使用REST模板Java Spring MVC从服务器下载大文件

Question

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

  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)

运行良好的服务器端REST服务代码是

@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();






    }

Answer 1

我是这样做的。基于这个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);

从上述Jira问题来看：

注意，您不能简单地从提取器返回InputStream，因为到execute方法返回时，底层连接和流已经关闭。

• 非阻塞、反应性，并以较少的硬件资源支持较高的并发性。
• 提供了一个利用Java 8 lambdas的函数API。
• 同时支持同步和异步方案。
• 支持从服务器上或下数据流。

要在Spring Boot中获得webclient，您需要以下依赖项：

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-webflux</artifactId>
</dependency>

目前，我坚持使用RestTemplate，因为我不想仅仅为了访问WebClient而引入另一个依赖项。