public class Test {
    public static void main(String[] args) {
        A a = new A();
        a.setDate(LocalDateTime.now());
        System.out.println(JSON.toJSONStringWithDateFormat(a, "yyyy-MM-dd HH:mm:ss.SSS"));
    }
}
class A {
    @JSONField( format = "yyyy-MM-dd")
    private LocalDateTime date;
    public LocalDateTime getDate() {
        return date;
    }
    public void setDate(LocalDateTime date) {
        this.date = date;
    }
}

输出时间格式化结果是: yyyy-MM-dd 而不是期望的 “yyyy-MM-dd HH:mm:ss.SSS”