下面是一个表格:

<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>

什么时候提交此表单，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“Request Payload”，可以看到表单中的两个参数，用户名和img(form-data; name="img"; filename="out.txt")，以及finename 是文件系统中的真实文件名(或路径)，您将在后端(例如 spring Controller )中按名称(而不是文件名)接收文件。
如果我们使用Apache Httpclient来模拟请求，我们会写这样的代码:

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

但是在 java 9 中，我们可以写这样的代码:

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());

现在你明白了，我该如何设置参数的“名称”？

最佳答案

我想在不需要引入 Apache 客户端的情况下为一个项目执行此操作，所以我写了一个 MultiPartBodyPublisher (Java 11，仅供引用):

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);
                }
            }
        }
    }
}

你可以大致像这样使用它:

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 addPart对于输入流，实际上需要一个 Supplier<InputStream>而不仅仅是 InputStream .

关于Java 9 HttpClient 发送多部分/表单数据请求，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/46392160/