詳解jackson註解(三)jackson包含屬性、忽略屬性的註解
jackson中,指定包含哪些屬性、忽略哪些屬性的註解:
註解類 | 描述 | |
---|---|---|
1 | JsonIgnoreProperties | 用於標記忽略一個或多個屬性。可以註解在類上、構造函數、方法、字段上。 |
2 | JsonIgnore | @JsonIgnore註解用於在字段級別標記要忽略的屬性。注意:系列化和反系列化時都會被忽略。 |
3 | JsonInclude | 使用@JsonInclude可以只包含非空的屬性,也即排除值爲empty、null的屬性。 |
4 | JsonAutoDetect | 默認情況下,jackson獲取public權限的字段進行系列化和反系列化。如果沒有public修飾的字段,就會去獲取public修飾的getter/setter。使用 JsonAutoDetect註解,我們就可以修改默認的行爲。 |
一、JsonIgnoreProperties
用於標記忽略一個或多個屬性。可以註解在類上、構造函數、方法、字段上。
import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.OneToMany;
import java.io.Serializable;
import java.util.HashSet;
import java.util.Set;
/**
* @author chushiyan
* @email [email protected]
* @description 自關聯的權限表。一個權限有一個父權限、多個子權限
*/
@Data
public class Permission implements Serializable {
private String id;
private String name;
@ManyToOne
@JoinColumn(name = "permission_parent_id", referencedColumnName = "permission_id")
private Permission parent;
// 必須使用JsonIgnoreProperties忽略parent屬性
// 否則查詢到子權限,子權限有parent屬性,又去查父權限,會導致系列化時出現死循環
@JsonIgnoreProperties(value = "parent")
@OneToMany(mappedBy = "parent")
private Set<Permission> children = new HashSet<Permission>();
}
二、JsonIgnore
@JsonIgnore註解用於在字段級別標記要忽略的屬性。注意:系列化和反系列化時都會被忽略。
1、bean
import com.fasterxml.jackson.annotation.JsonIgnore;
import lombok.Data;
import java.io.Serializable;
/**
* @author chushiyan
* @email [email protected]
* @description
*/
@Data
public class Article implements Serializable {
private String id;
private String name;
@JsonIgnore
private String category;
}
2、測試
@Test
public void testJsonIgnore() throws JsonProcessingException {
String json = "{"
+ "\"id\" : \"100\","
+ "\"name\" : \"詳解jackson註解","
+ "\"category\" : \"jackson\""
+ "}";
ObjectMapper mapper = new ObjectMapper();
Article article = mapper.readValue(json,Article.class);
System.out.println(article);
Article article2 = new Article();
article2.setId("100");
article2.setName("詳解jackson註解");
article2.setCategory("jackson");
String json2 = mapper.writeValueAsString(article2);
System.out.println(json2);
}
3、控制檯輸出
Article(id=100, name=詳解jackson註解, category=null)
{"id":"100","name":"詳解jackson註解"}
反系列化時,json數據中明明包含了category值,但是最後Article對象的category屬性值依然爲null。就是因爲使用了JsonIgnore。
三、JsonInclude
我們可以使用@JsonInclude排除某些empty、null、默認值的屬性。
import com.fasterxml.jackson.annotation.JsonInclude;
/**
* @author chushiyan
* @email [email protected]
* @description
*/
// 使用JsonInclude註解指明只包含非null的屬性,即排除值爲null的屬性
@JsonInclude(JsonInclude.Include.NON_NULL)
public class Result {
private boolean flag;// 是否成功
private Integer code;// 返回碼
private String message;// 返回信息
private Object data;// 返回數據
public Result() {
}
public Result(boolean flag, Integer code, String message) {
this.flag = flag;
this.code = code;
this.message = message;
}
public Result(boolean flag, Integer code, String message, Object data) {
this.flag = flag;
this.code = code;
this.message = message;
this.data = data;
}
public boolean isFlag() {
return flag;
}
public void setFlag(boolean flag) {
this.flag = flag;
}
public Integer getCode() {
return code;
}
public void setCode(Integer code) {
this.code = code;
}
public String getMessage() {
return message;
}
public void setMessage(String message) {
this.message = message;
}
public Object getData() {
return data;
}
public void setData(Object data) {
this.data = data;
}
@Override
public String toString() {
return "Result{" +
"flag=" + flag +
", code=" + code +
", message='" + message + '\'' +
", data=" + data +
'}';
}
}
2、controller
@GetMapping("/test8")
public Result testJsonInclude(){
return new Result(true,200,"查詢成功");
}
沒有在Result類上加 @JsonInclude(JsonInclude.Include.NON_NULL) 註解時,返回的響應:
{
"flag": true,
"code": 200,
"message": "查詢成功",
"data": null
}
加了之後的返回的響應:
{
"flag": true,
"code": 200,
"message": "查詢成功"
}
四、 JsonAutoDetect
默認情況下,jackson獲取public權限的字段進行系列化和反系列化。如果沒有public權限的字段,就會去獲取public修飾的getter/setter。使用 JsonAutoDetect註解,我們就可以修改默認的行爲。比如,下面的案例,即使字段都是private的、也沒有getter/setter,也照樣獲取字段。
1、bean
首先,我們定義一個屬性id/name都私有的而且沒有getter/setter的一個bean
import com.fasterxml.jackson.annotation.JsonAutoDetect;
import java.io.Serializable;
/**
* @author chushiyan
* @email [email protected]
* @description
*/
//@JsonAutoDetect(fieldVisibility = JsonAutoDetect.Visibility.ANY)
public class PrivateBean implements Serializable {
private String id;
private String name;
public PrivateBean() {
}
public PrivateBean(String id, String name) {
this.id = id;
this.name = name;
}
@Override
public String toString() {
return "PrivateBean{" +
"id='" + id + '\'' +
", name='" + name + '\'' +
'}';
}
}
2、反系列化測試:
@Test
public void testJsonAutoDetect() throws JsonProcessingException {
String json = "{"
+ "\"id\" : \"10\","
+ "\"name\" : \"chushiyan\""
+ "}";
ObjectMapper mapper = new ObjectMapper();
PrivateBean bean = mapper.readValue(json, PrivateBean.class);
System.out.println(bean);
}
報錯:
com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException: Unrecognized field "id" (class com.chushiyan.test.entity.PrivateBean), not marked as ignorable (0 known properties: ])
at [Source: (String)"{"id" : "10","name" : "chushiyan"}"; line: 1, column: 10] (through reference chain: com.chushiyan.test.entity.PrivateBean["id"])
3、系列化測試
@Test
public void testJsonAutoDetect2() throws JsonProcessingException {
ObjectMapper mapper = new ObjectMapper();
PrivateBean bean = new PrivateBean("11", "chushiyan");
String json = mapper.writeValueAsString(bean);
System.out.println(json);
}
報錯:
com.fasterxml.jackson.databind.exc.InvalidDefinitionException: No serializer found for class com.chushiyan.test.entity.PrivateBean and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS)
4、bean上加上註解
import com.fasterxml.jackson.annotation.JsonAutoDetect;
import java.io.Serializable;
/**
* @author chushiyan
* @email [email protected]
* @description
*/
@JsonAutoDetect(fieldVisibility = JsonAutoDetect.Visibility.ANY)
public class PrivateBean implements Serializable {
private String id;
private String name;
public PrivateBean() {
}
public PrivateBean(String id, String name) {
this.id = id;
this.name = name;
}
@Override
public String toString() {
return "PrivateBean{" +
"id='" + id + '\'' +
", name='" + name + '\'' +
'}';
}
}
5、再次分別測試反系列化、系列化
都運行正常,分別打印:
PrivateBean{id='10', name='chushiyan'}
{"id":"11","name":"chushiyan"}