Explanations of an application in Java Spring

Question

I made ​​a simple application in Java Spring that should read and write to a database with two varchar fields.

package learn.spring.example.dao;

import org.springframework.jdbc.core.PreparedStatementCreator;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.SQLException;

@Component
public class  PersonStoreDao implements PersonInter{
    @Autowired
    private JdbcTemplate jdbc;

    public Long saveData(Person person){
    final String querySample="insert into PersonName(first_name, last_name)       values (?, ?)";
   jdbc.update(new PreparedStatementCreator() {
       public PreparedStatement prepStatement(Connection c) throws SQLException {
        PreparedStatement prep = c.prepareStatement(querySample);
        prep.setString(1, person.getFirstName());
        prep.setString(2, preson.getSecondName());
        return prep;
        }
      ,key}
       }
}

Class Person is just a simple bean class and PersonName is the table from database with two fields. I have several questions about this.

First question is if something is wrong

What is the effect of using @Autowired in front of jdbc variable and @Component?

How can it embedded correctly in xml files assciated to this project?

I can connect to the database but can not do writing it. What should be done so that the database is not only read but also written?

Answer 1

What is the effect of using @Autowired in front of jdbc variable and @Component?

These make the Spring annotation-based wiring processor aware that this is a class that needs to be wired, and that a value should be injected into the jdbc variable.

How can it embedded correctly in xml files assciated to this project?

It can be. The wiring is done by the annotation processor. Presumably it will inject a bean whose type is JdbcTemplate that you have declared in your XML files.

I can connect to the database but can not do writing it. What should be done so that the database is not only read but also written?

You haven't shown us the XML, but I suspect that the problem is there. Presumably you have specified a JdbcTemplate bean with a DataSource, and the DataSource is connecting to a database account that only allows read access. If that is the case, you need to either use a different database account, or GRANT the required access for the account you are using.

Answer 2

@AutoWired is the annotation way of defining others beans required by your current bean. For example look at the following;

<bean id="person" class="com.Person">
<property name="jdbcTemplate" ref="jdbcTemplate"/>
</bean>

<bean id="jdbcTemplate" class="org.springframework.jdbc.core.JdbcTemplate">
    <property name="dataSource" ref="myDataSource" />
</bean>

With the following snippet as you can see we had to define a ref bean inside our Person class. But we can eliminate that when we use @AutoWired since then the jdbcTemplate is auto injected to the Person class.

One thing you have to note here is that if you are trying to auto wire by an interface type and your application has many implementations, then you should use the concept of @Qualifier in order to tell Spring which version of the implementation you want to inject to your current bean.

As for the @Component, by defining your bean as @Component, you tell the Spring Container to scan through all beans annotated with the annotation and make them available in the Spring Context. By doing this you do not have to define your bean within an XML file.More info on @Component and @Configuration which are more or less similar can be found in the following thread.

With regards to your issue with not being able to connect to the database, please provide the current application context XML file you are using so that we can see how you are wiring up the JDBCTemplate.