@Autowired注入为null问题原因分析

2019-11-26 09:30:40

字体：大中小

来源：转载

供稿：网友

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

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.h2.Driver"></property>    <property name="jdbcUrl"      value="jdbc:h2: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