使用Jackson进行JSON生成与解析的新手指南

<!-- 如果使用 Spring Boot Starter Web -->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>

ObjectMapper mapper = new ObjectMapper();
User user = new User("张三", 25);
String json = mapper.writeValueAsString(user);
// 输出：{"name":"张三","age":25}

String json = "{\"name\":\"李四\",\"age\":30}";
User user = mapper.readValue(json, User.class);

public class User {
    @JsonProperty("user_name")  // 自定义JSON字段名
    private String name;

    @JsonIgnore  // 忽略字段
    private String password;

    @JsonInclude(JsonInclude.Include.NON_NULL)  // 非空时序列化
    private String email;
}

public class Order {
    @JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss", timezone = "GMT+8")
    private LocalDateTime createTime;
}

@JsonTypeInfo(use = Id.NAME, property = "type")
@JsonSubTypes({
    @Type(value = Cat.class, name = "cat"),
    @Type(value = Dog.class, name = "dog")
})
public abstract class Animal {}

@Configuration
public class JacksonConfig {

    @Bean
    public ObjectMapper objectMapper() {
        return new ObjectMapper()
            .disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS)  // 日期不转时间戳
            .enable(DeserializationFeature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT)
            .setSerializationInclusion(JsonInclude.Include.NON_NULL);
    }
}

# application.yml
spring:
  jackson:
    date-format: yyyy-MM-dd HH:mm:ss
    time-zone: GMT+8
    default-property-inclusion: non_null
    deserialization:
      FAIL_ON_UNKNOWN_PROPERTIES: false  # 忽略未知字段

TypeReference<ResultDTO<List<User>>> typeRef = new TypeReference<>() {};
ResultDTO<List<User>> result = mapper.readValue(json, typeRef);

JsonFactory factory = mapper.getFactory();
try (JsonParser parser = factory.createParser(new File("large.json"))) {
    while (parser.nextToken() != null) {
        // 逐条处理
    }
}

public class MoneySerializer extends JsonSerializer<BigDecimal> {
    @Override
    public void serialize(BigDecimal value, JsonGenerator gen, SerializerProvider provider) {
        gen.writeString(value.setScale(2, RoundingMode.HALF_UP) + "元");
    }
}

// 使用注解
public class Product {
    @JsonSerialize(using = MoneySerializer.class)
    private BigDecimal price;
}

// 方法1：使用 @JsonIgnore 打断循环
public class Order {
    @JsonIgnore
    private User user;
}

// 方法2：配置全局忽略
mapper.configure(SerializationFeature.FAIL_ON_SELF_REFERENCES, false);

public enum Status {
    @JsonValue  // 序列化时使用 code
    OK(1), ERROR(2);

    private final int code;
    // 反序列化时根据 code 转换
    @JsonCreator
    public static Status fromCode(int code) { /* ... */ }
}

mapper.configure(JsonGenerator.Feature.ESCAPE_NON_ASCII, true);
// 输入：{"name":"张三"} → 输出：{"name":"\u5F20\u4E09"}

mapper.enable(MapperFeature.USE_ANNOTATIONS);
mapper.enable(MapperFeature.CAN_OVERRIDE_ACCESS_MODIFIERS);

ObjectMapper mapper = new ObjectMapper();
// 配置为线程安全
mapper.registerModule(new JavaTimeModule());
mapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);

<dependency>
    <groupId>com.fasterxml.jackson.datatype</groupId>
    <artifactId>jackson-datatype-jsr310</artifactId>
</dependency>

ObjectMapper mapper = new ObjectMapper().registerModule(new JavaTimeModule());

mapper.configure(JsonParser.Feature.ALLOW_EXTERNAL_PROCESSING, false);

// 启用类型检查
mapper.enableDefaultTyping(ObjectMapper.DefaultTyping.NON_FINAL);
// 或使用注解 @JsonTypeInfo