection ownednotes){this.ownednotes=ownednotes;}
@JsonIgnore
public int getOwnedSectionId(){
return this.ownednotes.getMsectionid();
}
@OneToMany(mappedBy = "mnotedata",fetch = FetchType.LAZY,cascade = CascadeType.REMOVE)
@JsonIgnore
private Set<GroupAttachments> mattachments = new HashSet<>();
public Set<GroupAttachments> getMattachments() {
return this.mattachments;
}
public void setMattachments(Set<GroupAttachments> mattachments) {
this.mattachments = mattachments;
}
@OneToMany(mappedBy = "mhistory",fetch = FetchType.LAZY,cascade = CascadeType.REMOVE)
@JsonIgnore
private Set<GroupNoteHistory> groupNoteHistorySet = new HashSet<>();
public Set<GroupNoteHistory> getGroupNoteHistorySet(){
return this.groupNoteHistorySet;
}
public void setGroupNoteHistorySet(Set<GroupNoteHistory> groupNoteHistorySet){
this.groupNoteHistorySet = groupNoteHistorySet;
}
@OneToMany(mappedBy = "unreadNotes",fetch = FetchType.LAZY,cascade = CascadeType.REMOVE)
@JsonIgnore
private Set<UnreadNotes> unreadNotesSet = new HashSet<>();
public Set<UnreadNotes> getUnreadNotesSet(){
return this.unreadNotesSet;
}
public void setUnreadNotesSet(Set<UnreadNotes> unreadNotesSet){
this.unreadNotesSet = unreadNotesSet;
}
//getters and setters ignored
}
Error log :
org.springframework.http.converter.HttpMessageNotWritableException: Could not write JSON: (was java.lang.NullPointerException) (through reference chain: java.util.ArrayList[0]->com.journaldev.spring.model.GroupNotes["ownedSectionId"]); nested exception is com.fasterxml.jackson.databind.JsonMappingException: (was java.lang.NullPointerException) (through reference chain: java.util.ArrayList[0]->com.journaldev.spring.model.GroupNotes["ownedSectionId"])
Kindly let me know what to do, as I am stuck on that error since some time.
What I think that happens is Jackson tries to serialize all fields in the hierarchy based on getter methods. In some situation NullPointerException is thrown in the following method:
@JsonIgnore
public int getOwnedSectionId(){
return this.ownednotes.getMsectionid();
}
replace it with the following method:
@JsonIgnore
public int getOwnedSectionId(){
if(this.ownednotes != null)
return this.ownednotes.getMsectionid();
return 1;
}
I don't have an explanation why jackson tries to serialize it when is market with @JsonIgnore but you can give a try with my proposal