JdbcTemplate NullPointerException

Question

我正在嘗試使用Spring的JdbcTemplate將數據保存到數據庫，但是卻收到此錯誤消息。 如果我使用PreparedStatements以正常方式進行操作，則它將正常工作。

我的CarDAO課程：

@Repository
@Service
public class CarDAO implements CarDAOService {

private JdbcTemplate jdbcTemplate;

public JdbcTemplate getJdbcTemplate() {
    return jdbcTemplate;
}

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



public void saveCarToDB(CarBean carbean) {

    final String sql = "insert into car (make, model) values (?,?)";

    Object[] parameters = new Object[] {carbean.getMake()+
            carbean.getModel()};

    //if I do here system.out.print(Arrays.toString(parameters)); 
    //it will print right make/model.

    jdbcTemplate.update(sql, parameters);

   //console says it is that row above, but I don't get how. Both parameters has values?
   //WARNING: StandardWrapperValve[spring-dispatcher]: Servlet.service() for servlet 
   //springdispatcher threw exception

}

Spring-base.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
   xmlns:context="http://www.springframework.org/schema/context"
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xmlns:mvc="http://www.springframework.org/schema/mvc"
   xsi:schemaLocation="http://www.springframework.org/schema/beans 
   http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
   http://www.springframework.org/schema/context 
   http://www.springframework.org/schema/context/spring-context-3.0.xsd
   http://www.springframework.org/schema/mvc 
   http://www.springframework.org/schema/mvc/spring-mvc-3.0.xsd">

<context:component-scan base-package="bean, dao" />


<bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
    <property name="prefix" value="/WEB-INF/Jsp/" />
    <property name="suffix" value=".jsp" />
</bean>


<!-- DATA SOURCE -->

<bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource"
      destroy-method="close">
    <property name="driverClassName" value="org.mariadb.jdbc.Driver" />
    <property name="url" value="jdbc:mariadb://XXXXX" />
    <property name="username" value="XXXXX" />
    <property name="password" value="XXXXX" />
    <property name="initialSize" value="1" />
    <property name="maxActive" value="5" />
</bean>

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

<mvc:annotation-driven />

</beans>

我沒有包括Controller或CarDAOService類，因為我認為問題不存在。 他們將正確的參數轉發給CarDAO類。

Answer 1

您需要在設置器上放置@Autowired批注：

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

Answer 2

通過@Autowired自動裝配bean，它可以應用於setter方法，構造函數或字段。

嘗試這個

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