将文件从Java客户端上传到HTTP服务器

69

我想将一些文件上传到HTTP服务器。基本上，我需要的是对服务器的某种POST请求，其中包含一些参数和文件。我看到了仅上传文件的示例，但是没有找到如何也传递其他参数的示例。

什么是最简单，免费的解决方案？有人有我可以学习的文件上传示例吗？我已经搜寻了几个小时，但是（也许只是那几天之一）找不到我真正需要的东西。最好的解决方案是不涉及任何第三方类或库的东西。

java  file-upload  urlconnection 
— 马吕斯
source

Answers:

101

通常，您会java.net.URLConnection用来触发HTTP请求。通常，您还可以multipart/form-data对混合的POST内容（二进制和字符数据）使用编码。单击链接，其中包含信息以及如何组成multipart/form-data请求正文的示例。该规范在RFC2388中有更详细的描述。

这是一个启动示例：

String url = "http://example.com/upload";
String charset = "UTF-8";
String param = "value";
File textFile = new File("/path/to/file.txt");
File binaryFile = new File("/path/to/file.bin");
String boundary = Long.toHexString(System.currentTimeMillis()); // Just generate some unique random value.
String CRLF = "\r\n"; // Line separator required by multipart/form-data.

URLConnection connection = new URL(url).openConnection();
connection.setDoOutput(true);
connection.setRequestProperty("Content-Type", "multipart/form-data; boundary=" + boundary);

try (
    OutputStream output = connection.getOutputStream();
    PrintWriter writer = new PrintWriter(new OutputStreamWriter(output, charset), true);
) {
    // Send normal param.
    writer.append("--" + boundary).append(CRLF);
    writer.append("Content-Disposition: form-data; name=\"param\"").append(CRLF);
    writer.append("Content-Type: text/plain; charset=" + charset).append(CRLF);
    writer.append(CRLF).append(param).append(CRLF).flush();

    // Send text file.
    writer.append("--" + boundary).append(CRLF);
    writer.append("Content-Disposition: form-data; name=\"textFile\"; filename=\"" + textFile.getName() + "\"").append(CRLF);
    writer.append("Content-Type: text/plain; charset=" + charset).append(CRLF); // Text file itself must be saved in this charset!
    writer.append(CRLF).flush();
    Files.copy(textFile.toPath(), output);
    output.flush(); // Important before continuing with writer!
    writer.append(CRLF).flush(); // CRLF is important! It indicates end of boundary.

    // Send binary file.
    writer.append("--" + boundary).append(CRLF);
    writer.append("Content-Disposition: form-data; name=\"binaryFile\"; filename=\"" + binaryFile.getName() + "\"").append(CRLF);
    writer.append("Content-Type: " + URLConnection.guessContentTypeFromName(binaryFile.getName())).append(CRLF);
    writer.append("Content-Transfer-Encoding: binary").append(CRLF);
    writer.append(CRLF).flush();
    Files.copy(binaryFile.toPath(), output);
    output.flush(); // Important before continuing with writer!
    writer.append(CRLF).flush(); // CRLF is important! It indicates end of boundary.

    // End of multipart/form-data.
    writer.append("--" + boundary + "--").append(CRLF).flush();
}

// Request is lazily fired whenever you need to obtain information about response.
int responseCode = ((HttpURLConnection) connection).getResponseCode();
System.out.println(responseCode); // Should be 200

当您使用第三方库（例如Apache Commons HttpComponents Client）时，此代码不太冗长。

某些错误建议表明，Apache Commons FileUpload仅在服务器端有用。您不能在客户端使用它，也不需要它。

也可以看看

— BalusC
source
谢谢，我会尝试的。问题是关于这一行：writer.println（paramToSend）; 我不应该使用编码器对此值进行编码吗？还是按原样发送？
— Marius
不multipart/form-data，不是application/x-www-form-urlencoded。但是，您想指定使用的字符集。我已经相应地更新了答案。
— BalusC 2010年
我刚试过 出了点问题:(另一端的PHP脚本将整个内容视为一个后置参数。它认为“ Content-type ... etc。”是该参数，其他所有内容都是该值。我正在使用linux，这是println的问题，因为AFAIK这些东西应该使用\ r \ n终端线吗？还是只是缺少一些东西？
— Marius
没关系，我认为内容类型不应该写入正文并作为标题发送，因此以下行对其进行了修复：connection.setRequestProperty（“ Content-Type”，“ multipart / form-data; boundary =” + boundary ）;
— Marius
1
@ Drifter64：嗯，只需将其添加throws IOException到中的方法中即可public void foo() throws IOException。到目前为止，尚无明智的方法来处理异常，因此调用者应对此负责。另请参见有关异常的Oracle基本Java教程。在这种特殊情况下，肯定需要嵌套的try块，因为必须保证在使用后释放外部资源，否则，您的应用程序或早或晚将由于耗尽资源而终止运行时环境。这绝对不是样式问题。只是以正确的方式编写代码。
— BalusC 2014年
37

这是使用Apache HttpClient的方式（此解决方案适用于那些不介意使用第3方库的用户）：

    HttpEntity entity = MultipartEntityBuilder.create()
                       .addPart("file", new FileBody(file))
                       .build();

    HttpPost request = new HttpPost(url);
    request.setEntity(entity);

    HttpClient client = HttpClientBuilder.create().build();
    HttpResponse response = client.execute(request);
— 伊曼纽尔·布尔格（Emmanuel Bourg）
source
13
不建议使用MultipartEntity，我们必须改用MultipartBuilder：HttpEntity entity = MultipartEntityBuilder.create().addTextBody("field1", "value1").addBinaryBody("myfile", new File("/path/file1.txt"), ContentType.create("application/octet-stream"), "file1.txt").build();
— 捕获
您还需要像这样替换已弃用的DefaultHttpClient：HttpClient client = HttpClientBuilder.create（）。build（）;
— mmaceachran
6

单击链接获取示例文件，使用apache HttpComponents上传clint java

http://hc.apache.org/httpcomponents-client-ga/httpmime/examples/org/apache/http/examples/entity/mime/ClientMultipartFormPost.java

和图书馆downalod链接

https://hc.apache.org/downloads.cgi

使用4.5.3.zip在我的代码中工作正常

和我的工作代码

import java.io.File;
import org.apache.http.HttpEntity;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.ContentType;
import org.apache.http.entity.mime.MultipartEntityBuilder;
import org.apache.http.entity.mime.content.FileBody;
import org.apache.http.entity.mime.content.StringBody;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;

public class ClientMultipartFormPost {

     public static void main(String[] args) throws Exception {

          CloseableHttpClient httpclient = HttpClients.createDefault();
          try {
             HttpPost httppost = new HttpPost("http://localhost:8080/MyWebSite1/UploadDownloadFileServlet");

             FileBody bin = new FileBody(new File("E:\\meter.jpg"));
             StringBody comment = new StringBody("A binary file of some kind", ContentType.TEXT_PLAIN);

             HttpEntity reqEntity = MultipartEntityBuilder.create()
                .addPart("bin", bin)
                .addPart("comment", comment)
                .build();


             httppost.setEntity(reqEntity);

             System.out.println("executing request " + httppost.getRequestLine());
             CloseableHttpResponse response = httpclient.execute(httppost);
           try {
                System.out.println("----------------------------------------");
                System.out.println(response.getStatusLine());
                HttpEntity resEntity = response.getEntity();
                if (resEntity != null) {
                     System.out.println("Response content length: " +    resEntity.getContentLength());
                }
              EntityUtils.consume(resEntity);
             } finally {
                 response.close();
            }
       } finally {
          httpclient.close();
      }
   }

}
— 普拉尚
source
1

这是使用Java 11的java.net.http软件包的方法：

    var fileA = new File("a.pdf");
    var fileB = new File("b.pdf");

    var mimeMultipartData = MimeMultipartData.newBuilder()
            .withCharset(StandardCharsets.UTF_8)
            .addFile("file1", fileA.toPath(), Files.probeContentType(fileA.toPath()))
            .addFile("file2", fileB.toPath(), Files.probeContentType(fileB.toPath()))
            .build();

    var request = HttpRequest.newBuilder()
            .header("Content-Type", mimeMultipartData.getContentType())
            .POST(mimeMultipartData.getBodyPublisher())
            .uri(URI.create("http://somehost/upload"))
            .build();

    var httpClient = HttpClient.newBuilder().build();
    var response = httpClient.send(request, BodyHandlers.ofString());

使用以下MimeMultipartData：

public class MimeMultipartData {

    public static class Builder {

        private String boundary;
        private Charset charset = StandardCharsets.UTF_8;
        private List<MimedFile> files = new ArrayList<MimedFile>();
        private Map<String, String> texts = new LinkedHashMap<>();

        private Builder() {
            this.boundary = new BigInteger(128, new Random()).toString();
        }

        public Builder withCharset(Charset charset) {
            this.charset = charset;
            return this;
        }

        public Builder withBoundary(String boundary) {
            this.boundary = boundary;
            return this;
        }

        public Builder addFile(String name, Path path, String mimeType) {
            this.files.add(new MimedFile(name, path, mimeType));
            return this;
        }

        public Builder addText(String name, String text) {
            texts.put(name, text);
            return this;
        }

        public MimeMultipartData build() throws IOException {
            MimeMultipartData mimeMultipartData = new MimeMultipartData();
            mimeMultipartData.boundary = boundary;

            var newline = "\r\n".getBytes(charset);
            var byteArrayOutputStream = new ByteArrayOutputStream();
            for (var f : files) {
                byteArrayOutputStream.write(("--" + boundary).getBytes(charset)); 
                byteArrayOutputStream.write(newline);
                byteArrayOutputStream.write(("Content-Disposition: form-data; name=\"" + f.name + "\"; filename=\"" + f.path.getFileName() + "\"").getBytes(charset));
                byteArrayOutputStream.write(newline);
                byteArrayOutputStream.write(("Content-Type: " + f.mimeType).getBytes(charset));
                byteArrayOutputStream.write(newline);
                byteArrayOutputStream.write(newline);
                byteArrayOutputStream.write(Files.readAllBytes(f.path));
                byteArrayOutputStream.write(newline);
            }
            for (var entry: texts.entrySet()) {
                byteArrayOutputStream.write(("--" + boundary).getBytes(charset));
                byteArrayOutputStream.write(newline);
                byteArrayOutputStream.write(("Content-Disposition: form-data; name=\"" + entry.getKey() + "\"").getBytes(charset));
                byteArrayOutputStream.write(newline);
                byteArrayOutputStream.write(newline);
                byteArrayOutputStream.write(entry.getValue().getBytes(charset));
                byteArrayOutputStream.write(newline);
            }
            byteArrayOutputStream.write(("--" + boundary + "--").getBytes(charset));

            mimeMultipartData.bodyPublisher = BodyPublishers.ofByteArray(byteArrayOutputStream.toByteArray());
            return mimeMultipartData;
        }

        public class MimedFile {

            public final String name;
            public final Path path;
            public final String mimeType;

            public MimedFile(String name, Path path, String mimeType) {
                this.name = name;
                this.path = path;
                this.mimeType = mimeType;
            }
        }
    }

    private String boundary;
    private BodyPublisher bodyPublisher;

    private MimeMultipartData() {
    }

    public static Builder newBuilder() {
        return new Builder();
    }

    public BodyPublisher getBodyPublisher() throws IOException {
        return bodyPublisher;
    }

    public String getContentType() {
        return "multipart/form-data; boundary=" + boundary;
    }

}
— 尼尔斯·萨缪尔森（Nils Samuelsson）
source
0 
public static String simSearchByImgURL(int  catid ,String imgurl) throws IOException{
    CloseableHttpClient httpClient = HttpClients.createDefault();
    CloseableHttpResponse response = null;
    String result =null;
    try {
        HttpPost httppost = new HttpPost("http://api0.visualsearchapi.com:8084/vsearchtech/api/v1.0/apisim_search");
        StringBody catidBody = new StringBody(catid+"" , ContentType.TEXT_PLAIN);
        StringBody keyBody = new StringBody(APPKEY , ContentType.TEXT_PLAIN);
        StringBody langBody = new StringBody(LANG , ContentType.TEXT_PLAIN);
        StringBody fmtBody = new StringBody(FMT , ContentType.TEXT_PLAIN);
        StringBody imgurlBody = new StringBody(imgurl , ContentType.TEXT_PLAIN);
        MultipartEntityBuilder builder = MultipartEntityBuilder.create();
        builder.addPart("apikey", keyBody).addPart("catid", catidBody)
        .addPart("lang", langBody)
        .addPart("fmt", fmtBody)
        .addPart("imgurl", imgurlBody);
        HttpEntity reqEntity =  builder.build();
        httppost.setEntity(reqEntity);
        response = httpClient.execute(httppost);
        HttpEntity resEntity = response.getEntity();
        if (resEntity != null) {
           // result = ConvertStreamToString(resEntity.getContent(), "UTF-8");
            String charset = "UTF-8";   
          String content=EntityUtils.toString(response.getEntity(), charset);   
            System.out.println(content);
        }
        EntityUtils.consume(resEntity);
    }catch(Exception e){
        e.printStackTrace();
    }finally {
        response.close();
        httpClient.close();
    }
    return result;
}
— 深层连结
source
尝试上面的示例。来自此站点visualsearchapi.com。完整的代码链接在此处visualsearchapi.com/apiDoc/apiDoc?apiDoc=V。祝好运。
— Deeplink's
-2 
protected void doPost(HttpServletRequest request,
        HttpServletResponse response) throws ServletException, IOException {

    boolean isMultipart = ServletFileUpload.isMultipartContent(request);

    if (!isMultipart) {
        return;
    }

    DiskFileItemFactory factory = new DiskFileItemFactory();

    factory.setSizeThreshold(MAX_MEMORY_SIZE);

    factory.setRepository(new File(System.getProperty("java.io.tmpdir")));

    String uploadFolder = getServletContext().getRealPath("")
            + File.separator + DATA_DIRECTORY;//DATA_DIRECTORY is directory where you upload this file on the server

    ServletFileUpload upload = new ServletFileUpload(factory);

    upload.setSizeMax(MAX_REQUEST_SIZE);//MAX_REQUEST_SIZE is the size which size you prefer

并在html中使用<form enctype="multipart/form-data">和使用<input type="file">

— 用户名
source
那是针对服务器端（servlet）的。OP要求使用Java CLIENT。
— Stefan Reich
没有理由仅仅因为它不能直接回答OP的问题而拒绝投票。来这里的大多数人都是来自Google框架设计不佳的人，他们会发现这样的回答很有帮助。
— Kinjal Dixit
-6

它可能取决于您的框架。（对于它们中的每一个都可以存在一个更简单的解决方案）。

但要回答您的问题：此功能有很多外部库。看这里如何使用文件上传Apache的百科全书。

— 卡塞尔
source
1
我没有拒绝投票，但我想是出于同样的原因，另一个答案也被拒绝了。您回答了如何使用servlet接收上传的文件，问题是询问如何发送文件。特别是在POST中带有其他数据。通常，如果您从链接到页面的页面上解释或复制有用/相关的部分，将使答案对读者更有用，并且在链接失效时仍能保留有用性。
— Arkaine55
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