fix DateConvert

hutool-core/src/main/java/cn/hutool/core/convert/ConverterRegistry.java

@@ -216,7 +216,7 @@ public class ConverterRegistry implements Serializable{
 		if(type instanceof TypeReference) {
 			type = ((TypeReference<?>)type).getType();
 		}
-		
+
 		// 标准转换器
 		final Converter<T> converter = getConverter(type, isCustomFirst);
 		if (null != converter) {

hutool-core/src/main/java/cn/hutool/core/convert/impl/DateConverter.java

@@ -7,6 +7,7 @@ import cn.hutool.core.util.StrUtil;
 
 import java.time.temporal.TemporalAccessor;
 import java.util.Calendar;
+import java.util.Date;
 
 /**
  * 日期转换器
@@ -65,19 +66,25 @@ public class DateConverter extends AbstractConverter<java.util.Date> {
 		if (value instanceof Calendar) {
 			// Handle Calendar
 			mills = ((Calendar) value).getTimeInMillis();
-		} else if (value instanceof Long) {
-			// Handle Long
-			mills = (Long) value;
+		} else if (value instanceof Number) {
+			// Handle Number
+			mills = ((Number) value).longValue();
 		}else if (value instanceof TemporalAccessor) {
 			return DateUtil.date((TemporalAccessor) value);
 		} else {
 			// 统一按照字符串处理
 			final String valueStr = convertToStr(value);
+			Date date = null;
 			try {
-				mills = StrUtil.isBlank(this.format) ? DateUtil.parse(valueStr).getTime() : DateUtil.parse(valueStr, this.format).getTime();
+				date = StrUtil.isBlank(this.format) //
+						? DateUtil.parse(valueStr) //
+						: DateUtil.parse(valueStr, this.format);
 			} catch (Exception e) {
 				// Ignore Exception
 			}
+			if(null != date){
+				mills = date.getTime();
+			}
 		}
 
 		if (null == mills) {

hutool-core/src/main/java/cn/hutool/core/date/DateTime.java

@@ -269,6 +269,7 @@ public class DateTime extends Date {
 	 */
 	public DateTime offset(DateField datePart, int offset) {
 		final Calendar cal = toCalendar();
+		//noinspection MagicConstant
 		cal.add(datePart.getValue(), offset);
 
 		DateTime dt = mutable ? this : ObjectUtil.clone(this);
@@ -286,6 +287,7 @@ public class DateTime extends Date {
 	 */
 	public DateTime offsetNew(DateField datePart, int offset) {
 		final Calendar cal = toCalendar();
+		//noinspection MagicConstant
 		cal.add(datePart.getValue(), offset);
 
 		DateTime dt = ObjectUtil.clone(this);
@@ -594,6 +596,7 @@ public class DateTime extends Date {
 			locale = Locale.getDefault(Locale.Category.FORMAT);
 		}
 		final Calendar cal = (null != zone) ? Calendar.getInstance(zone, locale) : Calendar.getInstance(locale);
+		//noinspection MagicConstant
 		cal.setFirstDayOfWeek(firstDayOfWeek.getValue());
 		cal.setTime(this);
 		return cal;

hutool-core/src/test/java/cn/hutool/core/convert/ConvertToSBCAndDBCTest.java

@@ -3,8 +3,6 @@ package cn.hutool.core.convert;
 import org.junit.Assert;
 import org.junit.Test;
 
-import cn.hutool.core.convert.Convert;
-
 /**
  * 类型转换工具单元测试
  * 全角半角转换

hutool-core/src/test/java/cn/hutool/core/convert/DateConvertTest.java

@@ -21,6 +21,14 @@ public class DateConvertTest {
 		Assert.assertEquals(timeLong, value2.getTime());
 	}
 
+	@Test
+	public void toDateFromIntTest() {
+		int dateLong = -1497600000;
+		Date value = Convert.toDate(dateLong);
+		Assert.assertNotNull(value);
+		Assert.assertEquals("Mon Dec 15 00:00:00 CST 1969", value.toString());
+	}
+
 	@Test
 	public void toDateFromLocalDateTimeTest() {
 		LocalDateTime localDateTime = LocalDateTime.parse("2017-05-06T08:30:00", DateTimeFormatter.ISO_DATE_TIME);

hutool-core/src/test/java/cn/hutool/core/date/DateUtilTest.java

@@ -2,6 +2,7 @@ package cn.hutool.core.date;
 
 import cn.hutool.core.collection.CollUtil;
 import cn.hutool.core.date.BetweenFormater.Level;
+import cn.hutool.core.lang.Console;
 import org.junit.Assert;
 import org.junit.Test;
 
@@ -624,6 +625,14 @@ public class DateUtilTest {
 		Assert.assertEquals("2017-05-06 08:30:00", date.toString());
 	}
 
+	@Test
+	public void dateTest2(){
+		// 测试负数日期
+		long dateLong = -1497600000;
+		final DateTime date = DateUtil.date(dateLong);
+		Assert.assertEquals("1969-12-15 00:00:00", date.toString());
+	}
+
 	@Test
 	public void ageTest(){
 		String d1 = "2000-02-29";