我如何从org.springframework.jdbc.datasource.DriverManagerDataSource类获取jdbc连接

Question

I'm trying to get jdbc connection using the below code.

I use mysql database jpa2 and spring 4. How can I get jdbc connection and retrieve this value from mysql database

    import java.io.Serializable;
    import java.sql.Connection;
    import java.sql.PreparedStatement;
    import java.sql.ResultSet;
    import java.sql.SQLException;
    import javax.faces.bean.ManagedBean;
    import javax.faces.bean.ViewScoped;
    import javax.sql.DataSource;
    import org.springframework.jdbc.core.JdbcTemplate;

    @ManagedBean
    @ViewScoped
    public class JDBCTest implements Serializable{
        private JdbcTemplate jdbcTemplate;
     void setDataSource(DataSource dataSource) {
            this.jdbcTemplate = new JdbcTemplate(dataSource);
        }
        private static final long serialVersionUID = 1L;
        public void testDB(){
            Connection con=null;
            try {
                con = getJdbcTemplate().getDataSource().getConnection();
                PreparedStatement pst=con.prepareStatement("select * from global_class");
                ResultSet st=pst.executeQuery();
                while(st.next()){
                    System.out.println("Class Name :"+st.getString(1));
                }
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }

        public JdbcTemplate getJdbcTemplate() {
            return jdbcTemplate;
        }

        public void setJdbcTemplate(JdbcTemplate jdbcTemplate) {
            this.jdbcTemplate = jdbcTemplate;
        }   
    }

When is run above this code then i get this exception

WARNING: #{jDBCTest.testDB}: java.lang.NullPointerException
javax.faces.FacesException: #{jDBCTest.testDB}: java.lang.NullPointerException
    at com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:118)
    at org.springframework.faces.webflow.FlowActionListener.processAction(FlowActionListener.java:71)
    at org.springframework.faces.model.SelectionTrackingActionListener.processAction(SelectionTrackingActionListener.java:64)
    at javax.faces.component.UICommand.broadcast(UICommand.java:315)

Answer 1

Specify your database configuration in context file as below

 <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="root" />
    <property name="password" value="password" />
</bean>

and then start inject this datasource object into the JDBCTest class using spring dependency injection. ex:

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

or

 <bean id="jdbcTest" class="JDBCTest"><property name="dataSource" ref="datasource"/></bean>

Answer 2

Your bean is a Jsf Managed bean so your JdbcTemplate property should be annotated with @ManagedProperty else nothing will be injected.

Fist add a JdbcTemplate as a bean to the application context.

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

Then in your bean annotate your JdbcTemplate with @ManagedProperty and create a setJdbcTemplate method.

@ManagedProperty("#{jdbcTemplate}")
private JdbcTemplate jdbcTemplate;

The JdbcTemplate is designed to make working with JDBC easier. So use it. What you have constructed is a very complex way to do the same ugly thing. Use the JdbcTemplate correctly and for what it is intended to.

Your code should be something like this.

getJdbcTemplate().query("select * from global_class", new RowCallbackHandler() {
    public void procesRow(ResultSet rs, int row) {
        System.out.println("Class Name :" + rs.getString(1));
    }
});

This does the same as your code, but uses the JdbcTemplate as it is intended.