What is JdbcDaoSupport used for?
According to these answers:
- Proper way to inject parent class dependencies with Spring annotations
- spring3-annotation-JdbcDaoSupport
- NamedParameterJdbcDaoSupport datasource autowire?
JdbcDaoSupport, NamedParameterJdbcDaoSupport, SimpleJdbcDaoSupport are unnecessary and are mental dust. They doesn't save any line of code because you need to inject data-source or template into.
What I recommend - to create templates in XML/class config per data source and reuse/inject them as templates are thread safe according to docs:
Once configured, a JdbcTemplate instance is threadsafe. You may want multiple JdbcTemplate instances if your application accesses multiple databases, which requires multiple DataSources, and subsequently multiple differently configured JdbcTemplates.
Compare applicationContext.xml
:
<bean id="dataSource"
class="org.apache.commons.dbcp.BasicDataSource"
destroy-method="close">
<property name="driverClassName" value="${jdbc.driverClassName}"/>
<property name="url" value="${jdbc.url}"/>
<property name="username" value="${jdbc.username}"/>
<property name="password" value="${jdbc.password}"/>
</bean>
<bean id="jdbcTemplate"
class="org.springframework.jdbc.core.namedparam.NamedParameterJdbcTemplate">
<constructor-arg ref="dataSource"/>
</bean>
and YourDaoImpl.java
:
public class YourDaoImpl implements YourDao {
@Autowired
private NamedParameterJdbcTemplate jdbcTemplate;
@Override
public int tableExists(String table) {
String sql = "select count(*) from all_tables"
+ " where table_name = :tbl";
return jdbcTemplate.queryForObject(
sql, new MapSqlParameterSource("tbl", table), Integer.class);
}
}
with JdbcDaoSupport.java
:
public class YourDaoImpl extends NamedParameterJdbcDaoSupport implements YourDao {
@Autowired
public void setDs(DataSource dataSource) {
setDataSource(dataSource);
}
@Override
public int tableExists(String table) {
String sql = "select count(*) from all_tables"
+ " where table_name = :tbl";
return getNamedParameterJdbcTemplate()
.queryForObject(
sql,
new MapSqlParameterSource("tbl", table), Integer.class);
}
}
UPDATE Official statement about stateless (and so thread safety) of JdbcTemplate
/NamedParameterJdbcTemplate
here https://jira.springsource.org/browse/SPR-11478
First lets point out the API specifies this class as a convenience class ("support"). I believe JdbcDaoSupport supports, aka provides you with, a base implementation of the DAO design for jdbc whereas a template class (see template pattern) will give you a singleton that is used to inject into your DAO classes.
In my experience I haven't found a reason to couple my DAO to a *Support class. I instead create my specific jdbcTemplate beans and inject them into my DAO classes favoring composition over inheritence -- generally a good object-oriented practice.
From the Spring docs, "You can choose whether to inherit from this class. The JdbcDaoSupport class is provided as a convenience only.".
As Spring states, JdbcDaoSupport is a convenience only. They say nothing about its advantages over using one of the template implementations.