使用REST模板Java Spring MVC从服务器下载大文件

Z时代
2024-01-10
分类：问答

我有一个REST服务，可以向我发送一个较大的ISO文件，REST服务中没有任何问题。现在，我编写了一个Web应用程序，该应用程序调用其余服务以获取文件，在客户端（Web应用程序）端，我收到内存不足异常。下面是我的代码

HttpHeaders headers = new HttpHeaders();//1 Line
    headers.setAccept(Arrays.asList(MediaType.APPLICATION_OCTET_STREAM));//2 Line
    headers.set("Content-Type","application/json");//3 Line
    headers.set("Cookie", "session=abc");//4 Line
    HttpEntity statusEntity=new HttpEntity(headers);//5 Line
    String uri_status=new String("http://"+ip+":8080/pcap/file?fileName={name}");//6 Line
    ResponseEntity<byte[]>resp_status=rt.exchange(uri_status, HttpMethod.GET, statusEntity, byte[].class,"File5.iso");//7 Line

我在第7行收到内存不足异常，我想我将不得不缓冲并分担一部分，但不知道如何从服务器获取此文件，文件大小约为500至700 MB。谁能帮忙。

异常堆栈：

org.springframework.web.util.NestedServletException: Handler processing failed; nested exception is java.lang.OutOfMemoryError: Java heap space org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:972) org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:852) org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:882) org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:778) javax.servlet.http.HttpServlet.service(HttpServlet.java:622) javax.servlet.http.HttpServlet.service(HttpServlet.java:729) org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) root cause java.lang.OutOfMemoryError: Java heap space java.util.Arrays.copyOf(Arrays.java:3236) java.io.ByteArrayOutputStream.grow(ByteArrayOutputStream.java:118) java.io.ByteArrayOutputStream.ensureCapacity(ByteArrayOutputStream.java:93) java.io.ByteArrayOutputStream.write(ByteArrayOutputStream.java:153) org.springframework.util.FileCopyUtils.copy(FileCopyUtils.java:113) org.springframework.util.FileCopyUtils.copyToByteArray(FileCopyUtils.java:164) org.springframework.http.converter.ByteArrayHttpMessageConverter.readInternal(ByteArrayHttpMessageConverter.java:58) org.springframework.http.converter.ByteArrayHttpMessageConverter.readInternal(ByteArrayHttpMessageConverter.java:1) org.springframework.http.converter.AbstractHttpMessageConverter.read(AbstractHttpMessageConverter.java:153) org.springframework.web.client.HttpMessageConverterExtractor.extractData(HttpMessageConverterExtractor.java:81) org.springframework.web.client.RestTemplate$ResponseEntityResponseExtractor.extractData(RestTemplate.java:627) org.springframework.web.client.RestTemplate$ResponseEntityResponseExtractor.extractData(RestTemplate.java:1) org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:454) org.springframework.web.client.RestTemplate.execute(RestTemplate.java:409) org.springframework.web.client.RestTemplate.exchange(RestTemplate.java:385) com.pcap.webapp.HomeController.getPcapFile(HomeController.java:186)

我的服务器端REST服务代码正常运行是

@RequestMapping(value = URIConstansts.GET_FILE, produces = { MediaType.APPLICATION_OCTET_STREAM_VALUE}, method = RequestMethod.GET)
public void getFile(@RequestParam(value="fileName", required=false) String fileName,HttpServletRequest request,HttpServletResponse response) throws IOException{
    byte[] reportBytes = null;
    File result=new File("/home/arpit/Documents/PCAP/dummyPath/"+fileName);
    if(result.exists()){
        InputStream inputStream = new FileInputStream("/home/arpit/Documents/PCAP/dummyPath/"+fileName); 
        String type=result.toURL().openConnection().guessContentTypeFromName(fileName);
        response.setHeader("Content-Disposition", "attachment; filename=" + fileName);
        response.setHeader("Content-Type",type);
        reportBytes=new byte[100];//New change
        OutputStream os=response.getOutputStream();//New change
        int read=0;
        while((read=inputStream.read(reportBytes))!=-1){
            os.write(reportBytes,0,read);
        }
        os.flush();
        os.close();
    }

回答：

这是我的方法。基于springJira问题的提示。

RestTemplate restTemplate // = ...;
// Optional Accept header
RequestCallback requestCallback = request -> request.getHeaders()
        .setAccept(Arrays.asList(MediaType.APPLICATION_OCTET_STREAM, MediaType.ALL));
// Streams the response instead of loading it all in memory
ResponseExtractor<Void> responseExtractor = response -> {
    // Here I write the response to a file but do what you like
    Path path = Paths.get("some/path");
    Files.copy(response.getBody(), path);
    return null;
};
restTemplate.execute(URI.create("www.something.com"), HttpMethod.GET, requestCallback, responseExtractor);

从前面提到的吉拉问题：

请注意，你不能简单地从提取器返回InputStream，因为到execute方法返回时，基础连接和流已经关闭。

Update for Spring 5

Spring 5引入了WebClient允许异步（例如，非阻塞）http请求的类。从文档：

与RestTemplate相比，WebClient是：