用可变的小数秒数反序列化日期的Java日期模式？

Question

@JsonFormat(pattern="yyyy-MM-dd'T'HH:mm:ss[.SSS]XXX", timezone = "UTC")
Instant timestamp;

它使用Jackson V2.6.6@JSONFormat注释来反序列化通过网络传输的JSON中的“时间戳”字段。

我所看到的是，当值类似于：

“2017-01-09T21:49:26.70Z”

Caused by: java.time.format.DateTimeParseException: Text '2017-01-09T21:49:26.7Z' could not be parsed at index 19
    at java.time.format.DateTimeFormatter.parseResolved0(DateTimeFormatter.java:1949) ~[?:1.8.0_65]
    at java.time.format.DateTimeFormatter.parse(DateTimeFormatter.java:1777) ~[?:1.8.0_65]
    at com.fasterxml.jackson.datatype.jsr310.deser.InstantDeserializer.deserialize(InstantDeserializer.java:150) ~[jackson-datatype-jsr310-2.6.6.jar:2.6.6]
    at com.fasterxml.jackson.datatype.jsr310.deser.InstantDeserializer.deserialize(InstantDeserializer.java:45) ~[jackson-datatype-jsr310-2.6.6.jar:2.6.6]
    at com.fasterxml.jackson.databind.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:520) ~[jackson-databind-2.6.6.jar:2.6.6]
    at com.fasterxml.jackson.databind.deser.impl.FieldProperty.deserializeAndSet(FieldProperty.java:101) ~[jackson-databind-2.6.6.jar:2.6.6]
    at com.fasterxml.jackson.module.afterburner.deser.SuperSonicBeanDeserializer.deserialize(SuperSonicBeanDeserializer.java:156) ~[jackson-module-afterburner-2.6.6.jar:2.6.6]
    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:3736) ~[jackson-databind-2.6.6.jar:2.6.6]
    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2764) ~[jackson-databind-2.6.6.jar:2.6.6]

我可以做些什么来修复这个模式，使它在接受小数点后第二位的小数位数方面变得灵活呢？我知道Java数据格式化中有一个宽松的概念:https://docs.oracle.com/javase/8/docs/api/Java/time/format/datetimeformatter.html

但我不确定如何将对象映射器设置为宽松模式。

Answer 1

只是一个猜测…

我怀疑您可能在Java8的早期版本中遇到了一些Java.time bug。有几个与解析相关的bug，有些在Java8的更新中得到了修复，有些在Java9中得到了修复。

我猜错误文本中的1.8.0_65字符串指的是Java8Update65。目前，Oracle实现处于更新121。

System.out.println ( "Java vendor: " + System.getProperty ( "java.vendor" ) );
System.out.println ( "Java version: " + System.getProperty ( "java.version" ) );

List<String> strings = new ArrayList<> ();
strings.add ( "2017-01-09T21:49:26.7Z" );
strings.add ( "2017-01-09T21:49:26.70Z" );
strings.add ( "2017-01-09T21:49:26.700Z" );
strings.add ( "2017-01-09T21:49:26.7000Z" );
strings.add ( "2017-01-09T21:49:26.70000Z" );

for ( String string : strings ) {
    try {
        Instant instant = Instant.parse ( string );
        System.out.println ( "GOOD - string: " + string + " parsed: " + instant );
    } catch ( DateTimeParseException e ) {
        System.out.println ( "ERROR - Failed to parse string: " + string );
    }
}
System.out.println ( "Done." );

Java vendor: Oracle Corporation
Java version: 1.8.0_121
GOOD - string: 2017-01-09T21:49:26.7Z parsed: 2017-01-09T21:49:26.700Z
GOOD - string: 2017-01-09T21:49:26.70Z parsed: 2017-01-09T21:49:26.700Z
GOOD - string: 2017-01-09T21:49:26.700Z parsed: 2017-01-09T21:49:26.700Z
GOOD - string: 2017-01-09T21:49:26.7000Z parsed: 2017-01-09T21:49:26.700Z
GOOD - string: 2017-01-09T21:49:26.70000Z parsed: 2017-01-09T21:49:26.700Z

您还可以看到相同的代码在ideone.com上运行，运行Oracle实现的Java8 Update121，没有问题。

我也试过你的格式化模式。它适用于.70和.700，但不适用于其他。

DateTimeFormatter f = DateTimeFormatter.ofPattern ( "yyyy-MM-dd'T'HH:mm:ss[.SSS]XXX" , Locale.US );
for ( String string : strings ) {
    try {
        OffsetDateTime odt = OffsetDateTime.parse ( string , f );
        System.out.println ( "GOOD - string: " + string + " parsed: " + odt );
    } catch ( DateTimeParseException e ) {
        System.out.println ( "ERROR - Failed to parse string: " + string );
    }
}
System.out.println ( "Done with 'DateTimeFormatter.ofPattern'." );

ERROR - Failed to parse string: 2017-01-09T21:49:26.7Z
GOOD - string: 2017-01-09T21:49:26.70Z parsed: 2017-01-09T21:49:26.700Z
GOOD - string: 2017-01-09T21:49:26.700Z parsed: 2017-01-09T21:49:26.700Z
ERROR - Failed to parse string: 2017-01-09T21:49:26.7000Z
ERROR - Failed to parse string: 2017-01-09T21:49:26.70000Z

仅供参考，字符串的格式如2017-01-09t21:49:26.70z是在ISO 8601标准中定义的。在解析或生成表示日期时间值的字符串时，java.time类默认使用这些标准的ISO 8601格式。