Spring 常用的注解

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Spring 常用注解

Spring Core Annotations

DI-Related Annotations

  1. @Autowried

    可以用于构造函数、setter 方法、属性注入。

    @Autowried 有一个 boolean 类型的参数required，默认值为 true。当没有找到合适的 bean 注入时，若是 true，则抛出异常，否则，不注入。

    注意：如果用在构造函数上，则构造函数所有的参数都是必需的。

    构造函数注入

    class Car {
    Engine engine;
 
    @Autowired
    Car(Engine engine) {
        this.engine = engine;
    }
}

    setter 方法注入

    class Car {
    Engine engine;
 
    @Autowired
    void setEngine(Engine engine) {
        this.engine = engine;
    }
}

    属性注入

    class Car {
    @Autowired
    Engine engine;
}

  2. @Bean

    标记一个工厂方法。

    @Bean
Engine engine() {
    return new Engine();
}

    返回的bean 与工厂方法名相同，如果想设置不同的名字，可以使用带有参数的注解，参数的值就是返回 bean 的别名。

    @Bean("engine")
Engine getEngine() {
    return new Engine();
}

    注意：所有使用@Bean 注解的方法必须在使用@Configuration 注解的类中。

  3. @Qualifier

    与@Autowired 注解一起使用，消除注入的歧义性，可以使用 bean id 或者 bean name。

    如下，两个 bean 实现同一个接口。

    class Bike implements Vehicle {}
 
class Car implements Vehicle {}

    如果 Spring 需要注入一个 Vehicle bean，将发现有多个 Vehicle 类型的 bean，我们可以使用@Qualifier 提供明确的类名。

    构造函数注入

    @Autowired
Biker(@Qualifier("bike") Vehicle vehicle) {
    this.vehicle = vehicle;
}

    setter 方法注入

    @Autowired
@Qualifier("bike")
void setVehicle(Vehicle vehicle) {
    this.vehicle = vehicle;
}

    属性注入

    @Autowired
@Qualifier("bike")
Vehicle vehicle;

  4. @Required

    用于标记我们想通过 xml注入的 setter 方法

    @Required
void setColor(String color) {
    this.color = color;
}

    <bean class="com.baeldung.annotations.Bike">
    <property name="color" value="green" />
</bean>

  5. @Value

    注入属性值，可以用于构造函数、setter 方法和属性。

    构造函数

    Engine(@Value("8") int cylinderCount) {
    this.cylinderCount = cylinderCount;
}

    setter方法

    @Autowired
void setCylinderCount(@Value("8") int cylinderCount) {
    this.cylinderCount = cylinderCount;
}

    @Value("8")
void setCylinderCount(int cylinderCount) {
    this.cylinderCount = cylinderCount;
}

    属性注入

    @Value("8")
int cylinderCount;

  6. @DependsOn

    Spring 在初始化这个 bean之前初始化其他 beans。一般的，这种依赖注入关系是自动的。

    当存在隐式依赖关系时才需要这个注解，例如，JDBC 驱动或者 static 变量初始化。

    @DependsOn("engine")
class Car implements Vehicle {}

    @Bean
@DependsOn("fuel")
Engine engine() {
    return new Engine();
}

  7. @Lazy

    懒加载

    可以使用在

    • @Bean 延迟工厂方法调用
    • @Configuration 所有包含@Bean 注解的方法都将受影响
    • @Component 延迟初始化
    • @Autowired 注解的构造函数、setter 方法或者属性，延迟加载依赖

  8. @Lookup

    返回方法返回类型的实例

    创建一个 prototype bean

    @Component
@Scope("prototype")
public class SchoolNotification {
    // ... prototype-scoped state
}

    创建一个单例

    @Component
public class StudentServices {
 
    // ... member variables, etc.
 
    @Lookup
    public SchoolNotification getNotification() {
        return null;
    }
 
    // ... getters and setters
}

    @Test
public void whenLookupMethodCalled_thenNewInstanceReturned() {
    // ... initialize context
    StudentServices first = this.context.getBean(StudentServices.class);
    StudentServices second = this.context.getBean(StudentServices.class);
        
    assertEquals(first, second); 
    assertNotEquals(first.getNotification(), second.getNotification()); 
}

  9. @Primary

    @Component
@Primary
class Car implements Vehicle {}
 
@Component
class Bike implements Vehicle {}
 
@Component
class Driver {
    @Autowired
    Vehicle vehicle;
}
 
@Component
class Biker {
    @Autowired
    @Qualifier("bike")
    Vehicle vehicle;
}

    Driver 类，spring 注入一个 Car bean，Biker 类，spring 注入一个 Bike 对象。

  10. @Scope

    @Scope 定义@Component 或者@Bean 定义的 bean 的范围，主要有：singleton、prototype、request、session、globalSession 或者其他自定 scope。

    @Component
@Scope("prototype")
class Engine {}

Context Configuration Annotations

  1. @Profile

    用于@Component 或者@Bean

    @Component
@Profile("sportDay")
class Bike implements Vehicle {}

  2. @Import

    不需要组件扫描，可以使用特定的@Configuration 类。

    @Import(VehiclePartSupplier.class)
class VehicleFactoryConfig {}

  3. @ImportResource

    导入 XML 配置

    @Configuration
@ImportResource("classpath:/annotations.xml")
class VehicleFactoryConfig {}

  4. @PropertySource

    属性文件

    @Configuration
@PropertySource("classpath:/annotations.properties")
class VehicleFactoryConfig {}

    @Configuration
@PropertySource("classpath:/annotations.properties")
@PropertySource("classpath:/vehicle-factory.properties")
class VehicleFactoryConfig {}

  5. @PropertySources

    @Configuration
@PropertySources({ 
    @PropertySource("classpath:/annotations.properties"),
    @PropertySource("classpath:/vehicle-factory.properties")
})
class VehicleFactoryConfig {}

Spring Web Annotations

  1. @RequestMapping

    使用在@Controller 注解的类中，标记 request 处理方法，可以使用以下配置：

    path, or its aliases, name, and value: which URL the method is mapped to method: compatible HTTP methods params: filters requests based on presence, absence, or value of HTTP parameters headers: filters requests based on presence, absence, or value of HTTP headers consumes: which media types the method can consume in the HTTP request body produces: which media types the method can produce in the HTTP response body

    @Controller
class VehicleController {
 
    @RequestMapping(value = "/vehicles/home", method = RequestMethod.GET)
    String home() {
        return "home";
    }
}

    @Controller
@RequestMapping(value = "/vehicles", method = RequestMethod.GET)
class VehicleController {
 
    @RequestMapping("/home")
    String home() {
        return "home";
    }
}

    @GetMapping, @PostMapping, @PutMapping, @DeleteMapping, @PatchMapping都是由@RequestMapping 转变而来的。

  2. @RequestBody

    自动封装客户端传递过来的 json 格式参数到 bean 中

    @PostMapping("/save")
void saveVehicle(@RequestBody Vehicle vehicle) {
    // ...
}

  3. @PathVariable

    @RequestMapping("/{id}")
Vehicle getVehicle(@PathVariable(required = false) long id) {
    // ...
}

  4. @RequestParam

    @RequestMapping("/buy")
Car buyCar(@RequestParam(defaultValue = "5") int seatCount) {
    // ...
}

    与@RequestParam 类似的注解，还有@CookieValue 和@RequestHeader ，可以获取 cookie 和 headers。

Response Handling Annotations

  1. @ResponseBody

    @ResponseBody
@RequestMapping("/hello")
String hello() {
    return "Hello World!";
}

  2. @ExceptionHandler

    自定义错误处理方法

    @ExceptionHandler(IllegalArgumentException.class)
void onIllegalArgumentException(IllegalArgumentException exception) {
    // ...
}

  3. @ResponseStatus

    @ExceptionHandler(IllegalArgumentException.class)
@ResponseStatus(HttpStatus.BAD_REQUEST)
void onIllegalArgumentException(IllegalArgumentException exception) {
    // ...
}

Other Web Annotations

  1. @Controller

  2. @RestController

    @RestController 包含@Controller 和@ResponseBody

    @Controller
@ResponseBody
class VehicleRestController {
    // ...
}

    @RestController
class VehicleRestController {
    // ...
}

  3. @ModelAttribute

    @ModelAttribute 可以用在方法参数或者方法上。

    @ModelAttribute methods are invoked before the controller methods annotated with @RequestMapping are invoked

    The View

    <form:form method="POST" action="/spring-mvc-basics/addEmployee"
  modelAttribute="employee">
    <form:label path="name">Name</form:label>
    <form:input path="name" />
     
    <form:label path="id">Id</form:label>
    <form:input path="id" />
     
    <input type="submit" value="Submit" />
</form:form>

    The Controller

    @Controller
@ControllerAdvice
public class EmployeeController {
 
    private Map<Long, Employee> employeeMap = new HashMap<>();
 
    @RequestMapping(value = "/addEmployee", method = RequestMethod.POST)
    public String submit(
      @ModelAttribute("employee") Employee employee,
      BindingResult result, ModelMap model) {
        if (result.hasErrors()) {
            return "error";
        }
        model.addAttribute("name", employee.getName());
        model.addAttribute("id", employee.getId());
 
        employeeMap.put(employee.getId(), employee);
 
        return "employeeView";
    }
 
    @ModelAttribute
    public void addAttributes(Model model) {
        model.addAttribute("msg", "Welcome to the Netherlands!");
    }
}

    The Model

    @XmlRootElement
public class Employee {
 
    private long id;
    private String name;
 
    public Employee(long id, String name) {
        this.id = id;
        this.name = name;
    }
 
    // standard getters and setters removed
}

    Results View

    <h3>${msg}</h3>
Name : ${name}
ID : ${id}

  4. @CrossOrigin

    @CrossOrigin
@RequestMapping("/hello")
String hello() {
    return "Hello World!";
}

    @CrossOrigin(maxAge = 3600)
@RestController
@RequestMapping("/account")
public class AccountController {
 
    @CrossOrigin("http://example.com")
    @RequestMapping("/{id}")
    public Account retrieve(@PathVariable Long id) {
        // ...
    }
 
    @RequestMapping(method = RequestMethod.DELETE, path = "/{id}")
    public void remove(@PathVariable Long id) {
        // ...
    }
}

    Global CORS Configuration

    JavaConfig

    @Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {
 
    @Override
    public void addCorsMappings(CorsRegistry registry) {
        registry.addMapping("/**");
    }
}

    XML Namespace

    <mvc:cors>
    <mvc:mapping path="/**" />
</mvc:cors>

    <mvc:cors>
 
    <mvc:mapping path="/api/**"
        allowed-origins="http://domain1.com, http://domain2.com"
        allowed-methods="GET, PUT"
        allowed-headers="header1, header2, header3"
        exposed-headers="header1, header2" allow-credentials="false"
        max-age="123" />
 
    <mvc:mapping path="/resources/**"
        allowed-origins="http://domain1.com" />
 
</mvc:cors>

Spring Boot Annotations

  1. @SpringBootApplication

    @SpringBootApplication 包含@Configuration、@EnableAutoConfiguration、@ComponentScan

    @SpringBootApplication
class VehicleFactoryApplication {
 
    public static void main(String[] args) {
        SpringApplication.run(VehicleFactoryApplication.class, args);
    }
}

  2. @EnableAutoConfiguration

    It means that Spring Boot looks for auto-configuration beans on its classpath and automatically applies them.

    注意：必须与@Configuration 注解一起使用

    @Configuration
@EnableAutoConfiguration
class VehicleFactoryConfig {}

Auto-Configuration Conditions

  1. @ConditionalOnClass and @ConditionalOnMissingClass

    the annotation’s argument is present/absent

    @Configuration
@ConditionalOnClass(DataSource.class)
class MySQLAutoconfiguration {
    //...
}

  2. @ConditionalOnBean and @ConditionalOnMissingBean

    the presence or absence of a specific bean

    @Bean
@ConditionalOnBean(name = "dataSource")
LocalContainerEntityManagerFactoryBean entityManagerFactory() {
    // ...
}

  3. @ConditionalOnProperty

    values of properties

    @Bean
@ConditionalOnProperty(
    name = "usemysql", 
    havingValue = "local"
)
DataSource dataSource() {
    // ...
}

  4. @ConditionalOnResource

    a specific resource is present:

    @ConditionalOnResource(resources = "classpath:mysql.properties")
Properties additionalProperties() {
    // ...
}

  5. @ConditionalOnWebApplication and @ConditionalOnNotWebApplication

    the current application is or isn’t a web application

    @ConditionalOnWebApplication
HealthCheckController healthCheckController() {
    // ...
}

  6. @ConditionalExpression

    the SpEL expression is evaluated to true

    @Bean
@ConditionalOnExpression("${usemysql} && ${mysqlserver == 'local'}")
DataSource dataSource() {
    // ...
}

  7. @Conditional

    For even more complex conditions, we can create a class evaluating the custom condition. We tell Spring to use this custom condition with @Conditional

    @Conditional(HibernateCondition.class)
Properties additionalProperties() {
    //...
}

Spring Scheduling Annotations

  1. @EnableAsync

    定义异步执行功能，必须与@Configuration 一起使用

    @Configuration
@EnableAsync
class VehicleFactoryConfig {}

    执行@Async 定义的方法

  2. @EnableScheduling

    必须与@Configuration 一起使用

    @Configuration
@EnableScheduling
class VehicleFactoryConfig {}

    执行@Scheduled 定义的方法

  3. @Async

    @Async
void repairCar() {
    // ...
}

    使用@Async 定义的方法要遵循以下限制

    1. 必须是 public 方法
    2. 同一类中，自调用不起作用，也就是同一类中，直接调用另一个异步方法不起作用

  4. @Scheduled

    @Scheduled(fixedRate = 10000)
void checkVehicle() {
    // ...
}

    @Scheduled(fixedRate = 10000)
@Scheduled(cron = "0 * * * * MON-FRI")
void checkVehicle() {
    // ...
}

    注意：使用@Scheduled 注解的方法返回类型应该是 void 类型的

  5. @Schedules

    @Schedules({ 
  @Scheduled(fixedRate = 10000), 
  @Scheduled(cron = "0 * * * * MON-FRI")
})
void checkVehicle() {
    // ...
}

Spring Bean Annotations

  1. @ComponentScan

    @Configuration
@ComponentScan(basePackages = "com.baeldung.annotations")
class VehicleFactoryConfig {}

    @Configuration
@ComponentScan(basePackageClasses = VehicleFactoryConfig.class)
class VehicleFactoryConfig {}

    @Configuration
@ComponentScan(basePackages = "com.baeldung.annotations")
@ComponentScan(basePackageClasses = VehicleFactoryConfig.class)
class VehicleFactoryConfig {}

    @Configuration
@ComponentScans({ 
  @ComponentScan(basePackages = "com.baeldung.annotations"), 
  @ComponentScan(basePackageClasses = VehicleFactoryConfig.class)
})
class VehicleFactoryConfig {}

    使用XML方法

    <context:component-scan base-package="com.baeldung" />

  2. @Component

    @Component
class CarUtility {
    // ...
}

  3. @Repository

    @Repository
class VehicleRepository {
    // ...
}

  4. @Service

    @Service
public class VehicleService {
    // ...    
}

  5. @Controller

    @Controller
public class VehicleController {
    // ...
}

  6. @Configuration

    @Configuration
class VehicleFactoryConfig {
 
    @Bean
    Engine engine() {
        return new Engine();
    }
 
}

AOP注解

@Aspect
@Component
public class PerformanceAspect {
    @Pointcut("within(@org.springframework.stereotype.Repository *)")
    public void repositoryClassMethods() {};
 
    @Around("repositoryClassMethods()")
    public Object measureMethodExecutionTime(ProceedingJoinPoint joinPoint) 
      throws Throwable {
        long start = System.nanoTime();
        Object returnValue = joinPoint.proceed();
        long end = System.nanoTime();
        String methodName = joinPoint.getSignature().getName();
        System.out.println(
          "Execution of " + methodName + " took " + 
          TimeUnit.NANOSECONDS.toMillis(end - start) + " ms");
        return returnValue;
    }
}

引自: www.baeldung.com/spring-core…

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