Question

I’m a Spring newbie, I’m following some examples from books and tutorials in the spring website and I can’t get my code to work.

I’m trying to access to a DataBase using JdbcTemplate. This is how my root-context.xml looks like:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">
<bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
    <property name="driverClassName" value="com.mysql.jdbc.Driver" />
    <property name="url" value="jdbc:mysql://localhost:3306/db" />
    <property name="username" value="userr" />
    <property name="password" value="password" />
</bean>
<bean id="jdbcTemplate" class="org.springframework.jdbc.core.simple.SimpleJdbcTemplate">
    <constructor-arg ref="dataSource"/>
</bean>
<bean id="myDao" class="com.me.myproj.persistence.JdbcMyaDao">
    <property name="dataSource" ref="dataSource"/>
</bean>

This is my JdbcMyDao (all imports are ok, I won’t paste them):

public class JdbcMyDao implements MyDao{

private JdbcTemplate jdbcTemplate;

public void setDataSource(DataSource dataSource) {
        this.jdbcTemplate = new JdbcTemplate(dataSource);
 }

public String getOpcionById(){
    String SQL_Q="select name from options where id=35";

    return (String)this.jdbcTemplate.queryForObject(SQL_Q, String.class);
}

}

Finally, my controller:

@Controller
public class myController {

    @RequestMapping(value = "/show", method = RequestMethod.GET)
    public String show(Model model){

        JdbcMyDao daoP=new JdbcMyDao();
        String op=daoP.getOpcionById();

        model.addAttribute("op",op);
        return "show";
    }
}

Ok, then, show.jsp just prints the return string.

So, this is a very simple access to a DataBase, but I get a nullPointerException when using JdbcTemplate (in function getOpcionById)

I think this is because function setDataSource is never runned, I thought spring runs it by IoC, I tried to put @Autowired to jdbcTemplate property i JdbcMyDao, but it didn’t work either. Can someone tell me the steps Spring does and which steps should I do? Or what changes should I make and why?

Answer 1

Your controller is instantiating its own JdbcMyDao and calling that, rather than using the bean you declared in root-context.xml. You need to inject the myDao bean into your controller and invoke that.

Also, is there a reason you’re defining a JdbcTemplate bean, and then not doing anything with it? The setDataSource method of the DAO is instantiating its own JdbcTemplate (which is fine), so there’s no reason to declare a bean.

I have a feeling you’ve not quite grasped the concept of dependency injection – you seem to have used direct instantiation and declared beans, rather than just the latter.