Jackson序列化（1）— [SpringBoot2.x]-Jackson在HttpMessageConverter（消息转换器）中的使用
Jackson序列化（2）— [SpringBoot2.x]-Spring容器中ObjectMapper配置
Jackson序列化（3）— Jackson中ObjectMapper配置详解
Jackson序列化（4）— Jackson“默认的”时间格式化类—StdDateFormat解析
Jackson序列化（5） — Jackson的ObjectMapper.DefaultTyping.NON_FINAL属性
Jackson序列化（6）— Java使用Jackson进行序列化
上文说到，SpringBoot2.x会自动装载MappingJackson2HttpMessageConverter进行消息转换。而MappingJackson2HttpMessageConverter会获取Spring容器中的ObjectMapper配置，来进行Jackson的序列化和反序列化。
注意：在SpringBoot2.x环境下，不要将自定义的ObjectMapper对象放入Spring容器！这样会将原有的ObjectMapper配置覆盖。
ObjectMapper是JSON操作的核心，Jackson的JSON操作都是在ObjectMapper中实现的。
1. SpringBoot2.x中的ObjectMapper
SpringBoot2.x默认装载了ObjectMapper到Spring容器，在yml配置文件中使用spring.jackson为前缀的配置可以修改，也可以在代码中实现Jackson2ObjectMapperBuilderCustomizer接口去修改ObjectMapper配置。
@Configuration
//注解通俗的说就是Spring工程中引用了Jackson的包 才会构建这个bean
@ConditionalOnClass(ObjectMapper.class)
public class JacksonAutoConfiguration {
//默认的feature配置
private static final Map FEATURE_DEFAULTS;
//SpringBoot2.x配置WRITE_DATES_AS_TIMESTAMPS=false，即Date日期不会转换为时间戳类型
static {
Map featureDefaults = new HashMap<>();
featureDefaults.put(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
FEATURE_DEFAULTS = Collections.unmodifiableMap(featureDefaults);
}
@Bean
public JsonComponentModule jsonComponentModule() {
return new JsonComponentModule();
}
@Configuration
@ConditionalOnClass(Jackson2ObjectMapperBuilder.class)
static class JacksonObjectMapperConfiguration {
@Bean
@Primary
//若自定义ObjectMapper放入Spring容器中，该配置不会生效！
@ConditionalOnMissingBean
//获取Spring容器中的Jackson2ObjectMapperBuilder 。
public ObjectMapper jacksonObjectMapper(Jackson2ObjectMapperBuilder builder) {
return builder.createXmlMapper(false).build();
}
}
@Configuration
@ConditionalOnClass(Jackson2ObjectMapperBuilder.class)
static class JacksonObjectMapperBuilderConfiguration {
private final ApplicationContext applicationContext;
JacksonObjectMapperBuilderConfiguration(ApplicationContext applicationContext) {
this.applicationContext = applicationContext;
}
@Bean
//若自定义配置Jackson2ObjectMapperBuilder 对象，那么该配置不会生效
@ConditionalOnMissingBean
//List会读取Spring容器中所有
//Jackson2ObjectMapperBuilderCustomizer子类Bean，并按照order优先级进行排序。
public Jackson2ObjectMapperBuilder jacksonObjectMapperBuilder(
List customizers) {
Jackson2ObjectMapperBuilder builder = new Jackson2ObjectMapperBuilder();
builder.applicationContext(this.applicationContext);
//按照order读取所有自定义的Jackson2ObjectMapperBuilderCustomizer 对象。
customize(builder, customizers);
return builder;
}
//调用子类实现customize方法定制Jackson2ObjectMapperBuilder 对象
private void customize(Jackson2ObjectMapperBuilder builder,
List customizers) {
for (Jackson2ObjectMapperBuilderCustomizer customizer : customizers) {
customizer.customize(builder);
}
}
}
//SpringBoot2.x提供的修改ObjectMapper的配置类，可以在配置文件中修改配置。
@Configuration
@ConditionalOnClass(Jackson2ObjectMapperBuilder.class)
//配置以`spring.jackson`作为前缀。
@EnableConfigurationProperties(JacksonProperties.class)
static class Jackson2ObjectMapperBuilderCustomizerConfiguration {
@Bean
public StandardJackson2ObjectMapperBuilderCustomizer standardJacksonObjectMapperBuilderCustomizer(
ApplicationContext applicationContext,
JacksonProperties jacksonProperties) {
return new StandardJackson2ObjectMapperBuilderCustomizer(applicationContext,
jacksonProperties);
}
static final class StandardJackson2ObjectMapperBuilderCustomizer
implements Jackson2ObjectMapperBuilderCustomizer, Ordered {
private final ApplicationContext applicationContext;
//配置文件中的属性
private final JacksonProperties jacksonProperties;
StandardJackson2ObjectMapperBuilderCustomizer(
ApplicationContext applicationContext,
JacksonProperties jacksonProperties) {
this.applicationContext = applicationContext;
this.jacksonProperties = jacksonProperties;
}
//优先级为0，若我们想自定义实现StandardJackson2ObjectMapperBuilderCustomizer类，那么order优先级要大于0
@Override
public int getOrder() {
return 0;
}
//根据配置去定制builder对象
@Override
public void customize(Jackson2ObjectMapperBuilder builder) {
if (this.jacksonProperties.getDefaultPropertyInclusion() != null) {
builder.serializationInclusion(
this.jacksonProperties.getDefaultPropertyInclusion());
}
if (this.jacksonProperties.getTimeZone() != null) {
builder.timeZone(this.jacksonProperties.getTimeZone());
}
//设置序列化和反序列化的特征
configureFeatures(builder, FEATURE_DEFAULTS);
configureVisibility(builder, this.jacksonProperties.getVisibility());
configureFeatures(builder, this.jacksonProperties.getDeserialization());
configureFeatures(builder, this.jacksonProperties.getSerialization());
configureFeatures(builder, this.jacksonProperties.getMapper());
configureFeatures(builder, this.jacksonProperties.getParser());
configureFeatures(builder, this.jacksonProperties.getGenerator());
configureDateFormat(builder);
//设置序列化的命名策略
configurePropertyNamingStrategy(builder);
configureModules(builder);
configureLocale(builder);
}
private void configureFeatures(Jackson2ObjectMapperBuilder builder,
Map features) {
features.forEach((feature, value) -> {
if (value != null) {
if (value) {
builder.featuresToEnable(feature);
}
else {
builder.featuresToDisable(feature);
}
}
});
}
private void configureVisibility(Jackson2ObjectMapperBuilder builder,
Map visibilities) {
visibilities.forEach(builder::visibility);
}
//配置Date格式化类
private void configureDateFormat(Jackson2ObjectMapperBuilder builder) {
// 支持全限定名的DateFormat或者时间格式串例如`yyyy-MM-dd HH:mm:ss`
String dateFormat = this.jacksonProperties.getDateFormat();
if (dateFormat != null) {
try {
Class dateFormatClass = ClassUtils.forName(dateFormat, null);
builder.dateFormat(
(DateFormat) BeanUtils.instantiateClass(dateFormatClass));
}
catch (ClassNotFoundException ex) {
//若不是上送DateFormat的全限定名，那么使用SimpleDateFormat 进行格式化
SimpleDateFormat simpleDateFormat = new SimpleDateFormat(
dateFormat);
// 在Jackson 2.6.3 我们需要设置一个 TimeZone时区，若未设置，则使用默认的时区（UTC）
TimeZone timeZone = this.jacksonProperties.getTimeZone();
if (timeZone == null) {
timeZone = new ObjectMapper().getSerializationConfig()
.getTimeZone();
}
simpleDateFormat.setTimeZone(timeZone);
builder.dateFormat(simpleDateFormat);
}
}
}
private void configurePropertyNamingStrategy(
Jackson2ObjectMapperBuilder builder) {
// We support a fully qualified class name extending Jackson's
// PropertyNamingStrategy or a string value corresponding to the constant
// names in PropertyNamingStrategy which hold default provided
// implementations
String strategy = this.jacksonProperties.getPropertyNamingStrategy();
if (strategy != null) {
try {
configurePropertyNamingStrategyClass(builder,
ClassUtils.forName(strategy, null));
}
catch (ClassNotFoundException ex) {
configurePropertyNamingStrategyField(builder, strategy);
}
}
}
private void configurePropertyNamingStrategyClass(
Jackson2ObjectMapperBuilder builder,
Class propertyNamingStrategyClass) {
builder.propertyNamingStrategy((PropertyNamingStrategy) BeanUtils
.instantiateClass(propertyNamingStrategyClass));
}
private void configurePropertyNamingStrategyField(
Jackson2ObjectMapperBuilder builder, String fieldName) {
// Find the field (this way we automatically support new constants
// that may be added by Jackson in the future)
Field field = ReflectionUtils.findField(PropertyNamingStrategy.class,
fieldName, PropertyNamingStrategy.class);
Assert.notNull(field, () -> "Constant named '" + fieldName
+ "' not found on " + PropertyNamingStrategy.class.getName());
try {
builder.propertyNamingStrategy(
(PropertyNamingStrategy) field.get(null));
}
catch (Exception ex) {
throw new IllegalStateException(ex);
}
}
private void configureModules(Jackson2ObjectMapperBuilder builder) {
Collection moduleBeans = getBeans(this.applicationContext,
Module.class);
builder.modulesToInstall(moduleBeans.toArray(new Module[0]));
}
private void configureLocale(Jackson2ObjectMapperBuilder builder) {
Locale locale = this.jacksonProperties.getLocale();
if (locale != null) {
builder.locale(locale);
}
}
private static Collection getBeans(ListableBeanFactory beanFactory,
Class type) {
return BeanFactoryUtils.beansOfTypeIncludingAncestors(beanFactory, type)
.values();
}
}
}
}
2. 修改方式
2.1 配置文件修改
spring:
jackson:
serialization:
write-dates-as-timestamps: true # date日期转换为时间戳
date-format: yyyy-MM-dd HH:mm:ss #指定日期格式，比如yyyy-MM-dd HH:mm:ss，或者具体的格式化类的全限定名
2.2 java代码配置
@Component
public class MyJackson2ObjectMapperBuilderCustomizer implements Jackson2ObjectMapperBuilderCustomizer, Ordered {
@Override
public void customize(Jackson2ObjectMapperBuilder jacksonObjectMapperBuilder) {
//禁止Date类型转化为时间戳。
jacksonObjectMapperBuilder.featuresToDisable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS);
}
@Override
public int getOrder() {
return 1;
}
}