fix: 修复 SimpleDateFormat 线程安全的问题

[gtn1024]

No description provided.

[Copilot]

Pull request overview

This PR fixes a critical thread safety issue in the CustomDateSerializer class by removing static SimpleDateFormat instances and creating new instances per serialization call instead.

Key Changes

• Removed static DATE_FORMAT and CALENDAR_FORMAT fields that caused thread safety issues
• Refactored serialize() method to instantiate SimpleDateFormat locally for each call

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[Copilot]

While creating a new SimpleDateFormat instance per call fixes the thread safety issue, this approach has a performance cost. Consider using DateTimeFormatter instead, which is thread-safe and can be stored as a static final field (similar to CustomLocalDateTimeSerializer).

For example:

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

@Override
public void serialize(Date value, JsonGenerator gen, SerializerProvider provider) throws IOException {
    if (value instanceof java.sql.Date) {
        gen.writeString(DATE_FORMATTER.format(value.toInstant().atZone(ZoneId.systemDefault()).toLocalDate()));
    } else {
        gen.writeString(DATETIME_FORMATTER.format(value.toInstant().atZone(ZoneId.systemDefault()).toLocalDateTime()));
    }
}

Alternatively, if you need to stick with SimpleDateFormat, use ThreadLocal<SimpleDateFormat> to avoid creating new instances on every call while maintaining thread safety.