Why Does My Java HttpClient File Upload to PHP Fail, and How Can I Fix It?

How to Successfully Upload a File Using Java HttpClient Library and PHP

When attempting to upload a file from a Java application to an Apache server running PHP using the Jakarta HttpClient library, you may encounter the following issue:

Problem Statement:

A Java application using the Jakarta HttpClient library to upload a file to an Apache server with PHP fails to register the file in PHP. The is_uploaded_file method returns false, and the $_FILES variable remains empty.

Solution:

The provided Java code contained an error that prevented successful file upload. The following corrected Java class addresses this issue:

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:9001/upload.php");
    File file = new File("c:/TRASH/zaba_1.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();
  }
}

Explanation:

The key difference between the previous and corrected Java code lies in the use of MultipartEntity. The PHP script expects data in a multipart/form-data format, which the previous code did not adhere to. By using MultipartEntity, the data is formatted correctly and the file upload process can be completed successfully.

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