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ObjectMapper 忽略字段大小寫

核心代碼：

ObjectMapper mapper = new ObjectMapper();
mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
mapper.configure(MapperFeature.ACCEPT_CASE_INSENSITIVE_PROPERTIES, true);

例子：

import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.MapperFeature;
import com.fasterxml.jackson.databind.ObjectMapper;
public class Test{
public static void main(String[] args) {
try {
A a = new A();
a.lastname = "jack";
ObjectMapper mapper = new ObjectMapper();
mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
mapper.configure(MapperFeature.ACCEPT_CASE_INSENSITIVE_PROPERTIES, true);
A2 convertValue = new A2();
mapper.updateValue(convertValue, a);
System.out.println(convertValue);
} catch (JsonMappingException e) {
e.printStackTrace();
}
}
public static class A{
String lastname;
public String getLastname() {
return lastname;
}
public void setLastname(String lastname) {
this.lastname = lastname;
}
}
public static class A2{
String lastName;
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
@Override
public String toString() {
return "A2 [lastName=" + lastName + "]";
}
}
}

ObjectMapper 的一些坑

相信做過Java 開發對這個類應該不陌生,沒錯,這個類是jackson提供的，主要是用來把對象轉換成為一個json字符串返回到前端,

現在大部分數據交換都是以json來傳輸的,所以這個很重要,那你到底又對這個類有著有多少了解呢，下面我說一下我遇到的一些坑

首先，先把我要說的幾個坑需要設置的屬性貼出來先

ObjectMapper objectMapper = new ObjectMapper();
//序列化的時候序列對象的所有屬性
objectMapper.setSerializationInclusion(Include.ALWAYS);
//反序列化的時候如果多了其他屬性,不拋出異常
objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
//如果是空對象的時候,不拋異常
objectMapper.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);
//取消時間的轉化格式,默認是時間戳,可以取消,同時需要設置要表現的時間格式
objectMapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
objectMapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"))

簡單說一下這個類的基本用法，以下采用代碼塊加截圖的形式來說明和部分文字件數

package com.shiro.test;
import java.text.SimpleDateFormat;
import java.util.Date;
import com.fasterxml.jackson.annotation.JsonInclude.Include;
import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;
public class Main2 {
public static void main(String[] args) throws Exception{
ObjectMapper objectMapper = new ObjectMapper();
//序列化的時候序列對象的所有屬性
objectMapper.setSerializationInclusion(Include.ALWAYS);
//取消時間的轉化格式,默認是時間戳,可以取消,同時需要設置要表現的時間格式
objectMapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
objectMapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"));
Person person = new Person(1, "zxc", new Date());
//這是最簡單的一個例子,把一個對象轉換為json字符串
String personJson = objectMapper.writeValueAsString(person);
System.out.println(personJson);
//默認為true,會顯示時間戳
objectMapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, true);
personJson = objectMapper.writeValueAsString(person);
System.out.println(personJson);
}
}

輸出的信息如下

ObjectMapper 如何忽略字段大小寫

objectMapper.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false)的作用

package com.shiro.test;
import java.text.SimpleDateFormat;
import java.util.Date;
import com.fasterxml.jackson.annotation.JsonInclude.Include;
import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;
public class Main2 {
public static void main(String[] args) throws Exception{
ObjectMapper objectMapper = new ObjectMapper();
//序列化的時候序列對象的所有屬性
objectMapper.setSerializationInclusion(Include.ALWAYS);
//如果是空對象的時候,不拋異常,也就是對應的屬性沒有get方法
objectMapper.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);
Person person = new Person(1, "zxc", new Date());
String personJson = objectMapper.writeValueAsString(person);
System.out.println(personJson);
//默認是true,即會拋異常
objectMapper.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, true);
personJson = objectMapper.writeValueAsString(person);
System.out.println(personJson);
}
}

對應的person類此時為

package com.shiro.test;
import java.util.Date;
public class Person {
private Integer id;
private String name;
private Date birthDate;
// 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;
// }
// public Date getBirthDate() {
// return birthDate;
// }
// public void setBirthDate(Date birthDate) {
// this.birthDate = birthDate;
// }
@Override
public String toString() {
return "Person [id=" + id + ", name=" + name + ", birthDate=" + birthDate + "]";
}
public Person(Integer id, String name, Date birthDate) {
super();
this.id = id;
this.name = name;
this.birthDate = birthDate;
}
public Person() {
// TODO Auto-generated constructor stub
}
}

結果如下

ObjectMapper 如何忽略字段大小寫

package com.shiro.test;
import com.fasterxml.jackson.annotation.JsonInclude.Include;
import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.ObjectMapper;
public class Main2 {
public static void main(String[] args) throws Exception{
ObjectMapper objectMapper = new ObjectMapper();
//序列化的時候序列對象的所有屬性
objectMapper.setSerializationInclusion(Include.ALWAYS);
//反序列化的時候如果多了其他屬性,不拋出異常
objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
// Person person = new Person(1, "zxc", new Date());
// String personJson = objectMapper.writeValueAsString(person);
// System.out.println(personJson);
//注意,age屬性是不存在在person對象中的
String personStr = "{\"id\":1,\"name\":\"zxc\",\"age\":\"zxc\"}";
Person person = objectMapper.readValue(personStr, Person.class);
System.out.println(person);
//默認為true
objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, true);
person = objectMapper.readValue(personStr, Person.class);
System.out.println(person);
}
}

執行后的結果如下

ObjectMapper 如何忽略字段大小寫

這些便是這幾個屬性的作用所以，由于第一個比較簡單我就這樣說一下吧

Include.ALWAYS 是序列化對像所有屬性

Include.NON_NULL 只有不為null的字段才被序列化

Include.NON_EMPTY 如果為null或者空字符串和空集合都不會被序列化

然后再說一下如何把一個對象集合轉換為一個 Java里面的數組

package com.shiro.test;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import com.fasterxml.jackson.annotation.JsonInclude.Include;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.JavaType;
import com.fasterxml.jackson.databind.ObjectMapper;
public class Main2 {
public static void main(String[] args) throws Exception{
ObjectMapper objectMapper = new ObjectMapper();
//序列化的時候序列對象的所有屬性
objectMapper.setSerializationInclusion(Include.NON_DEFAULT);
Person person1 = new Person(1, "zxc", new Date());
Person person2 = new Person(2, "ldh", new Date());
List<Person> persons = new ArrayList<>();
persons.add(person1);
persons.add(person2);
//先轉換為json字符串
String personStr = objectMapper.writeValueAsString(persons);
//反序列化為List<user> 集合,1需要通過 TypeReference 來具體傳遞值
List<Person> persons2 = objectMapper.readValue(personStr, new TypeReference<List<Person>>() {});
for(Person person : persons2) {
System.out.println(person);
}
//2,通過 JavaType 來進行處理返回
JavaType javaType = objectMapper.getTypeFactory().constructParametricType(List.class, Person.class);
List<Person> persons3 = objectMapper.readValue(personStr, javaType);
for(Person person : persons3) {
System.out.println(person);
}
}
}