Spring JDBC - ClassCastException when casting Object to Blob

Question

I have a table with few fields out of which 2 are of Varchar and Blob type. When I'm retrieving them using queryForMap, I'm getting a map instance with two keys(name of the column). I'm able to cast varchar to String simply but getting ClassCast Exception doing the same with Object.

file = new File(System.currentTimeMillis() + (String) map.get("SAMPLE_DOC_FILE_NAME"));
blob = (Blob) map.get("SAMPLE_DOC");

My DAO layer method is:

public Map<String, Object> getSampleDoc1(String docName) throws SQLException {

    String query = "select form.sample_doc_file_name as SAMPLE_DOC_FILE_NAME, form.sample_document as SAMPLE_DOC from forms form where form.document_name=?";
    return localJdbcTemplateObject.queryForMap(query, docName);
}

Exception - java.lang.ClassCastException: [B cannot be cast to java.sql.Blob

What can I do to get back this object as Blob?

you can use "byte[]" data type for image, it will cast to BLOB type in database — Ramaraj
– Ramaraj, Commented Nov 19, 2015 at 6:37
System.out.println(yourBlob.getClass().getName()); on this object, then use this class. — Krzysztof Cichocki
– Krzysztof Cichocki, Commented Nov 19, 2015 at 6:55

Lukas Eder · Accepted Answer · 2015-11-19 07:56:09Z

3

A Blob is just a wrapper for a (possibly large) byte[]. What you're getting back from Spring here is the interesting raw data, the byte[] (or B[ in the exception's notation). So, just use that instead, it'll be much easier to work with:

byte[] blob = (byte[]) map.get("SAMPLE_DOC");

answered Nov 19, 2015 at 7:56

Lukas Eder

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Krzysztof Cichocki · Accepted Answer · 2015-11-19 09:03:57Z

0

Please check what class it has as this:

System.out.println(map.get("SAMPLE_DOC").getClass().getName());

then cast to this type, then you can use the API of this type to do something with it.

answered Nov 19, 2015 at 9:03

Krzysztof Cichocki

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