Question

Are the database connections used by JSTL <sql:query> tag persistent?

1. I mean if I use a lot of <sql:query> tags on a page then will they
   share the same database connection?
2. What about across the page
   connections? Does JSTL provide a way to use persistent connections
   like mysql_pconnect() in PHP?

Answer 1

In JSTL for SQL tags you can give the datasource which you want to use for DB connections. It is upto the datasource which decides the management of DB connections. A SQL tag gives the datasource information like this:

<sql:query var="order" 
  dataSource="${applicationScope.orderDS}">
   select * from PUBLIC.orders where id = ?
   <sql:param value="${id}" />
</sql:query>

The datasource attribute value can be of the following types:

1. Datasource – in which case this datasource will be used.
2. String – in which case JDNI lookup will be done with that name.
3. NULL – in which case it will use the datasource set by tag.

In case you have a SQL query tags inside transaction tag. All the queries inside the transaction share the same connection for transaction management.

<sql:transaction>
   <sql:query var="order" 
      dataSource="${applicationScope.orderDS}">
         select * from PUBLIC.orders where id = ?
         <sql:param value="${id}" />
   </sql:query>
   <sql:update var="order" 
      sql="update PUBLIC.orders set book_name = ? where id = ?">
         <sql:param value="${name}" />
         <sql:param value="${id}" />
   </sql:query>
<sql:transaction>