Question

I try to write a transaction manager using JDBC in Spring.

my app-servlet.xml

<!-- JDBC Config -->
<bean   id="dataSource" 
        class="org.apache.commons.dbcp.BasicDataSource"
        destroy-method="close" 
        p:driverClassName="${jdbc.driverClassName}"
        p:url="${jdbc.databaseurl}" 
        p:username="${jdbc.username}" 
        p:password="${jdbc.password}" />

<!-- dataSource TransactionManager -->
<bean id="transactionManager"
    class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
    <property name="dataSource" ref="dataSource" />
</bean>

<bean id="UserDAOImpl" class="com.project.dao.impl.UserDAOImpl">
    <property name="transactionManager" ref="transactionManager"/>
</bean>

my UserDAOImpl.java

public class UserDAOImpl implements UserDAO {

//transaction manager
private DataSourceTransactionManager transactionManager;
private JdbcTemplate jdbcTemplate;

public UserDAOImpl() {
    super();
    DataSource dataSource = transactionManager.getDataSource();
    jdbcTemplate = new JdbcTemplate(dataSource);
}

public void setTransactionManager(DataSourceTransactionManager transactionManager)    {
    this.transactionManager = transactionManager;
}
....
}

Even though I have transactionManager Bean in my app-servlet, UserDAOImpl won’t be instatiated because transactionManager is null. Probably I miss some point but couldn’t find out what is wrong.

Answer 1

You should use constructor injection for your transaction manager. Spring is going to call the constructor before it can inject the transactionManager property.

 public UserDAOImpl() 
 {
    /* Transaction Manager NOT set yet */
    DataSource dataSource = transactionManager.getDataSource();
 }

Change it to use constructor injection

 public UserDAOImpl(TransactionManager transactionManager) ...

Then configuration

 <bean id="UserDAOImpl" class="com.project.dao.impl.UserDAOImpl">
   <constructor-arg ref="transactionManager"/>
 </bean>