我一直在寻找正确的方法来转换我的Student对象（带有嵌套Marks反对JSON format.
我尝试将获取类型组合为LAZY and EAGER，但这无济于事。得到StackOverflowException.
一段时间后，我找到了一个解决方案 - >使用注释@JsonIgnore嵌套中Marks对象，并把Students and Marks反对JSON分别作为下一个字符串：
String jsonStringStud = new ObjectMapper().writeValueAsString(student);
String jsonStringMarks = new ObjectMapper().writeValueAsString(student.getCtlgMarks());
之后我必须添加Marks代替Students，但我怀疑这是不好的做法。
这是我的期望：
String jsonStringStud = new ObjectMapper().writeValueAsString(student);
预期输出：Students{studentId=1, StudentName=Alex, ctlgMarks=Marks{marksId=1, markValue=Bad}}
您能否查看我的代码，并让我知道是否有正确的方法将我的对象转换为JSON format?
如果您编写“类似的”代码或之前/之后的代码，这将非常有帮助。
这是我的代码：
Table Student
CREATE TABLE "student" (
"id" INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT UNIQUE,
"name" NVARCHAR NOT NULL UNIQUE,
"marks_fk" INTEGER NOT NULL,
FOREIGN KEY("marks_fk") REFERENCES "ctlg_marks"("id")
);
Table Marks
CREATE TABLE "ctlg_marks" (
"id" INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT UNIQUE,
"mark_value" NVARCHAR NOT NULL UNIQUE
);
Entity Students
package entities;
import com.fasterxml.jackson.annotation.JsonIgnore;
import com.fasterxml.jackson.annotation.JsonPropertyOrder;
import java.io.Serializable;
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;
import lombok.AllArgsConstructor;
import lombok.Getter;
import lombok.Setter;
@Getter
@Setter
@AllArgsConstructor
@Entity
@Table(name = "student")
@JsonPropertyOrder({"id","name","ctlgMarks"})
public class Students implements Serializable {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "id")
private int studentId;
@Column(name = "name")
private String studentName;
@ManyToOne(cascade = CascadeType.ALL)
@JoinColumn(name = "marks_fk")
@JsonIgnore
private Marks ctlgMarks = new Marks();
public Students() {
}
@Override
public String toString() {
return "Students{" + "studentId=" + studentId +
", studentName=" + studentName +
", ctlgMarks=" + ctlgMarks + '}';
}
}
Entity Marks
package entities;
import java.io.Serializable;
import java.util.HashSet;
import java.util.Set;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;
import lombok.AllArgsConstructor;
import lombok.Getter;
import lombok.Setter;
import org.hibernate.annotations.Cascade;
@Getter
@Setter
@AllArgsConstructor
@Entity
@Table(name = "ctlg_marks")
public class Marks implements Serializable {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "id")
private int marksId;
@Column(name = "mark_value")
private String markValue;
@Cascade(org.hibernate.annotations.CascadeType.SAVE_UPDATE)
@OneToMany(mappedBy = "ctlgMarks", fetch = FetchType.LAZY)
private Set<Students> students = new HashSet<>();
public Marks() {
}
@Override
public String toString() {
return "Marks{" + "marksId=" + marksId +
", markValue=" + markValue + '}';
}
}
这是我用来获取的方法Student通过 id 获取对象并将其转换为JSON.
public String readWithinSession(int id) {
Students student = new Students();
String str = "";
SessionFactory factory1 = new Configuration()
.configure("hibernate.cfg.xml")
.addAnnotatedClass(Students.class)
.buildSessionFactory();
Session session = factory1.getCurrentSession();
try {
session.beginTransaction();
student = session.get(Students.class, id);
if (student != null) {
Hibernate.initialize(student.getCtlgMarks());
System.out.println("INITIALIZE USED");
}
//分别获取student和marks的json格式字符串
try {
String jsonStringStud = new ObjectMapper().writeValueAsString(student);
String jsonStringMarks = new ObjectMapper().writeValueAsString(student.getCtlgMarks());
/*
After getting json student string: {"studentId":1,"studentName":"Alex"}
After getting json marks string: {"marksId":1,"markValue":"Bad","students":[{"studentId":1,"studentName":"Alex"}]}
*/
//Separately get objects student and marks
try {
Students studObj = new ObjectMapper().readValue(jsonStringStud, Students.class);
Marks marksObj = new ObjectMapper().readValue(jsonStringMarks, Marks.class);
System.out.println("After got stud obj from string: " + studObj);
System.out.println("After got marks obj from string: " + marksObj);
/*
After getting stud obj from json string: Students{studentId=1, studentName=Alex, ctlgMarks=Marks{marksId=0, markValue=null}}
After getting marks obj from json string: Marks{marksId=1, markValue=Bad}
*/
//Join marks to student
studObj.setCtlgMarks(marksObj);
System.out.println("Student after got marks object" + studObj);
/*
Student after got marks objectStudents{studentId=1, studentName=Alex, ctlgMarks=Marks{marksId=1, markValue=Bad}}
*/
} catch (IOException ex) {
Logger.getLogger(StudentsDaoImpl.class.getName()).log(Level.SEVERE, null, ex);
}
} catch (JsonProcessingException ex) {
Logger.getLogger(Domain.class.getName()).log(Level.SEVERE, null, ex);
}
session.getTransaction().commit();
} finally {
factory1.close();
}
return str;
}
