Use annotations Development

Explanation

After spring4, you want to use annotation form, have to be introduced aop package
in the configuration file which is also dependent on the introduction of a context constraint

<?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">

</beans>

Bean added to the vessel

Before we are using the label bean bean injection, but the actual development, we will generally use the comment!
What notes in the package configuration scanning

   <!--指定注解扫描包-->
   <context:component-scan base-package="com.cong.pojo"/>

In the preparation of classes specified package, using annotation @Value injection properties

   @Component("user")// 相当于配置文件中 <bean id="user" class="当前注解的类"/>
   public class User {
       @Value("cong")// 相当于配置文件中 <property name="name" value="cong"/>
       private String name;
       
       @Override
       public String toString() {
           return "User{" +
                   "name='" + name + '\'' +
                   '}';
       }
   }

test

@Test
public void test1(){
   ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
   User user = (User) context.getBean("user");
   System.out.println(user.toString());
}

Spread

@Value method may also act on the

Back @Component value can not write, the default is the class of lowercase

@Component
public class User {
    private String name;
    
    @Value("cong")
    public void setName(String name) {
        this.name = name;
    }
    
    @Override
    public String toString() {
        return "User{" +
                "name='" + name + '\'' +
                '}';
    }
}

Derived comment

These annotations us, is replacing the configuration steps in the configuration file which it! More convenient!

@Component three-derived notes

In order to better stratify, Spring can use the other three notes, the same function, which function is currently using are the same.

@Controller: web layer
@Service: service layer
@Repository: dao layer

Write these notes, the equivalent of this class to manage the assembly of Spring!

Automatic assembly notes

There are four notes, talked about before

@Autowired

Automatically according to the type of injection

If a plurality of the same type of bean, automatically assembling the class name lowercase bean,

@Qualifier

It can not be used alone, with @Autowired, the assembly according to the corresponding bean id

@Resource

@Resource if specified attribute name, attribute byName the press fitting manner lookup;
Secondly, then the default byName assembled manner;
If the above are not successful, press byType way automatic assembly.
Not successful, reported abnormal.

@Nullable

Fields marked this can be null values

Scope

@scope

@scope

singleton: default, Spring will use the Singleton pattern to create the object. Closing factories, all objects will be destroyed.
prototype: Multi-pattern. Closing factories, all objects will not be destroyed. Garbage collection will reclaim internal

@Component
@Scope("singleton")
public class User {
    @Value("cong")
    private String name;
    @PostConstruct//指定初始化方法
    public void init(){
        System.out.println("对象初始化了...");
    }
    @PreDestroy//指定销毁方法
    public void destroy(){
        System.out.println("对象销毁了...");
    }
    @Override
    public String toString() {
        return "User{" +
                "name='" + name + '\'' +
                '}';
    }
}

Run again, the results

对象初始化了...
User{name='cong'}
对象销毁了...

summary

XML and compare notes

XML can be applied to any scene, clear structure, easy maintenance
Notes not provide their own class can not use, develop simple and convenient

xml and Notes Integration and Development : Recommended Best Practices

xml management Bean
Notes injected completed property
Course, you can not scan, the scan is to comment on the class

<context:annotation-config/>

effect:

Annotation-driven register, so that the notes into force
Those bean is used to activate the above comments already registered in the spring container, which is displayed to register with Spring
If no scan packages, it is necessary to manually configure the bean
If you do not add annotation-driven, the injection is null!

spring study notes developed 7-