I have to download multiple files from S3 bucket using node.js. For that I have to write a for loop
& call the s3.getObject(param)
method to download. After the files are downloaded I have to merge their contents.
I have written like this:
var fileContentList = new ArrayList();
for(i=0; i<fileNameList.length i++){
s3.getObject({ Bucket: "my-bucket", Key: fileNameList.get(i) }, function (error, data) {
if (error != null) {
alert("Failed to retrieve an object: " + error);
} else {
alert("Loaded " + data.ContentLength + " bytes");
fileContentList.add(data.Body.toString());
}
}
);
}
//Do merging with the fileContentList.
But as s3.getObject
is an asynchronous call the current thread moves on & nothing gets added to the fileContentList
while I am doing the merging.
How can I solve the problem? Any idea?
Is their any synchronous method in aws-sdk to download file?
Promises is better way,
var getObject = function(keyFile) {
return new Promise(function(success, reject) {
s3.getObject(
{ Bucket: "my-bucket", Key: keyFile },
function (error, data) {
if(error) {
reject(error);
} else {
success(data);
}
}
);
});
}
var promises = [];
var fileContentList = new ArrayList();
for(i=0; i<fileNameList.length i++){
promises.push(getObject(fileNameList.get(i)));
}
Promise.all(promises)
.then(function(results) {
for(var index in results) {
var data = results[index];
fileContentList.add(data.Body.toString());
}
// continue your process here
})
.catch(function(err) {
alert(err);
});