以下是表格：
<form action="/example/html5/demo_form.asp" method="post"
enctype=”multipart/form-data”>
<input type="file" name="img" />
<input type="text" name=username" value="foo"/>
<input type="submit" />
</form>
何时提交此表单，请求将如下所示：
POST /example/html5/demo_form.asp HTTP/1.1
Host: 10.143.47.59:9093
Connection: keep-alive
Content-Length: 326
Accept: application/json, text/javascript, */*; q=0.01
Origin: http://10.143.47.59:9093
X-Requested-With: XMLHttpRequest
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/60.0.3112.90 Safari/537.36
Content-Type: multipart/form-data; boundary=----WebKitFormBoundaryEDKBhMZFowP9Leno
Accept-Encoding: gzip, deflate
Accept-Language: en-US,en;q=0.8,zh-CN;q=0.6,zh;q=0.4
Request Payload
------WebKitFormBoundaryEDKBhMZFowP9Leno
Content-Disposition: form-data; name="username"
foo
------WebKitFormBoundaryEDKBhMZFowP9Leno
Content-Disposition: form-data; name="img"; filename="out.txt"
Content-Type: text/plain
------WebKitFormBoundaryEDKBhMZFowP9Leno--
请注意“请求有效负载”，你可以在表单中看到两个参数，用户名和img（form-data; name =“img”; filename =“out.txt”），并且名字是文件系统中的实际文件名（或路径），您将在后端按名称（而不是文件名）接收文件（例如spring controller）。 如果我们使用Apache Httpclient来模拟请求，我们将编写这样的代码：
MultipartEntity mutiEntity = newMultipartEntity();
File file = new File("/path/to/your/file");
mutiEntity.addPart("username",new StringBody("foo", Charset.forName("utf-8")));
mutiEntity.addPart("img", newFileBody(file)); //img is name, file is path
但在java 9中，我们可以编写这样的代码：
HttpClient client = HttpClient.newHttpClient();
HttpRequest request = HttpRequest.
newBuilder(new URI("http:///example/html5/demo_form.asp"))
.method("post",HttpRequest.BodyProcessor.fromString("foo"))
.method("post", HttpRequest.BodyProcessor.fromFile(Paths.get("/path/to/your/file")))
.build();
HttpResponse response = client.send(request, HttpResponse.BodyHandler.asString());
System.out.println(response.body());
现在你看，我怎么能设置参数的“名称”？
我想为一个项目做这个，而不必拉入Apache客户端，所以我写了一个MultiPartBodyPublisher（Java 11，fyi）：
import java.io.IOException;
import java.io.InputStream;
import java.io.UncheckedIOException;
import java.net.http.HttpRequest;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.*;
import java.util.function.Supplier;
public class MultiPartBodyPublisher {
private List<PartsSpecification> partsSpecificationList = new ArrayList<>();
private String boundary = UUID.randomUUID().toString();
public HttpRequest.BodyPublisher build() {
if (partsSpecificationList.size() == 0) {
throw new IllegalStateException("Must have at least one part to build multipart message.");
}
addFinalBoundaryPart();
return HttpRequest.BodyPublishers.ofByteArrays(PartsIterator::new);
}
public String getBoundary() {
return boundary;
}
public MultiPartBodyPublisher addPart(String name, String value) {
PartsSpecification newPart = new PartsSpecification();
newPart.type = PartsSpecification.TYPE.STRING;
newPart.name = name;
newPart.value = value;
partsSpecificationList.add(newPart);
return this;
}
public MultiPartBodyPublisher addPart(String name, Path value) {
PartsSpecification newPart = new PartsSpecification();
newPart.type = PartsSpecification.TYPE.FILE;
newPart.name = name;
newPart.path = value;
partsSpecificationList.add(newPart);
return this;
}
public MultiPartBodyPublisher addPart(String name, Supplier<InputStream> value, String filename, String contentType) {
PartsSpecification newPart = new PartsSpecification();
newPart.type = PartsSpecification.TYPE.STREAM;
newPart.name = name;
newPart.stream = value;
newPart.filename = filename;
newPart.contentType = contentType;
partsSpecificationList.add(newPart);
return this;
}
private void addFinalBoundaryPart() {
PartsSpecification newPart = new PartsSpecification();
newPart.type = PartsSpecification.TYPE.FINAL_BOUNDARY;
newPart.value = "--" + boundary + "--";
partsSpecificationList.add(newPart);
}
static class PartsSpecification {
public enum TYPE {
STRING, FILE, STREAM, FINAL_BOUNDARY
}
PartsSpecification.TYPE type;
String name;
String value;
Path path;
Supplier<InputStream> stream;
String filename;
String contentType;
}
class PartsIterator implements Iterator<byte[]> {
private Iterator<PartsSpecification> iter;
private InputStream currentFileInput;
private boolean done;
private byte[] next;
PartsIterator() {
iter = partsSpecificationList.iterator();
}
@Override
public boolean hasNext() {
if (done) return false;
if (next != null) return true;
try {
next = computeNext();
} catch (IOException e) {
throw new UncheckedIOException(e);
}
if (next == null) {
done = true;
return false;
}
return true;
}
@Override
public byte[] next() {
if (!hasNext()) throw new NoSuchElementException();
byte[] res = next;
next = null;
return res;
}
private byte[] computeNext() throws IOException {
if (currentFileInput == null) {
if (!iter.hasNext()) return null;
PartsSpecification nextPart = iter.next();
if (PartsSpecification.TYPE.STRING.equals(nextPart.type)) {
String part =
"--" + boundary + "\r\n" +
"Content-Disposition: form-data; name=" + nextPart.name + "\r\n" +
"Content-Type: text/plain; charset=UTF-8\r\n\r\n" +
nextPart.value + "\r\n";
return part.getBytes(StandardCharsets.UTF_8);
}
if (PartsSpecification.TYPE.FINAL_BOUNDARY.equals(nextPart.type)) {
return nextPart.value.getBytes(StandardCharsets.UTF_8);
}
String filename;
String contentType;
if (PartsSpecification.TYPE.FILE.equals(nextPart.type)) {
Path path = nextPart.path;
filename = path.getFileName().toString();
contentType = Files.probeContentType(path);
if (contentType == null) contentType = "application/octet-stream";
currentFileInput = Files.newInputStream(path);
} else {
filename = nextPart.filename;
contentType = nextPart.contentType;
if (contentType == null) contentType = "application/octet-stream";
currentFileInput = nextPart.stream.get();
}
String partHeader =
"--" + boundary + "\r\n" +
"Content-Disposition: form-data; name=" + nextPart.name + "; filename=" + filename + "\r\n" +
"Content-Type: " + contentType + "\r\n\r\n";
return partHeader.getBytes(StandardCharsets.UTF_8);
} else {
byte[] buf = new byte[8192];
int r = currentFileInput.read(buf);
if (r > 0) {
byte[] actualBytes = new byte[r];
System.arraycopy(buf, 0, actualBytes, 0, r);
return actualBytes;
} else {
currentFileInput.close();
currentFileInput = null;
return "\r\n".getBytes(StandardCharsets.UTF_8);
}
}
}
}
}
您可以大致使用它：
MultiPartBodyPublisher publisher = new MultiPartBodyPublisher()
.addPart("someString", "foo")
.addPart("someInputStream", () -> this.getClass().getResourceAsStream("test.txt"), "test.txt", "text/plain")
.addPart("someFile", pathObject);
HttpRequest request = HttpRequest.newBuilder()
.uri(URI.create("https://www.example.com/dosomething"))
.header("Content-Type", "multipart/form-data; boundary=" + publisher.getBoundary())
.timeout(Duration.ofMinutes(1))
.POST(publisher.build())
.build();
请注意，输入流的addPart实际上需要一个Supplier<InputStream>而不仅仅是InputStream。
您可以进行多形式数据通话的方向如下：
BodyProcessor可以与其默认实现一起使用，或者也可以使用自定义实现。几乎没有使用它们的方法是：
HttpRequest.BodyProcessor dataProcessor = HttpRequest.BodyProcessor.fromString("{\"username\":\"foo\"}")
Path path = Paths.get("/path/to/your/file"); // in your case path to 'img'
HttpRequest.BodyProcessor fileProcessor = HttpRequest.BodyProcessor.fromFile(path);
要么
apache.commons.lang（或您可以提供的自定义方法）将文件输入转换为字节数组，以添加一个小的util，如：
org.apache.commons.fileupload.FileItem file;
org.apache.http.HttpEntity multipartEntity = org.apache.http.entity.mime.MultipartEntityBuilder.create()
.addPart("username",new StringBody("foo", Charset.forName("utf-8")))
.addPart("img", newFileBody(file))
.build();
multipartEntity.writeTo(byteArrayOutputStream);
byte[] bytes = byteArrayOutputStream.toByteArray();
然后byte []可以与BodyProcessor一起使用：
HttpRequest.BodyProcessor byteProcessor = HttpRequest.BodyProcessor.fromByteArray();
此外，您可以创建请求：
HttpRequest request = HttpRequest.newBuilder()
.uri(new URI("http:///example/html5/demo_form.asp"))
.headers("Content-Type","multipart/form-data","boundary","boundaryValue") // appropriate boundary values
.POST(dataProcessor)
.POST(fileProcessor)
.POST(byteProcessor) //self-sufficient
.build();
相同的响应可以作为文件处理，并使用新的HttpClient
HttpResponse.BodyHandler bodyHandler = HttpResponse.BodyHandler.asFile(Paths.get("/path"));
HttpClient client = HttpClient.newBuilder().build();
如：
HttpResponse response = client.send(request, bodyHandler);
System.out.println(response.body());
即使看到并阅读此页面，我仍然在这个问题上挣扎了一段时间。但是，使用此页面上的答案指出我正确的方向，阅读更多关于多部分形式和边界，并修补，我能够创建一个有效的解决方案。
解决方案的要点是使用Apache的MultipartEntityBuilder来创建实体及其边界（HttpExceptionBuilder是一个本土类）：
import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.util.Optional;
import java.util.function.Supplier;
import org.apache.commons.lang3.Validate;
import org.apache.http.HttpEntity;
import org.apache.http.entity.BufferedHttpEntity;
import org.apache.http.entity.ContentType;
import org.apache.http.entity.mime.MultipartEntityBuilder;
/**
* Class containing static helper methods pertaining to HTTP interactions.
*/
public class HttpUtils {
public static final String MULTIPART_FORM_DATA_BOUNDARY = "ThisIsMyBoundaryThereAreManyLikeItButThisOneIsMine";
/**
* Creates an {@link HttpEntity} from a {@link File}, loading it into a {@link BufferedHttpEntity}.
*
* @param file the {@link File} from which to create an {@link HttpEntity}
* @param partName an {@link Optional} denoting the name of the form data; defaults to {@code data}
* @return an {@link HttpEntity} containing the contents of the provided {@code file}
* @throws NullPointerException if {@code file} or {@code partName} is null
* @throws IllegalStateException if {@code file} does not exist
* @throws HttpException if file cannot be found or {@link FileInputStream} cannot be created
*/
public static HttpEntity getFileAsBufferedMultipartEntity(final File file, final Optional<String> partName) {
Validate.notNull(file, "file cannot be null");
Validate.validState(file.exists(), "file must exist");
Validate.notNull(partName, "partName cannot be null");
final HttpEntity entity;
final BufferedHttpEntity bufferedHttpEntity;
try (final FileInputStream fis = new FileInputStream(file);
final BufferedInputStream bis = new BufferedInputStream(fis)) {
entity = MultipartEntityBuilder.create().setBoundary(MULTIPART_FORM_DATA_BOUNDARY)
.addBinaryBody(partName.orElse("data"), bis, ContentType.APPLICATION_OCTET_STREAM, file.getName())
.setContentType(ContentType.MULTIPART_FORM_DATA).build();
try {
bufferedHttpEntity = new BufferedHttpEntity(entity);
} catch (final IOException e) {
throw HttpExceptionBuilder.create().withMessage("Unable to create BufferedHttpEntity").withThrowable(e)
.build();
}
} catch (final FileNotFoundException e) {
throw HttpExceptionBuilder.create()
.withMessage("File does not exist or is not readable: %s", file.getAbsolutePath()).withThrowable(e)
.build();
} catch (final IOException e) {
throw HttpExceptionBuilder.create()
.withMessage("Unable to create multipart entity from file: %s", file.getAbsolutePath())
.withThrowable(e).build();
}
return bufferedHttpEntity;
}
/**
* Returns a {@link Supplier} of {@link InputStream} containing the content of the provided {@link HttpEntity}. This
* method closes the {@code InputStream}.
*
* @param entity the {@link HttpEntity} from which to get an {@link InputStream}
* @return an {@link InputStream} containing the {@link HttpEntity#getContent() content}
* @throws NullPointerException if {@code entity} is null
* @throws HttpException if something goes wrong
*/
public static Supplier<? extends InputStream> getInputStreamFromHttpEntity(final HttpEntity entity) {
Validate.notNull(entity, "entity cannot be null");
return () -> {
try (final InputStream is = entity.getContent()) {
return is;
} catch (final UnsupportedOperationException | IOException e) {
throw HttpExceptionBuilder.create().withMessage("Unable to get InputStream from HttpEntity")
.withThrowable(e).build();
}
};
}
}
然后是使用这些辅助方法的方法：
private String doUpload(final File uploadFile, final String filePostUrl) {
assert uploadFile != null : "uploadFile cannot be null";
assert uploadFile.exists() : "uploadFile must exist";
assert StringUtils.notBlank(filePostUrl, "filePostUrl cannot be blank");
final URI uri = URI.create(filePostUrl);
final HttpEntity entity = HttpUtils.getFileAsBufferedMultipartEntity(uploadFile, Optional.of("partName"));
final String response;
try {
final Builder requestBuilder = HttpRequest.newBuilder(uri)
.POST(BodyPublisher.fromInputStream(HttpUtils.getInputStreamFromHttpEntity(entity)))
.header("Content-Type", "multipart/form-data; boundary=" + HttpUtils.MULTIPART_FORM_DATA_BOUNDARY);
response = this.httpClient.send(requestBuilder.build(), BodyHandler.asString());
} catch (InterruptedException | ExecutionException e) {
throw HttpExceptionBuilder.create().withMessage("Unable to get InputStream from HttpEntity")
.withThrowable(e).build();
}
LOGGER.info("Http Response: {}", response);
return response;
}
可以使用multipart/form-data或任何其他内容类型 - 但您必须自己以正确的格式对身体进行编码。客户端本身不根据内容类型进行任何编码。
这意味着你最好的选择是使用另一个类似Apache HttpComponents客户端的HTTP客户端，或者只使用另一个库的编码器，如@nullpointer的答案示例。
如果你自己编码身体，请注意你不能多次调用像POST这样的方法。 POST只需设置BodyProcessor并再次调用它将覆盖任何以前设置的处理器。您必须实现一个以正确格式生成整个身体的处理器。
对于multipart/form-data，这意味着：
boundary标头设置为适当的值boundary + "\nContent-Disposition: form-data; name=\"" + name + "\"\n\n" + value + "\n"
这里，名称是指HTML表单中的name属性。对于问题中的文件输入，这将是img，值将是编码的文件内容。