CMP & blob's

[car]

Hi

My question is how do I read and write to a CMP entity bean's blob object ?

I have an CMP entity bean which maps to a table in a MS SQL server database containing a blob field of type 'image' which is translates to a jdbc LONGVARBINARY sql type.

The standardjbosscmp-jdbc.xml maps the MS SQL image type to a java object as follows:


<java-type>java.lang.Object</java-type>
<jdbc-type>JAVA_OBJECT</jdbc-type>
<sql-type>IMAGE</sql-type>


My entity bean has methods as follows:

public abstract java.lang.Object getNte_memo();
public abstract void setNte_memo(java.lang.Object value);

This all works fine.

But what do I do with this object returned in order to read the blob's data and how do I write data back to the blob via a java.lang.Object ?

thanks in advance,
CaR

[car]

After many hours investigating this problem I have found a solution myself.

Here the mapping required in standardjbosscmp-jdbc.xml if you want to read and write to blob fields using an byte[] java type rather than some serialized java.lang.Object:


<java-type>[B</java-type>
<jdbc-type>VARBINARY</jdbc-type>
<sql-type>IMAGE</sql-type>


and the entity bean abstract get & set methods will be as below:

public abstract byte[] getField();
public abstract void setField(byte[] value);

Now I can read and write to the blob using array's of bytes just like any byte[] which is simple, neat and tidy coding exercise.

I guess you would need to be a bit careful with really big blobs as when the entity bean is read from the DB it will bring the whole blob into memory and hold it in a byte[].

The <java-type> of '[B' means a byte[] type. This you will not find in any documentation. I found this by looking at the JBoss source code in the process of trying to understand what was going on with blobs. The class in where I found the '[B' is:

org.jboss.ejb.plugins.cmp.jdbc.JDBCUtil

CaR.

[kentxu]

You can always rely on the container to figure out the java type from your abstract cmp field methods.

The only thing you need to do in jbosscmp-jdbc is to define specific jdbc/sql mapping (without saying anything about the java-type. So "[B" really is optional.

Here is an example in jbosscmp-jdbc.

<cmp-field>
.........
<jdbc-type>VARCHAR</jdbc-type>
<sql-type>BLOB</sql-type>

</cmp-field>