SpringBoot中Jackson ObjectMapper应用及说明

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import java.io.IOException;
public final class JsonUtil {
    private static ObjectMapper mapper = new ObjectMapper();
    private JsonUtil() {
    }
    /**
     * Serialize any Java value as a String.
     */
    public static String generate(Object object) throws JsonProcessingException {
        return mapper.writeValueAsString(object);
    }
    /**
     * Deserialize JSON content from given JSON content String.
     */
    public static <T> T parse(String content, Class<T> valueType) throws IOException {
        return mapper.readValue(content, valueType);
    }
}

import java.util.Date;
public class Hero {
    public static void main(String[] args) throws Exception {
        System.out.println(JsonUtil.generate(new Hero("Jason", new Date())));
    }
    private String name;
    private Date birthday;
    public Hero() {
    }
    public Hero(String name, Date birthday) {
        this.name = name;
        this.birthday = birthday;
    }
    public String getName() {
        return name;
    }
    public Date getBirthday() {
        return birthday;
    }
}

public ObjectMapper(JsonFactory jf, DefaultSerializerProvider sp, DefaultDeserializationContext dc) {
...
    BaseSettings base = DEFAULT_BASE.withClassIntrospector(defaultClassIntrospector());
    _configOverrides = new ConfigOverrides();
    _serializationConfig = new SerializationConfig(base, _subtypeResolver, mixins, rootNames, _configOverrides);
    ...
}

public SerializationConfig(BaseSettings base, SubtypeResolver str, SimpleMixInResolver mixins, RootNameLookup rootNames,
        ConfigOverrides configOverrides)
{
    super(base, str, mixins, rootNames, configOverrides);
    _serFeatures = collectFeatureDefaults(SerializationFeature.class);
    _filterProvider = null;
    _defaultPrettyPrinter = DEFAULT_PRETTY_PRINTER;
    _generatorFeatures = 0;
    _generatorFeaturesToChange = 0;
    _formatWriteFeatures = 0;
    _formatWriteFeaturesToChange = 0;
}

/**
 * For efficiency, we will serialize Dates as longs, instead of
 * potentially more readable Strings.
 */
@JacksonStdImpl
@SuppressWarnings("serial")
public class DateSerializer extends DateTimeSerializerBase<Date> {
    ...
    @Override
    protected long _timestamp(Date value) {
        return (value == null) ? 0L : value.getTime();
    }
    @Override
    public void serialize(Date value, JsonGenerator g, SerializerProvider provider) throws IOException {
        if (_asTimestamp(provider)) {
            g.writeNumber(_timestamp(value));
            return;
        }
        _serializeAsString(value, g, provider);
    }
}

protected boolean _asTimestamp(SerializerProvider serializers)
{
    if (_useTimestamp != null) {
        return _useTimestamp.booleanValue();
    }
    if (_customFormat == null) {
        if (serializers != null) {
            return serializers.isEnabled(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS);
        }
        // 12-Jun-2014, tatu: Is it legal not to have provider? Was NPE:ing earlier so leave a check
        throw new IllegalArgumentException("Null SerializerProvider passed for "+handledType().getName());
    }
    return false;
}

mapper.disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS);

{"name":"Jason","birthday":"2018-10-31T03:07:34.485+0000"}

@JsonFormat(shape = JsonFormat.Shape.STRING)
private Date birthday;

@JsonFormat(shape = JsonFormat.Shape.STRING, pattern = "yyyy-MM-dd")
private Date birthday;

public JsonSerializer<?> createContextual(SerializerProvider serializers, BeanProperty property) throws JsonMappingException
{
  ...
  if (format.hasPattern()) {
      final Locale loc = format.hasLocale() ? format.getLocale() : serializers.getLocale();
      SimpleDateFormat df = new SimpleDateFormat(format.getPattern(), loc);
      TimeZone tz = format.hasTimeZone() ? format.getTimeZone() : serializers.getTimeZone();
      df.setTimeZone(tz);
      return withFormat(Boolean.FALSE, df);
  }
  ...
}

private List<HttpMessageConverter<?>> getDefaultConverters() {
    List<HttpMessageConverter<?>> converters = new ArrayList<>();
    if (ClassUtils.isPresent("org.springframework.web.servlet.config.annotation.WebMvcConfigurationSupport", null)) {
        converters.addAll(new WebMvcConfigurationSupport() {
            public List<HttpMessageConverter<?>> defaultMessageConverters() {
                return super.getMessageConverters();
            }
        }.defaultMessageConverters());
    }
    else {
        converters.addAll(new RestTemplate().getMessageConverters());
    }
    reorderXmlConvertersToEnd(converters);
    return converters;
}

protected final void addDefaultHttpMessageConverters(List<HttpMessageConverter<?>> messageConverters) {
    StringHttpMessageConverter stringHttpMessageConverter = new StringHttpMessageConverter();
    stringHttpMessageConverter.setWriteAcceptCharset(false);  // see SPR-7316
    messageConverters.add(new ByteArrayHttpMessageConverter());
    messageConverters.add(stringHttpMessageConverter);
    messageConverters.add(new ResourceHttpMessageConverter());
    messageConverters.add(new ResourceRegionHttpMessageConverter());
    messageConverters.add(new SourceHttpMessageConverter<>());
    messageConverters.add(new AllEncompassingFormHttpMessageConverter());
    ...
    if (jackson2Present) {
        Jackson2ObjectMapperBuilder builder = Jackson2ObjectMapperBuilder.json();
        if (this.applicationContext != null) {
            builder.applicationContext(this.applicationContext);
        }
        messageConverters.add(new MappingJackson2HttpMessageConverter(builder.build()));
    }
    ...
}

public <T extends ObjectMapper> T build() {
    ObjectMapper mapper;
    if (this.createXmlMapper) {
        mapper = (this.defaultUseWrapper != null ?
                new XmlObjectMapperInitializer().create(this.defaultUseWrapper) :
                new XmlObjectMapperInitializer().create());
    }
    else {
        mapper = (this.factory != null ? new ObjectMapper(this.factory) : new ObjectMapper());
    }
    configure(mapper);
    return (T) mapper;
}

private void customizeDefaultFeatures(ObjectMapper objectMapper) {
    if (!this.features.containsKey(MapperFeature.DEFAULT_VIEW_INCLUSION)) {
        configureFeature(objectMapper, MapperFeature.DEFAULT_VIEW_INCLUSION, false);
    }
    if (!this.features.containsKey(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES)) {
        configureFeature(objectMapper, DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
    }
}

static {
    Map<Object, Boolean> featureDefaults = new HashMap<>();
    featureDefaults.put(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
    FEATURE_DEFAULTS = Collections.unmodifiableMap(featureDefaults);
}

@DateTimeFormat(pattern = "yyyy-MM-dd")
private Date startDate;

@JsonFormat(shape = JsonFormat.Shape.STRING, pattern = "yyyy-MM-dd")
@DateTimeFormat(pattern = "yyyy-MM-dd")
private Date startDate;