'尝试修复配置Integer的ToStringSerializer不生效问题'

core/src/main/java/com/alibaba/fastjson2/writer/ObjectWriterCreator.java

@@ -1312,6 +1312,13 @@ protected ObjectWriter getInitWriter(ObjectWriterProvider provider, Class fieldC
                     return objectWriter;
                 }
             }
+        } else if (fieldClass == int.class || fieldClass == Integer.class) {
+            if ((provider.userDefineMask & ObjectWriterProvider.TYPE_INT32_MASK) != 0) {
+                ObjectWriter objectWriter = provider.cache.get(Integer.class);
+                if (objectWriter != ObjectWriterImplInt32.INSTANCE) {
+                    return objectWriter;
+                }
+            }
         } else if (fieldClass == long.class || fieldClass == Long.class) {
             if ((provider.userDefineMask & ObjectWriterProvider.TYPE_INT64_MASK) != 0) {
                 ObjectWriter objectWriter = provider.cache.get(Long.class);

core/src/test/java/com/alibaba/fastjson2/issues_3100/Issue3157Test.java

@@ -0,0 +1,54 @@
+package com.alibaba.fastjson2.issues_3100;
+
+import com.alibaba.fastjson.JSON;
+import com.alibaba.fastjson.serializer.SerializeConfig;
+import com.alibaba.fastjson.serializer.SerializerFeature;
+import com.alibaba.fastjson.serializer.ToStringSerializer;
+import org.junit.Assert;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Issue3157测试类
+ * @author changyi.ccy
+ */
+public class Issue3157Test {
+    /**
+     * 测试: Issue3157
+     */
+    @Test
+    public void testIssue3157() {
+        SerializeConfig stringSerializeConfig = new SerializeConfig();
+        stringSerializeConfig.put(Integer.class, ToStringSerializer.instance);
+        stringSerializeConfig.put(Long.class, ToStringSerializer.instance);
+        People people = new People("Test", 10, 10000000L);
+        String jsonText = "{\"age\":\"10\",\"hairNums\":\"10000000\",\"name\":\"Test\"}";
+        Assert.assertEquals("JSON文本不一致", jsonText, JSON.toJSONString(people, stringSerializeConfig, new SerializerFeature[0]));
+    }
+
+    /**
+     * People类
+     */
+    public static class People {
+        private String name;
+        private Integer age;
+        private Long hairNums;
+
+        public People(String name, Integer age, Long hairNums) {
+            this.name = name;
+            this.age = age;
+            this.hairNums = hairNums;
+        }
+
+        public String getName() {
+            return name;
+        }
+
+        public Integer getAge() {
+            return age;
+        }
+
+        public Long getHairNums() {
+            return hairNums;
+        }
+    }
+}