JDBC dataSource从bean获取null值，抛出java.lang.NullPointerException

Question

dataSource没有获得任何价值。 dataSource.getConnection抛出java.lang.NullPointerException。

servlet的context.xml中

<!-- DispatcherServlet Context: defines this servlet's request-processing 
    infrastructure -->

<!-- Enables the Spring MVC @Controller programming model -->
<annotation-driven />

<!-- Handles HTTP GET requests for /resources/** by efficiently serving 
    up static resources in the ${webappRoot}/resources directory -->
<resources mapping="/resources/**" location="/resources/" />

<!-- Resolves views selected for rendering by @Controllers to .jsp resources 
    in the /WEB-INF/views directory -->
<beans:bean
    class="org.springframework.web.servlet.view.InternalResourceViewResolver">
    <beans:property name="prefix" value="/WEB-INF/views/" />
    <beans:property name="suffix" value=".jsp" />
</beans:bean>

<beans:bean id="dataSource"
    class="org.springframework.jdbc.datasource.DriverManagerDataSource">
    <beans:property name="driverClassName" value="com.mysql.jdbc.Driver" ></beans:property>
    <beans:property name="url" value="jdbc:mysql://localhost:3306/mydb" ></beans:property>
    <beans:property name="username" value="root"></beans:property>
    <beans:property name="password" value="nannu"></beans:property>
</beans:bean>

    <beans:bean id="vehicleDaoImpl" class="com.myapp.dataaccess.vehicle.VehicleDaoImpl">
    <beans:property name="dataSource" ref="dataSource"></beans:property>
    </beans:bean>

<context:component-scan base-package="com.myapp.dataaccess" />

DAO实施

public class VehicleDaoImpl implements VehicleDao {
    private DataSource dataSource;

    public void setDataSource(DataSource dataSource1) {
        this.dataSource = dataSource1;
    }

    public void insert(Vehicle vehicle) {
        String sql = "INSERT INTO Vehicle (VEHICLE_NO, COLOR, WHEEL, SEAT) "
                + "VALUES (?, ?, ?, ?)";
                Connection conn = null;
                try {
                conn = dataSource.getConnection();
                PreparedStatement ps = conn.prepareStatement(sql);
                ps.setString(1, "gaurav");
                ps.setString(2, "rai");
                ps.setInt(3, 4);
                ps.setInt(4, 7);
                ps.executeUpdate();
                ps.close();
                } catch (SQLException e) {
                throw new RuntimeException(e);
                } finally {
                if (conn != null) {
                try {
                conn.close();
                } catch (SQLException e) {}
                }
                }
    }

    @Override
    public void update(Vehicle vehicle) { ... }

    @Override
    public void delete(Vehicle vehicle) { ... }

    @Override
    public Vehicle findByVehicleNo(String vehicleNo) {
        return null;
    }

}