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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(); }
}
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