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java - Servlet Gson().toJson 死循环

转载 作者:数据小太阳 更新时间:2023-10-29 06:06:39 29 4
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我在 servlet 中遇到了一些问题,每次我更改下拉菜单中的选项时,一个不同的值将传递给 servlet,然后它会导致无限循环。当我没有更改下拉列表中的选项(值没有变化)时,没有错误。

这是我的代码:

我的Javascript:

<script>

function loadStaff(){
//dropdown
var positionDropDown = document.getElementById("positionsDropdown");
//value of the drop down
var positionID = positionDropDown.options[positionDropDown.selectedIndex].value;

$.getJSON('loadStaff?positionID=' + positionID, function(data) {
-- no populate code yet
});
}
</script>

我的 AjaxServlet:

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

String userPath = request.getServletPath();

if (userPath.equals("/loadStaff")) {

String positionID = request.getParameter("positionID");
Position position = positionFacade.find(Integer.parseInt(positionID));
Collection staffCollection = position.getStaffCollection();
List<Staff> staffList = new ArrayList(staffCollection);

String staffListJson = new Gson().toJson(staffList);
response.setContentType("application/json");
response.setCharacterEncoding("UTF-8");
response.getWriter().write(staffListJson);

}

}

调试时。错误出现在行:

String staffListJson = new Gson().toJson(staffList);

输出错误:

> INFO:   WebModule[null] ServletContext.log(): The server side
> component of the HTTP Monitor has detected a
> java.lang.StackOverflowError. This happens when there is an infinite
> loop in the web module. Correct the cause of the infinite loop before
> running the web module again.
>
> INFO: The server side component of the HTTP Monitor has detected a
> java.lang.StackOverflowError. This happens when there is an infinite
> loop in the web module. Correct the cause of the infinite loop before
> running the web module again. WARNING:
> StandardWrapperValve[AjaxServlet]: Servlet.service() for servlet
> AjaxServlet threw exception java.lang.StackOverflowError

> WARNING: StandardWrapperValve[AjaxServlet]: Servlet.service() for
> servlet AjaxServlet threw exception java.lang.StackOverflowError at
> sun.util.calendar.ZoneInfo.getOffsets(ZoneInfo.java:248) at
> java.util.GregorianCalendar.computeFields(GregorianCalendar.java:2276)
> at
> java.util.GregorianCalendar.computeFields(GregorianCalendar.java:2248)
> at java.util.Calendar.setTimeInMillis(Calendar.java:1140) at
> java.util.Calendar.setTime(Calendar.java:1106) at
> java.text.SimpleDateFormat.format(SimpleDateFormat.java:955) at
> java.text.SimpleDateFormat.format(SimpleDateFormat.java:948) at
> java.text.DateFormat.format(DateFormat.java:336) at
> com.google.gson.internal.bind.DateTypeAdapter.write(DateTypeAdapter.java:90)
> at
> com.google.gson.internal.bind.DateTypeAdapter.write(DateTypeAdapter.java:41)
> at
> com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)
> at
> com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.write(ReflectiveTypeAdapterFactory.java:89)
> at
> com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:195)
> at com.google.gson.Gson$FutureTypeAdapter.write(Gson.java:892) at
> com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)
> at
> com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.write(ReflectiveTypeAdapterFactory.java:89)
> at
> com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:195)
> at
> com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)
> at
> com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.write(ReflectiveTypeAdapterFactory.java:89)
> at
> com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:195)
> at com.google.gson.Gson$FutureTypeAdapter.write(Gson.java:892) at
> com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)
> at
> com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.write(ReflectiveTypeAdapterFactory.java:89)
> at
> com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:195)
> at
> com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)
> at
> com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.write(ReflectiveTypeAdapterFactory.java:89)
> at
> com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:195)
> at com.google.gson.Gson$FutureTypeAdapter.write(Gson.java:892)

我还注意到这个跟踪只是堆栈跟踪的重复输出;

编辑:员工类

@Entity
public class Staff implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Basic(optional = false)
@Column(name = "id")
private Integer id;
@Basic(optional = false)
@NotNull
@Size(min = 1, max = 45)
@Column(name = "last_name")
private String lastName;
@Basic(optional = false)
@NotNull
@Size(min = 1, max = 45)
@Column(name = "first_name")
private String firstName;
@Size(max = 45)
@Column(name = "middle_name")
private String middleName;
@Basic(optional = false)
@NotNull
@Size(min = 1, max = 6)
@Column(name = "gender")
private String gender;
@Basic(optional = false)
@NotNull
@Column(name = "date_of_birth")
@Temporal(TemporalType.DATE)
private Date dateOfBirth;
@Basic(optional = false)
@NotNull
@Size(min = 1, max = 45)
@Column(name = "nationality")
private String nationality;
@Basic(optional = false)
@NotNull
@Column(name = "date_hired")
@Temporal(TemporalType.TIMESTAMP)
private Date dateHired;
@Size(max = 20)
@Column(name = "status")
private String status;
@OneToMany(cascade = CascadeType.ALL, mappedBy = "staff")
private Collection<StaffApointments> staffApointmentsCollection;
@OneToOne(cascade = CascadeType.ALL, mappedBy = "staff")
private StaffContact staffContact;
@JoinColumn(name = "account_id", referencedColumnName = "id")
@ManyToOne(optional = false)
private Account accountId;
@JoinColumn(name = "position_id", referencedColumnName = "id")
@ManyToOne(optional = false)
private Position positionId;

public Staff() {
}

public Staff(Integer id) {
this.id = id;
}

public Staff(Integer id, String lastName, String firstName, String gender, Date dateOfBirth, String nationality, Date dateHired) {
this.id = id;
this.lastName = lastName;
this.firstName = firstName;
this.gender = gender;
this.dateOfBirth = dateOfBirth;
this.nationality = nationality;
this.dateHired = dateHired;
}

public Integer getId() {
return id;
}

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

public String getLastName() {
return lastName;
}

public void setLastName(String lastName) {
this.lastName = lastName;
}

public String getFirstName() {
return firstName;
}

public void setFirstName(String firstName) {
this.firstName = firstName;
}

public String getMiddleName() {
return middleName;
}

public void setMiddleName(String middleName) {
this.middleName = middleName;
}

public String getGender() {
return gender;
}

public void setGender(String gender) {
this.gender = gender;
}

public Date getDateOfBirth() {
return dateOfBirth;
}

public void setDateOfBirth(Date dateOfBirth) {
this.dateOfBirth = dateOfBirth;
}

public String getNationality() {
return nationality;
}

public void setNationality(String nationality) {
this.nationality = nationality;
}

public Date getDateHired() {
return dateHired;
}

public void setDateHired(Date dateHired) {
this.dateHired = dateHired;
}

public String getStatus() {
return status;
}

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

@XmlTransient
public Collection<StaffApointments> getStaffApointmentsCollection() {
return staffApointmentsCollection;
}

public void setStaffApointmentsCollection(Collection<StaffApointments> staffApointmentsCollection) {
this.staffApointmentsCollection = staffApointmentsCollection;
}

public StaffContact getStaffContact() {
return staffContact;
}

public void setStaffContact(StaffContact staffContact) {
this.staffContact = staffContact;
}

public Account getAccountId() {
return accountId;
}

public void setAccountId(Account accountId) {
this.accountId = accountId;
}

public Position getPositionId() {
return positionId;
}

public void setPositionId(Position positionId) {
this.positionId = positionId;
}

@Override
public int hashCode() {
int hash = 0;
hash += (id != null ? id.hashCode() : 0);
return hash;
}

@Override
public boolean equals(Object object) {
// TODO: Warning - this method won't work in the case the id fields are not set
if (!(object instanceof Staff)) {
return false;
}
Staff other = (Staff) object;
if ((this.id == null && other.id != null) || (this.id != null && !this.id.equals(other.id))) {
return false;
}
return true;
}

@Override
public String toString() {
return "entity.Staff[ id=" + id + " ]";
}

}

这也是 Position 类:

@Entity
public class Position implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Basic(optional = false)
@Column(name = "id")
private Integer id;
@Basic(optional = false)
@NotNull
@Size(min = 1, max = 45)
@Column(name = "name")
private String name;
@OneToMany(cascade = CascadeType.ALL, mappedBy = "positionId")
private Collection<Staff> staffCollection;

public Position() {
}

public Position(Integer id) {
this.id = id;
}

public Position(Integer id, String name) {
this.id = id;
this.name = name;
}

public Integer getId() {
return id;
}

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

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

@XmlTransient
public Collection<Staff> getStaffCollection() {
return staffCollection;
}

public void setStaffCollection(Collection<Staff> staffCollection) {
this.staffCollection = staffCollection;
}

@Override
public int hashCode() {
int hash = 0;
hash += (id != null ? id.hashCode() : 0);
return hash;
}

@Override
public boolean equals(Object object) {
// TODO: Warning - this method won't work in the case the id fields are not set
if (!(object instanceof Position)) {
return false;
}
Position other = (Position) object;
if ((this.id == null && other.id != null) || (this.id != null && !this.id.equals(other.id))) {
return false;
}
return true;
}

@Override
public String toString() {
return "entity.Position[ id=" + id + " ]";
}

}

编辑 2:

除了 staffCollection 之外,我在 staff 类的属性中添加了 @expose。但我仍然有 1 个问题。每次选择下拉列表中的第一个值(值= 1)时,它仍然会出现无限循环错误。谁能帮帮我?

编辑 3:

修复了!我添加了 final GsonBuilder builder = new GsonBuilder(); builder.excludeFieldsWithoutExposeAnnotation();作为一个整体。现在可以了

最佳答案

问题是每个Staff对象包含一个包含 Collection 的 Position 对象的 Staff对象,每个对象包含一个 CollectionStaff再次对象等。GSON 将永远继续走这棵树,因为它永远不会停止。

要解决它,您可以查看 this 的答案。问题。

关于java - Servlet Gson().toJson 死循环,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/24094130/

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