和数据直传到 OSS 相比，以上方法有三个缺点：
通过小程序，如微信小程序、支付宝小程序等，利用 OSS 提供的 PostObject 接口来实现表单上传.
本文以Java语言为例，讲解在服务端通过Java代码完成签名，并且设置上传回调，然后通过表单直传数据到OSS。
Java 1.6以上版本（执行命令java -version进行查看）。客户端进行表单直传到OSS时，会从浏览器向OSS发送带有Origin的请求消息。OSS对带有Origin头的请求消息会进行跨域规则（CORS）的验证。因此需要为Bucket设置跨域规则以支持Post方法。
应用服务器源码包含了签名直传服务和上传回调服务两个功能。
签名直传服务响应客户端发送给应用服务器的GET消息，代码片段如下：
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String accessId = "<yourAccessKeyId>"; // 请填写您的AccessKeyId。
String accessKey = "<yourAccessKeySecret>"; // 请填写您的AccessKeySecret。
String endpoint = "oss-cn-hangzhou.aliyuncs.com"; // 请填写您的 endpoint。
String bucket = "bucket-name"; // 请填写您的 bucketname 。
String host = "https://" + bucket + "." + endpoint; // host的格式为 bucketname.endpoint
// callbackUrl为 上传回调服务器的URL，请将下面的IP和Port配置为您自己的真实信息。
String callbackUrl = "http://88.88.88.88:8888";
String dir = "user-dir-prefix/"; // 用户上传文件时指定的前缀。
// 创建OSSClient实例。
OSS ossClient = new OSSClientBuilder().build(endpoint, accessId, accessKey);
try {
long expireTime = 30;
long expireEndTime = System.currentTimeMillis() + expireTime * 1000;
Date expiration = new Date(expireEndTime);
// PostObject请求最大可支持的文件大小为5 GB，即CONTENT_LENGTH_RANGE为5*1024*1024*1024。
PolicyConditions policyConds = new PolicyConditions();
policyConds.addConditionItem(PolicyConditions.COND_CONTENT_LENGTH_RANGE, 0, 1048576000);
policyConds.addConditionItem(MatchMode.StartWith, PolicyConditions.COND_KEY, dir);
String postPolicy = ossClient.generatePostPolicy(expiration, policyConds);
byte[] binaryData = postPolicy.getBytes("utf-8");
String encodedPolicy = BinaryUtil.toBase64String(binaryData);
String postSignature = ossClient.calculatePostSignature(postPolicy);
Map<String, String> respMap = new LinkedHashMap<String, String>();
respMap.put("accessid", accessId);
respMap.put("policy", encodedPolicy);
respMap.put("signature", postSignature);
respMap.put("dir", dir);
respMap.put("host", host);
respMap.put("expire", String.valueOf(expireEndTime / 1000));
// respMap.put("expire", formatISO8601Date(expiration));
JSONObject jasonCallback = new JSONObject();
jasonCallback.put("callbackUrl", callbackUrl);
jasonCallback.put("callbackBody",
"filename=${object}&size=${size}&mimeType=${mimeType}&height=${imageInfo.height}&width=${imageInfo.width}");
jasonCallback.put("callbackBodyType", "application/x-www-form-urlencoded");
String base64CallbackBody = BinaryUtil.toBase64String(jasonCallback.toString().getBytes());
respMap.put("callback", base64CallbackBody);
JSONObject ja1 = JSONObject.fromObject(respMap);
// System.out.println(ja1.toString());
response.setHeader("Access-Control-Allow-Origin", "*");
response.setHeader("Access-Control-Allow-Methods", "GET, POST");
response(request, response, ja1.toString());
} catch (Exception e) {
// Assert.fail(e.getMessage());
System.out.println(e.getMessage());
} finally {
ossClient.shutdown();
}
}
上传回调服务响应OSS发送给应用服务器的POST消息，代码片段如下：
protected boolean VerifyOSSCallbackRequest(HttpServletRequest request, String ossCallbackBody)
throws NumberFormatException, IOException {
boolean ret = false;
String autorizationInput = new String(request.getHeader("Authorization"));
String pubKeyInput = request.getHeader("x-oss-pub-key-url");
byte[] authorization = BinaryUtil.fromBase64String(autorizationInput);
byte[] pubKey = BinaryUtil.fromBase64String(pubKeyInput);
String pubKeyAddr = new String(pubKey);
if (!pubKeyAddr.startsWith("https://gosspublic.alicdn.com/")
&& !pubKeyAddr.startsWith("https://gosspublic.alicdn.com/")) {
System.out.println("pub key addr must be oss addrss");
return false;
}
String retString = executeGet(pubKeyAddr);
retString = retString.replace("-----BEGIN PUBLIC KEY-----", "");
retString = retString.replace("-----END PUBLIC KEY-----", "");
String queryString = request.getQueryString();
String uri = request.getRequestURI();
String decodeUri = java.net.URLDecoder.decode(uri, "UTF-8");
String authStr = decodeUri;
if (queryString != null && !queryString.equals("")) {
authStr += "?" + queryString;
}
authStr += "\n" + ossCallbackBody;
ret = doCheck(authStr, authorization, retString);
return ret;
}
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String ossCallbackBody = GetPostBody(request.getInputStream(),
Integer.parseInt(request.getHeader("content-length")));
boolean ret = VerifyOSSCallbackRequest(request, ossCallbackBody);
System.out.println("verify result : " + ret);
// System.out.println("OSS Callback Body:" + ossCallbackBody);
if (ret) {
response(request, response, "{\"Status\":\"OK\"}", HttpServletResponse.SC_OK);
} else {
response(request, response, "{\"Status\":\"verify not ok\"}", HttpServletResponse.SC_BAD_REQUEST);
}
}
原文：https://www.cnblogs.com/dalianpai/p/12984850.html