exception in update query

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Java

MySQL

I want to update one file to a Blob fileld in mysql table, and I tried this way

String sqlUpdateXSLT = "UPDATE mailer_details.auto_mailer_2 set xslt=? where auto_mailer_name='" + mailerName + "'";
            PreparedStatement stmt = con.prepareStatement(sqlUpdateXSLT);
            FileInputStream fis = new FileInputStream(mFile);
            stmt.setBlob(1, fis, (int) mFile.length());
            int ra = stmt.executeUpdate(sqlUpdateXSLT);

but I got an exception such as:

com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '? where auto_mailer_name='atm4'' at line 1

What is problem this?

I performed insert operation similar way, and there were no problem.