背景
项目中开发导入功能,因为数据量比较大，所以要求后端异步操作。发现改为异步之后，相同代码的情况下会报(No such file or directory)异常
2020-02-28 16:22:51.322 [pool-2-thread-1] ERROR c.c.l.m.business.service.impl.CommonServiceImpl - /private/var/folders/gj/_gbl0m854pn1lw6dn2k4w1gr0000gn/T/tomcat.5469750062936240832.8081/work/Tomcat/localhost/lm-admin/upload_bc9f994f_f4dc_4a2e_9933_dbcec37b3a7e_00000001.tmp (No such file or directory) com.alibaba.fastjson.JSONException: write javaBean error, fastjson version 1.2.45, class org.springframework.web.multipart.support.StandardMultipartHttpServletRequest$StandardMultipartFile at com.alibaba.fastjson.serializer.JavaBeanSerializer.write(JavaBeanSerializer.java:465) at com.alibaba.fastjson.serializer.JavaBeanSerializer.write(JavaBeanSerializer.java:120) at com.alibaba.fastjson.serializer.JSONSerializer.write(JSONSerializer.java:280) at com.alibaba.fastjson.JSON.toJSONString(JSON.java:673) at com.alibaba.fastjson.JSON.toJSONString(JSON.java:611) at com.alibaba.fastjson.JSON.toJSONString(JSON.java:576) at com.citi.lm.modules.business.service.impl.CommonServiceImpl.readAndHandleFile(CommonServiceImpl.java:93) at com.citi.lm.modules.business.service.impl.CommonServiceImpl$$FastClassBySpringCGLIB$$82c8f695.invoke(<generated>) at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204) at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:684) at com.citi.lm.modules.business.service.impl.CommonServiceImpl$$EnhancerBySpringCGLIB$$5f90c28f.readAndHandleFile(<generated>) at com.citi.lm.modules.business.controller.CommonController$1.call(CommonController.java:84) at java.util.concurrent.FutureTask.run$$$capture(FutureTask.java:266) at java.util.concurrent.FutureTask.run(FutureTask.java) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) at java.lang.Thread.run(Thread.java:748) Caused by: java.lang.reflect.InvocationTargetException at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at com.alibaba.fastjson.util.FieldInfo.get(FieldInfo.java:484) at com.alibaba.fastjson.serializer.FieldSerializer.getPropertyValueDirect(FieldSerializer.java:135) at com.alibaba.fastjson.serializer.JavaBeanSerializer.write(JavaBeanSerializer.java:249) ... 16 more Caused by: java.io.FileNotFoundException: /private/var/folders/gj/_gbl0m854pn1lw6dn2k4w1gr0000gn/T/tomcat.5469750062936240832.8081/work/Tomcat/localhost/lm-admin/upload_bc9f994f_f4dc_4a2e_9933_dbcec37b3a7e_00000001.tmp (No such file or directory) at java.io.FileInputStream.open0(Native Method) at java.io.FileInputStream.open(FileInputStream.java:195) at java.io.FileInputStream.<init>(FileInputStream.java:138) at org.apache.tomcat.util.http.fileupload.disk.DiskFileItem.getInputStream(DiskFileItem.java:194) at org.apache.catalina.core.ApplicationPart.getInputStream(ApplicationPart.java:100) at org.springframework.web.multipart.support.StandardMultipartHttpServletRequest$StandardMultipartFile.getBytes(StandardMultipartHttpServletRequest.java:245) ... 23 more
纠错
不啰嗦过程，最后将焦点集中在接口接收的MultipartFile类型参数上。debug跟踪MultipartFile类型参数发现，在主线程结束响应之后，MultipartFile类型参数就消失了。
分析
说明在响应结束之后，file的内存区域被清除回收了，和servlet规范一致。个人理解，file参数对象就像servlet的request和response对象一样，请求一结束就被清理了。
解决
目前没有解决办法，因为后来项目需求把接收的文件保存下来，那么对我来说就不是问题了。但是我想可以在创建处理线程之前把file中的二进制流转成其他形式保留下来，然后对新保留的数据进行处理。