Jackson反序列化@JsonFormat不⽣效的解决⽅案今天在线上发现⼀个问题，在使⽤Jackson进⾏时间的反序列化时，配置的@JsonFormat没有⽣效查看源码发现，Jackson在反序列化时间时，会判断json字段值类型，如下：由于在我们服务⾥，前端传时间值到后端时采⽤了时间戳的⽅式，json值被判断为数字类型，所以Jackson在反序列化时直接简单粗暴的⽅式处理，将时间戳转换为Date类型：为了能够按照正确的格式解析时间，抹去后⾯的时间点，精确到⽇，只好⾃定义⼀个时间解析器。
⾃定义的时间解析器很好实现，⽹上已经有很多实例代码，只需要继承 JsonDeserializer<T> 就可以。
问题的关键点在于，如何获取到注解上的时间格式，按照注解上的格式去解析，否则每个解析器的实现只能使⽤⼀种固定的格式去解析时间。
1. 所以第⼀步是获取注解上配置的信息想要获取字段对应的注解信息，只有找到相应的字段，然后通过字段属性获取注解信息，再通过注解信息获取配置的格式。
但找了很久，也没有在既有的参数⾥找到获取相关字段的⽅法，只能去翻看源码，最后在这⾥发现了获取字段信息的⽅法以及解析器的⽣成过程，源代码如下：第⼀个红框表⽰解析器是在这⾥⽣成的，第⼆个红框就是获取注解信息的地⽅2. 注解获取以后便创建⾃定义的时间解析器猜想，我们可不可以也实现这个类，重写⽣成解析器的⽅法？那就试试呗～我们在⾃定义的时间解析器上同样实现这个类，重写了⽣成时间解析器的⽅法，并初始化⼀些⾃定义的信息供解析时间使⽤（当然猜想是正确的，因为官⽅就是这么搞的，只是官⽅的是⼀个内部类实现的），具体代码如下：时间解析器代码：import com.fasterxml.jackson.annotation.JsonFormat;import com.fasterxml.jackson.core.JsonParser;import com.fasterxml.jackson.databind.BeanProperty;import com.fasterxml.jackson.databind.DeserializationContext;import com.fasterxml.jackson.databind.JsonDeserializer;import com.fasterxml.jackson.databind.deser.ContextualDeserializer;import com.fasterxml.jackson.databind.util.StdDateFormat;import mon.collect.Lists;import ErrorCode;import Exception;import java.io.IOException;import java.text.DateFormat;import java.text.ParseException;import java.text.SimpleDateFormat;import java.util.Date;import java.util.List;import java.util.Locale;import java.util.TimeZone;import ng.StringUtils;import ng3.time.DateUtils;import org.slf4j.Logger;import org.slf4j.LoggerFactory;/*** @author ⽆名⼩⽣ Date: 2019-02-19 Time: 19:00* @version $Id$*/public class DateJsonDeserializer extends JsonDeserializer<Date> implements ContextualDeserializer {private final static Logger logger = LoggerFactory.getLogger(DateJsonDeserializer.class);private final static List<String> FORMATS = Lists.newArrayList("yyyy-MM-dd HH:mm:ss", "yyyy-MM-dd HH:mm", "yyyyMMdd-HHmmss", "yyyy-MM-dd", "MM-dd", "HH:mm:ss", "yyyy-MM");public final DateFormat df;public final String formatString;public DateJsonDeserializer() {this.df = null;this.formatString = null;this.df = df;this.formatString = "";}public DateJsonDeserializer(DateFormat df, String formatString) {this.df = df;this.formatString = formatString;}@Overridepublic Date deserialize(JsonParser p, DeserializationContext ctxt) throws IOException {try {String dateValue = p.getText();if (df == null || StringUtils.isEmpty(dateValue)) {return null;}("使⽤⾃定义解析器解析字段:{}:时间:{}",p.getCurrentName(),p.getText());Date date;if (StringUtils.isNumeric(dateValue)){date = new Date(Long.valueOf(dateValue));}else {String[] patterns = FORMATS.toArray(new String[0]);date = DateUtils.parseDate(p.getText(),patterns);}return df.parse(df.format(date));} catch (ParseException | SecurityException e) {logger.error("JSON反序列化，时间解析失败", e);throw new BizException(BizErrorCode.UNEXPECTED_ERROR);}}@Overridepublic JsonDeserializer<?> createContextual(DeserializationContext ctxt, BeanProperty property) {if (property != null) {JsonFormat.Value format = ctxt.getAnnotationIntrospector().findFormat(property.getMember());if (format != null) {TimeZone tz = format.getTimeZone();// First: fully custom pattern?if (format.hasPattern()) {final String pattern = format.getPattern();if (!FORMATS.contains(pattern)){FORMATS.add(pattern);}final Locale loc = format.hasLocale() ? format.getLocale() : ctxt.getLocale();SimpleDateFormat df = new SimpleDateFormat(pattern, loc);if (tz == null) {tz = ctxt.getTimeZone();}df.setTimeZone(tz);return new DateJsonDeserializer(df, pattern);}// But if not, can still override timezoneif (tz != null) {DateFormat df = ctxt.getConfig().getDateFormat();// one shortcut: with our custom format, can simplify handling a bitif (df.getClass() == StdDateFormat.class) {final Locale loc = format.hasLocale() ? format.getLocale() : ctxt.getLocale();StdDateFormat std = (StdDateFormat) df;std = std.withTimeZone(tz);std = std.withLocale(loc);df = std;} else {// otherwise need to clone, re-set timezone:df = (DateFormat) df.clone();df.setTimeZone(tz);}return new DateJsonDeserializer(df);}}}return this;}}⾄此，⾃定义时间解析器就完成了但是，为了能够更灵活的控制时间的解析（例如：输⼊的时间格式和⽬标时间格式不同），我⼜重新⾃定义了⼀个时间解析的注解，基本仿照官⽅的@Format注解，具体代码如下⾃定义时间解析注解：import com.fasterxml.jackson.annotation.JacksonAnnotation;import ng.annotation.ElementType;import ng.annotation.Retention;import ng.annotation.RetentionPolicy;import ng.annotation.Target;import java.util.Locale;import java.util.TimeZone;/*** @author ⽆名⼩⽣ Date: 2019-02-21 Time: 11:03* @version $Id$*/@Target({ElementType.ANNOTATION_TYPE, ElementType.FIELD, ElementType.METHOD, ElementType.PARAMETER,ElementType.TYPE})@Retention(RetentionPolicy.RUNTIME)@JacksonAnnotationpublic @interface DeserializeFormat {/*** Value that indicates that default {@link java.util.Locale}* (from deserialization or serialization context) should be used:* annotation does not define value to use.*/public final static String DEFAULT_LOCALE = "##default";/*** Value that indicates that default {@link java.util.TimeZone}* (from deserialization or serialization context) should be used:* annotation does not define value to use.*/public final static String DEFAULT_TIMEZONE = "##default";/*** 按照特定的时间格式解析*/public String pattern() default "";/*** ⽬标格式* @return*/public String format() default "";/*** Structure to use for serialization: definition of mapping depends on datatype,* but usually has straight-forward counterpart in data format (JSON).* Note that commonly only a subset of shapes is available; and if 'invalid' value* is chosen, defaults are usually used.*/public DeserializeFormat.Shape shape() default DeserializeFormat.Shape.ANY;* {@link java.util.Locale} to use for serialization (if needed).* Special value of {@link #DEFAULT_LOCALE}* can be used to mean "just use the default", where default is specified* by the serialization context, which in turn defaults to system* defaults ({@link java.util.Locale#getDefault()}) unless explicitly* set to another locale.*/public String locale() default DEFAULT_LOCALE;/*** {@link java.util.TimeZone} to use for serialization (if needed).* Special value of {@link #DEFAULT_TIMEZONE}* can be used to mean "just use the default", where default is specified* by the serialization context, which in turn defaults to system* defaults ({@link java.util.TimeZone#getDefault()}) unless explicitly* set to another locale.*/public String timezone() default DEFAULT_TIMEZONE;/*/**********************************************************/* Value enumeration(s), value class(es)/***********************************************************//*** Value enumeration used for indicating preferred Shape; translates* loosely to JSON types, with some extra values to indicate less precise* choices (i.e. allowing one of multiple actual shapes)*/public enum Shape{/*** Marker enum value that indicates "default" (or "whatever") choice; needed* since Annotations can not have null values for enums.*/ANY,/*** Value that indicates shape should not be structural (that is, not* {@link #ARRAY} or {@link #OBJECT}, but can be any other shape.*/SCALAR,/*** Value that indicates that (JSON) Array type should be used.*/ARRAY,/*** Value that indicates that (JSON) Object type should be used.*/OBJECT,/*** Value that indicates that a numeric (JSON) type should be used* (but does not specify whether integer or floating-point representation* should be used)*/NUMBER,/*** Value that indicates that floating-point numeric type should be used*/NUMBER_FLOAT,/*** Value that indicates that integer number type should be used* (and not {@link #NUMBER_FLOAT}).*/NUMBER_INT,/*** Value that indicates that (JSON) String type should be used.*/STRING,/*** Value that indicates that (JSON) boolean type* (true, false) should be used.*/BOOLEAN;public boolean isNumeric() {return (this == NUMBER) || (this == NUMBER_INT) || (this == NUMBER_FLOAT);}public boolean isStructured() {return (this == OBJECT) || (this == ARRAY);}}/*** Helper class used to contain information from a single {@link DeserializeFormat}* annotation.*/public static class Value{private final String pattern;private final String format;private final DeserializeFormat.Shape shape;private final Locale locale;private final String timezoneStr;// lazily constructed when created from annotationsprivate TimeZone _timezone;public Value() {this("", "", DeserializeFormat.Shape.ANY, "", "");}public Value(DeserializeFormat ann) {this(ann.pattern(),ann.format(), ann.shape(), ann.locale(), ann.timezone());}public Value(String p, String f, DeserializeFormat.Shape sh, String localeStr, String tzStr) {this(p,f, sh,(localeStr == null || localeStr.length() == 0 || DEFAULT_LOCALE.equals(localeStr)) ? null : new Locale(localeStr),(tzStr == null || tzStr.length() == 0 || DEFAULT_TIMEZONE.equals(tzStr)) ?null : tzStr,null);}/*** @since 2.1*/public Value(String p, String f, DeserializeFormat.Shape sh, Locale l, TimeZone tz){pattern = p;format = f;shape = (sh == null) ? DeserializeFormat.Shape.ANY : sh;locale = l;_timezone = tz;timezoneStr = null;}/*** @since 2.4public Value(String p, String f, DeserializeFormat.Shape sh, Locale l, String tzStr, TimeZone tz){pattern = p;format = f;shape = (sh == null) ? DeserializeFormat.Shape.ANY : sh;locale = l;_timezone = tz;timezoneStr = tzStr;}/*** @since 2.1*/public DeserializeFormat.Value withPattern(String p,String f) {return new DeserializeFormat.Value(p, f, shape, locale, timezoneStr, _timezone);}/*** @since 2.1*/public DeserializeFormat.Value withShape(DeserializeFormat.Shape s) {return new DeserializeFormat.Value(pattern, format, s, locale, timezoneStr, _timezone);}/*** @since 2.1*/public DeserializeFormat.Value withLocale(Locale l) {return new DeserializeFormat.Value(pattern, format, shape, l, timezoneStr, _timezone);}/*** @since 2.1*/public DeserializeFormat.Value withTimeZone(TimeZone tz) {return new DeserializeFormat.Value(pattern, format, shape, locale, null, tz);}public String getPattern() { return pattern; }public String getFormat() { return format; }public DeserializeFormat.Shape getShape() { return shape; }public Locale getLocale() { return locale; }/*** Alternate access (compared to {@link #getTimeZone()}) which is useful* when caller just wants time zone id to convert, but not as JDK* provided {@link TimeZone}** @since 2.4*/public String timeZoneAsString() {if (_timezone != null) {return _timezone.getID();}return timezoneStr;}public TimeZone getTimeZone() {TimeZone tz = _timezone;if (tz == null) {if (timezoneStr == null) {return null;}tz = TimeZone.getTimeZone(timezoneStr);_timezone = tz;}return tz;}/*** @since 2.4*/public boolean hasShape() { return shape != DeserializeFormat.Shape.ANY; }/*** @since 2.4*/public boolean hasPattern() {return (pattern != null) && (pattern.length() > 0);}/*** @since 2.4*/public boolean hasFormat() {return (format != null) && (format.length() > 0);}/*** @since 2.4*/public boolean hasLocale() { return locale != null; }/*** @since 2.4*/public boolean hasTimeZone() {return (_timezone != null) || (timezoneStr != null && !timezoneStr.isEmpty());}}}使⽤⾃定义解析注解的时间解析器import com.fasterxml.jackson.core.JsonParser;import com.fasterxml.jackson.databind.BeanProperty;import com.fasterxml.jackson.databind.DeserializationContext;import com.fasterxml.jackson.databind.JsonDeserializer;import com.fasterxml.jackson.databind.deser.ContextualDeserializer;import com.fasterxml.jackson.databind.util.StdDateFormat;import mon.collect.Lists;import ErrorCode;import Exception;import java.io.IOException;import java.text.DateFormat;import java.text.ParseException;import java.text.SimpleDateFormat;import java.util.Date;import java.util.List;import java.util.Locale;import java.util.TimeZone;import ng.StringUtils;import ng3.time.DateUtils;import org.slf4j.Logger;import org.slf4j.LoggerFactory;/*** @author ⽆名⼩⽣ Date: 2019-02-19 Time: 19:00* @version $Id$*/public class DateJsonDeserializer extends JsonDeserializer<Date> implements ContextualDeserializer {private final static Logger logger = LoggerFactory.getLogger(DateJsonDeserializer.class);private final static List<String> FORMATS = Lists.newArrayList("yyyy-MM-dd HH:mm:ss", "yyyy-MM-dd HH:mm", "yyyyMMdd-HHmmss", "yyyy-MM-dd", "MM-dd", "HH:mm:ss",public final DateFormat df;public final String formatString;public DateJsonDeserializer() {this.df = null;this.formatString = null;}public DateJsonDeserializer(DateFormat df) {this.df = df;this.formatString = "";}public DateJsonDeserializer(DateFormat df, String formatString) {this.df = df;this.formatString = formatString;}@Overridepublic Date deserialize(JsonParser p, DeserializationContext ctxt) throws IOException {try {String dateValue = p.getText();if (df == null || StringUtils.isEmpty(dateValue)) {return null;}Date date;if (StringUtils.isNumeric(dateValue)){date = new Date(Long.valueOf(dateValue));}else {String[] formatArray = FORMATS.toArray(new String[0]);date = DateUtils.parseDate(p.getText(),formatArray);}return df.parse(df.format(date));} catch (ParseException | SecurityException e) {logger.error("JSON反序列化，时间解析失败", e);throw new BizException(BizErrorCode.UNEXPECTED_ERROR);}}@Overridepublic JsonDeserializer<?> createContextual(DeserializationContext ctxt, BeanProperty property) {if (property != null) {// JsonFormat.Value format = ctxt.getAnnotationIntrospector().findFormat(property.getMember());DeserializeFormat deFormat = property.getAnnotation(DeserializeFormat.class);DeserializeFormat.Value format = (deFormat == null) ? null : new DeserializeFormat.Value(deFormat); if (format != null) {TimeZone tz = format.getTimeZone();// First: fully custom pattern?if (format.hasPattern() && !FORMATS.contains(format.getPattern())){FORMATS.add(format.getPattern());}if (format.hasFormat()) {final String dateFormat = format.getFormat();final Locale loc = format.hasLocale() ? format.getLocale() : ctxt.getLocale();SimpleDateFormat df = new SimpleDateFormat(dateFormat, loc);if (tz == null) {tz = ctxt.getTimeZone();}df.setTimeZone(tz);return new DateJsonDeserializer(df, dateFormat);}// But if not, can still override timezoneif (tz != null) {DateFormat df = ctxt.getConfig().getDateFormat();// one shortcut: with our custom format, can simplify handling a bitif (df.getClass() == StdDateFormat.class) {final Locale loc = format.hasLocale() ? format.getLocale() : ctxt.getLocale();StdDateFormat std = (StdDateFormat) df;std = std.withTimeZone(tz);std = std.withLocale(loc);df = std;} else {// otherwise need to clone, re-set timezone:df = (DateFormat) df.clone();df.setTimeZone(tz);}return new DateJsonDeserializer(df);}}}return this;}}@JsonFormat的使⽤实体类字段中添加@JsonFormat注解（），返回 yyyy-MM-dd HH:mm:ss 时间格式@JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss"， timezone = "GMT+8")private Date joinedDate;pattern：⽇期格式timezone：时区以上为个⼈经验，希望能给⼤家⼀个参考，也希望⼤家多多⽀持。
