关于SpringBoot项目打成jar包后无法读取到resource下的文件的问题

遇到这个bug，花费了不少时间

报错

java.io.FileNotFoundException: class path resource [fastdfs-client.properties] cannot be resolved to absolute file path because it does not reside in the file system: jar:file:/data/FastDFS/fastdfs-1.0-SNAPSHOT.jar!/BOOT-INF/classes!/fastdfs-client.properties
	at org.springframework.util.ResourceUtils.getFile(ResourceUtils.java:217) ~[spring-core-5.0.5.RELEASE.jar!/:5.0.5.RELEASE]
	at org.springframework.core.io.AbstractFileResolvingResource.getFile(AbstractFileResolvingResource.java:133) ~[spring-core-5.0.5.RELEASE.jar!/:5.0.5.RELEASE]
	at com.lsh.unit.FastDFSUtil.upload(FastDFSUtil.java:26) ~[classes!/:1.0-SNAPSHOT]
	at com.lsh.controller.FileController.upload(FileController.java:34) ~[classes!/:1.0-SNAPSHOT]
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_161]
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_161]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_161]
	at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_161]
	at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:209) ~[spring-web-5.0.5.RELEASE.jar!/:5.0.5.RELEASE]
	at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:136) ~[spring-web-5.0.5.RELEASE.jar!/:5.0.5.RELEASE]
	at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:102) ~[spring-webmvc-5.0.5.RELEASE.jar!/:5.0.5.RELEASE]
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:877) ~[spring-webmvc-5.0.5.RELEASE.jar!/:5.0.5.RELEASE]
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:783) ~[spring-webmvc-5.0.5.RELEASE.jar!/:5.0.5.RELEASE]
	at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.0.5.RELEASE.jar!/:5.0.5.RELEASE]
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:991) ~[spring-webmvc-5.0.5.RELEASE.jar!/:5.0.5.RELEASE]
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:925) ~[spring-webmvc-5.0.5.RELEASE.jar!/:5.0.5.RELEASE]
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:974) ~[spring-webmvc-5.0.5.RELEASE.jar!/:5.0.5.RELEASE]
	at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:877) ~[spring-webmvc-5.0.5.RELEASE.jar!/:5.0.5.RELEASE]
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:661) ~[tomcat-embed-core-8.5.29.jar!/:8.5.29]
	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:851) ~[spring-webmvc-5.0.5.RELEASE.jar!/:5.0.5.RELEASE]
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:742) ~[tomcat-embed-core-8.5.29.jar!/:8.5.29]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-8.5.29.jar!/:8.5.29]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.29.jar!/:8.5.29]
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) ~[tomcat-embed-websocket-8.5.29.jar!/:8.5.29]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.29.jar!/:8.5.29]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.29.jar!/:8.5.29]
	at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99) ~[spring-web-5.0.5.RELEASE.jar!/:5.0.5.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.0.5.RELEASE.jar!/:5.0.5.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.29.jar!/:8.5.29]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.29.jar!/:8.5.29]
	at org.springframework.web.filter.HttpPutFormContentFilter.doFilterInternal(HttpPutFormContentFilter.java:109) ~[spring-web-5.0.5.RELEASE.jar!/:5.0.5.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.0.5.RELEASE.jar!/:5.0.5.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.29.jar!/:8.5.29]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.29.jar!/:8.5.29]
	at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:81) ~[spring-web-5.0.5.RELEASE.jar!/:5.0.5.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.0.5.RELEASE.jar!/:5.0.5.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.29.jar!/:8.5.29]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.29.jar!/:8.5.29]
	at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200) ~[spring-web-5.0.5.RELEASE.jar!/:5.0.5.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.0.5.RELEASE.jar!/:5.0.5.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.29.jar!/:8.5.29]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.29.jar!/:8.5.29]
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:198) ~[tomcat-embed-core-8.5.29.jar!/:8.5.29]
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) [tomcat-embed-core-8.5.29.jar!/:8.5.29]
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:496) [tomcat-embed-core-8.5.29.jar!/:8.5.29]
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140) [tomcat-embed-core-8.5.29.jar!/:8.5.29]
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81) [tomcat-embed-core-8.5.29.jar!/:8.5.29]
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87) [tomcat-embed-core-8.5.29.jar!/:8.5.29]
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342) [tomcat-embed-core-8.5.29.jar!/:8.5.29]
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:803) [tomcat-embed-core-8.5.29.jar!/:8.5.29]
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) [tomcat-embed-core-8.5.29.jar!/:8.5.29]
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:790) [tomcat-embed-core-8.5.29.jar!/:8.5.29]
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1459) [tomcat-embed-core-8.5.29.jar!/:8.5.29]
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-8.5.29.jar!/:8.5.29]
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_161]
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_161]
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-8.5.29.jar!/:8.5.29]
	at java.lang.Thread.run(Thread.java:748) [na:1.8.0_161]

原因

项目在本地的时候，启动项目运行可以读取到我们resources目录中的文件。但是项目构建成jar的形式之后，resources目录中的文件并不是直接存在系统中，而是嵌套在jar文件中。所以就获取不到，我们只能使用流的方式获取。

需要使用org.apache.commons.io包下的FileUtils.copyInputStreamToFile();方法。

依赖

		<dependency>
            <groupId>org.apache.directory.studio</groupId>
            <artifactId>org.apache.commons.io</artifactId>
            <version>2.4</version>
        </dependency>

解决

		ClassPathResource classPathResource = new ClassPathResource("fastdfs-client.properties");
		InputStream inputStream = classPathResource.getInputStream();
		File fastdfsfile = new File("/data/FastDFS/fastdfs-client.properties");
		FileUtils.copyInputStreamToFile(inputStream,fastdfsfile);
		log.info("fastdfs配置文件："+fastdfsfile.getAbsolutePath());

意思就是获取这个文件的流，通过流再复制一份新的文件，这个文件的位置是我们自己指定。
（有一种更简单的方式，就是将这个需要的配置文件复制在服务器的一个目录下，项目不读取jar包中的，而是读取我们这个目录下的文件）