修复Condition的Condition("discount_end_time", "!=", (String) null)方法生成SQL时，生成SQL不符合预期要求的错误（pr#4042@Github）

hutool-db/src/main/java/cn/hutool/v7/db/sql/Condition.java

@@ -285,6 +285,16 @@ public class Condition implements Cloneable, Serializable {
 		return OPERATOR_IS.equalsIgnoreCase(this.operator);
 	}
 
+	/**
+	 * 是否 IS NOT条件
+	 *
+	 * @return 是否IS NOT条件
+	 * @since 5.8.41
+	 */
+	public boolean isOperatorIsNot() {
+		return OPERATOR_IS_NOT.equalsIgnoreCase(this.operator);
+	}
+
 	/**
 	 * 是否LIKE条件
 	 *
@@ -296,13 +306,18 @@ public class Condition implements Cloneable, Serializable {
 	}
 
 	/**
-	 * 检查值是否为null，如果为null转换为 "IS NULL"形式
+	 * 检查值是否为null，如果为null转换为 "IS NULL"或"IS NOT NULL"形式
 	 *
 	 * @return this
 	 */
 	public Condition checkValueNull() {
 		if (null == this.value) {
-			this.operator = OPERATOR_IS;
+			// 检查是否为"不等于"操作符（包括!=和<>）
+			if ("!=".equalsIgnoreCase(this.operator) || "<>".equalsIgnoreCase(this.operator)) {
+				this.operator = OPERATOR_IS_NOT;
+			} else {
+				this.operator = OPERATOR_IS;
+			}
 			this.value = VALUE_NULL;
 		}
 		return this;
@@ -375,8 +390,8 @@ public class Condition implements Cloneable, Serializable {
 			// 类似：" (?,?,?)" 或者 " (1,2,3,4)"
 			buildValuePartForIN(conditionStrBuilder, paramValues);
 		} else {
-			if (isPlaceHolder() && !isOperatorIs()) {
+			if (isPlaceHolder() && !isOperatorIs() && !isOperatorIsNot()) {
-				// 使用条件表达式占位符，条件表达式并不适用于 IS NULL
+				// 使用条件表达式占位符，条件表达式并不适用于 IS NULL和 IS NOT NULL
 				conditionStrBuilder.append(" ?");
 				if (null != paramValues) {
 					paramValues.add(this.value);

hutool-db/src/test/java/cn/hutool/v7/db/sql/ConditionTest.java

@@ -21,60 +21,71 @@ import org.junit.jupiter.api.Test;
 
 import java.math.BigDecimal;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
 public class ConditionTest {
 
 	@Test
 	public void toStringTest() {
 		final Condition conditionNull = new Condition("user", null);
-		Assertions.assertEquals("user IS NULL", conditionNull.toString());
+		assertEquals("user IS NULL", conditionNull.toString());
+
+		final Condition conditionNull2 = new Condition("user", "=", (String) null);
+		assertEquals("user IS NULL", conditionNull2.toString());
 
 		final Condition conditionNotNull = new Condition("user", "!= null");
-		Assertions.assertEquals("user IS NOT NULL", conditionNotNull.toString());
+		assertEquals("user IS NOT NULL", conditionNotNull.toString());
+
+		final Condition conditionNotNull2 = new Condition("user", "!=", (String) null);
+		assertEquals("user IS NOT NULL", conditionNotNull2.toString());
+
+		final Condition conditionNotNull3 = new Condition("user", "<>", (String) null);
+		assertEquals("user IS NOT NULL", conditionNotNull3.toString());
 
 		final Condition condition2 = new Condition("user", "= zhangsan");
-		Assertions.assertEquals("user = ?", condition2.toString());
+		assertEquals("user = ?", condition2.toString());
 
 		final Condition conditionLike = new Condition("user", "like %aaa");
-		Assertions.assertEquals("user LIKE ?", conditionLike.toString());
+		assertEquals("user LIKE ?", conditionLike.toString());
 
 		final Condition conditionIn = new Condition("user", "in 1,2,3");
-		Assertions.assertEquals("user IN (?,?,?)", conditionIn.toString());
+		assertEquals("user IN (?,?,?)", conditionIn.toString());
 
 		final Condition conditionBetween = new Condition("user", "between 12 and 13");
-		Assertions.assertEquals("user BETWEEN ? AND ?", conditionBetween.toString());
+		assertEquals("user BETWEEN ? AND ?", conditionBetween.toString());
 	}
 
 	@Test
 	public void toStringNoPlaceHolderTest() {
 		final Condition conditionNull = new Condition("user", null);
 		conditionNull.setPlaceHolder(false);
-		Assertions.assertEquals("user IS NULL", conditionNull.toString());
+		assertEquals("user IS NULL", conditionNull.toString());
 
 		final Condition conditionNotNull = new Condition("user", "!= null");
 		conditionNotNull.setPlaceHolder(false);
-		Assertions.assertEquals("user IS NOT NULL", conditionNotNull.toString());
+		assertEquals("user IS NOT NULL", conditionNotNull.toString());
 
 		final Condition conditionEquals = new Condition("user", "= zhangsan");
 		conditionEquals.setPlaceHolder(false);
-		Assertions.assertEquals("user = zhangsan", conditionEquals.toString());
+		assertEquals("user = zhangsan", conditionEquals.toString());
 
 		final Condition conditionLike = new Condition("user", "like %aaa");
 		conditionLike.setPlaceHolder(false);
-		Assertions.assertEquals("user LIKE '%aaa'", conditionLike.toString());
+		assertEquals("user LIKE '%aaa'", conditionLike.toString());
 
 		final Condition conditionIn = new Condition("user", "in 1,2,3");
 		conditionIn.setPlaceHolder(false);
-		Assertions.assertEquals("user IN (1,2,3)", conditionIn.toString());
+		assertEquals("user IN (1,2,3)", conditionIn.toString());
 
 		final Condition conditionBetween = new Condition("user", "between 12 and 13");
 		conditionBetween.setPlaceHolder(false);
-		Assertions.assertEquals("user BETWEEN 12 AND 13", conditionBetween.toString());
+		assertEquals("user BETWEEN 12 AND 13", conditionBetween.toString());
 	}
 
 	@Test
 	public void parseTest(){
 		final Condition age = Condition.parse("age", "< 10");
-		Assertions.assertEquals("age < ?", age.toString());
+		assertEquals("age < ?", age.toString());
 		// issue I38LTM
 		Assertions.assertSame(BigDecimal.class, age.getValue().getClass());
 	}
@@ -82,12 +93,12 @@ public class ConditionTest {
 	@Test
 	public void parseInTest(){
 		final Condition age = Condition.parse("age", "in 1,2,3");
-		Assertions.assertEquals("age IN (?,?,?)", age.toString());
+		assertEquals("age IN (?,?,?)", age.toString());
 	}
 
 	@Test
 	void notInTest() {
 		final Condition age = Condition.parse("age", "not in 1,2,3");
-		Assertions.assertEquals("age NOT IN (?,?,?)", age.toString());
+		assertEquals("age NOT IN (?,?,?)", age.toString());
 	}
 }