DI 注解开发

1.目前面临问题

建立 mapper

public interface EmployeeMapper {void save();
}

建立 mapper 实现类

@Repository
public class EmployeeMapperImpl implements EmployeeMapper {public void save(){System.out.println("保存员工信息");}
}

建立 service

public interface IEmployeeService {void save();
}

建立 service 实现类

@Service
public class EmployeeServiceImpl implements IEmployeeService {private EmployeeMapper employeeMapper;public void setEmployeeMapper(EmployeeMapper employeeMapper){this.employeeMapper = employeeMapper;}public void save() {employeeMapper.save();}
}

设置配置类

@Configuration
@ComponentScan("cn.sycoder.di.di01")
public class DiConfig {
}

出现空指针异常

2.使用类型注入

@Autowired按照类型注入

通过构造器注入

@Autowired
public EmployeeServiceImpl(EmployeeMapper employeeMapper) {this.employeeMapper = employeeMapper;
}

通过setter 方法注入

@Autowired
public void setEmployeeMapper(EmployeeMapper employeeMapper) {this.employeeMapper = employeeMapper;
}

直接在属性上使用(是以后用得最多的)

@Service
public class EmployeeServiceImpl implements IEmployeeService {@Autowiredprivate EmployeeMapper employeeMapper;public void save() {employeeMapper.save();}
}

注意：不提供setter 方法以及构造器是使用反射创建对象的

@Testpublic void autowired() throws Exception {final Class<?> aClass = Class.forName("cn.sycoder.di.di01.service.impl.EmployeeServiceImpl");final Object o = aClass.newInstance();final Field[] fields = aClass.getDeclaredFields();AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(DiConfig.class);final EmployeeMapper bean = context.getBean(EmployeeMapper.class);for (Field field : fields) {field.setAccessible(true);field.set(o,bean);}final EmployeeServiceImpl service = (EmployeeServiceImpl) o;service.save();}

根据类型注入必须只有一个实现类，否则会报错，添加名称也不行

属性required=false，如果找不到不会报错

3.使用名称注入

@Autowired & @Qualifier
@Autowired & @Qualifier必须同时使用，缺一不可
解决刚才出现两个实现类没法注入的问题

配置mapper 并且指定实现类的名称

public interface EmployeeMapper {void save();
}@Repository("empMapper2")
public class EmployeeMapperImpl implements EmployeeMapper {public void save(){System.out.println("保存员工信息");}
}@Repository("empMapper1")
public class EmployeeMapperImpl1 implements EmployeeMapper{public void save() {System.out.println("save");}
}

注入的时候使用名称注入

@Service
public class EmployeeServiceImpl implements IEmployeeService {@Autowired(required = false)@Qualifier("empMapper1")private EmployeeMapper employeeMapper;public void save() {employeeMapper.save();}}

4.简单数据类型注入

@Value

@Component
public class DbProperties {@Value("sy")private String username;@Value("123456")private String password;}

硬编码，太垃圾了，需要改成动态

5.注解读取配置文件参数

@Value

修改配置类

@Configuration
@ComponentScan("cn.sycoder.di.di01")
@PropertySource("db.properties")
public class DiConfig {
}

修改获取方式使用 ${} 的方式

@Component
public class DbProperties {@Value("${username}")private String username;@Value("${password}")private String password;public void test(){System.out.println(username + ":" + password);}
}

5.1@PropertySource

@PropertySource 加载配置文件
位置：配置类上
作用导入配置文件

对于多个配置文件

@Configuration
@ComponentScan("cn.sycoder.di.di01")
@PropertySource({"db.properties","xx.properties"})
public class DiConfig {
}

6.注解配置第三方bean

6.1配置 druid

添加依赖

<dependency><groupId>com.alibaba</groupId><artifactId>druid</artifactId><version>1.2.8</version>
</dependency>

先添加配置类 SpringConfig

@Configuration
public class SpringConfig {public DataSource dataSource(){final DruidDataSource source = new DruidDataSource();source.setUsername("root");source.setPassword("123456");source.setDriverClassName("com.mysql.cj.jdbc.Driver");source.setUrl("jdbc:mysql://localhost:3306/mybatis");return source;}}

传统做法存在硬编码，DataSource 并且没有交给 spring 管理,每次都需要重新新建 DataSource ,并不存在单例一说

@Testpublic void testDruid(){AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(SpringConfig.class);final SpringConfig bean = context.getBean(SpringConfig.class);System.out.println(bean.dataSource());}

6.2@Bean 配置 druid

使用@Bean 交给 spring 管理

@Configuration
public class SpringConfig {@Beanpublic DataSource dataSource(){final DruidDataSource source = new DruidDataSource();source.setUsername("root");source.setPassword("123456");source.setDriverClassName("com.mysql.cj.jdbc.Driver");source.setUrl("jdbc:mysql://localhost:3306/mybatis");return source;}}

修改配置的硬编码改成软编码

@Configuration
@PropertySource("druidDb.properties")
public class SpringConfig {@Value("${jdbc.username}")private String username;@Value("${jdbc.password}")private String password;@Value("${jdbc.url}")private String url;@Value("${jdbc.driverClassName}")private String driver;@Beanpublic DataSource dataSource(){final DruidDataSource source = new DruidDataSource();source.setUsername(username);source.setPassword(password);source.setDriverClassName(driver);source.setUrl(url);return source;}}

jdbc.username=root
jdbc.password=123456
jdbc.driverClassName=com.mysql.cj.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/mybatis

@Bean 与 xml 对应

7.使用@Import 实现配置导入

目前存在：任何类都配置到配置类里面，不方便管理，也不方便维护

7.1配置 Component 解决

@Component

@Component
public class DruidConfig {@Value("{jdbc.username}")private String username;@Value("{jdbc.password}")private String password;@Value("{jdbc.url}")private String url;@Value("{jdbc.driverClassName}")private String driver;@Beanpublic DataSource dataSource(){final DruidDataSource source = new DruidDataSource();source.setUsername(username);source.setPassword(password);source.setDriverClassName(driver);source.setUrl(url);return source;}
}

7.2使用@import

修改druidConfig

@Configuration
public class DruidConfig {@Value("{jdbc.username}")private String username;@Value("{jdbc.password}")private String password;@Value("{jdbc.url}")private String url;@Value("{jdbc.driverClassName}")private String driver;@Beanpublic DataSource dataSource(){final DruidDataSource source = new DruidDataSource();source.setUsername(username);source.setPassword(password);source.setDriverClassName(driver);source.setUrl(url);return source;}
}

修改spring配置类

@Configuration
@PropertySource("druidDb.properties")
@Import({DruidConfig.class})
public class SpringConfig {
}

如果需要传参，只需要将参数交给spring管理就行了

@Configuration
public class RepositoryConfig {@Beanpublic AccountRepository accountRepository(DataSource dataSource) {return new JdbcAccountRepository(dataSource);}
}

8.注解开发总结

注解配置	xml 配置	功能说明
@Component @Controller @Service @Repository	bean 标签（id,class）	定义bean
@ComponentScan	<context:component-scan base-package=“cn.sycoder.ioc.xmlAnnotationBean”/>	扫描包加载bean
@Autowired @Qualifier @Value	setter 注入构造器注入自动装配	依赖注入
@Bean	bean 标签，静态工厂模式，实例工厂模式，FactoryBean	配置第三方bean
@Scope	bean 标签中的 scope 属性	设置作用域
@PostConstructor @PreDestroy	bean 标签中的 init-method / destroy-method	生命周期相关
@Import		导入其它的配置类
@PropertySource({“db.properties”,“xx.properties”})	<context:property-placeholder system-properties-mode=“NEVER” location=“*.properties”/>	导入配置文件