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 com.google.common.collect.Lists;
import com.tujia.rba.framework.core.remote.api.BizErrorCode;
import com.tujia.rba.framework.core.remote.api.BizException;
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 org.apache.commons.lang.StringUtils;
import org.apache.commons.lang3.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;
}
public DateJsonDeserializer(DateFormat df) {
this.df = df;
this.formatString = "";
}
public DateJsonDeserializer(DateFormat df, String formatString) {
this.df = df;
this.formatString = formatString;
}
@Override
public Date deserialize(JsonParser p, DeserializationContext ctxt) throws IOException {
try {
String dateValue = p.getText();
if (df == null || StringUtils.isEmpty(dateValue)) {
return null;
}
logger.info("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);
}
}
@Override
public 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 timezone
if (tz != null) {
DateFormat df = ctxt.getConfig().getDateFormat();
// one shortcut: with our custom format, can simplify handling a bit
if (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 java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.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)
@JacksonAnnotation
public @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 annotations
private 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 2.4
*/
public 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 com.google.common.collect.Lists;
import com.tujia.rba.framework.core.remote.api.BizErrorCode;
import com.tujia.rba.framework.core.remote.api.BizException;
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 org.apache.commons.lang.StringUtils;
import org.apache.commons.lang3.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;
}
public DateJsonDeserializer(DateFormat df) {
this.df = df;
this.formatString = "";
}
public DateJsonDeserializer(DateFormat df, String formatString) {
this.df = df;
this.formatString = formatString;
}
@Override
public 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);
}
}
@Override
public 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 timezone
if (tz != null) {
DateFormat df = ctxt.getConfig().getDateFormat();
// one shortcut: with our custom format, can simplify handling a bit
if (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服务器之家。
原文链接：https://blog.csdn.net/qq_26881739/article/details/87862506