Spring之IoC容器：通过注解的方式实现依赖注入

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前言

常用注解：
@Component，用于把当前类对象存入spring容器；
@AutoWired，自动按照类型注入数据，会根据容器中的key和变量名称进行匹配；
@Qualifier，在@AutoWired的基础上，再按照指定名称注入，给类成员注入时不可单独使用，给方法注入参数时，才可以单独使用；
@Value：用于注入基本类型和String类型;
@Scop：指定bean的作用范围；
@Configuration：指定当前类是一个配置类；
@ComponentScan：指定spring在创建容器时要扫面的包；
@Bean：把当前方法的返回值当作bean对象存入容器；
@Import：导入其他配置类；
@PropertySource：用于指定properties文件的位置，之后配置类中的成员变量就可以引用文件中的值。

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提示：以下是本篇文章正文内容，下面案例可供参考

环境说明

1、pom文件的依赖

<dependencies>
        <dependency>
            <groupId>org.projectlombokgroupId>
            <artifactId>lombokartifactId>
            <version>1.18.12version>
        dependency>
        <dependency>
            <groupId>org.springframeworkgroupId>
            <artifactId>spring-contextartifactId>
            <version>5.3.7version>
        dependency>
        <dependency>
            <groupId>mysqlgroupId>
            <artifactId>mysql-connector-javaartifactId>
            <version>5.1.6version>
        dependency>
        <dependency>
            <groupId>junitgroupId>
            <artifactId>junitartifactId>
            <version>4.12version>
        dependency>
        <dependency>
            <groupId>c3p0groupId>
            <artifactId>c3p0artifactId>
            <version>0.9.1.2version>
        dependency>
        <dependency>
            <groupId>commons-dbutilsgroupId>
            <artifactId>commons-dbutilsartifactId>
            <version>1.4version>
        dependency>
    dependencies>

2、spring的xml文件的配置

<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">
beans>

一、借助xml文件实现的注解

1、Dao层的实现类：添加的两个注解@Component @Autowired，届时spring在获取到xml配置文件后，会根据配置文件内的信息读取到对应的类以此创建对象和注入数据

package com.mediacomm.dao;

@Component(value = "userDao")
public class UserDaoImpl implements UserDao{
  @Autowired
  private QueryRunner queryRunner ;

  public List<User> findAll() throws SQLException {
    return queryRunner.query("select * from user",new BeanListHandler<User>(User.class));
  }

  public User findUserById(User user) throws SQLException{
    return queryRunner.query("select * from user where id = ?",new BeanHandler<User>(User.class),user.getId());
  }
}

2、修改xml配置文件，由于需要注入一个QueryRunner对象，而QueryRunner对象创建的时候传入DataSource连接池对象，因此配置如下

<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">
	
	<bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource">
        <property name="driverClass" value="com.mysql.jdbc.Driver">property>
        <property name="jdbcUrl" value="jdbc:mysql://localhost:3306/day17">property>
        <property name="user" value="root">property>
        <property name="password" value="123456">property>
    bean>
    
    <bean id="queryRunner" class="org.apache.commons.dbutils.QueryRunner" scope="prototype">
        <constructor-arg name="ds" ref="dataSource">constructor-arg>
    bean>
    
<context:component-scan base-package="com.mediacomm.dao">context:component-scan>

3、同样的方法配置完service层的UserServiceImpl的类，进行测试
（1）创建IoC核心容器对象
（2）根据id查找容器中的对象

public class SpringByXMLTest {
  private ApplicationContext context;
  private UserDao userDao;
  private UserService service;
  @Before
  public void init(){
    context = new ClassPathXmlApplicationContext("Spring.xml");
    //context = new AnnotationConfigApplicationContext(SpringConfiguration.class);
    userDao = context.getBean("userDao",UserDao.class);
    service = context.getBean("userService",UserService.class);
  }
  @Test
  public void test01(){
    List<User> users = service.findAll();
    for (User user:users) {
      System .out.println(user);
    }
  }
  

七月 20, 2021 6:56:25 下午 com.mchange.v2.log.MLog <clinit>
信息: MLog clients using java 1.4+ standard logging.
七月 20, 2021 6:56:26 下午 com.mchange.v2.c3p0.C3P0Registry banner
信息: Initializing c3p0-0.9.1.2 [built 21-May-2007 15:04:56; debug? true; trace: 10]
七月 20, 2021 6:56:26 下午 com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource getPoolManager
信息: Initializing c3p0 pool... com.mchange.v2.c3p0.ComboPooledDataSource [ acquireIncrement -> 3, acquireRetryAttempts -> 30, acquireRetryDelay -> 1000, autoCommitOnClose -> false, automaticTestTable -> null, breakAfterAcquireFailure -> false, checkoutTimeout -> 0, connectionCustomizerClassName -> null, connectionTesterClassName -> com.mchange.v2.c3p0.impl.DefaultConnectionTester, dataSourceName -> 1hge2xaai1i9e3nwqcb2vr|7b9a4292, debugUnreturnedConnectionStackTraces -> false, description -> null, driverClass -> com.mysql.jdbc.Driver, factoryClassLocation -> null, forceIgnoreUnresolvedTransactions -> false, identityToken -> 1hge2xaai1i9e3nwqcb2vr|7b9a4292, idleConnectionTestPeriod -> 0, initialPoolSize -> 3, jdbcUrl -> jdbc:mysql://192.168.0.143:3306/day17, maxAdministrativeTaskTime -> 0, maxConnectionAge -> 0, maxIdleTime -> 0, maxIdleTimeExcessConnections -> 0, maxPoolSize -> 15, maxStatements -> 0, maxStatementsPerConnection -> 0, minPoolSize -> 3, numHelperThreads -> 3, numThreadsAwaitingCheckoutDefaultUser -> 0, preferredTestQuery -> null, properties -> {user=******, password=******}, propertyCycle -> 0, testConnectionOnCheckin -> false, testConnectionOnCheckout -> false, unreturnedConnectionTimeout -> 0, usesTraditionalReflectiveProxies -> false ]
User(username=admin, password=admin, address=新西兰, id=1)
User(username=ffff, password=123456, address=水星, id=2)
User(username=改改, password=321, address=成交价.., id=4)

说明一下@Qualifier的用法：
如果xml文件中配置的QueryRunner对象的id跟UserDaoImpl类中自动注入的成员变量名不相同，那个这个时候可以在上面加上@Qualifier(“xxx”)来指定对应IoC容器中对象的id。

@Component(value = "userDao")
public class UserDaoImpl implements UserDao{
  @Autowired
  @Qualifier("query1")
  private QueryRunner queryRunner ;

    <bean id="query1" class="org.apache.commons.dbutils.QueryRunner" scope="prototype">

二、借助类文件实现的注解

1、新建类文件SpringConfig.java
@Configuration指明这是一个配置类，@ComponentScan({“com.mediacomm”})让spring届时扫面指定包下的类来读取注解，@PropertySource(“classpath:jdbcProperties.properties”)指定读入Properties文件的位置

@Configuration
@ComponentScan({"com.mediacomm"})
@PropertySource("classpath:jdbcProperties.properties")
public class SpringConfiguration {

}

2、新建jdbcProperties.properties文件

JDBC_Driver=com.mysql.jdbc.Driver
JDBC_Url=jdbc:mysql://localhost:3306/day17
JDBC_User=root
JDBC_Password=123456

3、修改SpringConfig.java
@Value获取properties文件中的值，@Bean(“dataSource”)创建对象并指定id，@Scope(“prototype”)指定对象作用范围为多例，被@Bean标识后的方法，如果需要传入参数，spring会根据参数的变量名去容器中查找有没有可用的bean对象。

@Configuration
@ComponentScan({"com.mediacomm"})
@PropertySource("classpath:jdbcProperties.properties")
public class SpringConfiguration {
  @Value("${JDBC_Driver}")
  private String driver;
  @Value("${JDBC_Url}")
  private String url;
  @Value("${JDBC_User}")
  private String user;
  @Value("${JDBC_Password}")
  private String password;
  @Bean("queryRunner")
  @Scope("prototype")
  public QueryRunner createQueryRunner(DataSource dataSource){
    return new QueryRunner(dataSource);
  }
  @Bean("dataSource")
  public DataSource createDataSource() throws PropertyVetoException {
    ComboPooledDataSource dataSource = new ComboPooledDataSource();
    dataSource.setDriverClass(driver);
    dataSource.setJdbcUrl(url);
    dataSource.setUser(user);
    dataSource.setPassword(password);
    return dataSource;
  }
}

4、进行测试
这里创建IoC容器对象的方式是new AnnotationConfigApplicationContext(SpringConfiguration.class)。

public class SpringByXMLTest {
  private ApplicationContext context;
  private UserDao userDao;
  private UserService service;
  @Before
  public void init(){
    //context = new ClassPathXmlApplicationContext("Spring.xml");
    context = new AnnotationConfigApplicationContext(SpringConfiguration.class);
    userDao = context.getBean("userDao",UserDao.class);
    service = context.getBean("userService",UserService.class);
  }
  @Test
  public void test01(){
    List<User> users = service.findAll();
    for (User user:users) {
      System .out.println(user);
    }
  }

@Import标签是当你有多个类配置文件时，用于导入其他配置类，在引入其他配置类时，可以不用再写@Configuration 注解。

总结

总的来说，个人偏向于使用第一种方式，可以通过xml文件更加清晰的呈现，方便以后的修改和阅读。