Jackson应用指北
1. 概述
Jackson是目前在web开发中应用最多，速度最快的一种json序列化和反序列化框架。本文次要联合Jackson在我的项目中的理论应用进行介绍。
2. 字段疏忽
2.1 json转POJO时，疏忽某些字段
只须要在实体类上加上@JsonIgnoreProperties(ignoreUnknown = true)注解就能够。
2.2 POJO转json时，疏忽某些字段
@JsonIgnore注解用来疏忽某些字段，能够用在Field或者Getter办法上，用在Setter办法时，和Filed成果一样
3. json转换为POJO
3.1 json字符串间接转POJO
objectMapper.readValue(json, xxx.class)
实用于json字符串与POJO间接一一对应。
3.2 json字符串转JsonNode
JsonNode rootNode = objectMapper.readTree(json); // 获取其中某个字段的数据 JsonNode dataNode = rootNode.findValue("xxx"); // 将数据反序列化为POJO objectMapper.treeToValue(dataNode, xxx.class);实用于Json字符串的某一部分与JsonNode对应。先获取json响应中的某一部分数据，再将该数据转换为POJO
3.3 json转泛型类
AiReply<SensitiveImageReply> reply = objectMapper.readValue(json, new TypeReference<AiReply<SensitiveImageReply>>() {});3.4 json转数组和列表
List<Person> personList = new ArrayList<Person>() { { add(new Person("yangjian", 22)); add(new Person("zhanghaoman", 22)); } }; String personJson = this.objectMapper.writeValueAsString(personList); List<Person> persons = this.objectMapper.readValue(personJson, List.class); System.out.println("persons = " + persons);3.5 类拷贝
// 拷贝成map Person person = new Person("yangjian", 23); String json = this.objectMapper.writeValueAsString(person); Map<String, Object> map = this.objectMapper.convertValue(person, Map.class); // 链表到数组拷贝 List<String> list = new ArrayList<String>() { { add("one"); add("two"); } }; String[] strings = this.objectMapper.convertValue(list, String[].class); System.out.println("this.objectMapper.writeValueAsString(strings) = " + this.objectMapper.writeValueAsString(strings));4. POJO转换为json
4.1 设置视图
@JsonView(xxx.class)注解能够实现视图显示，序列化的json只会蕴含有雷同视图润饰的字段。并且，视图能够继承。此注解，POJO类上和controller的办法上都须要加。
4.2 自定义某个字段的序列化/反序列化形式
应用SpringMVC的@RestController时，咱们都晓得如果返回的是一个POJO，那么SpringMVC将会主动进行POJO的序列化。但有些时候咱们往往须要对该POJO某个字段的序列化和反序列化的形式进行一些批改，以满足咱们的业务需要。这时候就能够用到@JsonSerialize和@JsonDeserialize
用法：
POJO
/**
*
- @author rainbow
- @since 2020/3/20 10:56
*/
@Data
@EqualsAndHashCode(callSuper = false)
@Accessors(chain = true)
@JsonIgnoreProperties(ignoreUnknown = true)
@NoArgsConstructor
public class IdCardOcrData {
private String name; private String sex; private String nation; @JsonDeserialize(using = IdCardLocalDateDeserializer.class) @JsonSerialize(using = IdCardLocalDateSerializer.class) private LocalDate birth; private String address; private String id; private String authority; /** * 无效时限 */ private String valid_date;}
- IdCardLocalDateSerializer类/**
- @author rainbow
- @since 2020/3/20 16:25
*/
public class IdCardLocalDateSerializer extends JsonSerializer<LocalDate> {
@Override public void serialize(LocalDate value, JsonGenerator gen, SerializerProvider serializers) throws IOException { DateTimeFormatter timeFormatter = DateTimeFormatter.ofPattern("yyyy-MM-dd"); gen.writeString(timeFormatter.format(value)); }}
- IdCardLocalDateDeserializer类/**
- @author rainbow
- @since 2020/3/20 13:05
*/
public class IdCardLocalDateDeserializer extends JsonDeserializer<LocalDate> {
@Override public LocalDate deserialize(JsonParser p, DeserializationContext ctxt) throws IOException { String dateString = p.getText(); if (StringUtils.isNotBlank(dateString)) { String[] split = dateString.split("/"); return LocalDate.of(Integer.parseInt(split[0]), Integer.parseInt(split[1]), Integer.parseInt(split[2])); } return null; }}
以上的例子能够将 “2020/2/1” 格局的字符串反序列化为LocalDate类，并将其序列化为 “2020-02-02” 格局的json数据。### 4.3 自定义字段序列化形式@JsonFormat此注解用于属性或者办法上（最好是属性上），能够不便的把Date类型间接转化为咱们想要的模式，比方`@JsonFormat(pattern = "yyyy-MM-dd HH-mm-ss"， timezone = "GMT+8")`## 5. 自定义objectMapper应用SpringBoot主动拆卸的ObjectMapper在某些状况不太实用，比方它会将值为null的字段也进行序列化返回。因而，咱们对ObjectMapper进行设置，达到本人想要的成果。具体配置类为：@Configuration
public class JacksonConfig {
private static final String FORMAT = "yyyy-MM-dd HH:mm:ss";@Beanpublic Jackson2ObjectMapperBuilderCustomizer customizer() { return builder -> { builder.locale(Locale.CHINA); builder.timeZone(TimeZone.getTimeZone(ZoneId.systemDefault())); builder.simpleDateFormat(FORMAT); JavaTimeModule javaTimeModule = new JavaTimeModule(); javaTimeModule.addSerializer(LocalDateTime.class, new LocalDateTimeSerializer( DateTimeFormatter.ofPattern(FORMAT))); javaTimeModule.addSerializer(LocalDate.class, new LocalDateSerializer(DateTimeFormatter.ofPattern("yyyy-MM-dd"))); javaTimeModule.addSerializer(LocalTime.class, new LocalTimeSerializer(DateTimeFormatter.ofPattern("HH:mm:ss"))); javaTimeModule.addDeserializer(LocalDateTime.class, new LocalDateTimeDeserializer(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"))); javaTimeModule.addDeserializer(LocalDate.class, new LocalDateDeserializer(DateTimeFormatter.ofPattern("yyyy-MM-dd"))); javaTimeModule.addDeserializer(LocalTime.class, new LocalTimeDeserializer(DateTimeFormatter.ofPattern("HH:mm:ss"))); builder.modules(javaTimeModule); };}@Bean@Primarypublic ObjectMapper jacksonObjectMapper(Jackson2ObjectMapperBuilder builder){ ObjectMapper objectMapper = builder.createXmlMapper(false).build(); // 通过该办法对mapper对象进行设置，所有序列化的对象都将按改规定进行系列化 // Include.Include.ALWAYS 默认 // Include.NON_DEFAULT 属性为默认值不序列化 // Include.NON_EMPTY 属性为 空（""） 或者为 NULL 都不序列化，则返回的json是没有这个字段的 // Include.NON_NULL 属性为NULL 不序列化 objectMapper.setSerializationInclusion(JsonInclude.Include.NON_NULL); // 容许呈现特殊字符和本义符 objectMapper.configure(JsonParser.Feature.ALLOW_UNQUOTED_CONTROL_CHARS, true); // 容许呈现单引号 objectMapper.configure(JsonParser.Feature.ALLOW_SINGLE_QUOTES, true); //objectMapper.disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS); //objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false); /** * 将Long,BigInteger序列化的时候,转化为String */ // SimpleModule simpleModule = new SimpleModule(); // // simpleModule.addSerializer(Long.class, ToStringSerializer.instance); // simpleModule.addSerializer(Long.TYPE, ToStringSerializer.instance); // simpleModule.addSerializer(BigInteger.class, ToStringSerializer.instance); // // objectMapper.registerModule(simpleModule); return objectMapper;}}
该配置类能对类的`LocalDateTime`等新工夫类进行序列化，也能对序列化和反序列化解析形式进行设置。