calculatePostSignature support signature v4.

Author: huiguangjun

src/main/java/com/aliyun/oss/OSS.java

@@ -3001,6 +3001,17 @@ public CompleteMultipartUploadResult completeMultipartUpload(CompleteMultipartUp
      */
     public String calculatePostSignature(String postPolicy);
 
+    /**
+     * Calculates the signature based on the policy and access key secret.
+     *
+     * @param postPolicy
+     *            Post policy string in JSON which is generated from
+     *            {@link #generatePostPolicy(Date, PolicyConditions)}.
+     * @param date the signing time
+     * @return Post signature in bas464 string.
+     */
+    public String calculatePostSignature(String postPolicy, Date date);
+
     /**
      * Sets the {@link Bucket}'s lifecycle rule.
      * 

src/main/java/com/aliyun/oss/OSSClient.java

@@ -1187,6 +1187,11 @@ public String calculatePostSignature(String postPolicy) throws ClientException {
         }
     }
 
+    @Override
+    public String calculatePostSignature(String postPolicy, Date date) {
+        return objectOperation.calculatePostSignature(postPolicy, date);
+    }
+
     @Override
     public VoidResult setBucketLifecycle(SetBucketLifecycleRequest setBucketLifecycleRequest)
             throws OSSException, ClientException {

src/main/java/com/aliyun/oss/internal/OSSObjectOperation.java

@@ -1440,7 +1440,7 @@ public String calculatePostSignature(String postPolicy, Date date) throws Client
                 params.setRegion(region);
                 params.setCloudBoxId(cloudBoxId);
                 OSSV4Signer singer = (OSSV4Signer)OSSSignerBase.createRequestSigner(signVersion, params);
-                return singer.signPolicy(postPolicy, date);
+                return singer.signPolicy(encPolicy, date);
             } else {
                 return ServiceSignature.create().computeSignature(credsProvider.getCredentials().getSecretAccessKey(),
                         encPolicy);