Connection con;
...

con.setAutoCommit(false);

Statement st = con.createStatement();
st.execute(
  "begin execute immediate 'drop table TEST_BLOB'; exception when others then if sqlcode != -00942 then raise; end if; end;"
);
st.execute("create table TEST_BLOB as select empty_blob() pic from DUAL");

ResultSet rs = st.executeQuery("select pic from TEST_BLOB for update");
rs.next();
Blob blob = rs.getBlob("pic");
rs.close();

OutputStream os = blob.setBinaryStream(1L);
byte[] bytes = {1, 2, 3, 4, 5 ,6 ,7 ,8, 9, 10};
os.write(bytes, 0, bytes.length);
os.close();

rs = st.executeQuery("select pic, length(pic) length_pic from TEST_BLOB");
rs.next();
blob = rs.getBlob("pic");
System.out.println("blob.length()=" + blob.length() + ", length_pic=" + rs.getInt("length_pic"));

rs.close();
st.close();
con.close();

blob.length()=10, length_pic=10