ObjectMapper 如何忽略字段大小写

ObjectMapper 忽略字段大小写

核心代码：

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

例子：

1. import com.fasterxml.jackson.databind.DeserializationFeature;
2. import com.fasterxml.jackson.databind.JsonMappingException;
3. import com.fasterxml.jackson.databind.MapperFeature;
4. import com.fasterxml.jackson.databind.ObjectMapper;
5. public class Test{
6. public static void main(String[] args) {
7. try {
8. A a = new A();
9. a.lastname = "jack";
10. ObjectMapper mapper = new ObjectMapper();
11. mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
12. mapper.configure(MapperFeature.ACCEPT_CASE_INSENSITIVE_PROPERTIES, true);
13. A2 convertValue = new A2();
14. mapper.updateValue(convertValue, a);
15. System.out.println(convertValue);
16. } catch (JsonMappingException e) {
17. e.printStackTrace();
18. }
19. }
20.  
21. public static class A{
22. String lastname;
23. public String getLastname() {
24. return lastname;
25. }
26.  
27. public void setLastname(String lastname) {
28. this.lastname = lastname;
29. }
30. }
31.  
32. public static class A2{
33. String lastName;
34.  
35. public String getLastName() {
36. return lastName;
37. }
38.  
39. public void setLastName(String lastName) {
40. this.lastName = lastName;
41. }
42.  
43. @Override
44. public String toString() {
45. return "A2 [lastName=" + lastName + "]";
46. }
47. }
48. }

ObjectMapper 的一些坑

相信做过Java 开发对这个类应该不陌生,没错,这个类是jackson提供的，主要是用来把对象转换成为一个json字符串返回到前端,

现在大部分数据交换都是以json来传输的,所以这个很重要,那你到底又对这个类有着有多少了解呢，下面我说一下我遇到的一些坑

首先，先把我要说的几个坑需要设置的属性贴出来先

1. ObjectMapper objectMapper = new ObjectMapper();
2.  
3. //序列化的时候序列对象的所有属性
4. objectMapper.setSerializationInclusion(Include.ALWAYS);
5.  
6. //反序列化的时候如果多了其他属性,不抛出异常
7. objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
8.  
9. //如果是空对象的时候,不抛异常
10. objectMapper.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);
11.  
12. //取消时间的转化格式,默认是时间戳,可以取消,同时需要设置要表现的时间格式
13. objectMapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
14. objectMapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"))

简单说一下这个类的基本用法，以下采用代码块加截图的形式来说明和部分文字件数

1. package com.shiro.test;
2. import java.text.SimpleDateFormat;
3. import java.util.Date;
4. import com.fasterxml.jackson.annotation.JsonInclude.Include;
5. import com.fasterxml.jackson.databind.DeserializationFeature;
6. import com.fasterxml.jackson.databind.ObjectMapper;
7. import com.fasterxml.jackson.databind.SerializationFeature;
8. public class Main2 {
9. public static void main(String[] args) throws Exception{
10. ObjectMapper objectMapper = new ObjectMapper();
11. //序列化的时候序列对象的所有属性
12. objectMapper.setSerializationInclusion(Include.ALWAYS);
13. //取消时间的转化格式,默认是时间戳,可以取消,同时需要设置要表现的时间格式
14. objectMapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
15. objectMapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"));
16.  
17. Person person = new Person(1, "zxc", new Date());
18. //这是最简单的一个例子,把一个对象转换为json字符串
19. String personJson = objectMapper.writeValueAsString(person);
20. System.out.println(personJson);
21.  
22. //默认为true,会显示时间戳
23. objectMapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, true);
24. personJson = objectMapper.writeValueAsString(person);
25. System.out.println(personJson);
26. }
27. }

输出的信息如下

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

1. package com.shiro.test;
2. import java.text.SimpleDateFormat;
3. import java.util.Date;
4. import com.fasterxml.jackson.annotation.JsonInclude.Include;
5. import com.fasterxml.jackson.databind.DeserializationFeature;
6. import com.fasterxml.jackson.databind.ObjectMapper;
7. import com.fasterxml.jackson.databind.SerializationFeature;
8. public class Main2 {
9. public static void main(String[] args) throws Exception{
10. ObjectMapper objectMapper = new ObjectMapper();
11. //序列化的时候序列对象的所有属性
12. objectMapper.setSerializationInclusion(Include.ALWAYS);
13. //如果是空对象的时候,不抛异常,也就是对应的属性没有get方法
14. objectMapper.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);
15.  
16. Person person = new Person(1, "zxc", new Date());
17.  
18. String personJson = objectMapper.writeValueAsString(person);
19. System.out.println(personJson);
20.  
21. //默认是true,即会抛异常
22. objectMapper.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, true);
23. personJson = objectMapper.writeValueAsString(person);
24. System.out.println(personJson);
25. }
26. }

对应的person类此时为

1. package com.shiro.test;
2. import java.util.Date;
3. public class Person {
4. private Integer id;
5. private String name;
6. private Date birthDate;
7. // public Integer getId() {
8. // return id;
9. // }
10. // public void setId(Integer id) {
11. // this.id = id;
12. // }
13. // public String getName() {
14. // return name;
15. // }
16. // public void setName(String name) {
17. // this.name = name;
18. // }
19. // public Date getBirthDate() {
20. // return birthDate;
21. // }
22. // public void setBirthDate(Date birthDate) {
23. // this.birthDate = birthDate;
24. // }
25. @Override
26. public String toString() {
27. return "Person [id=" + id + ", name=" + name + ", birthDate=" + birthDate + "]";
28. }
29. public Person(Integer id, String name, Date birthDate) {
30. super();
31. this.id = id;
32. this.name = name;
33. this.birthDate = birthDate;
34. }
35. public Person() {
36. // TODO Auto-generated constructor stub
37. }
38. }

结果如下

1. package com.shiro.test;
2. import com.fasterxml.jackson.annotation.JsonInclude.Include;
3. import com.fasterxml.jackson.databind.DeserializationFeature;
4. import com.fasterxml.jackson.databind.ObjectMapper;
5. public class Main2 {
6. public static void main(String[] args) throws Exception{
7. ObjectMapper objectMapper = new ObjectMapper();
8. //序列化的时候序列对象的所有属性
9. objectMapper.setSerializationInclusion(Include.ALWAYS);
10. //反序列化的时候如果多了其他属性,不抛出异常
11. objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
12.  
13. // Person person = new Person(1, "zxc", new Date());
14.  
15. // String personJson = objectMapper.writeValueAsString(person);
16. // System.out.println(personJson);
17.  
18. //注意,age属性是不存在在person对象中的
19. String personStr = "{\"id\":1,\"name\":\"zxc\",\"age\":\"zxc\"}";
20.  
21. Person person = objectMapper.readValue(personStr, Person.class);
22. System.out.println(person);
23.  
24. //默认为true
25. objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, true);
26. person = objectMapper.readValue(personStr, Person.class);
27. System.out.println(person);
28. }
29. }

执行后的结果如下

这些便是这几个属性的作用所以，由于第一个比较简单我就这样说一下吧

Include.ALWAYS 是序列化对像所有属性

Include.NON_NULL 只有不为null的字段才被序列化

Include.NON_EMPTY 如果为null或者 空字符串和空集合都不会被序列化

然后再说一下如何把一个对象集合转换为一个 Java里面的数组

1. package com.shiro.test;
2. import java.util.ArrayList;
3. import java.util.Date;
4. import java.util.List;
5. import com.fasterxml.jackson.annotation.JsonInclude.Include;
6. import com.fasterxml.jackson.core.type.TypeReference;
7. import com.fasterxml.jackson.databind.JavaType;
8. import com.fasterxml.jackson.databind.ObjectMapper;
9. public class Main2 {
10. public static void main(String[] args) throws Exception{
11. ObjectMapper objectMapper = new ObjectMapper();
12. //序列化的时候序列对象的所有属性
13. objectMapper.setSerializationInclusion(Include.NON_DEFAULT);
14.  
15. Person person1 = new Person(1, "zxc", new Date());
16. Person person2 = new Person(2, "ldh", new Date());
17.  
18. List<Person> persons = new ArrayList<>();
19. persons.add(person1);
20. persons.add(person2);
21.  
22. //先转换为json字符串
23. String personStr = objectMapper.writeValueAsString(persons);
24.  
25. //反序列化为List<user> 集合,1需要通过 TypeReference 来具体传递值
26. List<Person> persons2 = objectMapper.readValue(personStr, new TypeReference<List<Person>>() {});
27.  
28. for(Person person : persons2) {
29. System.out.println(person);
30. }
31.  
32. //2,通过 JavaType 来进行处理返回
33. JavaType javaType = objectMapper.getTypeFactory().constructParametricType(List.class, Person.class);
34. List<Person> persons3 = objectMapper.readValue(personStr, javaType);
35.  
36. for(Person person : persons3) {
37. System.out.println(person);
38. }
39. }
40. }

以上为个人经验，希望能给大家一个参考，也希望大家多多支持我们。

原文链接：https://blog.csdn.net/weixin_42713970/article/details/88061100