title: spring基于注解開發(fā)
date: 2019-03-03 10:29:05
tags: spring

spring基于注解開發(fā)

一、bean的加載

1.@Configuration，@Bean

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

測試：

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

@Bean 注解默認采用方法名作為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
{

}

測試:

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

    String[] beanDefinitionNames = context.getBeanDefinitionNames();

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

結果:

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

可以通過excludeFilters參數(shù)來限制掃描的范圍。例如

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

值得一提的是@ComponentScan里的一個字段boolean useDefaultFilters() default true;默認為true，也就是默認會加載指定包下的所有bean，如果只想指定的bean被加載，應設定為false，此時通過includeFilters來指定需要加載的bean才會生效，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
{

}

還可以定制化Filter來過濾需要加載的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
{

}

這樣包含"Dao"字符串的類才會被spring容器加載。

3.@Scope、@Lazy

常用的

• @Scope("singleton") 該bean在spring容器中為單例，每次取bean都是同一個，而且該bean在spring容器啟動的時候就會被實例化
• @Scope("prototype") 每次獲取bean都是重新實例化。
• @Lazy如果bean的作用域為單例，而且不希望在spring容器剛啟動時就被加載，可以用此注解，這樣只有在獲取該bean時才會被實例化。

4.@Conditional

可以通過該注解來決定當前的bean是否應該被加載到spring容器，比如以下的兩個bean，希望在Windows環(huán)境下加載"bill"這個bean，而在“l(fā)inux”環(huán)境下加載‘’linas‘這個bean，代碼如下

@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類實現(xiàn)Condition接口，在實現(xiàn)方法中來判斷環(huán)境

public class WindowCondition implements Condition
{
    public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata)
    {
        Environment environment = context.getEnvironment();
        //這里可以通過context、metadata參數(shù)實現(xiàn)多樣的判斷條件
        if(environment.getProperty("os.name").contains("Windows"))
        {
            return true;
        }

        return false;
    }
}

5.@import

在配置類上通過@Import注解也可以加載bean

• 直接指定需要加載的類

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

}

• 通過實現(xiàn)ImportSelector接口，來指定需要加載的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 {

}

• 通過實現(xiàn)ImportBeanDefinitionRegistrar接口來實現(xiàn)加載bean，例如如果有名為apple的bean就加載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.通過工廠類來裝配bean，可以實現(xiàn)FactoryBean接口來注入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;
    }
}

該bean在spring容器里的名稱為appleFactory，但是通過獲取該bean的實際類型，可以發(fā)現(xiàn)為Apple，如果需要獲取AppleFactory本身的bean的話，可以在名稱前加&,如applicationContext.getBean("&appleFactory");

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

todo...