Singleton vs prototype JdbcTemplate - spring

Question

In the Spring documentation the recommended way to use JdbcTemplate is to create new template for every class you use it in...
public class JdbcCorporateEventDao implements CorporateEventDao {
private JdbcTemplate jdbcTemplate;
public void setDataSource(DataSource dataSource) {
this.jdbcTemplate = new JdbcTemplate(dataSource);
}
}
I was wondering, what is the advantage of this solution over define the jdbctemplate as singleton in the context and directly inject it in the Dao
public class JdbcCorporateEventDao implements CorporateEventDao {
#Autowired
private JdbcTemplate jdbcTemplate;
public void setJdbcTemplate(JdbcTemplate jdbcTemplate) {
this.jdbcTemplate = jdbcTemplate;
}
}

Answer 1

From the class-level documentation of JdbcTemplate:
* Can be used within a service implementation via direct instantiation
* with a DataSource reference, or get prepared in an application context
* and given to services as bean reference.
Either is ok. Here I have a large application (50 DAOs, 100 concurrent users) and there is one jdbcTemplate object for the entire application, defined in the spring context. This works fine.

Answer 2

One drawback of injecting the JdbcTemplate directly is if you need to/decide to use a SQLExceptionTranslator.
If your JdbcTemplate is a singleton, setting a SQLExceptionTranslator in any class affects all classes using that template.
For example...
public class JbdcUserDAO implements UserDAO{
#Autowired
private JdbcTemplate jdbcTemplate;
public JbdcUserDAO() {
this.jdbcTemplate.setExceptionTranslator(new UserSQLExceptionTranslator());
}
public void setJdbcTemplate(JdbcTemplate jdbcTemplate) {
this.jdbcTemplate = jdbcTemplate;
}
}
AND
public class JdbcCompanyDAO implements CompanyDAO{
#Autowired
private JdbcTemplate jdbcTemplate;
public JdbcCompanyDAO() {
}
public void setJdbcTemplate(JdbcTemplate jdbcTemplate) {
this.jdbcTemplate = jdbcTemplate;
}
}
SQLExceptions raised through JdbcCompanyDAO will also be run through UserSQLExceptionTranslator even though it looks like no translator is registered.