本文示例工程下载:https://files.cnblogs.com/files/xiandedanteng/WebFileDownload20191026.rar
制作一个Webapp,让其中一个网页提供下载链接,以使用户能下载本地文件或是临时生成的文件,这些都不是难事,网上也有很多既存的解决方案。
但是,这个问题难点在,但生成文件过大时,产生java.lang.OutOfMemoryError异常怎么办?有人提出修改JVM内存参数,如-Xms<min>m -Xmx<max>m方式,但终究是治标不治本的方法,如果下载数据量又超过设定的上限呢?
其实问题的本质是:在为大数据生成准备过程中,大量对象产生了来不及释放,因为还需要在接下来的步骤中使用,所以驻留在内存中,内存越积越多,终究导致java.lang.OutOfMemoryError异常。举个例子来说,有个emp表,存储员工的id姓名年龄等,当只有千百条时,取出结果集转成链表再写入csv文件自然没什么问题,但如果数据越来越多,还是结果集放链表里又来不及释放,总有内存不够的时候。
2019-10-25 14:43:05.518 ERROR 40016 --- [nio-8080-exec-6] o.a.c.c.C.[.[.[/].[dispatcherServlet] : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Handler dispatch failed; nested exception is java.lang.OutOfMemoryError: GC overhead limit exceeded] with root cause java.lang.OutOfMemoryError: GC overhead limit exceeded at java.lang.Integer.toString(Unknown Source) ~[na:1.8.0_201] at java.lang.String.valueOf(Unknown Source) ~[na:1.8.0_201] at com.example.demo.CsvUtil.exportBigCsv(CsvUtil.java:78) ~[classes/:na] at com.example.demo.SpringBootWeb1Application.downloadBigCsvFile(SpringBootWeb1Application.java:141) ~[classes/:na] at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_201] at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) ~[na:1.8.0_201] at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) ~[na:1.8.0_201] at java.lang.reflect.Method.invoke(Unknown Source) ~[na:1.8.0_201] at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:190) ~[spring-web-5.1.9.RELEASE.jar:5.1.9.RELEASE] at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138) ~[spring-web-5.1.9.RELEASE.jar:5.1.9.RELEASE] at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:104) ~[spring-webmvc-5.1.9.RELEASE.jar:5.1.9.RELEASE] at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:892) ~[spring-webmvc-5.1.9.RELEASE.jar:5.1.9.RELEASE] at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:797) ~[spring-webmvc-5.1.9.RELEASE.jar:5.1.9.RELEASE] at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.1.9.RELEASE.jar:5.1.9.RELEASE] at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1039) ~[spring-webmvc-5.1.9.RELEASE.jar:5.1.9.RELEASE] at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:942) ~[spring-webmvc-5.1.9.RELEASE.jar:5.1.9.RELEASE] at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1005) ~[spring-webmvc-5.1.9.RELEASE.jar:5.1.9.RELEASE] at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:897) ~[spring-webmvc-5.1.9.RELEASE.jar:5.1.9.RELEASE] at javax.servlet.http.HttpServlet.service(HttpServlet.java:634) ~[tomcat-embed-core-9.0.24.jar:9.0.24] at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:882) ~[spring-webmvc-5.1.9.RELEASE.jar:5.1.9.RELEASE] at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) ~[tomcat-embed-core-9.0.24.jar:9.0.24] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-9.0.24.jar:9.0.24] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.24.jar:9.0.24] at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.24.jar:9.0.24] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.24.jar:9.0.24] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.24.jar:9.0.24] at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99) ~[spring-web-5.1.9.RELEASE.jar:5.1.9.RELEASE] at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:118) ~[spring-web-5.1.9.RELEASE.jar:5.1.9.RELEASE] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.24.jar:9.0.24] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.24.jar:9.0.24] at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:92) ~[spring-web-5.1.9.RELEASE.jar:5.1.9.RELEASE] at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:118) ~[spring-web-5.1.9.RELEASE.jar:5.1.9.RELEASE]
要解决这个问题,就得耐下心来,将整体读整体写改成分批读分批写(分批方案和分页方案类似,诸位可自行寻找合适自己DB的DB dialect),最后再下载。
示例页面:
<!DOCTYPE html> <html lang="utf-8"> <meta http-equiv="Content-Type" content="text/html; charset=utf-8"/> <head> <title>happy go lucky</title> </head> <body> <h2>文件下载测试</h2> <hr/> <ol> <li><a href="/dldLocalFile">下载本地文件dld.rar</a></li> <li><a href="/dldGeneratedFile/100">下载生成百行CSV文件</a></li> <li><a href="/dldGeneratedFile/100000000">下载生成亿行CSV文件</a></li> <li><a href="/dldGeneratedFile2/10000000">下载生成千万行CSV文件 可能 出现java.lang.OutOfMemoryError: GC overhead limit exceeded</a></li> <li><a href="/dldGeneratedFile3/10000000">下载生成千万行CSV文件 不会可能 出现java.lang.OutOfMemoryError: GC overhead limit exceeded</a></li> </ol> </body> </html> <script type="text/javascript"> <!-- // 脚本 //--> </script>
控制类:
package com.example.demo; import java.io.File; import java.io.FileInputStream; import java.net.URLDecoder; import java.text.SimpleDateFormat; import java.util.ArrayList; import java.util.Date; import java.util.List; import javax.servlet.ServletOutputStream; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import org.apache.log4j.Logger; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; import org.springframework.stereotype.Controller; import org.springframework.web.bind.annotation.PathVariable; import org.springframework.web.bind.annotation.RequestMapping; @Controller @SpringBootApplication public class WebFileDownloadApplication { private static Logger logger = Logger.getLogger(WebFileDownloadApplication.class); public static void main(String[] args) { SpringApplication.run(WebFileDownloadApplication.class, args); } @RequestMapping("/") public String index() { logger.info("进入index页"); return "index.html"; } @RequestMapping("/dldLocalFile") public void downloadLocalFile(HttpServletResponse res, HttpServletRequest req) throws Exception { logger.info("下载本地文件"); String localFilename = "dld.rar"; String localFilepath = getClass().getResource("/static/" + localFilename).getPath(); res.setContentType("multipart/form-data"); res.setCharacterEncoding("UTF-8"); res.setContentType("text/html"); String userAgent = req.getHeader("User-Agent"); if (userAgent.contains("MSIE") || userAgent.contains("Trident")) { // IE Core localFilename = java.net.URLEncoder.encode(localFilename, "UTF-8"); } else { // Non-IE Core localFilename = new String((localFilename).getBytes("UTF-8"), "ISO-8859-1"); } res.setHeader("Content-Disposition", "attachment;fileName=" + localFilename); localFilepath = URLDecoder.decode(localFilepath, "UTF-8"); FileInputStream instream = new FileInputStream(localFilepath); ServletOutputStream outstream = res.getOutputStream(); int b = 0; byte[] buffer = new byte[1024]; while ((b = instream.read(buffer)) != -1) { outstream.write(buffer, 0, b); } instream.close(); if (outstream != null) { outstream.flush(); outstream.close(); } } @RequestMapping("/dldGeneratedFile/{count}") public void downloadGeneratedCsvFile(HttpServletResponse res, HttpServletRequest req,@PathVariable String count) throws Exception { logger.info("Start downloadGeneratedCsvFile"); SimpleDateFormat dfs = new SimpleDateFormat("yyyyMMddHHmmss"); Date time = new Date(); String tStamp = dfs.format(time); String localFilename = tStamp+".csv"; String path=req.getSession().getServletContext().getRealPath("/"); String localFilepath = path+localFilename; logger.info("准备生成的本地路径文件名="+localFilepath); res.setContentType("multipart/form-data"); res.setCharacterEncoding("UTF-8"); res.setContentType("text/html"); String userAgent = req.getHeader("User-Agent"); if (userAgent.contains("MSIE") || userAgent.contains("Trident")) { // IE Core localFilename = java.net.URLEncoder.encode(localFilename, "UTF-8"); } else { // Non-IE Core localFilename = new String((localFilename).getBytes("UTF-8"), "ISO-8859-1"); } res.setHeader("Content-Disposition", "attachment;fileName=" + localFilename); localFilepath = URLDecoder.decode(localFilepath, "UTF-8"); List<String> dataList=new ArrayList<String>(); for(int i=0;i<100;i++) { dataList.add(String.valueOf(i)); } File file=new File(localFilepath); CsvUtil.generateCsv(file,Integer.parseInt(count)); logger.info("已经生成文件:"+localFilepath); FileInputStream instream = new FileInputStream(localFilepath); ServletOutputStream outstream = res.getOutputStream(); int b = 0; byte[] buffer = new byte[1024]; while ((b = instream.read(buffer)) != -1) { outstream.write(buffer, 0, b); } instream.close(); if (outstream != null) { outstream.flush(); outstream.close(); boolean isDeleted=file.delete(); if(isDeleted) { logger.info("已经删除文件:"+localFilepath); } } } @RequestMapping("/dldGeneratedFile2/{count}") public void downloadGeneratedCsvFile2(HttpServletResponse res, HttpServletRequest req,@PathVariable String count) throws Exception { logger.info("Start downloadGeneratedCsvFile2"); SimpleDateFormat dfs = new SimpleDateFormat("yyyyMMddHHmmss"); Date time = new Date(); String tStamp = dfs.format(time); String localFilename = tStamp+".csv"; String path=req.getSession().getServletContext().getRealPath("/"); String localFilepath = path+localFilename; logger.info("准备生成的本地路径文件名="+localFilepath); res.setContentType("multipart/form-data"); res.setCharacterEncoding("UTF-8"); res.setContentType("text/html"); String userAgent = req.getHeader("User-Agent"); if (userAgent.contains("MSIE") || userAgent.contains("Trident")) { // IE Core localFilename = java.net.URLEncoder.encode(localFilename, "UTF-8"); } else { // Non-IE Core localFilename = new String((localFilename).getBytes("UTF-8"), "ISO-8859-1"); } res.setHeader("Content-Disposition", "attachment;fileName=" + localFilename); localFilepath = URLDecoder.decode(localFilepath, "UTF-8"); List<String> dataList=new ArrayList<String>(); for(int i=0;i<100;i++) { dataList.add(String.valueOf(i)); } File file=new File(localFilepath); CsvUtil.generateCsv2(file,Integer.parseInt(count)); logger.info("已经生成文件:"+localFilepath); FileInputStream instream = new FileInputStream(localFilepath); ServletOutputStream outstream = res.getOutputStream(); int b = 0; byte[] buffer = new byte[1024]; while ((b = instream.read(buffer)) != -1) { outstream.write(buffer, 0, b); } instream.close(); if (outstream != null) { outstream.flush(); outstream.close(); boolean isDeleted=file.delete(); if(isDeleted) { logger.info("已经删除文件:"+localFilepath); } } } @RequestMapping("/dldGeneratedFile3/{count}") public void downloadGeneratedCsvFile3(HttpServletResponse res, HttpServletRequest req,@PathVariable String count) throws Exception { logger.info("Start downloadGeneratedCsvFile3"); SimpleDateFormat dfs = new SimpleDateFormat("yyyyMMddHHmmss"); Date time = new Date(); String tStamp = dfs.format(time); String localFilename = tStamp+".csv"; String path=req.getSession().getServletContext().getRealPath("/"); String localFilepath = path+localFilename; logger.info("准备生成的本地路径文件名="+localFilepath); res.setContentType("multipart/form-data"); res.setCharacterEncoding("UTF-8"); res.setContentType("text/html"); String userAgent = req.getHeader("User-Agent"); if (userAgent.contains("MSIE") || userAgent.contains("Trident")) { // IE Core localFilename = java.net.URLEncoder.encode(localFilename, "UTF-8"); } else { // Non-IE Core localFilename = new String((localFilename).getBytes("UTF-8"), "ISO-8859-1"); } res.setHeader("Content-Disposition", "attachment;fileName=" + localFilename); localFilepath = URLDecoder.decode(localFilepath, "UTF-8"); List<String> dataList=new ArrayList<String>(); for(int i=0;i<100;i++) { dataList.add(String.valueOf(i)); } File file=new File(localFilepath); CsvUtil.generateCsv3(file,Integer.parseInt(count)); logger.info("已经生成文件:"+localFilepath); FileInputStream instream = new FileInputStream(localFilepath); ServletOutputStream outstream = res.getOutputStream(); int b = 0; byte[] buffer = new byte[1024]; while ((b = instream.read(buffer)) != -1) { outstream.write(buffer, 0, b); } instream.close(); if (outstream != null) { outstream.flush(); outstream.close(); boolean isDeleted=file.delete(); if(isDeleted) { logger.info("已经删除文件:"+localFilepath); } } } }
数据生成类:
package com.example.demo; import java.io.File; import java.io.FileWriter; import java.io.IOException; import java.util.ArrayList; import java.util.List; import org.apache.log4j.Logger; public class CsvUtil { private static Logger logger = Logger.getLogger(CsvUtil.class); // 这种方式不会内存溢出,因为创建的数组对象用于写完文件后在一个循环结束就释放了 public static boolean generateCsv(File file,int rowCount) { try { FileWriter fileWriter =new FileWriter(file, true); for(int j=0;j<rowCount;j++) { int lineNo=j; String[] arr=new String[20]; for(int k=0;k<arr.length;k++) { arr[k]=String.valueOf(k); } String info=String.valueOf(lineNo)+","+String.join(",", arr)+System.getProperty("line.separator"); fileWriter.write(info); } fileWriter.flush(); fileWriter.close(); } catch (IOException e) { e.printStackTrace(); } return true; } // 这种方式因为生成一个大list,容易造成内存驻留过多而溢出 public static boolean generateCsv2(File file,int rowCount) { try { // 先模拟访问数据库创建集合,当数据量大时会出现outofmemory异常 List<String[]> list=new ArrayList<String[]>(); for(int i=0;i<rowCount;i++) { String[] arr=new String[20]; for(int k=0;k<arr.length;k++) { arr[k]=String.valueOf(k); } list.add(arr); } // 再将集合写文件 FileWriter fileWriter =new FileWriter(file, true); int index=0; for(String[] arr:list) { index++; String info=String.valueOf(index)+","+String.join(",", arr)+System.getProperty("line.separator"); fileWriter.write(info); } fileWriter.flush(); fileWriter.close(); } catch (IOException e) { e.printStackTrace(); } return true; } // 这种方式改成分批写入文件方式,以规避内存溢出 public static boolean generateCsv3(File file,int rowCount) { logger.info("generateCsv3"); try { final int LinesOnceTime=10000; int count=rowCount/LinesOnceTime; for(int i=0;i<count;i++) { // 再将集合写文件 FileWriter fileWriter =new FileWriter(file, true); List<String[]> list=new ArrayList<String[]>(); // 这回list被限制在了LinesOnceTime件,这一步代表着从数据库分批取,oracle有townum支持,mysql有limit支持 for(int j=0;j<LinesOnceTime;j++) { String[] arr=new String[20]; for(int k=0;k<arr.length;k++) { arr[k]=String.valueOf(k); } list.add(arr); } int index=0; for(String[] arr:list) { index++; int lineNo=i*LinesOnceTime+index; String info=String.valueOf(lineNo)+","+String.join(",", arr)+System.getProperty("line.separator"); fileWriter.write(info); } fileWriter.flush(); fileWriter.close(); } } catch (IOException e) { e.printStackTrace(); } return true; } }
续篇请看:https://www.cnblogs.com/xiandedanteng/p/11747855.html
--END-- 2019年10月26日14:49:02