spring基于注解开发

---

title: spring基于注解开发
date: 2019-03-03 10:29:05
tags: spring

---

spring基于注解开发

一、bean的加载

1.@Configuration，@Bean

@Configuration
public class Config
{
    @Bean("person")
    public Person personA()
    {
        Person a =new Person(10,"jerry");
        return a;
    }
}

测试：

public static void main(String[] args)
{
    ApplicationContext applicationContext = new                                                                                         AnnotationConfigApplicationContext(Config.class);
    Person person = applicationContext.getBean("person", Person.class);
    System.out.println(person);
}

@Bean 注解默认采用方法名作为bean的名字，也可以指定bean名。

2.@ComponentScan、@Component、@Service等

@ComponentScan(basePackages = "com.tiger")
public class Config
{
}

@Component
public class Person
{
    
}

@Service
public class PersonService
{

}

测试:

@Test
public void test1()
{
    AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(
        Config.class);

    String[] beanDefinitionNames = context.getBeanDefinitionNames();

    for(String beanName:beanDefinitionNames)
    {
        System.out.println(beanName);
    }
}

结果:

org.springframework.context.annotation.internalConfigurationAnnotationProcessor
org.springframework.context.annotation.internalAutowiredAnnotationProcessor
org.springframework.context.annotation.internalCommonAnnotationProcessor
org.springframework.context.event.internalEventListenerProcessor
org.springframework.context.event.internalEventListenerFactory
config
person
personDao
personService

可以通过excludeFilters参数来限制扫描的范围。例如

@ComponentScan(basePackages = "com.tiger", excludeFilters = { @Filter(type = FilterType.ANNOTATION,classes = {
    Controller.class}) })

值得一提的是@ComponentScan里的一个字段boolean useDefaultFilters() default true;默认为true，也就是默认会加载指定包下的所有bean，如果只想指定的bean被加载，应设定为false，此时通过includeFilters来指定需要加载的bean才会生效，如下

@ComponentScan(basePackages = "com.tiger", includeFilters = {
    @Filter(type = FilterType.ANNOTATION, classes = { Service.class }),
    @Filter(type = FilterType.ASSIGNABLE_TYPE, classes = { Person.class }) },useDefaultFilters = false)
public class Config
{

}

还可以定制化Filter来过滤需要加载的bean，如下

public class MyFilter implements TypeFilter
{
    public boolean match(MetadataReader metadataReader, MetadataReaderFactory metadataReaderFactory)
        throws IOException
    {
        ClassMetadata classMetadata = metadataReader.getClassMetadata();
        String className = classMetadata.getClassName();
        if(className.contains("Dao"))
        {
            return true;
        }
        return false;
    }
}

@ComponentScan(basePackages = "com.tiger", includeFilters = {
    @Filter(type = FilterType.CUSTOM,classes = MyFilter.class)
},useDefaultFilters = false)
public class Config
{

}

这样包含"Dao"字符串的类才会被spring容器加载。

3.@Scope、@Lazy

常用的

• @Scope("singleton") 该bean在spring容器中为单例，每次取bean都是同一个，而且该bean在spring容器启动的时候就会被实例化
• @Scope("prototype") 每次获取bean都是重新实例化。
• @Lazy如果bean的作用域为单例，而且不希望在spring容器刚启动时就被加载，可以用此注解，这样只有在获取该bean时才会被实例化。

4.@Conditional

可以通过该注解来决定当前的bean是否应该被加载到spring容器，比如以下的两个bean，希望在Windows环境下加载"bill"这个bean，而在“linux”环境下加载‘’linas‘这个bean，代码如下

@Conditional(WindowCondition.class)
@Bean("bill")
public Person person()
{
    return new Person(19,"bill Gates");
}

@Conditional(LinuxCondition.class)
@Bean("linas")
public Person person2()
{
    return new Person(20,"linas");
}

WindowCondition类实现Condition接口，在实现方法中来判断环境

public class WindowCondition implements Condition
{
    public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata)
    {
        Environment environment = context.getEnvironment();
        //这里可以通过context、metadata参数实现多样的判断条件
        if(environment.getProperty("os.name").contains("Windows"))
        {
            return true;
        }

        return false;
    }
}

5.@import

在配置类上通过@Import注解也可以加载bean

• 直接指定需要加载的类

@Configuration
@Import(Apple.class)
public class Config {

}

• 通过实现ImportSelector接口，来指定需要加载的bean，如下

public class MySelector implements ImportSelector {
    @Override
    public String[] selectImports(AnnotationMetadata importingClassMetadata) {
        return new String[]{"com.example.demo.bean.Apple", "com.example.demo.controller.TestController"};
    }
}

@Configuration
@Import(MySelector.class)
public class Config {

}

• 通过实现ImportBeanDefinitionRegistrar接口来实现加载bean，例如如果有名为apple的bean就加载TestControllerbean

public class MyImportBeanDefinitionRegister implements ImportBeanDefinitionRegistrar {
    @Override
    public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
        String[] beanDefinitionNames = registry.getBeanDefinitionNames();
        for (String beanName : beanDefinitionNames) {
            if (beanName.contains("apple")) {
                RootBeanDefinition testConDef = new RootBeanDefinition(TestController.class);
                registry.registerBeanDefinition("testController",testConDef);
            }
        }
    }
}

@Configuration
@Import(MyImportBeanDefinitionRegister.class)
public class Config {

    @Bean("apple")
    public Apple apple() {
        return new Apple();
    }
}

6.通过工厂类来装配bean，可以实现FactoryBean接口来注入bean

@Component
public class AppleFactory implements FactoryBean<Apple> {
    @Override
    public Apple getObject() throws Exception {
        return new Apple();
    }
    @Override
    public Class<?> getObjectType() {
        return Apple.class;
    }
    @Override
    public boolean isSingleton() {
        return true;
    }
}

该bean在spring容器里的名称为appleFactory，但是通过获取该bean的实际类型，可以发现为Apple，如果需要获取AppleFactory本身的bean的话，可以在名称前加&,如applicationContext.getBean("&appleFactory");

Object apple = applicationContext.getBean("appleFactory");
System.out.println(apple.getClass());
//打印内容:class com.example.demo.bean.Apple

---

todo...