将Entity对象转换为JSON [英] Convert Entity object to JSON
问题描述
我需要将实体对象转换为json。我把
I need to convert entity object to json. I put
<bean class = "org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter">
<property name="messageConverters">
<array>
<bean class = "org.springframework.http.converter.StringHttpMessageConverter">
<property name="supportedMediaTypes" value = "text/plain;charset=UTF-8" />
</bean>
<bean class="org.springframework.http.converter.json.MappingJacksonHttpMessageConverter">
<property name="supportedMediaTypes" value="application/json" />
<property name="objectMapper">
<ref bean="JacksonObjectMapper" />
</property>
</bean>
</array>
</property>
</bean>
<bean id="JacksonObjectMapper" class="org.codehaus.jackson.map.ObjectMapper" />
到servlet配置文件,所以Spring可以自动将对象转换为json格式。但是春天不会这样做。我还将jackson jar添加到项目中。
to servlet configuration file, so Spring could convert object to json format autonatically. But Spring does not do it. I also added jackson jar to project.
控制器方法
@RequestMapping(value = "/addData.html", method = RequestMethod.POST)
public @ResponseBody GroupStudent addNewGroup(@RequestBody GroupStudent group) {
return group;
}
GroupStudent
GroupStudent
@Entity
@Table(name = "GroupStudent")
@NamedQueries({
@NamedQuery(name = "GroupStudent.getAllGroups", // get all groups
query = "select g from GroupStudent g"),
@NamedQuery(name = "GroupStudent.getGroupByName", // get group by name
query = "select g from GroupStudent g where g.groupStudentNumber = :name")
})
public class GroupStudent implements Serializable {
public GroupStudent() {}
public GroupStudent(String groupStudentNumber) {
this.groupStudentNumber = groupStudentNumber;
}
// create connectivity with table Student
private Set<Student> students = new HashSet<Student>();
@OneToMany(mappedBy = "groupStudent", cascade = CascadeType.ALL, orphanRemoval = true)
public Set<Student> getStudents() {
return this.students;
}
public void setStudents(Set<Student> students) {
this.students = students;
}
@Id
@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "group_id_seq")
@SequenceGenerator(name = "group_id_seq", sequenceName = "GroupStudent_seq", allocationSize = 1)
@Column(name = "GroupStudentId")
public Long getGroupStudentId() {
return this.groupStudentId;
}
public void setGroupStudentId(Long groupStudentId) {
this.groupStudentId = groupStudentId;
}
@Column(name = "GroupStudentNumber")
public String getGroupStudentNumber() {
return this.groupStudentNumber;
}
public void setGroupStudentNumber(String groupStudentNumber) {
this.groupStudentNumber = groupStudentNumber;
}
// table GroupStudent fields
private Long groupStudentId;
private String groupStudentNumber;
}
在浏览器中,我发现我有406错误和错误窗口错误[object Object]。
In browser I found that I have 406 error and error window error[object Object].
如果有人知道问题是什么,我会很乐意寻求帮助。
If anyone knows what the problem is, I will be gratfull for help.
谢谢。
推荐答案
如果您的对象加入了其他表,那么您只能在以下方式。
If your object joined other table then you can only do this in the following way.
首先,让我们注释与@JsonManagedReference,@ JsonBackReference的关系,让Jackson更好地处理这种关系:
First, let’s annotate the relationship with @JsonManagedReference, @JsonBackReference to allow Jackson to better handle the relation:
这是用户实体:
public class User {
public int id;
public String name;
@JsonBackReference
public List<Item> userItems;
}
和项目:
public class Item {
public int id;
public String itemName;
@JsonManagedReference
public User owner;
}
我们现在测试新实体:
@Test
public void
givenBidirectionRelation_whenUsingJacksonReferenceAnnotation_thenCorrect()
throws JsonProcessingException {
User user = new User(1, "John");
Item item = new Item(2, "book", user);
user.addItem(item);
String result = new ObjectMapper().writeValueAsString(item);
assertThat(result, containsString("book"));
assertThat(result, containsString("John"));
assertThat(result, not(containsString("userItems")));
}
以下是序列化的输出:
{
"id":2,
"itemName":"book",
"owner":
{
"id":1,
"name":"John"
}
}
请注意:
@JsonManagedReference是引用的前向部分 - 正常序列化的部分。
@JsonBackReference是引用的后半部分 - 它将从序列化中省略。
@JsonManagedReference is the forward part of reference – the one that gets serialized normally. @JsonBackReference is the back part of reference – it will be omitted from serialization.
引自下面的链接。您可以访问更多。
Quoted from the link below. You can visit for more.
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