@Autowired注入为null问题分析

Posted 2021-01-22 cat-

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2018-11-24 22:57:33

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

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <beans xmlns="http://www.springframework.org/schema/beans"
 3     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 4     xmlns:context="http://www.springframework.org/schema/context"
 5     xsi:schemaLocation="
 6         http://www.springframework.org/schema/beans
 7         http://www.springframework.org/schema/beans/spring-beans.xsd
 8         http://www.springframework.org/schema/context
 9         http://www.springframework.org/schema/context/spring-context.xsd">
10 
11     <!-- Spring注解扫描 -->
12     <context:component-scan base-package="com.*" />
13 
14     <!-- 1. 数据源对象: C3P0连接池 -->
15     <bean id="dataSource"
16         class="com.mchange.v2.c3p0.ComboPooledDataSource">
17         <property name="driverClass" value="org.h2.Driver"></property>
18         <property name="jdbcUrl"
19             value="jdbc:h2:tcp://192.168.190.1/~/test"></property>
20         <property name="user" value="sa"></property>
21         <property name="password" value="123"></property>
22     </bean>
23 
24     <!-- 2. JdbcTemplate工具类实例 -->
25     <bean id="jdbcTemplate"
26         class="org.springframework.jdbc.core.JdbcTemplate">
27         <property name="dataSource" ref="dataSource"></property>
28     </bean>
29 
30     <!-- 3.配置事务 -->
31     <bean id="dataSourceTransactionManager"
32         class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
33         <property name="dataSource" ref="dataSource"></property>
34     </bean>
35 
36 </beans>

Spring.xml

Test.java

1 public class Test {
2     public static void main(String[] args) {
3         ClassPathXmlApplicationContext classPathXmlApplicationContext = new ClassPathXmlApplicationContext(
4                 "spring.xml");
5         ServiceIF service = (ServiceIF) classPathXmlApplicationContext.getBean("serviceImpl");
6         service.add("小王", 23);
7     }
8 }

TransactionUtil.java

 1 @Component("transactionUtil")
 2 public class TransactionUtil {
 3 
 4     /**
 5      * 初始化数据源
 6      */
 7     @Autowired
 8     private DataSourceTransactionManager dataSourceTransactionManager;
 9 
10     /**
11      * 开启事务
12      * 
13      * @return
14      */
15     public TransactionStatus begin() {
16         TransactionStatus transaction = dataSourceTransactionManager.getTransaction(new DefaultTransactionDefinition());
17         System.out.println(" 开启事务成功 ");
18         return transaction;
19     }
20 
21     /**
22      * 提交事物
23      * 
24      * @param transaction
25      */
26     public void commit(TransactionStatus transaction) {
27         dataSourceTransactionManager.commit(transaction);
28         System.out.println(" 事物提交成功 ");
29     }
30 
31     /**
32      * 回滚事务
33      * 
34      * @param transaction
35      */
36     public void rollback(TransactionStatus transaction) {
37         dataSourceTransactionManager.rollback(transaction);
38         System.err.println(" 事物进行回滚 ");
39     }
40 }

TransactionUtil.java

ServiceImpl.java

 1 @Service("serviceImpl")
 2 public class ServiceImpl implements ServiceIF {
 3 
 4     @Autowired
 5     TransactionUtil transactionUtil;
 6 
 7     private TransactionStatus transactionStatus = null;
 8 
 9     @Override
10     public void add(String name, Integer age) {
11         transactionStatus = transactionUtil.begin();
12         try {
13             new DaoImpl().add(name, age);
14             transactionUtil.commit(transactionStatus);
15         } catch (Exception e) {
16             System.err.println("ERROR >>> 执行出现异常 即将进行回滚操作");
17             transactionUtil.rollback(transactionStatus);
18         }
19     }
20 }

DaoImpl.java

 1 public class DaoImpl implements DaoIF{
 2 
 3     /**
 4      * 注入jdbc模板类
 5      */
 6     @Autowired
 7     private JdbcTemplate jdbcTemplate;
 8 
 9     /**
10      * 第一条插入语句
11      */
12     private final String SQL_INSERT_01 = "insert into user values (?,?)";
13 
14     /**
15      * 添加sql执行
16      * 
17      * @param name
18      * @param age
19      */
20     public void add(String name, Integer age) {
21         jdbcTemplate.update(SQL_INSERT_01, name, age);
22     }
23 }