如何将Java时间戳字符串转换为Java时间戳对象？以及如何解析无符号时区偏移的时间字符串为java.time.Instant？

Let's tackle both of your questions, with a deep dive into the second one since that's the tricky part you're stuck on.

1. Converting a Timestamp String to a Java Timestamp Object #

First, note that "timestamp string" can refer to two common types—here's how to handle both:

• Epoch timestamp string (e.g., "1609459200000" for milliseconds since the Unix epoch):
  Parse it to a numeric type and use Instant's factory methods directly:

  String epochStr = "1609459200000";
  Instant instant = Instant.ofEpochMilli(Long.parseLong(epochStr));
  // Use Instant.ofEpochSecond(...) if the string represents seconds since epoch
  

• Human-readable formatted timestamp string (like your example):
  You'll need a DateTimeFormatter to parse it, which leads straight to your core problem.

2. Parsing "2021010112:12:12.10:00" to Instant #

The issue here is that the timezone offset (10:00) lacks a required sign—Java's default DateTimeFormatter expects offsets to include + or - per ISO-8601 standards. Since you know this offset represents UTC+10:00, here are two reliable solutions:

Solution 1: Preprocess the String to Add the Sign #

This is the simplest fix if you're confident all unsigned offsets are positive:

String input = "2021010112:12:12.10:00";
// Insert a "+" right after the final dot where the offset begins
int lastDotIndex = input.lastIndexOf('.');
String adjustedInput = new StringBuilder(input)
    .insert(lastDotIndex + 1, "+")
    .toString();

// Use a standard formatter for the adjusted string
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyyMMddHH:mm:ss.XXX");
ZonedDateTime zonedDateTime = ZonedDateTime.parse(adjustedInput, formatter);
Instant instant = zonedDateTime.toInstant();

Solution 2: Build a Custom Formatter for Unsigned Offsets #

If you need to support both unsigned (positive) and signed offsets (e.g., -05:00), use DateTimeFormatterBuilder to create a formatter that treats unsigned offsets as positive values:

String input = "2021010112:12:12.10:00";

DateTimeFormatter customFormatter = new DateTimeFormatterBuilder()
    // Append the main date-time pattern
    .appendPattern("yyyyMMddHH:mm:ss.")
    // Define an offset parser that accepts unsigned values (defaults to positive)
    .appendOffset("HH:mm", "+00:00")
    .toFormatter();

// Parse directly to ZonedDateTime, then convert to Instant
ZonedDateTime zonedDateTime = ZonedDateTime.parse(input, customFormatter);
Instant instant = zonedDateTime.toInstant();

Verify the Result #

Both solutions will output the same Instant for your input: 2021-01-01T02:12:12Z (since 12:12:12 UTC+10:00 translates to 02:12:12 UTC).

内容的提问来源于stack exchange，提问作者Kuldeep Singh