fix: Spring AI 流式 API 请求 400 错误

在对 RestController 返回对象 json 格式化时，将所有 Long 类型转为 String 类型返回，避免前端数据精度丢失的问题。
 主要是为了取代 spring.jackson.generator.write-numbers-as-strings=true 配置，避免影响全局的 ObjectMapper

novel-common/src/main/java/com/java2nb/novel/core/advice/CustomResponseBodyAdvice.java

@@ -0,0 +1,45 @@
+package com.java2nb.novel.core.advice;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.module.SimpleModule;
+import com.fasterxml.jackson.databind.ser.std.ToStringSerializer;
+import org.springframework.core.MethodParameter;
+import org.springframework.http.MediaType;
+import org.springframework.http.converter.HttpMessageConverter;
+import org.springframework.http.converter.json.Jackson2ObjectMapperBuilder;
+import org.springframework.http.server.ServerHttpRequest;
+import org.springframework.http.server.ServerHttpResponse;
+import org.springframework.web.bind.annotation.RestControllerAdvice;
+import org.springframework.web.servlet.mvc.method.annotation.ResponseBodyAdvice;
+
+/**
+ * 在对 RestController 返回对象 json 格式化时，将所有 Long 类型转为 String 类型返回，避免前端数据精度丢失的问题
+ * 取代 spring.jackson.generator.write-numbers-as-strings=true 配置，避免影响全局的 ObjectMapper 配置
+ * */
+@RestControllerAdvice
+public class CustomResponseBodyAdvice implements ResponseBodyAdvice<Object> {
+
+    private final ObjectMapper customObjectMapper;
+
+    public CustomResponseBodyAdvice(Jackson2ObjectMapperBuilder builder) {
+        customObjectMapper = builder.createXmlMapper(false).build();
+        SimpleModule simpleModule = new SimpleModule();
+        simpleModule.addSerializer(Long.class, ToStringSerializer.instance);
+        simpleModule.addSerializer(Long.TYPE, ToStringSerializer.instance);
+        customObjectMapper.registerModule(simpleModule);
+    }
+
+    @Override
+    public boolean supports(MethodParameter returnType, Class<? extends HttpMessageConverter<?>> converterType) {
+        // 返回 true 表示对所有 Controller 的响应都生效
+        return true;
+    }
+
+    @Override
+    public Object beforeBodyWrite(Object body, MethodParameter returnType, MediaType selectedContentType, Class<? extends HttpMessageConverter<?>> selectedConverterType, ServerHttpRequest request, ServerHttpResponse response) {
+        // 使用自定义的 ObjectMapper 序列化响应体
+        return customObjectMapper.valueToTree(body);
+    }
+
+}
+