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POSave blob using a stream from EJB to database (in a memory efficient way)
 

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    <p>I want to save large attachments (500Mb, maybe, if possible, even > 2Gb) in a database. I know the pros and cons of doing so are discussed very frequently, but that's not the focus of my question.</p> <p>The conventional way of storing Blob fields in EJB3 with JPA is to use a code as following:</p> <pre><code>@Lob private byte[] data; </code></pre> <p>This becomes a problem when handling huge data sources, because the whole byte array is saved in memory.</p> <p>I tried to change it to Blob:</p> <pre><code>@Lob private Blob data; </code></pre> <p>But this results in the same problem. When calling</p> <pre><code>// session: Hibernate session. // Actually, I'd like to stay with JPA's abstraction and not // reference Hibernate directly, if possible Blob data = session.createBlob(inputStream, lengthOfStream); </code></pre> <p>the createBlob method creates a byteArray from the inputStream.</p> <p>Because of the ORM mapping, I also wonder how to handle the insertion of the data. One idea was to make an entity variable</p> <pre><code>@Lob private byte[] data; </code></pre> <p>That I will never use. This way, the database schema get's build. But because the @Lob annotation is lazy, it will not bloat my memory.</p> <p>And then write</p> <pre><code>entityManager.persist(dataObject); // The following lines are _completely_ imaginatory!! query.prepare("update DataObject d set d.data = :dataInputStream where d = :dataObject"); query.setProperty("dataObject", dataObject); query.setProperty("dataInputStream", someDataInputStream); </code></pre> <p>One solution I stumbled across looks nice, but doesn't use JPA: <a href="https://stackoverflow.com/questions/324104/grooviest-way-to-store-a-blob-in-a-database">Grooviest way to store a BLOB in a database?</a></p> <p>Does anybody have an advice on how to do this?</p>
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    1. USThomas Walther
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    1. COIs there any reason for you to use a blob in stead of a file path?
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    2. COYes, portability. The idea is to store the data in the database and cache it on the filesystem. This way, only the DB and the jar have to be copied to a new system - the files will get cached from the DB to the filesystem automatically.
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      1. USThomas Walther
    3. COI don't think this is an efficient way of storage. If the path of storage is configurable the path in the database only needs to be a postfix of the initial path. The downside is that you need to move the db, jar and files. But I think the pros outweigh the cons here.
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