!83 isEmpty修改减少定义变量

Merge pull request !83 from XiaoBingBy/3.0

mybatis-plus-core/src/main/java/com/baomidou/mybatisplus/core/toolkit/StringUtils.java

@@ -108,11 +108,10 @@ public class StringUtils {
      * @return 判断结果
      */
     public static boolean isEmpty(final CharSequence cs) {
-        int strLen;
-        if (cs == null || (strLen = cs.length()) == 0) {
+        if (cs == null || cs.length() == 0) {
             return true;
         }
-        for (int i = 0; i < strLen; i++) {
+        for (int i = 0; i < cs.length(); i++) {
             if (!Character.isWhitespace(cs.charAt(i))) {
                 return false;
             }

mybatis-plus/src/test/java/com/baomidou/mybatisplus/test/toolkit/StringUtilsTests.java

@@ -0,0 +1,24 @@
+package com.baomidou.mybatisplus.test.toolkit;
+
+import com.baomidou.mybatisplus.core.toolkit.Assert;
+import com.baomidou.mybatisplus.core.toolkit.StringUtils;
+import org.junit.jupiter.api.Test;
+
+/**
+ * 测试 StringUtils工具类测试
+ *
+ * @author XiaoBingBy
+ * @since 2019-08-30
+ */
+public class StringUtilsTests {
+
+    @Test
+    public void isEmptyTest() {
+        Assert.isTrue(StringUtils.isEmpty(""), "error not empty");
+
+        Assert.isTrue(StringUtils.isEmpty(null), "error not empty");
+
+        Assert.isTrue(StringUtils.isEmpty("   "), "error not empty");
+    }
+
+}