使用 java HTTP POST 连接发送图像文件 [英] Send image file using java HTTP POST connections

问题描述

我正在尝试使用 Java HTTP POST 请求将图像发送到网站.

I'm trying to send an image to a website using Java HTTP POST requests.

我正在使用此处使用的基本代码将文件从 Java 客户端上传到 HTTP 服务器:

I'm using the base code used here Upload files from Java client to a HTTP server:

这是我的修改:

String urlToConnect = "http://localhost:9000/upload";
File fileToUpload = new File("C:\Users\joao\Pictures\bla.jpg");
String boundary = Long.toHexString(System.currentTimeMillis()); // Just generate some unique random value.

URLConnection connection = new URL(urlToConnect).openConnection();
connection.setDoOutput(true); // This sets request method to POST.
connection.setRequestProperty("Content-Type", "multipart/form-data; boundary=" + boundary);
PrintWriter writer = null;
try {
    writer = new PrintWriter(new OutputStreamWriter(connection.getOutputStream()));
    writer.println("--" + boundary);
    writer.println("Content-Disposition: form-data; name="picture"; filename="bla.jpg"");
    writer.println("Content-Type: image/jpeg");
    writer.println();
    BufferedReader reader = null;
    try {
        reader = new BufferedReader(new InputStreamReader(new FileInputStream(fileToUpload)));
        for (String line; (line = reader.readLine()) != null;) {
            writer.println(line);
        }
    } finally {
        if (reader != null) try { reader.close(); } catch (IOException logOrIgnore) {}
    }
    writer.println("--" + boundary + "--");
} finally {
    if (writer != null) writer.close();
}

// Connection is lazily executed whenever you request any status.
int responseCode = ((HttpURLConnection) connection).getResponseCode();
System.out.println(responseCode); // Should be 200

最后我得到了 200 响应代码，但图像有问题，如随机颜色，这让我认为这是字符编码错误.我尝试在原始示例中使用 UTF-8，但这只会创建损坏的图像.

I get a 200 response code in the end, but the image is buggy, as in, random colors, which make me think it's an error in character encoding. I tried using UTF-8 as in the original example, but that just creates a corrupt image.

我也 100% 确定这不是服务器端问题，因为我可以使用其他客户端，例如 Advanced Rest Client/Postman，并且它们可以毫无问题地发送图像.

I am also 100% sure it's not a serverside problem, because I can use rest clients such as Advanced Rest Client/Postman and they can send an image with no problems.

你能帮我找出问题所在吗?谢谢.

Can you help me pinpoint what's wrong? Thank you.

推荐答案

import java.io.File;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.HttpVersion;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.mime.MultipartEntity;
import org.apache.http.entity.mime.content.ContentBody;
import org.apache.http.entity.mime.content.FileBody;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.params.CoreProtocolPNames;
import org.apache.http.util.EntityUtils;


public class PostFile {
  public static void main(String[] args) throws Exception {
    HttpClient httpclient = new DefaultHttpClient();
    httpclient.getParams().setParameter(CoreProtocolPNames.PROTOCOL_VERSION, HttpVersion.HTTP_1_1);

    HttpPost httppost = new HttpPost("http://localhost:9000/upload");
    File file = new File("C:\Users\joao\Pictures\bla.jpg"");

    MultipartEntity mpEntity = new MultipartEntity();
    ContentBody cbFile = new FileBody(file, "image/jpeg");
    mpEntity.addPart("userfile", cbFile);


    httppost.setEntity(mpEntity);
    System.out.println("executing request " + httppost.getRequestLine());
    HttpResponse response = httpclient.execute(httppost);
    HttpEntity resEntity = response.getEntity();

    System.out.println(response.getStatusLine());
    if (resEntity != null) {
      System.out.println(EntityUtils.toString(resEntity));
    }
    if (resEntity != null) {
      resEntity.consumeContent();
    }

    httpclient.getConnectionManager().shutdown();
  }
}

使用 HttpClient 来计算此代码.使用稳定的库总是比从头开始处理更好，除非需要以自定义方式处理.

Use HttpClient to work out this code. Its always better to use stable libraries other than handling from scratch, unless there is something to be handled in custom way.

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