Convert an apex attachment into a blob?

Question

I am attempting to convert an apex attachment into a blob. My visualforce code is

    <div class="mt-5 row">
        <div class="d-flex justify-content-center col-lg-12">
            <h1>Upload an Attachment To S3</h1>
        </div>
    </div>
    <div class="row">
        <div class="d-flex justify-content-center col-lg-12">
            <apex:inputfile value="{!myfile.body}" filename="{!myfile.Name}" />
        </div>
    </div>
    <div class="mt-1 row">
        <div class="d-flex justify-content-center col-lg-12">
            <apex:commandbutton value="Save" action="{!convertDocToBlob}" id="saveButtonForS3" />
        </div>
    </div>

My apex is

public Pagereference convertDocForS3(){
    String sObjID = System.currentPagereference().getParameters().get('id');

    Attachment a = new Attachment(parentId = sObjID, name=myfile.name, body = myfile.body);

    Blob testBlob = convertToBlob(a);

    return null;
}

public Blob convertToBlob(Attachment attach){
    Blob testBlob = EncodingUtil.base64Decode(attach.body.ToString());
    return testBlob;
}

When I attempt to upload at png file, the error I get back is

 System.StringException: BLOB is not a valid UTF-8 string

EDIT: The correct thing to do in this case was

 Blob testBlob = a.body;

as the attachment was already coming through as a blob.

Answer 1

Since you're pulling the info from an uploaded file, the body of the attachment is already a blob. If the requirement is just to pass the blob to another location then there's no need to manipulate it.

The error was you using base64Decode which expects a Base64-encoded String which .toString does not return

https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_classes_restful_encodingUtil.htm