bug fix for readStringNotMatch, for issue #3438

Author: wenshao

core/src/main/java/com/alibaba/fastjson2/JSONReader.java

@@ -4733,7 +4733,12 @@ protected final String readStringNotMatch() {
                 List array = readArray();
                 if (array.size() == 1) {
                     Object item = array.get(0);
-                    return item == null ? null : item.toString();
+                    if (item == null) {
+                        return null;
+                    }
+                    if (item instanceof String) {
+                        return item.toString();
+                    }
                 }
                 return toString(array);
             case '{':

core/src/test/java/com/alibaba/fastjson2/issues_3400/Issue3438.java

@@ -0,0 +1,21 @@
+package com.alibaba.fastjson2.issues_3400;
+
+import com.alibaba.fastjson2.JSON;
+import lombok.Data;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class Issue3438 {
+    @Test
+    public void test() {
+        String aaa = "{\"file\":[{\"url\":\"http\"}]}";
+        Bbb bbb = JSON.parseObject(aaa, Bbb.class);
+        assertEquals("[{\"url\":\"http\"}]", bbb.file);
+    }
+
+    @Data
+    public static class Bbb {
+        String file;
+    }
+}

core/src/test/java/com/alibaba/fastjson2/read/ParserTest_string.java

@@ -163,13 +163,13 @@ void lexerTest(JSONReader lexer) {
         assertEquals(Fnv.hashCode64("v12"), lexer.readFieldNameHashCode());
         assertEquals(Fnv.hashCode64LCase("v12"), lexer.getNameHashCodeLCase());
         assertEquals("v12", lexer.getFieldName());
-        assertEquals("1234", lexer
+        assertEquals("[1234]", lexer
                 .readString());
 
         assertEquals(Fnv.hashCode64("v13"), lexer.readFieldNameHashCode());
         assertEquals(Fnv.hashCode64LCase("v13"), lexer.getNameHashCodeLCase());
         assertEquals("v13", lexer.getFieldName());
-        assertEquals("12.34", lexer.readString());
+        assertEquals("[12.34]", lexer.readString());
 
         assertEquals(Fnv.hashCode64("v14"), lexer.readFieldNameHashCode());
         assertEquals(Fnv.hashCode64LCase("v14"), lexer.getNameHashCodeLCase());