Spring Boot Uploaded Files End Up in Classpath

In this commodity, we are going to explore AWS' Simple Storage Service (S3) together with Spring Kicking to build a custom file-sharing awarding (just like in the good old days before Google Drive, Dropbox & co).

As we will larn, S3 is an extremely versatile and easy to utilise solution for a variety of use cases.

Check Out the Book!

This commodity gives but a kickoff impression of what you tin can do with AWS.

If you want to go deeper and learn how to deploy a Spring Kick awarding to the AWS cloud and how to connect information technology to cloud services similar RDS, Cognito, and SQS, make certain to cheque out the book Stratospheric - From Zilch to Production with Jump Boot and AWS!

Example Code

This commodity is accompanied past a working code example on GitHub.

What is S3?

S3 stands for "elementary storage service" and is an object store service hosted on Amazon Web Services (AWS) - simply what does this exactly mean?

You are probably familiar with databases (of any kind). Let's take Postgres for example. Postgres is a relational database, very well suited for storing structured data that has a schema that won't change too much over its lifetime (e.thou. financial transaction records). But what if we want to store more than just plain information? What if nosotros want to store a picture, a PDF, a certificate, or a video?

It is technically possible to shop those binary files in Postgres but object stores like S3 might be better suited for storing unstructured data.

Object Store vs. File Shop

And so we might ask ourselves, how is an object store different from a file shop? Without going into the gory details, an object store is a repository that stores objects in a apartment structure, similar to a key-value store.

Every bit opposed to file-based storage where we have a hierarchy of files within folders, inside folders,… the only thing nosotros need to get an item out of an object store is the key of the object we want to remember. Additionally, we can provide metadata (data about data) that we attach to the object to further enrich information technology.

Understanding Basic S3 Concepts

S3 was ane of the start services offered by AWS in 2006. Since then, a lot of features have been added but the core concepts of S3 are nonetheless Buckets and Objects.

Buckets

Buckets are containers of objects we want to store. An important thing to notation hither is that S3 requires the proper name of the bucket to be globally unique.

Objects

Objects are the actual things we are storing in S3. They are identified by a central which is a sequence of Unicode characters whose UTF-8 encoding is at most 1,024 bytes long.

Key Delimiter

By default, the "/" grapheme gets special treatment if used in an object fundamental. As written above, an object store does non apply directories or folders just but keys. However, if we use a "/" in our object key, the AWS S3 console will render the object equally if it was in a folder.

So, if our object has the fundamental "foo/bar/test.json" the panel will show a "binder" foo that contains a "folder" bar which contains the actual object. This key delimiter helps u.s. to group our data into logical hierarchies.

Building an S3 Sample Application

Going frontward nosotros are going to explore the bones operations of S3. Nosotros do then by building our ain file-sharing application (lawmaking on GitHub) that lets usa share files with other people securely and, if nosotros desire, temporarily limited.

The sample application does include a lot of code that is not directly related to S3. The io.jgoerner.s3.adapter.out.s3 packet is solely focused on the S3 specific bits.

The application's README has all instructions needed to launch it. You don't have to use the application to follow this article. It is merely meant every bit supportive means to explain certain S3 concepts.

Setting up AWS & AWS SDK

The get-go step is to prepare an AWS business relationship (if we haven't already) and to configure our AWS credentials. Hither is another commodity that explains this set up in great detail (only the initial configuration paragraphs are needed here, so feel gratuitous to come dorsum later on nosotros are all set).

Spring Boot & S3

Our sample application is going to use the Spring Cloud for Amazon Web Services projection. The chief advantage over the official AWS SDK for Coffee is the convenience and head start we get by using the Spring project. A lot of common operations are wrapped into higher-level APIs that reduce the corporeality of boilerplate lawmaking.

Spring Cloud AWS gives us the org.springframework.deject:jump-deject-starter-aws dependency which bundles all the dependencies nosotros need to communicate with S3.

Configuring Spring Boot

Just as with any other Spring Kick application, nosotros can make use of an application.backdrop/application.yaml file to store our configuration:

                          ## application.yaml              cloud:              aws:              region:              static:              eu-cardinal-1              stack:              auto:              imitation              credentials:              profile-proper noun:              dev                      

The snippet above does a few things:

• region.static: nosotros statically set up our AWS region to exist european union-central-1 (because that is the region that is closest to me).
• stack.motorcar: this option would have enabled the automatic stack name detection of the application. Equally nosotros don't rely on the AWS CloudFormation service, we want to disable that setting (only here is a great article well-nigh automatic deployment with CloudFormation in case nosotros desire to larn more well-nigh information technology).
• credentials.profile-name: we tell the application to apply the credentials of the profile named dev (that'southward how I named my AWS contour locally).

If nosotros configured our credentials properly we should be able to start the application. However, due to a known issue we might want to add the following snippet to the configuration file to prevent noise in the awarding logs:

                          logging:              level:              com:              amazonaws:              util:              EC2MetadataUtils:              error                      

What the higher up configuration does is just adjusting the log level for the class com.amazonaws.util.EC2MetadataUtils to error so we don't see the alarm logs anymore.

Amazon S3 Client

The core class to handle the communication with S3 is the com.amazonaws.services.s3.AmazonS3Client. Thanks to Bound Kicking's dependency injection we can simply utilize the constructor to get a reference to the customer:

                          public              form              S3Repository              {              private              final              AmazonS3Client s3Client;              public              S3Repository              (AmazonS3Client s3Client)              {              this              .              s3Client              =              s3Client;              }              // other repository methods                                          }                      

Creating a Bucket

Before we tin can upload whatsoever file, nosotros accept to have a bucket. Creating a saucepan is quite like shooting fish in a barrel:

            s3Client.              createBucket              (              "my-awesome-bucket"              );                      

We simply apply the createBucket() method and specify the name of the bucket. This sends the request to S3 to create a new saucepan for us. As this request is going to be handled asynchronously, the client gives u.s.a. the way to cake our application until that saucepan exists:

                          // optionally block to look until creation is finished                            s3Client              .              waiters              ()              .              bucketExists              ()              .              run              (              new              WaiterParameters<>(              new              HeadBucketRequest(              "my-awesome-bucket"              )              )              );                      

Nosotros but apply the client'southward waiters() method and run a HeadBucketRequest (like to the HTTP head method).

As mentioned before, the name of the S3 bucket has to exist globally unique, so often I finish up with rather long or non-man readable bucket names. Unfortunately, nosotros can't adhere any metadata to the bucket (as opposed to objects). Therefore, the sample awarding uses a little lookup tabular array to map human and UI friendly names to globally unique ones. This is not required when working with S3, but something to amend the usability.

Creating a Bucket in the Sample Awarding

1. Navigate to the Spaces section
2. Click on New Space
3. Enter the name and click Submit
4. A message should popular up to point success

Uploading a File

Now that our bucket is created nosotros are all set to upload a file of our choice. The client provides us with the overloaded putObject() method. Besides the fine-grained PutObjectRequest nosotros can utilize the function in iii ways:

                          // String-based                            Cord content              =              ...;              s3Client.              putObject              (              "my-bucket"              ,              "my-central"              ,              content);              // File-based                            File file              =              ...;              s3Client.              putObject              (              "my-bucket"              ,              "my-key"              ,              file);              // InputStream-based                            InputStream input              =              ...;              Map<String,              Cord>              metadata              =              ...;              s3Client.              putObject              (              "my-bucket"              ,              "my-key"              ,              input,              metadata);                      

In the simplest case, nosotros tin can directly write the content of a String into an object. We tin likewise put a File into a bucket. Or we tin can utilise an InputStream.

Simply the concluding option gives us the possibility to directly adhere metadata in the form of a Map<String, String> to the uploaded object.

In our sample application, nosotros attach a human being-readable proper name to the object while making the key random to avert collisions inside the bucket - and then we don't demand any additional lookup tables.

Object metadata can be quite useful, merely we should note that S3 does not give usa the possibility to directly search an object by metadata. If nosotros are looking for a specific metadata key (east.m. section existence set to Engineering) we have to bear upon all objects in our bucket and filter based on that property.

At that place are some upper boundaries worth mentioning when it comes to the size of the uploaded object. At the fourth dimension of writing this article, we can upload an detail of max 5GB inside a single functioning equally we did with putObject(). If nosotros use the client'due south initiateMultipartUpload() method, it is possible to upload an object of max 5TB through a Multipart upload.

Uploading a File in the Sample Application

1. Navigate to the Spaces department
2. Select Details on the target Space/Bucket
3. Click on Upload File
4. Selection the file, provide a name and click Submit
5. A message should pop up to point success

Listing Files

Once we have uploaded our files, nosotros want to exist able to recollect them and list the content of a bucket. The simplest style to practise and then is the client's listObjectV2() method:

            s3Client              .              listObjectsV2              (              "my-awesome-bucket"              )              .              getObjectSummaries              ();                      

Like to concepts of the JSON API, the object keys are non direct returned but wrapped in a payload that as well contains other useful information almost the request (eastward.g. such equally pagination information). We get the object details by using the getObjectSummaries() method.

What does V2 mean?

AWS released version 2 of their AWS SDK for Java in late 2018. Some of the client's methods offer both versions of the role, hence the V2 suffix of the listObjectsV2() method.

As our sample application doesn't use the S3ObjectSummary model that the client provides the states, we map those results into our domain model:

            s3Client.              listObjectsV2              (bucket).              getObjectSummaries              ()              .              stream              ()              .              map              (S3ObjectSummary::getKey)              .              map              (cardinal              ->              mapS3ToObject(bucket,              cardinal))              // custom mapping office                                          .              collect              (Collectors.              toList              ());                      

Thanks to Java's stream() nosotros can only append the transformation to the request.

Another noteworthy aspect is the handling of buckets that contain more than 1000 objects. By default, the customer might only render a fraction, requiring pagination. However, the newer V2 SDK provides college-level methods, that follow an autopagination approach.

Listing all Objects in the Sample Application

1. Navigate to the Spaces section
2. Select Details on the target Infinite/Bucket
3. You see a list of all objects stored in the bucket

Making a File Public

Every object in S3 has a URL that can exist used to access that object. The URL follows a specific pattern of bucket proper noun, region, and object key. Instead of manually creating this URL, nosotros can utilize the getUrl() method, providing a saucepan name and an object key:

            s3Client              .              getUrl              (              "my-awesome-bucket"              ,              "some-cardinal"              );                      

Depending on the region we are in, this yields an URL like the following (given that we are in the european union-central-i region):

            https://my-awesome-bucket.s3.european union-central-one.amazonaws.com/some-key                      

Getting an Object's URL in the Sample Awarding

1. Navigate to the Spaces department
2. Select Details on the target Space/Bucket
3. Select Download on the target object
4. The object's URL shall be opened in a new tab

When accessing this URL directly later on uploading an object we should get an Access Denied fault, since all objects are private by default:

                          <Error>              <Code>AccessDenied</Code>              <Message>Access Denied</Message>              <RequestId>...</RequestId>              <HostId>...</HostId>              </Mistake>                      

As our application is all about sharing things, we do want those objects to exist publicly available though.

Therefore, we are going to change the object'southward Access Control List (ACL).

An ACL is a list of admission rules. Each of those rules contains the information of a grantee (who) and a permission (what). By default, only the saucepan owner (grantee) has total command (permission) only we can hands change that.

We tin can make objects public past altering their ACL like the post-obit:

            s3Client              .              setObjectAcl              (              "my-awesome-bucket"              ,              "some-key"              ,              CannedAccessControlList.              PublicRead              );                      

Nosotros are using the the clients' setObjectAcl() in combination with the high level CannedAccessControlList.PublicRead. The PublicRead is a prepared rule, that allows anyone (grantee) to have read admission (permission) on the object.

Making an Object Public in the Sample Application

1. Navigate to the Spaces section
2. Select Details on the target Space/Bucket
3. Select Brand Public on the target object
4. A message should pop up to indicate success

If we reload the folio that gave u.s. an Access Denied error over again, we volition now be prompted to download the file.

Making a File Private

One time the recipient downloaded the file, we might desire to revoke the public admission. This tin can be done following the same logic and methods, with slightly different parameters:

            s3Client              .              setObjectAcl              (              "my-awesome-saucepan"              ,              "some-key"              ,              CannedAccessControlList.              BucketOwnerFullControl              );                      

The above snippet sets the object's ACL so that just the bucket possessor (grantee) has full control (permission), which is the default setting.

Making an Object Private in the Sample Awarding

1. Navigate to the Spaces section
2. Select Details on the target Space/Bucket
3. Select Make Private on the target object
4. A message should pop up to indicate success

Deleting Files & Buckets

You might not desire to brand the file individual again, because once it was downloaded there is no need to keep information technology.

The client too gives us the option to easily delete an object from a bucket:

            s3Client              .              deleteObject              (              "my-awesome-bucket"              ,              "some-key"              );                      

The deleteObject() method simply takes the proper noun of the bucket and the key of the object.

Deleting an Object in the Sample Application

1. Navigate to the Spaces section
2. Select Details on the target Space/Bucket
3. Select Delete on the target object
4. The list of objects should reload without the deleted i

One noteworthy aspect around deletion is that we can't delete not-empty buckets. And then if we want to get rid of a complete bucket, we offset have to make sure that nosotros delete all the items commencement.

Deleting a Bucket in the Sample Application

1. Navigate to the Spaces section
2. Select Delete on the target Infinite/Saucepan
3. The listing of buckets should reload without the deleted one

Using Pre-Signed URLs

Reflecting on our approach, we did achieve what we wanted to: making files easily shareable temporarily. However, there are some features that S3 offers which greatly improve the way we share those files.

Our current approach to making a file shareable contains quite a lot of steps:

1. Update ACL to make the file public
2. Look until the file was downloaded
3. Update ACL to make the file private once more

What if nosotros forget to brand the file private again?

S3 offers a concept chosen "pre-signed URLs". A pre-signed URL is the link to our object containing an admission token, that allows for a temporary download (or upload). We can easily create such a pre-signed URL by specifying the bucket, the object, and the expiration date:

                          // duration measured in seconds                            var date              =              new              Date(              new              Date().              getTime              ()              +              duration              *              yard);              s3Client              .              generatePresignedUrl              (bucket,              primal,              date);                      

The client gives u.s. the generatePresignedUrl() method, which accepts a java.util.Appointment as the expiration parameter. So if we think of a certain duration as opposed to a concrete expiration engagement, we have to convert that duration into a Date.

In the above snippet, we exercise so by simply multiplying the duration (in seconds) by 1000 (to convert information technology to milliseconds) and add that to the electric current time (in UNIX milliseconds).

The official documentation has some more than information effectually the limitations of pre-signed URLs.

Generating a Pre-Signed URL in the Sample Application

1. Navigate to the Spaces section
2. Select Details on the target Space/Bucket
3. Select Magic Link on the target object
4. A bulletin should pop up, containing a pre-signed URL for that object (which is valid for 15 minutes)

Using Saucepan Lifecycle Policies

Some other improvement we can implement is the deletion of the files. Even though the AWS free tier gives us 5GB of S3 storage infinite before we have to pay, we might want to get rid of one-time files we accept shared already. Like to the visibility of objects, we tin manually delete objects, just wouldn't information technology be more convenient if they get automatically cleaned up?

AWS gives us multiple ways to automatically delete objects from a saucepan, nevertheless nosotros'll use S3's concept of Object Life Bike rules. An object life cycle rule basically contains the information when to do what with the object:

                          // delete files a week after upload                            s3Client              .              setBucketLifecycleConfiguration              (              "my-awesome-bucket"              ,              new              BucketLifecycleConfiguration()              .              withRules              (              new              BucketLifecycleConfiguration.              Dominion              ()              .              withId              (              "custom-expiration-id"              )              .              withFilter              (              new              LifecycleFilter())              .              withStatus              (BucketLifecycleConfiguration.              ENABLED              )              .              withExpirationInDays              (7)              )              );                      

Nosotros use the client'southward setBucketLifecycleConfiguration() method, given the bucket's name and the desired configuration. The configuration above consists of a single rule, having:

• an id to brand the rule uniquely identifiable
• a default LifecycleFilter, so this rule applies to all objects in the bucket
• a status of existence ENABLED, then every bit before long as this dominion is created, it is effective
• an expiration of 7 days, and so after a week the object gets deleted

It shall be noted that the snippet to a higher place overrides the erstwhile lifecycle configuration. That is ok for our use example but we might want to fetch the existing rules get-go and upload the combination of sometime and new rules.

Setting a Bucket'due south Expiration in the Sample Awarding

1. Navigate to the Spaces section
2. Select Make Temporary on the target Space/Bucket
3. A bulletin should popular upwardly to bespeak success

Lifecycle rules are very versatile, every bit we tin can use the filter to merely apply the rule to objects with a certain central prefix or carry out other actions similar archiving of objects.

Determination

In this article, nosotros've learned the basics of AWS' Simple Storage Service (S3) and how to use Spring Boot and the Spring Cloud project to go started with it.

We used S3 to build a custom file-sharing application (code on GitHub), that lets us upload & share our files in different ways. But information technology shall be said, that S3 is way more versatile, often besides quoted to exist the backbone of the internet.

As this is a getting started commodity, we did not bear upon other topics like storage tiers, object versioning, or static content hosting. And so I can simply recommend you go your easily dingy, and play effectually with S3!

Check Out the Volume!

This article gives only a first impression of what you can do with AWS.

If you lot want to go deeper and larn how to deploy a Spring Kicking application to the AWS cloud and how to connect it to cloud services like RDS, Cognito, and SQS, make sure to check out the book Stratospheric - From Zilch to Production with Spring Kicking and AWS!

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Source: https://reflectoring.io/spring-boot-s3/