@Autowired注入为null问题原因分析

发布时间：2020-10-09 10:39:37 作者：吃鱼不挑刺
来源：脚本之家阅读：646

问题说明

最近看到Spring事务,在学习过程中遇到一个很苦恼问题

搭建好Spring的启动环境后出现了一点小问题

在启动时候却出现[java.lang.NullPointerException]

不过因为当时一个小小的疏忽很low的问题请往下看...

工程结构

@Autowired注入为null问题原因分析

代码片段

spring.xml

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

  <!-- Spring注解扫描 -->
  <context:component-scan base-package="com.*" />

  <!-- 1. 数据源对象: C3P0连接池 -->
  <bean id="dataSource"
    class="com.mchange.v2.c3p0.ComboPooledDataSource">
    <property name="driverClass" value="org.h3.Driver"></property>
    <property name="jdbcUrl"
      value="jdbc:h3:tcp://192.168.190.1/~/test"></property>
    <property name="user" value="sa"></property>
    <property name="password" value="123"></property>
  </bean>

  <!-- 2. JdbcTemplate工具类实例 -->
  <bean id="jdbcTemplate"
    class="org.springframework.jdbc.core.JdbcTemplate">
    <property name="dataSource" ref="dataSource"></property>
  </bean>

  <!-- 3.配置事务 -->
  <bean id="dataSourceTransactionManager"
    class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
    <property name="dataSource" ref="dataSource"></property>
  </bean>

</beans>

Test.java

public class Test {
  public static void main(String[] args) {
    ClassPathXmlApplicationContext classPathXmlApplicationContext = new ClassPathXmlApplicationContext(
        "spring.xml");
    ServiceIF service = (ServiceIF) classPathXmlApplicationContext.getBean("serviceImpl");
    service.add("小王", 23);
  }
}

TransactionUtil.java

@Component("transactionUtil")
public class TransactionUtil {

  /**
   * 初始化数据源
   */
  @Autowired
  private DataSourceTransactionManager dataSourceTransactionManager;

  /**
   * 开启事务
   * 
   * @return
   */
  public TransactionStatus begin() {
    TransactionStatus transaction = dataSourceTransactionManager.getTransaction(new DefaultTransactionDefinition());
    System.out.println(" 开启事务成功 ");
    return transaction;
  }

  /**
   * 提交事物
   * 
   * @param transaction
   */
  public void commit(TransactionStatus transaction) {
    dataSourceTransactionManager.commit(transaction);
    System.out.println(" 事物提交成功 ");
  }

  /**
   * 回滚事务
   * 
   * @param transaction
   */
  public void rollback(TransactionStatus transaction) {
    dataSourceTransactionManager.rollback(transaction);
    System.err.println(" 事物进行回滚 ");
  }
}

ServiceImpl.java

@Service("serviceImpl")
public class ServiceImpl implements ServiceIF {

  @Autowired
  TransactionUtil transactionUtil;

  private TransactionStatus transactionStatus = null;

  @Override
  public void add(String name, Integer age) {
    transactionStatus = transactionUtil.begin();
    try {
      new DaoImpl().add(name, age);
      transactionUtil.commit(transactionStatus);
    } catch (Exception e) {
      System.err.println("ERROR >>> 执行出现异常 即将进行回滚操作");
      transactionUtil.rollback(transactionStatus);
    }
  }
}

DaoImpl.java

public class DaoImpl implements DaoIF{

  /**
   * 注入jdbc模板类
   */
  @Autowired
  private JdbcTemplate jdbcTemplate;

  /**
   * 第一条插入语句
   */
  private final String SQL_INSERT_01 = "insert into user values (?,?)";

  /**
   * 添加sql执行
   * 
   * @param name
   * @param age
   */
  public void add(String name, Integer age) {
    jdbcTemplate.update(SQL_INSERT_01, name, age);
  }
}

运行结果

@Autowired注入为null问题原因分析