[英]Spring-MVC, Hibernate : Creating DTO objects from Domain objects
我正在开发一个Spring-MVC应用程序,在该应用程序中我试图在数据库中搜索GroupNotes列表。 我项目中的映射是GroupCanvas具有与GroupSection的一对多映射,而GroupSection具有与GroupNotes的一对多映射。 由于这些映射,我得到了LazyInitializationException。 正如在SO上建议的那样,我应该将对象转换为DTO对象以进行传输。 我在网上检查过,但找不到合适的方法来翻译这些内容。
我刚刚创建了一个新列表来避免该错误,但是一个字段仍然给我一个错误。 如果有人告诉我如何解决此错误或将对象转换为DTO对象以便可以传输它们,我将不胜感激。
控制器代码:
@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模型:
@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模型:
@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模型:
@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
}
错误日志:
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"])
请让我知道该怎么办,因为一段时间以来我一直坚持该错误。
我认为发生的事情是Jackson尝试基于getter方法序列化层次结构中的所有字段。 在某些情况下,可以通过以下方法抛出NullPointerException
:
@JsonIgnore
public int getOwnedSectionId(){
return this.ownednotes.getMsectionid();
}
用以下方法替换它:
@JsonIgnore
public int getOwnedSectionId(){
if(this.ownednotes != null)
return this.ownednotes.getMsectionid();
return 1;
}
我没有解释为什么杰克逊在使用@JsonIgnore上市时为何尝试对其进行序列化,但是您可以尝试一下我的建议
如果有人告诉我如何解决此错误或将对象转换为DTO对象以便可以传输它们,我将不胜感激。
为此 ,我们在工作中使用DozerMapper 。
与其手动进行映射, 不如看看Blaze-Persistence实体视图 ,该视图可用于通过JPA有效地实现DTO模式。 这里有一个快速的代码示例如何解决您的问题
首先,您将DTO定义为实体视图
@EntityView(GroupNotes.class)
public interface GroupNoteView {
@IdMapping("mnoticesid") int getId();
String getMnotecolor();
String getMnotetag();
String getMnotetext();
String getNoteDate();
Timestamp getNoteCreationTime();
int getAttachCount();
}
接下来,调整您的DAO以使用它
@Override
public List<GroupNoteView> searchNotesByDays(int days, int mcanvasid) {
EntityManager entityManager = // get the entity manager from somewhere
CriteriaBuilderFactory cbf = // factory for query building from Blaze-Persistence
EntityViewManager evm = // factory for applying entity views on query builders
Calendar cal = Calendar.getInstance();
cal.add(Calendar.DAY_OF_YEAR, -days);
long daysAgo = cal.getTimeInMillis();
Timestamp nowMinusDaysAsTimestamp = new Timestamp(daysAgo);
CriteriaBuilder<GroupNotes> cb = cbf.create(entityManager, GroupNotes.class, "note")
.where("noteCreationTime").gt(nowMinusDaysAsTimestamp)
.where("ownednotes.ownedcanvas.mcanvasid").eq(mcanvasid);
return evm.applySetting(EntityViewSetting.create(GroupNoteView.class), cb)
.getResultList();
}
最后是调用代码
@RequestMapping(value = "/findgroupnotes/{days}/{canvasid}")
public @ResponseBody List<GroupNoteView> findGroupNotesByDays(@PathVariable("days")int days, @PathVariable("canvasid")int canvasid){
return this.groupNotesService.findGroupNotesByDays(days, canvasid);
}
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