@Conditional
@Conditional是Spring4新提供的注解，它的作用是按照一定的条件进行判断，满足条件给容器注册bean。
创建ConfigConditional类和测试类ConfigConditionalTest
@Configuration
public class ConfigConditional {
@Bean(name = "xiaoming")
public Student getStudent1(){
Student student = new Student();
student.setName("xiaoming");
student.setAge(18);
return student;
}
@Bean(name = "xiaohong")
public Student getStudent2(){
Student student = new Student();
student.setName("xiaohong");
student.setAge(17);
return student;
}
}
测试类ConfigConditionalTest
输出结果为{xiaoming=Student(age=18, name=xiaoming), xiaohong=Student(age=17, name=xiaohong)}，说明两个Student实例被注入进容器。
public class ConfigConditionalTest {
AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(ConfigConditional.class);
@Test
public void test1() {
Map<String, Student> map = applicationContext.getBeansOfType(Student.class);
System.out.println(map);
}
}
//输出为{xiaoming=Student(age=18, name=xiaoming), xiaohong=Student(age=17, name=xiaohong)}
如果我想根据当前操作系统来注入Student实例，只有在非windows操作系统的情况下注入xiaoming。
这就需要我们用到@Conditional注解了。
@Conditional作用
Class<? extends Condition>[] value()说明@Conditional注解传入的是一个Class数组，存在多种条件类的情况。@Target({ElementType.TYPE, ElementType.METHOD})说明@Conditional可以作用在方法和类上，一个方法只能注入一个bean实例，所以@Conditional标注在方法上只能控制一个bean实例是否注入。标注在类上：一个类中可以注入很多实例，@Conditional标注在类上就决定了一批bean是否注入。
@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Conditional {
/**
* All {@link Condition} classes that must {@linkplain Condition#matches match}
* in order for the component to be registered.
*/
Class<? extends Condition>[] value();
}
@Conditional举例
创建WindowsConfig，非windows系统，返回true。
public class WindowsConfig implements Condition {
@Override
public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
//获取ioc使用的beanFactory
ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
//获取类加载器
ClassLoader classLoader = context.getClassLoader();
//获取当前环境信息
Environment environment = context.getEnvironment();
//获取bean定义的注册类
BeanDefinitionRegistry registry = context.getRegistry();
//获得当前系统名
String property = environment.getProperty("os.name");
//不包含Windows则说明不是windows系统，返回true
if (!property.contains("Windows")) {
return true;
}
return false;
}
}
@Conditional作用在方法上
@Configuration
public class ConfigConditional {
@Bean(name = "xiaoming")
@Conditional(WindowsConfig.class)
public Student getStudent1(){
Student student = new Student();
student.setName("xiaoming");
student.setAge(18);
return student;
}
@Bean(name = "xiaohong")
public Student getStudent2(){
Student student = new Student();
student.setName("xiaohong");
student.setAge(17);
return student;
}
}
因为只在非windows系统注入xiaoming,因此输出为{xiaohong=Student(age=17, name=xiaohong)}。
@Conditional作用在类上
@Configuration
@Conditional(WindowsConfig.class)
public class ConfigConditional {
@Bean(name = "xiaoming")
public Student getStudent1(){
Student student = new Student();
student.setName("xiaoming");
student.setAge(18);
return student;
}
@Bean(name = "xiaohong")
public Student getStudent2(){
Student student = new Student();
student.setName("xiaohong");
student.setAge(17);
return student;
}
}
因为只在非windows系统注入xiaoming和xiaohong,因此输出为{}
@import
@Import注解用来帮助我们把一些需要定义为Bean的类导入到IOC容器里面。如果配置类在标准的springboot的包结构下，就是SpringbootApplication启动类在包的根目录下，配置类在子包下。就不需要使用@Import导入配置类，如果配置类在第三方的jar下，我们想要引入这个配置类，就需要@Import对其引入到工程中才能生效。因为这个时候配置类不再springboot默认的扫描范围内。
@Import源码注释里可以知道，value里面传递的Class会被Spring识别成为component组件。
@Import源码注释里面的一段说明，指出了@Import的用法：
- 导入一个@Configuration类
- 导入ImportSelector，ImportBeanDefinitionRegistrar的实现类
- 导入一个普通的类
/*
*<p>Provides functionality equivalent to the {@code <import/>} element in Spring XML.
* Allows for importing {@code @Configuration} classes, {@link ImportSelector} and
* {@link ImportBeanDefinitionRegistrar} implementations, as well as regular component
* classes (as of 4.2; analogous to {@link AnnotationConfigApplicationContext#register}).
*/
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Import {
/**
* {@link Configuration @Configuration}, {@link ImportSelector},
* {@link ImportBeanDefinitionRegistrar}, or regular component classes to import.
*/
Class<?>[] value();
}
@Import引入普通类
@Import引入普通的类可以帮助我们把普通的类定义为Bean。@Import可以添加在@SpringBootApplication(启动类)、@Configuration(配置类)、@Component(组件类)对应的类上。
定义Teacher类
@Data
public class Teacher {
private int age;
private String name;
}
在springboot的启动类@Import Teacher类，这个类就可以被其他类当做bean来引用。
输出结果Teacher(age=0, name=null)
@SpringBootApplication
@Import({Teacher.class})
public class SpringbootReviewApplication {
public static void main(String[] args) {
ConfigurableApplicationContext run = SpringApplication.run(SpringbootReviewApplication.class, args);
Teacher teacher = run.getBean(Teacher.class);
System.out.println(teacher);
}
}
//输出结果Teacher(age=0, name=null)
@Import引入配置类(@Configuration修饰的类)
@Import除了可以把普通的类定义为Bean，@Import还可以引入一个@Configuration修饰的类(引入配置类)，从而把让配置类生效(配置类下的所有Bean添加到IOC容器里面去)如果配置类在标准的SpringBoot包结构下(SpringBootApplication启动类包的根目录下)。是不需要@Import导入配置类的，SpringBoot自动帮做了。上面的情况一般用于@Configuration配置类不在标准的SpringBoot包结构下面。所以一般在自定义starter的时候用到。
public class ImportDemo {
public void doSomething () {
System.out.println("ImportDemo.doSomething()");
}
}
@Configuration
@Import({ImportDemo.class})
public class ImportConfig{
@Bean
public Student returnOneStudent(){
return new Student();
}
}
@RestController
public class ImportDemoController {
@Autowired
private Student student;
@Autowired
private ImportDemo importDemo;
@RequestMapping("/importDemo")
public String demo() throws Exception {
importDemo.doSomething();
return "ImportDemo" + student.toString;
}
}