我想要将一些文件上传到HTTP服务器上。基本上我需要的是向服务器发出POST请求，带上一些参数和文件。我看过一些仅上传文件的例子，但是没有找到如何传递额外参数的方法。
有没有最简单和免费的解决方案？是否有任何上传文件的示例可以供我学习？我已经谷歌了几个小时，但是（也许只是那种日子）没有找到我需要的东西。最好的解决方案是不涉及任何第三方类或库。
8个回答
112
通常情况下，您会使用java.net.URLConnection发送HTTP请求。对于混合POST内容（二进制和字符数据），通常也会使用multipart/form-data编码。点击链接以获取有关如何组成multipart/form-data请求正文的信息和示例。该规范在RFC2388中进行了更详细的描述。
这是一个入门示例：
String url = "http://example.com/upload";
String charset = "UTF-8";
String param = "value";
File textFile = new File("/path/to/file.txt");
File binaryFile = new File("/path/to/file.bin");
String boundary = Long.toHexString(System.currentTimeMillis()); // Just generate some unique random value.
String CRLF = "\r\n"; // Line separator required by multipart/form-data.
URLConnection connection = new URL(url).openConnection();
connection.setDoOutput(true);
connection.setRequestProperty("Content-Type", "multipart/form-data; boundary=" + boundary);
try (
OutputStream output = connection.getOutputStream();
PrintWriter writer = new PrintWriter(new OutputStreamWriter(output, charset), true);
) {
// Send normal param.
writer.append("--" + boundary).append(CRLF);
writer.append("Content-Disposition: form-data; name=\"param\"").append(CRLF);
writer.append("Content-Type: text/plain; charset=" + charset).append(CRLF);
writer.append(CRLF).append(param).append(CRLF).flush();
// Send text file.
writer.append("--" + boundary).append(CRLF);
writer.append("Content-Disposition: form-data; name=\"textFile\"; filename=\"" + textFile.getName() + "\"").append(CRLF);
writer.append("Content-Type: text/plain; charset=" + charset).append(CRLF); // Text file itself must be saved in this charset!
writer.append(CRLF).flush();
Files.copy(textFile.toPath(), output);
output.flush(); // Important before continuing with writer!
writer.append(CRLF).flush(); // CRLF is important! It indicates end of boundary.
// Send binary file.
writer.append("--" + boundary).append(CRLF);
writer.append("Content-Disposition: form-data; name=\"binaryFile\"; filename=\"" + binaryFile.getName() + "\"").append(CRLF);
writer.append("Content-Type: " + URLConnection.guessContentTypeFromName(binaryFile.getName())).append(CRLF);
writer.append("Content-Transfer-Encoding: binary").append(CRLF);
writer.append(CRLF).flush();
Files.copy(binaryFile.toPath(), output);
output.flush(); // Important before continuing with writer!
writer.append(CRLF).flush(); // CRLF is important! It indicates end of boundary.
// End of multipart/form-data.
writer.append("--" + boundary + "--").append(CRLF).flush();
}
// Request is lazily fired whenever you need to obtain information about response.
int responseCode = ((HttpURLConnection) connection).getResponseCode();
System.out.println(responseCode); // Should be 200
使用第三方库比如Apache Commons HttpComponents Client可以使这段代码更加简洁。
有些人在这里错误地建议使用Apache Commons FileUpload，但实际上它只适用于服务器端，客户端不能使用也不需要使用。
另请参阅
- BalusC
13
45
以下是如何使用Apache HttpClient执行操作的方法（适用于不介意使用第三方库的人）：
HttpEntity entity = MultipartEntityBuilder.create()
.addPart("file", new FileBody(file))
.build();
HttpPost request = new HttpPost(url);
request.setEntity(entity);
HttpClient client = HttpClientBuilder.create().build();
HttpResponse response = client.execute(request);
- Emmanuel Bourg
3
16MultipartEntity已经被弃用，我们需要使用MultipartBuilder来代替：
HttpEntity entity = MultipartEntityBuilder.create().addTextBody("field1", "value1").addBinaryBody("myfile", new File("/path/file1.txt"), ContentType.create("application/octet-stream"), "file1.txt").build(); - encrest1您还需要像这样替换已弃用的DefaultHttpClient：HttpClient client = HttpClientBuilder.create().build(); - mmaceachran
Emmanuel - 我仍然从端点收到400个错误请求。您能否请检查 https://stackoverflow.com/questions/70543352/how-to-send-binary-file-using-httpclient-approach？ - ezhil
6
点击链接获取示例：使用Apache HttpComponents在Java中上传文件
下载相关库：
https://hc.apache.org/downloads.cgi
我在我的代码中使用的是4.5.3.zip版本，可以正常工作。
以下是我的可工作代码：
import java.io.File;
import org.apache.http.HttpEntity;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.ContentType;
import org.apache.http.entity.mime.MultipartEntityBuilder;
import org.apache.http.entity.mime.content.FileBody;
import org.apache.http.entity.mime.content.StringBody;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;
public class ClientMultipartFormPost {
public static void main(String[] args) throws Exception {
CloseableHttpClient httpclient = HttpClients.createDefault();
try {
HttpPost httppost = new HttpPost("http://localhost:8080/MyWebSite1/UploadDownloadFileServlet");
FileBody bin = new FileBody(new File("E:\\meter.jpg"));
StringBody comment = new StringBody("A binary file of some kind", ContentType.TEXT_PLAIN);
HttpEntity reqEntity = MultipartEntityBuilder.create()
.addPart("bin", bin)
.addPart("comment", comment)
.build();
httppost.setEntity(reqEntity);
System.out.println("executing request " + httppost.getRequestLine());
CloseableHttpResponse response = httpclient.execute(httppost);
try {
System.out.println("----------------------------------------");
System.out.println(response.getStatusLine());
HttpEntity resEntity = response.getEntity();
if (resEntity != null) {
System.out.println("Response content length: " + resEntity.getContentLength());
}
EntityUtils.consume(resEntity);
} finally {
response.close();
}
} finally {
httpclient.close();
}
}
}
- prashant00101
1
Prashant - 我仍然从端点收到400个错误请求。你能否请检查一下 https://stackoverflow.com/questions/70543352/how-to-send-binary-file-using-httpclient-approach ？ - ezhil
2
以下是使用Java 11的java.net.http包实现的方法：
var fileA = new File("a.pdf");
var fileB = new File("b.pdf");
var mimeMultipartData = MimeMultipartData.newBuilder()
.withCharset(StandardCharsets.UTF_8)
.addFile("file1", fileA.toPath(), Files.probeContentType(fileA.toPath()))
.addFile("file2", fileB.toPath(), Files.probeContentType(fileB.toPath()))
.build();
var request = HttpRequest.newBuilder()
.header("Content-Type", mimeMultipartData.getContentType())
.POST(mimeMultipartData.getBodyPublisher())
.uri(URI.create("http://somehost/upload"))
.build();
var httpClient = HttpClient.newBuilder().build();
var response = httpClient.send(request, BodyHandlers.ofString());
使用以下MimeMultipartData：
public class MimeMultipartData {
public static class Builder {
private String boundary;
private Charset charset = StandardCharsets.UTF_8;
private List<MimedFile> files = new ArrayList<MimedFile>();
private Map<String, String> texts = new LinkedHashMap<>();
private Builder() {
this.boundary = new BigInteger(128, new Random()).toString();
}
public Builder withCharset(Charset charset) {
this.charset = charset;
return this;
}
public Builder withBoundary(String boundary) {
this.boundary = boundary;
return this;
}
public Builder addFile(String name, Path path, String mimeType) {
this.files.add(new MimedFile(name, path, mimeType));
return this;
}
public Builder addText(String name, String text) {
texts.put(name, text);
return this;
}
public MimeMultipartData build() throws IOException {
MimeMultipartData mimeMultipartData = new MimeMultipartData();
mimeMultipartData.boundary = boundary;
var newline = "\r\n".getBytes(charset);
var byteArrayOutputStream = new ByteArrayOutputStream();
for (var f : files) {
byteArrayOutputStream.write(("--" + boundary).getBytes(charset));
byteArrayOutputStream.write(newline);
byteArrayOutputStream.write(("Content-Disposition: form-data; name=\"" + f.name + "\"; filename=\"" + f.path.getFileName() + "\"").getBytes(charset));
byteArrayOutputStream.write(newline);
byteArrayOutputStream.write(("Content-Type: " + f.mimeType).getBytes(charset));
byteArrayOutputStream.write(newline);
byteArrayOutputStream.write(newline);
byteArrayOutputStream.write(Files.readAllBytes(f.path));
byteArrayOutputStream.write(newline);
}
for (var entry: texts.entrySet()) {
byteArrayOutputStream.write(("--" + boundary).getBytes(charset));
byteArrayOutputStream.write(newline);
byteArrayOutputStream.write(("Content-Disposition: form-data; name=\"" + entry.getKey() + "\"").getBytes(charset));
byteArrayOutputStream.write(newline);
byteArrayOutputStream.write(newline);
byteArrayOutputStream.write(entry.getValue().getBytes(charset));
byteArrayOutputStream.write(newline);
}
byteArrayOutputStream.write(("--" + boundary + "--").getBytes(charset));
mimeMultipartData.bodyPublisher = BodyPublishers.ofByteArray(byteArrayOutputStream.toByteArray());
return mimeMultipartData;
}
public class MimedFile {
public final String name;
public final Path path;
public final String mimeType;
public MimedFile(String name, Path path, String mimeType) {
this.name = name;
this.path = path;
this.mimeType = mimeType;
}
}
}
private String boundary;
private BodyPublisher bodyPublisher;
private MimeMultipartData() {
}
public static Builder newBuilder() {
return new Builder();
}
public BodyPublisher getBodyPublisher() throws IOException {
return bodyPublisher;
}
public String getContentType() {
return "multipart/form-data; boundary=" + boundary;
}
}
- Nils Samuelsson
0
public static String simSearchByImgURL(int catid ,String imgurl) throws IOException{
CloseableHttpClient httpClient = HttpClients.createDefault();
CloseableHttpResponse response = null;
String result =null;
try {
HttpPost httppost = new HttpPost("http://api0.visualsearchapi.com:8084/vsearchtech/api/v1.0/apisim_search");
StringBody catidBody = new StringBody(catid+"" , ContentType.TEXT_PLAIN);
StringBody keyBody = new StringBody(APPKEY , ContentType.TEXT_PLAIN);
StringBody langBody = new StringBody(LANG , ContentType.TEXT_PLAIN);
StringBody fmtBody = new StringBody(FMT , ContentType.TEXT_PLAIN);
StringBody imgurlBody = new StringBody(imgurl , ContentType.TEXT_PLAIN);
MultipartEntityBuilder builder = MultipartEntityBuilder.create();
builder.addPart("apikey", keyBody).addPart("catid", catidBody)
.addPart("lang", langBody)
.addPart("fmt", fmtBody)
.addPart("imgurl", imgurlBody);
HttpEntity reqEntity = builder.build();
httppost.setEntity(reqEntity);
response = httpClient.execute(httppost);
HttpEntity resEntity = response.getEntity();
if (resEntity != null) {
// result = ConvertStreamToString(resEntity.getContent(), "UTF-8");
String charset = "UTF-8";
String content=EntityUtils.toString(response.getEntity(), charset);
System.out.println(content);
}
EntityUtils.consume(resEntity);
}catch(Exception e){
e.printStackTrace();
}finally {
response.close();
httpClient.close();
}
return result;
}
- deeplinks
1
尝试上面的示例。它来自这个网站http://www.visualsearchapi.com。完整的代码链接在这里http://www.visualsearchapi.com/apiDoc/apiDoc?apiDoc=V。祝你好运。 - deeplinks
0
我建议使用Apache http类而不是Vanilla Java。这是一个与Java 8兼容的简单解决方案：
// Create http client.
CloseableHttpClient httpClient = HttpClients.createDefault();
final File file = new File("<FILE PATH TO POST>");
// Specify the content type of the attached file.
FileBody filebody = new FileBody(file, ContentType.MULTIPART_FORM_DATA);
MultipartEntityBuilder entitybuilder = MultipartEntityBuilder.create();
entitybuilder.setMode(HttpMultipartMode.BROWSER_COMPATIBLE);
// Add the binary file to the entity we send later on.
entitybuilder.addBinaryBody("file", file);
HttpEntity mutiPartHttpEntity = entitybuilder.build();
RequestBuilder reqbuilder = RequestBuilder.post("URL TO POST DATA WITH ALL THE PARAMETERS");
reqbuilder.setEntity(mutiPartHttpEntity);
HttpUriRequest multipartRequest = reqbuilder.build();
// Using the http client, execute http post. Variable httpresponse would contain the reply back explaining http response code, and ...
HttpResponse httpresponse = httpClient.execute(multipartRequest);
httpClient.close();
为了将参数嵌入到POST消息中，您可以将它们简单地嵌入到用于发布数据的URL中。使用此规则：?=&=。例如： https://company.com/jobs/status?jobId=876&apiKey=123 要找出与使用Http post发布的文件适合的数据类型，请参阅此链接：https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/MIME_types 导入org.apache.http.*包
如果导入未起作用，则可能需要更改pom.xml文件（如果您正在使用Maven），并将Apache软件包添加到此xml文件中。请查看此处。
- Farzan
-1
protected void doPost(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
boolean isMultipart = ServletFileUpload.isMultipartContent(request);
if (!isMultipart) {
return;
}
DiskFileItemFactory factory = new DiskFileItemFactory();
factory.setSizeThreshold(MAX_MEMORY_SIZE);
factory.setRepository(new File(System.getProperty("java.io.tmpdir")));
String uploadFolder = getServletContext().getRealPath("")
+ File.separator + DATA_DIRECTORY;//DATA_DIRECTORY is directory where you upload this file on the server
ServletFileUpload upload = new ServletFileUpload(factory);
upload.setSizeMax(MAX_REQUEST_SIZE);//MAX_REQUEST_SIZE is the size which size you prefer
在 HTML 中使用 <form enctype="multipart/form-data"> 和 <input type="file">。
- user1693371
2
这是针对服务器端（servlet）的。OP正在寻找Java客户端。 - Stefan Reich
1没有理由因为它没有直接回答 OP 的问题就给它点踩。大多数来这里的人都是从糟糕的谷歌搜索中来的，他们会发现像这样的答案很有帮助。 - Kinjal Dixit
网页内容由stack overflow 提供, 点击上面的可以查看英文原文，
原文链接
原文链接
throws IOException，如public void foo() throws IOException。到目前为止，代码中没有明智的处理异常的方式，因此调用者负责处理异常。另请参阅Oracle关于Java异常的基本教程。在这种特殊情况下，嵌套的try块绝对是必需的，因为外部资源必须在使用后得到释放，否则您的应用程序最终会让运行时环境耗尽资源而崩溃。这绝不是一个风格问题。这只是以正确的方式编写代码。 - BalusC