In this source code example, we will write a Java program that uses HTTP Client API to upload a resource.
We will use Java 11 HttpClient API to upload a resource file.
Java HttpClient Upload File Example
import java.io.IOException;
import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.*;
public class Main {
public static void main(String[] args) throws IOException, InterruptedException {
Map<Object, Object> data = new LinkedHashMap<>();
data.put("author", "Lorem Ipsum Generator");
data.put("filefield", Path.of("sample.txt"));
String boundary = UUID.randomUUID().toString().replaceAll("-", "");
HttpClient client = HttpClient.newHttpClient();
HttpRequest request = HttpRequest.newBuilder()
.header("Content-Type", "multipart/form-data;boundary=" + boundary)
.POST(ofMultipart(data, boundary))
.uri(URI.create("http://jkorpela.fi/cgi-bin/echoraw.cgi"))
.build();
HttpResponse<String> response = client.send(request, HttpResponse.BodyHandlers.ofString());
System.out.println("Status code: " + response.statusCode());
System.out.println("\n Body: " + response.body());
}
private static final String LINE_SEPARATOR = System.lineSeparator();
public static HttpRequest.BodyPublisher ofMultipart(
Map<Object, Object> data, String boundary) throws IOException {
final byte[] separator = ("--" + boundary + LINE_SEPARATOR
+ "Content-Disposition: form-data; name=").getBytes(StandardCharsets.UTF_8);
final List<byte[]> body = new ArrayList<>();
for (Object dataKey : data.keySet()) {
body.add(separator);
Object dataValue = data.get(dataKey);
if (dataValue instanceof Path) {
Path path = (Path) dataValue;
String mimeType = fetchMimeType(path);
body.add(("\"" + dataKey + "\"; filename=\"" + path.getFileName()
+ "\"" + LINE_SEPARATOR + "Content-Type: "
+ mimeType + LINE_SEPARATOR + LINE_SEPARATOR)
.getBytes(StandardCharsets.UTF_8));
body.add(Files.readAllBytes(path));
body.add(LINE_SEPARATOR.getBytes(StandardCharsets.UTF_8));
} else {
body.add(("\"" + dataKey + "\""
+ LINE_SEPARATOR + LINE_SEPARATOR + dataValue + LINE_SEPARATOR)
.getBytes(StandardCharsets.UTF_8));
}
}
body.add(("--" + boundary + "--").getBytes(StandardCharsets.UTF_8));
return HttpRequest.BodyPublishers.ofByteArrays(body);
}
private static String fetchMimeType(Path filenamePath) throws IOException {
String mimeType = Files.probeContentType(filenamePath);
if (mimeType == null) {
throw new IOException("Mime type could not be fetched");
}
return mimeType;
}
}