background

1.1 problem

Spring Boot When dealing with serialization and deserialization of objects , By default, the built-in JackSon To configure . Use the frame default , We usually face the following problems ：
  1. Date Return date format （ It is not recommended to use Date, But old projects should be compatible ）, with T, Such as 2018-05-15T24:59:59：
  1. LocalDate The returned Date object is an array （ The framework inherits WebMvcConfigurationSupport）;
  1. LocalDateTime Time conversion failed ;
  1. Defines the date type , Such as LocalDate, Front end docking （post/get）, If you pass in a date string （"2022-05-05"）, Will be submitted to the String Convert to LocalDate Failure ;
  1. return long Type data , front end js There is accuracy problem , Conversion required ;
  1. Some special objects need special business transformation , Such as encryption and decryption ;

1.2 Solution

For the above problems , There are many solutions . Because the underlying framework uniformly configures different implementation modes of interception classes , There will still be differences , This article mainly explains that in different configuration scenarios , Customize Jackson Some considerations for configuration and reasons for differentiation ：
In order to solve special objects （ Such as date ） Serialization and deserialization of , Common schemes are as follows ：
  1. For a particular specific object , Use annotations on objects , Such as ：
@JsonSerialize(using= JsonDateSerializer.class)

private Date taskEndTime;

@ApiModelProperty(value = " Inspection date ")

@JsonFormat(pattern = "yyyy-MM-dd")

private LocalDate checkDate;
  1. Re actualize WebMvcConfigurer Interface , Customize JackSon To configure .
  1. Inherit WebMvcConfigurationSupport class , Customize JackSon To configure .

1.3 In particular

  • programme 1 The pattern of , Annotate the corresponding variable , It can solve the problem , But the code is seriously duplicated , Not elegant ;
  • Realization WebMvcConfigurer Interface and inheritance WebMvcConfigurationSupport class , yes Spring Boot It provides two modes for developers to make unified global configuration classes , Notice the difference between the two modes , See the following chapters for details （ Two different modes , Improper use , The configuration will not take effect ）;

Customize Jackson

  1. JackSon Configuration instructions

Customize a Jackson Configuration information , Need to know Jackson Some configuration standards for , Such as ： 

// Ignored in deserialization  json  There is but  Java  Object does not exist 

mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES,

false);

// The date format defaults to  yyyy-MM-dd'T'HH:mm:ss.SSSZ , For example, if a class has private Date date; This date attribute , Serialized as ：{"date" : 1413800730456}, If not true, Then for {"date" : "2014-10-20T10:26:06.604+0000"}

mapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS,false);

// Ignore the value... When serializing  null  Properties of 

mapper.setSerializationInclusion(Include.NON_NULL);

// Ignore properties with default values 

mapper.setDefaultPropertyInclusion(Include.NON_DEFAULT);

//  Beautify the output 

mapper.enable(SerializationFeature.INDENT_OUTPUT);

//  Allow serialization of empty POJO class 

// ( Otherwise, an exception will be thrown )

mapper.disable(SerializationFeature.FAIL_ON_EMPTY_BEANS);

//  hold java.util.Date, Calendar Output to digital ( Time stamp )

mapper.disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS);

//  Don't throw an exception when you encounter an unknown property 

mapper.disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);

//  mandatory JSON  An empty string ("") Convert to null The object is worth :

mapper.enable(DeserializationFeature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT);

//  stay JSON It is allowed that C/C++  Comments on styles ( Nonstandard , Default disabled )

mapper.configure(JsonParser.Feature.ALLOW_COMMENTS, true);

//  Allow field names without quotes ( Nonstandard )

mapper.configure(JsonParser.Feature.ALLOW_UNQUOTED_FIELD_NAMES, true);

//  Single quotation marks are allowed ( Nonstandard )

mapper.configure(JsonParser.Feature.ALLOW_SINGLE_QUOTES, true);

//  Mandatory escape is not ASCII character 

mapper.configure(JsonGenerator.Feature.ESCAPE_NON_ASCII, true);

//  Wrap the content into a JSON attribute , The attribute name is from @JsonRootName Annotation assignment 

mapper.configure(SerializationFeature.WRAP_ROOT_VALUE, true);

// Serializing enumerations starts with toString() To output , Default false, That is to say, by default name() To output 

mapper.configure(SerializationFeature.WRITE_ENUMS_USING_TO_STRING,true);

// serialize Map When the key Sort operations , Default false

mapper.configure(SerializationFeature.ORDER_MAP_ENTRIES_BY_KEYS,true);

// serialize char[] Time and space json Array output , Default false

mapper.configure(SerializationFeature.WRITE_CHAR_ARRAYS_AS_JSON_ARRAYS,true);

// serialize BigDecimal Between the output of the original number or scientific counting , Default false, That is to say, whether to use toPlainString() Output by scientific counting 

mapper.configure(SerializationFeature.WRITE_CHAR_ARRAYS_AS_JSON_ARRAYS,true);

  1. Realization WebMvcConfigurer Interface

Rewrite a ObjectMapper, Replace the system default bean, You can implement the interface in post Request mode , Object serialization and deserialization define the configuration information .
Rewrite Jackson after , It doesn't deal with get When asked , Serialization of special objects such as dates ; in the light of get request , Write the serialization rule function of the object , By implementing addFormatters（） Interface , Scalable support ;

To write LocalDateTime Conversion function 

/**

 * java 8 LocalDateTime converter 

 *

 * @author wangling

 */

public class LocalDateTimeFormatter implements Formatter<LocalDateTime> {

    private final DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");

    @Override

    public LocalDateTime parse(String text, Locale locale) throws ParseException {

        return LocalDateTime.parse(text, formatter);

    }

    @Override

    public String print(LocalDateTime object, Locale locale) {

        return formatter.format(object);

    }

}

To write LocalDate Conversion function 

/**

 * java 8 localDate converter 

 *

 * @author wangling

 */

public class LocalDateFormatter implements Formatter<LocalDate> {

    private final DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd");

    @Override

    public LocalDate parse(String text, Locale locale) throws ParseException {

        return LocalDate.parse(text, formatter);

    }

    @Override

    public String print(LocalDate object, Locale locale) {

        return formatter.format(object);

    }

}

To write Jackson To configure

Write a custom ObjectMapper bean object , Set priority to replace default bean. 
/**

 *  Project global configuration class 

 *

 * @author wangling

 * @date 2022/06/10

 */

@Configuration

@RequiredArgsConstructor

public class WebConfig implements WebMvcConfigurer {

  @Override

  public void addFormatters(FormatterRegistry registry) {

    registry.addFormatterForFieldType(LocalDate.class, new LocalDateFormatter());

    registry.addFormatterForFieldType(LocalDateTime.class, new LocalDateTimeFormatter());

  }

  @Bean

  @Primary

  public ObjectMapper ObjectMapper() {

    String dateTimeFormat = "yyyy-MM-dd HH:mm:ss";

    String dateFormat = "yyyy-MM-dd";

    String timeFormat = "HH:mm:ss";

    ObjectMapper objectMapper = new ObjectMapper();

    objectMapper.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);

    objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);

    JavaTimeModule javaTimeModule = new JavaTimeModule();

    //  serialize 

    javaTimeModule.addSerializer(

        LocalDateTime.class,

        new LocalDateTimeSerializer(DateTimeFormatter.ofPattern(dateTimeFormat)));

    javaTimeModule.addSerializer(

        LocalDate.class,

        new LocalDateSerializer(DateTimeFormatter.ofPattern(dateFormat)));

    javaTimeModule.addSerializer(

        LocalTime.class,

        new LocalTimeSerializer(DateTimeFormatter.ofPattern(timeFormat)));

    javaTimeModule.addSerializer(

        Date.class,

        new DateSerializer(false, new SimpleDateFormat(dateTimeFormat)));

    //  Deserialization 

    javaTimeModule.addDeserializer(

        LocalDateTime.class,

        new LocalDateTimeDeserializer(DateTimeFormatter.ofPattern(dateTimeFormat)));

    javaTimeModule.addDeserializer(

        LocalDate.class,

        new LocalDateDeserializer(DateTimeFormatter.ofPattern(dateFormat)));

    javaTimeModule.addDeserializer(

        LocalTime.class,

        new LocalTimeDeserializer(DateTimeFormatter.ofPattern(timeFormat)));

    javaTimeModule.addDeserializer(Date.class, new DateDeserializers.DateDeserializer() {

      @SneakyThrows

      @Override

      public Date deserialize(JsonParser jsonParser, DeserializationContext dc) {

        String text = jsonParser.getText().trim();

        SimpleDateFormat sdf = new SimpleDateFormat(dateTimeFormat);

        return sdf.parse(text);

      }

    });

    javaTimeModule.addSerializer(Long.class, ToStringSerializer.instance);

    javaTimeModule.addSerializer(BigInteger.class, ToStringSerializer.instance);

    objectMapper.registerModule(javaTimeModule);

    return objectMapper;

  }

}

  1. WebMvcConfigurationSupport class

To write Jackson To configure

Rewrite Jackson after , It doesn't deal with get When asked , Serialization of special objects such as dates ; in the light of get request , Write the serialization rule function of the object , By implementing addFormatters（） Interface , Scalable support ;
Write custom configuration Jackson Information , Need to rewrite extendMessageConverters Method . Specific technical details , Please refer to the documentation 《 Spring Boot Realization WebMvcConfigurationSupport Lead to custom JSON The time return format does not take effect 》

/**

 *  Project global configuration class 

 *

 * @author wangling

 * @date 2022/06/10

 */

@Configuration

public class MvcInterceptorConfig extends WebMvcConfigurationSupport {

  @Override

  protected void addFormatters(FormatterRegistry registry) {

    //  be used for get  Global format date conversion 

    registry.addFormatterForFieldType(LocalDate.class, new LocalDateFormatter());

    registry.addFormatterForFieldType(LocalDateTime.class, new LocalDateTimeFormatter());

  }

  @Override

  protected void extendMessageConverters(List<HttpMessageConverter<?>> converters) {

    //  Replace the frame default JackSon To configure   be used for post  Global format date conversion ,long Turn the string 

    MappingJackson2HttpMessageConverter jackson2HttpMessageConverter =

        new MappingJackson2HttpMessageConverter();

    jackson2HttpMessageConverter.setObjectMapper(ObjectMapper());

    //  Based on order , First, execute the customized 

    converters.add(0, jackson2HttpMessageConverter);

  }

  private ObjectMapper ObjectMapper() {

    String dateTimeFormat = "yyyy-MM-dd HH:mm:ss";

    String dateFormat = "yyyy-MM-dd";

    String timeFormat = "HH:mm:ss";

    ObjectMapper objectMapper = new ObjectMapper();

    // Ignore empty Bean turn json Error of 

    objectMapper.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);

    // Ignore   stay json There is... In the string , But there is no corresponding attribute in the object , Prevent mistakes .

    //  for example json There are more fields in the data , There is no such field in the object . If you set true, Throw an exception , Because the field does not correspond to ;false Then ignore the extra fields , The default value is null, Deserialize other fields successfully 

    objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);

    JavaTimeModule javaTimeModule = new JavaTimeModule();

    //  serialize 

    javaTimeModule.addSerializer(

        LocalDateTime.class,

        new LocalDateTimeSerializer(DateTimeFormatter.ofPattern(dateTimeFormat)));

    javaTimeModule.addSerializer(

        LocalDate.class,

        new LocalDateSerializer(DateTimeFormatter.ofPattern(dateFormat)));

    javaTimeModule.addSerializer(

        LocalTime.class,

        new LocalTimeSerializer(DateTimeFormatter.ofPattern(timeFormat)));

    javaTimeModule.addSerializer(

        Date.class,

        new DateSerializer(false, new SimpleDateFormat(dateTimeFormat)));

    //  Deserialization 

    javaTimeModule.addDeserializer(

        LocalDateTime.class,

        new LocalDateTimeDeserializer(DateTimeFormatter.ofPattern(dateTimeFormat)));

    javaTimeModule.addDeserializer(

        LocalDate.class,

        new LocalDateDeserializer(DateTimeFormatter.ofPattern(dateFormat)));

    javaTimeModule.addDeserializer(

        LocalTime.class,

        new LocalTimeDeserializer(DateTimeFormatter.ofPattern(timeFormat)));

    javaTimeModule.addDeserializer(Date.class, new DateDeserializers.DateDeserializer() {

      @SneakyThrows

      @Override

      public Date deserialize(JsonParser jsonParser, DeserializationContext dc) {

        String text = jsonParser.getText().trim();

        SimpleDateFormat sdf = new SimpleDateFormat(dateTimeFormat);

        return sdf.parse(text);

      }

    });

    javaTimeModule.addSerializer(Long.class, ToStringSerializer.instance);

    javaTimeModule.addSerializer(BigInteger.class, ToStringSerializer.instance);

    objectMapper.registerModule(javaTimeModule);

    return objectMapper;

  }

}

WebMvcConfigurer And WebMvcConfigurationSupport Related knowledge

  1. Basic knowledge points

Spring Of WebMvcConfigurer Interfaces provide many ways for developers to customize SpringMVC Configuration of .
WebMvcConfigurationSupport implements ApplicationContextAware, ServletContextAware. More and more customized configurations are supported ,WebMvcConfigurerAdapter There are ways , This class also has . This kind of annotation content is translated ： This is to provide MVC Java config The main classes configured behind . Usually by putting @EnableWebMvc Added to the application @Configuration Class . Another more advanced option is to extend directly from this class and rewrite methods as needed , Remember to add subclasses @Configuration, Rewrite with @Bean We should also add @Bean.

  1. Precautions for use

          Reference documents ： 《 Reason for interception failure 》
  1. Realization WebMvcConfigurer： Will not cover WebMvcAutoConfiguration Configuration of
  1. Realization WebMvcConfigurer+ annotation @EnableWebMvc： Will be covered WebMvcAutoConfiguration Configuration of
  1. Inherit WebMvcConfigurationSupport： Will be covered WebMvcAutoConfiguration Configuration of
  1. Inherit DelegatingWebMvcConfiguration： Will be covered WebMvcAutoConfiguration Configuration of

  1. Recommended use mode

  1. It's not necessary , It's best to avoid WebMvcConfigurer,WebMvcConfigurationSupport Use... Simultaneously in a project ;
  1. Intercept configuration for security , Recommended for the project WebMvcConfigurer Interface for global configuration ;
  1. date , It is suggested to use LocalDate, Replace historical Date data type ;
 

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