Simulating Post Object Form Upload to OSS in Java

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Alibaba Cloud Object Storage Service (OSS) is an easy-to-use service that enables you to store, backup and archive large amounts of data on the cloud. It acts as an encrypted central repository from where one can securely access files from around the globe. Further, it guarantees up to 99.9% availability and is a perfect fit for global teams and international project management.

The Procedure

Let us look at the steps that a user needs to follow.

Content-Disposition: form-data; name="file"; filename="MyFilename.jpg"
Content-Type: image/jpeg
Content-Disposition: form-data; name="key"
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  1. Parse the content of various fields until the flow reaches the ‘file’ form field;
  2. Parse the ‘file’ form field.
import javax.activation.MimetypesFileTypeMap;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.Map;
* Created by yushuting on 16/4/17.
public class OssPostObject {
private String postFileName = "your_file";
Make sure that the file exists at the path indicated in the run code.
private String ossEndpoint = "your_endpoint";
For example:
private String ossAccessId = "your_accessid"; This is your access AK
private String ossAccessKey = "your_accesskey"; This is your access AK
private String objectName = "your_object_name"; This is the object name after you upload the file
private String bucket = "your_bucket"; Make sure that the bucket you created previously has been created.
private void PostObject() throws Exception { String filepath=postFileName;
String urlStr = ossEndpoint.replace("http://", "http://"+bucket+"."); This is the URL for the submitted form is the bucket domain name
LinkedHashMap<String, String> textMap = new LinkedHashMap<String, String>();
// key
String objectName = this.objectName;
textMap.put("key", objectName);
// Content-Disposition
textMap.put("Content-Disposition", "attachment;filename="+filepath);
// OSSAccessKeyId
textMap.put("OSSAccessKeyId", ossAccessId);
// policy
String policy = "{\"expiration\": \"2120-01-01T12:00:00.000Z\",\"conditions\": [[\"content-length-range\", 0, 104857600]]}";
String encodePolicy = java.util.Base64.getEncoder().encodeToString(policy.getBytes());
textMap.put("policy", encodePolicy);
// Signature
String signaturecom = com.aliyun.oss.common.auth.ServiceSignature.create().computeSignature(ossAccessKey, encodePolicy);
textMap.put("Signature", signaturecom);
Map<String, String> fileMap = new HashMap<String, String>();
fileMap.put("file", filepath);
String ret = formUpload(urlStr, textMap, fileMap);
System.out.println("[" + bucket + "] post_object:" + objectName);
System.out.println("post reponse:" + ret);
private static String formUpload(String urlStr, Map<String, String> textMap, Map<String, String> fileMap) throws Exception {
String res = "";
HttpURLConnection conn = null;
String BOUNDARY = "9431149156168";
try {
URL url = new URL(urlStr);
conn = (HttpURLConnection) url.openConnection();
"Mozilla/5.0 (Windows; U; Windows NT 6.1; zh-CN; rv:");
"multipart/form-data; boundary=" + BOUNDARY);
OutputStream out = new DataOutputStream(conn.getOutputStream());
// text
if (textMap != null) {
StringBuffer strBuf = new StringBuffer();
Iterator iter = textMap.entrySet().iterator();
int i = 0;
while (iter.hasNext()) {
Map.Entry entry = (Map.Entry);
String inputName = (String) entry.getKey();
String inputValue = (String) entry.getValue();
if (inputValue == null) {
if (i == 0) {
strBuf.append("Content-Disposition: form-data; name=\""
+ inputName + "\"\r\n\r\n");
} else {
strBuf.append("Content-Disposition: form-data; name=\""
+ inputName + "\"\r\n\r\n");
// file
if (fileMap != null) {
Iterator iter = fileMap.entrySet().iterator();
while (iter.hasNext()) {
Map.Entry entry = (Map.Entry);
String inputName = (String) entry.getKey();
String inputValue = (String) entry.getValue();
if (inputValue == null) {
File file = new File(inputValue);
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("Content-Disposition: form-data; name=\""
+ inputName + "\"; 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 = != -1) {
out.write(bufferOut, 0, bytes);
StringBuffer strBuf = new StringBuffer();
byte[] endData = ("\r\n--" + BOUNDARY + "--\r\n").getBytes();
// Read the returned data
StringBuffer strBuf = new StringBuffer();
BufferedReader reader = new BufferedReader(new InputStreamReader(
String line = null;
while ((line = reader.readLine()) != null) {
res = strBuf.toString();
reader = null;
} catch (Exception e) {
System.err.println("Error in sending a POST request: " + urlStr);
throw e;
} finally {
if (conn != null) {
conn = null;
return res;
public static void main(String[] args) throws Exception {
OssPostObject ossPostObject = new OssPostObject();


Post Object makes it possible to upload files to a bucket based on the browser. Encoding the message body of Post Object utilizes multipart/form-data. In the Post Object operation, the program transfers the parameters as the form fields in the message body. Post Object uses AccessKeySecret to compute the signature for the policy. Although the post form field is optional for uploading public-read-write buckets, we recommend you use this field to limit POST requests.

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