Jackson消息转换器

本文主要是介绍Jackson消息转换器，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

Jackson

json的概念

json是一种应用广泛的数据交换格式，例如：

{"name": "admin","age": 20,"hobbies":["唱","跳","rap"]
}

Jackson就是将Java对象与Json数据进行相互转换的工具。

public class {private String name;private int age;private String[] hobbies
}

Jackson是Spring默认使用的Json转化器，有依赖少，稳定性高，API丰富等优点

使用方法：

引入依赖

<dependency><groupId>com.fasterxml.jackson.core</groupId><artifactId>jackson-core</artifactId>
</dependency><dependency><groupId>com.fasterxml.jackson.core</groupId><artifactId>jackson-annotations</artifactId>
</dependency><dependency><groupId>com.fasterxml.jackson.core</groupId><artifactId>jackson-databind</artifactId>
</dependency>
<!--对LocalDateTime等jdk8时间日期api的转化支持-->
<dependency><groupId>com.fasterxml.jackson.datatype</groupId><artifactId>jackson-datatype-jsr310</artifactId><version>2.10.1</version>
</dependency>

如果采用Spring boot框架开发，会自动引入Jackson的全部依赖

1. 序列化

Jackson需要使用ObjectMapper进行序列化，并且他是线程安全的，可以设定为成员变量

@SpringBootTest
class JacksonApplicationTests {private static final String DATE_TIME_FORMAT = "yyyy-MM--dd HH:mm:ss";//json转化器private static ObjectMapper objectMapper = new ObjectMapper();//全局配置序列化static {//设置为不包含null值objectMapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);//对于单个的bean进行配置可以在其实体类上添加@JsonInclude(JsonInclude.Include.NON_NULL)注解}/*** 序列化*/@Testvoid serializeTest() throws JsonProcessingException {User user = new User();String[] hobbies = {"sing","dance","rap"};//Jackson默认包含null值//user.setId(1L);user.setUsername("kunkun");user.setAge(22);user.setHobbies(hobbies);user.setRegisterDate(new Date());user.setBirthday(LocalDateTime.now());String json = objectMapper.writeValueAsString(user);System.out.println(json);}
}

2.对于日期格式化

//首先可以在实体类上添加注解
@JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss",timezone = "GMT+8")
private Date registerDate;@JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss",timezone = "GMT+8")
private LocalDateTime birthday;//修改全局配置
//自动通过spi发现jackson的module并注册
objcetMapper.findAndRegisterModules();
//手动配置JavaTimeModule
JavaTimeModule javaTimeModule = new JavaTimeModule( );
javaTimeModule.addSerializer(LocalDateTime.class，new LocalDateTimeSerializer(DateTimeFormatter.ofPattern(DATE_TIME_FORMAT)));
javaTimeModule.addDeserializer(LocalDateTime.class, new LocalDateTimeDeserializer(DateTimeFormatter.ofPattern(DATE_TIME_FORMAT)));
//注册
objectMapper.registerModule(javaTimeModule);

3. 反序列化

//前端传来的json字符串
String str = "Json字符串";
//需要传入json和指定的反序列化类型
User usedr = objectMapper.readValue(str, User.class);//忽略不存在的key，当json中含有实体类中不存在的属性，忽略
//FastJson默认就选择忽略
//在静态代码块中配置属性，这两种写法都可以
objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES,false);
objectMapper.disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);//对泛型的处理
String str = "前端传来的带有泛型的json";ResultDTO<User> userResultDTO = objectMapper.readValue(str, new TypeReference<ResultDTO<User>>()) {};

4. 通用配置

//通用配置统一在静态代码块中
//驼峰转下划线  userName <---> user_name
objectMapper.setPropertyNamingStrategy(PropertyNamingStrategy.SNAKE_CASE);//在实体类上标注@JsonIgnore  表示忽略该属性
@JsonIgnore
private String password;

5. 对象更新

//对象更新，如果后者有值，则使用后者，否则前者的值不变
@Test
void test() throws Exception {User originalUser = new User();originalUser.setId(1L);originalUser.setName("Angelday");originalUser.setAge(21);User newUser = new User();newUser.setId(2L);newUser.setAge(22);User updatedUser = objectMapper.updateValue(originalUser, newUser);//id: 2 name: Angelday age: 22System.out.println(updatedUser);
}

应用

我们自定义的Jackson配置信息可以写到配置文件中

# 设置日期格式  
spring.jackson.date-format=yyyy-MM-dd HH:mm:ss  # 设置时区  
spring.jackson.time-zone=Asia/Shanghai  # 忽略无法识别的字段  
spring.jackson.deserialization.fail-on-unknown-properties=false  # 忽略空值字段  
spring.jackson.default-property-inclusion=non_null

spring:  jackson:  date-format: yyyy-MM-dd HH:mm:ss  time-zone: Asia/Shanghai  deserialization:  fail-on-unknown-properties: false  default-property-inclusion: non_null

也可以自定义ObjectMapper Bean，SpringBoot会自动使用这个Bean来替代默认的ObjectMapper

@Configuration
public class JacksonConfig {  @Bean  public ObjectMapper jacksonObjectMapper(Jackson2ObjectMapperBuilder builder) {  return builder  .serializationInclusion(JsonInclude.Include.NON_NULL) //忽略空值  .featuresToDisable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS) //禁用时间戳 // 可以添加更多的自定义配置  .build();  }
}