A, Java annotations configuration is the Spring 4. the X- recommended configuration, you can completely replace the xml configuration. Spring of Java annotations configuration is through @Configuration and @Bean achieve these two notes:
. 1 , @Configuration at class, corresponding to a xml configuration file;
2 , @Bean acting on the method, which corresponds xml configuration < the bean > ;
Example: The two annotations usage
1, create entity classes: User.java
public class User implements Serializable {
private static final long serialVersionUID = 1L;
private String username;
private String password;
private Integer age;
// omitted set / get method
}
2, create Dao layer, simulation database access: UserDao.java
public class UserDao {
public List<User> findAll(){
List<User> users = new ArrayList<User>();
for(int i=1;i<10;i++) {
User user = new User();
user.setUsername(i+"号");
user.setPassword(i+"1234");
user.setAge(i+21);
users.add(user);
}
return users;
}
}
3. Create Service Layer: UserService.java
@Service
public class UserService {
@Autowired
private UserDao userDao;
public List<User> findAllUser(){
return userDao.findAll();
}
}
4, create class notes, the equivalent spring of the main configuration file applicationContext.xml
@Configuration // by the annotations to indicate the class is a Spring configuration, the equivalent of a xml file
@ComponentScan ( basePackages = "com.boot.service" ) // Configure scan package
public class SpringAnnotation {
@Bean // 通过该注解来表明是一个Bean对象，相当于xml中的<bean>
public UserDao getUserDao()
{
return new UserDao();
}
}
5、测试：
public class Main {
public static void main(String[] args) {
AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(SpringAnnotation.class);
UserService userService = context.getBean(UserService.class);
List<User> list = userService.findAllUser();
for(User u : list) {
System.out.println(u.getUsername()+"\t"+u.getPassword()+"\t"+u.getAge());
}
context.close();
}
}
6、
从以上的示例中可以看出，使用Java代码就完美的替代xml配置文件，并且结构更加的清晰。
二、读取外部的资源配置文件,
通过@PropertySource可以指定读取的配置文件，通过@Value注解获取值，具体用法：
@PropertySource(value= {"classpath:jdbc.properties"})
public class SpringAnnotation {
@Value("${jdbc.driver}")
private String driver_class;
@Value("${jdbc.url}")
private String jdbc_url;
@Value("${jdbc.username}")
private String username;
@Value("${jdbc.password}")
private String password;
@Bean
public DataSource getDataSource() {
DataSource dataSource = new DataSource();
dataSource.setDriverClassName(driver_class);
dataSource.setUrl(jdbc_url);
dataSource.setUsername(username);
dataSource.setPassword(password);
return dataSource;
}
@Bean
public SqlSessionFactoryBean getSqlSessionFactory() throws Exception {
SqlSessionFactoryBean sessionFactory = new SqlSessionFactoryBean();
sessionFactory.setDataSource(this.getDataSource());
return sessionFactory;
}