表单上传是使用HTML表单形式上传文件（Object）到指定存储空间（Bucket）中，文件最大不能超过5 GB。

以下代码用于表单上传：

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public class PostObjectSample {
    // 上传文件
    private String localFilePath = "<yourLocalFile>";
    // Endpoint以杭州为例，其它Region请按实际情况填写。
    private String endpoint = "http://oss-cn-hangzhou.aliyuncs.com";
    // 阿里云主账号AccessKey拥有所有API的访问权限，风险很高。强烈建议您创建并使用RAM账号进行API访问或日常运维，请登录RAM控制台创建RAM账号。
    private String accessKeyId = "<yourAccessKeyId>";
    private String accessKeySecret = "<yourAccessKeySecret>";
    // 设置存储空间名称。
    private String bucketName = "<yourBucketName>";
    // 设置文件名称。
    private String objectName = "<yourObjectName>";
    /**
     * 表单上传。
     * @throws Exception
     */
    private void PostObject() throws Exception {
        // 在URL中添加存储空间名称，添加后URL如下：http://yourBucketName.oss-cn-hangzhou.aliyuncs.com。
        String urlStr = endpoint.replace("http://", "http://" + bucketName+ ".");
        // 设置表单Map。
        Map<String, String> formFields = new LinkedHashMap<String, String>();
        // 设置文件名称。
        formFields.put("key", this.objectName);
        // 设置Content-Disposition。
        formFields.put("Content-Disposition", "attachment;filename="
                + localFilePath);
        // 设置回调参数。
        Callback callback = new Callback();
        // 设置回调服务器地址，如http://oss-demo.aliyuncs.com:23450或http://127.0.0.1:9090。
        callback.setCallbackUrl("<yourCallbackServerUrl>");
        // 设置回调请求消息头中Host的值，如oss-cn-hangzhou.aliyuncs.com。
        callback.setCallbackHost("<yourCallbackServerHost>");
        // 设置发起回调时请求body的值。
        callback.setCallbackBody("{\\\"mimeType\\\":${mimeType},\\\"size\\\":${size}}");
        // 设置发起回调请求的Content-Type。
        callback.setCalbackBodyType(CalbackBodyType.JSON);
        // 设置发起回调请求的自定义参数，由Key和Value组成，Key必须以x:开始，且必须小写。
        callback.addCallbackVar("x:var1", "value1");
        callback.addCallbackVar("x:var2", "value2");
        // 在表单Map中设置回调参数。
        setCallBack(formFields, callback);
        // 设置OSSAccessKeyId。
        formFields.put("OSSAccessKeyId", accessKeyId);
        String policy = "{\"expiration\": \"2120-01-01T12:00:00.000Z\",\"conditions\": [[\"content-length-range\", 0, 104857600]]}";
        String encodePolicy = new String(Base64.encodeBase64(policy.getBytes()));
        // 设置policy。
        formFields.put("policy", encodePolicy);
        // 生成签名。
        String signaturecom = com.aliyun.oss.common.auth.ServiceSignature.create().computeSignature(accessKeySecret, encodePolicy);
        // 设置签名。
        formFields.put("Signature", signaturecom);
        String ret = formUpload(urlStr, formFields, localFilePath);
        System.out.println("Post Object [" + this.objectName + "] to bucket [" + bucketName + "]");
        System.out.println("post reponse:" + ret);
    }
    private static String formUpload(String urlStr, Map<String, String> formFields, String localFile)
            throws Exception {
        String res = "";
        HttpURLConnection conn = null;
        String boundary = "9431149156168";
        try {
            URL url = new URL(urlStr);
            conn = (HttpURLConnection) url.openConnection();
            conn.setConnectTimeout(5000);
            conn.setReadTimeout(30000);
            conn.setDoOutput(true);
            conn.setDoInput(true);
            conn.setRequestMethod("POST");
            conn.setRequestProperty("User-Agent",
                    "Mozilla/5.0 (Windows; U; Windows NT 6.1; zh-CN; rv:1.9.2.6)");
            // 设置MD5值。MD5值由整个body计算得出。
            conn.setRequestProperty("Content-MD5", "<yourContentMD5>");
            conn.setRequestProperty("Content-Type",
                    "multipart/form-data; boundary=" + boundary);
            OutputStream out = new DataOutputStream(conn.getOutputStream());
            // 遍历读取表单Map中的数据，将数据写入到输出流中。
            if (formFields != null) {
                StringBuffer strBuf = new StringBuffer();
                Iterator<Entry<String, String>> iter = formFields.entrySet().iterator();
                int i = 0;
                while (iter.hasNext()) {
                    Entry<String, String> entry = iter.next();
                    String inputName = entry.getKey();
                    String inputValue = entry.getValue();
                    if (inputValue == null) {
                        continue;
                    }
                    if (i == 0) {
                        strBuf.append("--").append(boundary).append("\r\n");
                        strBuf.append("Content-Disposition: form-data; name=\""
                                + inputName + "\"\r\n\r\n");
                        strBuf.append(inputValue);
                    } else {
                        strBuf.append("\r\n").append("--").append(boundary).append("\r\n");
                        strBuf.append("Content-Disposition: form-data; name=\""
                                + inputName + "\"\r\n\r\n");
                        strBuf.append(inputValue);
                    }
                    i++;
                }
                out.write(strBuf.toString().getBytes());
            }
            // 读取文件信息，将要上传的文件写入到输出流中。
            File file = new File(localFile);
            String filename = file.getName();
            String contentType = new MimetypesFileTypeMap().getContentType(file);
            if (contentType == null || contentType.equals("")) {
                contentType = "application/octet-stream";
            }
            StringBuffer strBuf = new StringBuffer();
            strBuf.append("\r\n").append("--").append(boundary)
                    .append("\r\n");
            strBuf.append("Content-Disposition: form-data; name=\"file\"; "
                    + "filename=\"" + filename + "\"\r\n");
            strBuf.append("Content-Type: " + contentType + "\r\n\r\n");
            out.write(strBuf.toString().getBytes());
            DataInputStream in = new DataInputStream(new FileInputStream(file));
            int bytes = 0;
            byte[] bufferOut = new byte[1024];
            while ((bytes = in.read(bufferOut)) != -1) {
                out.write(bufferOut, 0, bytes);
            }
            in.close();
            byte[] endData = ("\r\n--" + boundary + "--\r\n").getBytes();
            out.write(endData);
            out.flush();
            out.close();
            // 读取返回数据。
            strBuf = new StringBuffer();
            BufferedReader reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));
            String line = null;
            while ((line = reader.readLine()) != null) {
                strBuf.append(line).append("\n");
            }
            res = strBuf.toString();
            reader.close();
            reader = null;
        } catch (Exception e) {
            System.err.println("Send post request exception: " + e);
            throw e;
        } finally {
            if (conn != null) {
                conn.disconnect();
                conn = null;
            }
        }
        return res;
    }
     private static void setCallBack(Map<String, String> formFields, Callback callback) {
        if (callback != null) {
            String jsonCb = OSSUtils.jsonizeCallback(callback);
            String base64Cb = BinaryUtil.toBase64String(jsonCb.getBytes());
            formFields.put("callback", base64Cb);
            if (callback.hasCallbackVar()) {
                Map<String, String> varMap = callback.getCallbackVar();
                for (Entry<String, String> entry : varMap.entrySet()) {
                    formFields.put(entry.getKey(), entry.getValue());
                }
            }
        }
    }
    public static void main(String[] args) throws Exception {
        PostObjectSample ossPostObject = new PostObjectSample();
        ossPostObject.PostObject();
    }
}

有关表单上传的适用场景及详细介绍，请参见表单上传和PostObject。有关回调的详细介绍，请参见Callback。