使用REST模板Java Spring MVC从服务器下载大文件

发布时间：2020-12-15 07:38:17 所属栏目：Java 来源：网络整理

导读：我有一个REST服务,它向我发送一个大的ISO文件,REST服务中没有问题. 现在我已经编写了一个Web应用程序,它调用其余服务来获取文件,在客户端(Web应用程序)端我收到Out Of memory Exception.Below是我的代码 HttpHeaders headers = new HttpHeaders();//1 Line h

我有一个REST服务,它向我发送一个大的ISO文件,REST服务中没有问题.
现在我已经编写了一个Web应用程序,它调用其余服务来获取文件,在客户端(Web应用程序)端我收到Out Of memory Exception.Below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7行收到内存异常,我想我将不得不缓冲并获取部分内容,但不知道如何从服务器获取此文件,文件大小约为500到700 MB.
谁能请你帮忙.

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服务代码工作正常

@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,read);
        }
        os.flush();
        os.close();






    }

解决方法

我就是这样做的.基于此 Spring Jira issue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"),requestCallback,responseExtractor);

从前面提到的Jira问题：

Note that you cannot simply return the InputStream from the extractor,because by the time the execute method returns,the underlying connection and stream are already closed.

春季5的更新

Spring 5引入了WebClient类,它允许异步(例如非阻塞)http请求.来自doc：

By comparison to the RestTemplate,the WebClient is:

non-blocking,reactive,and supports higher concurrency with less hardware resources.

provides a functional API that takes advantage of Java 8 lambdas.

supports both synchronous and asynchronous scenarios.

supports streaming up or down from a server.

（编辑：李大同）

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