Spring常用註解

目錄

一、註冊Bean

@Component

@Repository/@Service/@Controller

@RestController

二、注入Bean

@Autowired

@Qualifier

@Resource

@Inject

三、Controller參數接收

@RequestParam

@RequestBody

@ModelAttribute

@PathVariable

四、配置

@Configuration

@Bean

@Primary

五、屬性注入

@Value

六、事務

@Transactional

七、映射

@RequestMapping

@GetMapping/@PostMapping/@PutMapping/@PatchMapping/@DeleteMapping

八、異步任務

@EnableAsync

@Async

九、元註解

@Target

@Retention

@Documented

@Inherited

---

一、註冊Bean

@Component

所有受Spring管理組件的通用形式

@Repository/@Service/@Controller

分別對應持久層/服務層/控制層的Bean註冊，內部也是由@Component實現

package org.springframework.stereotype;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

import org.springframework.core.annotation.AliasFor;

/**
 * Indicates that an annotated class is a "Controller" (e.g. a web controller).
 *
 * <p>This annotation serves as a specialization of {@link Component @Component},
 * allowing for implementation classes to be autodetected through classpath scanning.
 * It is typically used in combination with annotated handler methods based on the
 * {@link org.springframework.web.bind.annotation.RequestMapping} annotation.
 *
 * @author Arjen Poutsma
 * @author Juergen Hoeller
 * @since 2.5
 * @see Component
 * @see org.springframework.web.bind.annotation.RequestMapping
 * @see org.springframework.context.annotation.ClassPathBeanDefinitionScanner
 */
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component
public @interface Controller {

	/**
	 * The value may indicate a suggestion for a logical component name,
	 * to be turned into a Spring bean in case of an autodetected component.
	 * @return the suggested component name, if any (or empty String otherwise)
	 */
	@AliasFor(annotation = Component.class)
	String value() default "";

}

@Repository/@Service與@Controller代碼結構相同，不再展示。

@RestController

Spring4之後加入的註解，@Controller+@ResponseBody來配合，默認返回json格式

使用該註解後就不需要再使用@ResponseBody

package org.springframework.web.bind.annotation;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

import org.springframework.core.annotation.AliasFor;
import org.springframework.stereotype.Controller;

/**
 * A convenience annotation that is itself annotated with
 * {@link Controller @Controller} and {@link ResponseBody @ResponseBody}.
 * <p>
 * Types that carry this annotation are treated as controllers where
 * {@link RequestMapping @RequestMapping} methods assume
 * {@link ResponseBody @ResponseBody} semantics by default.
 *
 * <p><b>NOTE:</b> {@code @RestController} is processed if an appropriate
 * {@code HandlerMapping}-{@code HandlerAdapter} pair is configured such as the
 * {@code RequestMappingHandlerMapping}-{@code RequestMappingHandlerAdapter}
 * pair which are the default in the MVC Java config and the MVC namespace.
 *
 * @author Rossen Stoyanchev
 * @author Sam Brannen
 * @since 4.0
 */
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Controller
@ResponseBody
public @interface RestController {

	/**
	 * The value may indicate a suggestion for a logical component name,
	 * to be turned into a Spring bean in case of an autodetected component.
	 * @return the suggested component name, if any (or empty String otherwise)
	 * @since 4.0.1
	 */
	@AliasFor(annotation = Controller.class)
	String value() default "";

}

二、注入Bean

@Autowired

默認情況下，@Autowired默認是根據類型（byType）進行自動裝配的，是Spring自帶的註解。

如果容器中有多個相同類型的bean，則框架將拋出NoUniqueBeanDefinitionException，以提示有多個滿足條件的bean進行自動裝配，程序無法正確做出判斷使用哪一個。

@Target({ElementType.CONSTRUCTOR, ElementType.METHOD, ElementType.PARAMETER, ElementType.FIELD, ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Autowired {

	/**
	 * Declares whether the annotated dependency is required.
	 * <p>Defaults to {@code true}.
	 */
	boolean required() default true;

}

@Autowired中required屬性默認爲true，此時如果容器中沒有對應的bean，則拋出NoSuchBeanDefinitionException

可以配置爲false，這樣當沒有找到相應bean的時候系統不會拋異常

@Qualifier

使用@Autowired時，如果有多個類型一樣的Bean，需要指定按照名稱（byName）進行裝配，則需要配合@Qualifier。

該註解是用來消除依賴注入衝突的。當@Autowired 和 @Qualifier 結合使用時，自動注入的策略就從byType轉變成byName 了。另外，需要在註冊Bean的註解中聲明value屬性以確定名稱。

@Target({ElementType.FIELD, ElementType.METHOD, ElementType.PARAMETER, ElementType.TYPE, ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Inherited
@Documented
public @interface Qualifier {

	String value() default "";

}

@Resource

默認根據屬性名稱進行自動裝配的，如果沒有匹配，則根據類型進行匹配，如果有多個類型一樣的Bean候選者，則可以通過name進行指定進行注入，是JSR250規範的實現。

如果指定了name，則查找名稱匹配的bean進行裝配，找不到則拋出異常

如果指定了type，則查找類型匹配的唯一bean進行裝配，找不到或者找到多個，都會拋出異常

如果同時指定name和type，則找到唯一的bean進行裝配，找不到則拋出異常

package javax.annotation;

import java.lang.annotation.*;
import static java.lang.annotation.ElementType.*;
import static java.lang.annotation.RetentionPolicy.*;


@Target({TYPE, FIELD, METHOD})
@Retention(RUNTIME)
public @interface Resource {
  
    String name() default "";

    String lookup() default "";

    Class<?> type() default java.lang.Object.class;

    enum AuthenticationType {
            CONTAINER,
            APPLICATION
    }

    AuthenticationType authenticationType() default AuthenticationType.CONTAINER;

    boolean shareable() default true;
    
    String mappedName() default "";
  
    String description() default "";
}

@Inject

根據類型進行自動裝配的，如果需要按名稱進行裝配，則需要配合@Named（相當於@Qualifier），是JSR330中的規範

對比：

@Autowired、@Inject是默認按照byType匹配的，@Autowired+@Qualifier實現byName，@Inject+@Name實現byName

@Resource是按照名稱匹配的，通過name屬性進行指定

@Autowired是Spring的，@Resource是JSR250規範的，@Inject是JSR330規範的

三、Controller參數接收

@RequestParam

此註解用在請求方法的參數上，用於將http請求參數（Param）的值賦值給方法中的形參。

處理Content-Type: 爲 application/x-www-form-urlencoded編碼的內容

package org.springframework.web.bind.annotation;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.util.Map;

import org.springframework.core.annotation.AliasFor;


@Target(ElementType.PARAMETER)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface RequestParam {

	/**
	 * Alias for {@link #name}.
	 */
	@AliasFor("name")
	String value() default "";

	/**
	 * The name of the request parameter to bind to.
	 * @since 4.2
	 */
	@AliasFor("value")
	String name() default "";

	/**
	 * Whether the parameter is required.
	 * <p>Defaults to {@code true}, leading to an exception being thrown
	 * if the parameter is missing in the request. Switch this to
	 * {@code false} if you prefer a {@code null} value if the parameter is
	 * not present in the request.
	 * <p>Alternatively, provide a {@link #defaultValue}, which implicitly
	 * sets this flag to {@code false}.
	 */
	boolean required() default true;

	/**
	 * The default value to use as a fallback when the request parameter is
	 * not provided or has an empty value.
	 * <p>Supplying a default value implicitly sets {@link #required} to
	 * {@code false}.
	 */
	String defaultValue() default ValueConstants.DEFAULT_NONE;

}

@RequestBody

此註解用在請求方法的參數上，用於將http請求體（Body）映射綁定到方法中的形參。

接收json格式的數據，並轉換成對應的數據類型。

常用來處理Content-Type: application/json, application/xml等編碼的內容；

也可以處理Content-Type: 爲 application/x-www-form-urlencoded編碼的內容。

package org.springframework.web.bind.annotation;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

import org.springframework.http.converter.HttpMessageConverter;


@Target(ElementType.PARAMETER)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface RequestBody {

	/**
	 * Whether body content is required.
	 * <p>Default is {@code true}, leading to an exception thrown in case
	 * there is no body content. Switch this to {@code false} if you prefer
	 * {@code null} to be passed when the body content is {@code null}.
	 * @since 3.2
	 */
	boolean required() default true;

}

@ModelAttribute

此註解用在請求方法的參數上，用於將參數綁定到Model對象

package org.springframework.web.bind.annotation;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

import org.springframework.core.annotation.AliasFor;
import org.springframework.ui.Model;

@Target({ElementType.PARAMETER, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface ModelAttribute {

	/**
	 * Alias for {@link #name}.
	 */
	@AliasFor("name")
	String value() default "";

	/**
	 * The name of the model attribute to bind to.
	 * <p>The default model attribute name is inferred from the declared
	 * attribute type (i.e. the method parameter type or method return type),
	 * based on the non-qualified class name:
	 * e.g. "orderAddress" for class "mypackage.OrderAddress",
	 * or "orderAddressList" for "List&lt;mypackage.OrderAddress&gt;".
	 * @since 4.3
	 */
	@AliasFor("value")
	String name() default "";

	/**
	 * Allows declaring data binding disabled directly on an {@code @ModelAttribute}
	 * method parameter or on the attribute returned from an {@code @ModelAttribute}
	 * method, both of which would prevent data binding for that attribute.
	 * <p>By default this is set to {@code true} in which case data binding applies.
	 * Set this to {@code false} to disable data binding.
	 * @since 4.3
	 */
	boolean binding() default true;

}

@PathVariable

spring3.0的新功能：接收請求路徑中佔位符的值

舉個例子

127.0.0.1:8080/project/get/1           使用@PathVariable

@GetMapping("/get/{id}")
public Object getObject(@PathVariable String id) {}

127.0.0.1:8080/project/get?id=1     使用@RequestParam

@GetMapping("/get")
public Object getObject (@RequestParam String id) {}

package org.springframework.web.bind.annotation;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

import org.springframework.core.annotation.AliasFor;


@Target(ElementType.PARAMETER)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface PathVariable {

	/**
	 * Alias for {@link #name}.
	 */
	@AliasFor("name")
	String value() default "";

	/**
	 * The name of the path variable to bind to.
	 * @since 4.3.3
	 */
	@AliasFor("value")
	String name() default "";

	/**
	 * Whether the path variable is required.
	 * <p>Defaults to {@code true}, leading to an exception being thrown if the path
	 * variable is missing in the incoming request. Switch this to {@code false} if
	 * you prefer a {@code null} or Java 8 {@code java.util.Optional} in this case.
	 * e.g. on a {@code ModelAttribute} method which serves for different requests.
	 * @since 4.3.3
	 */
	boolean required() default true;

}

四、配置

@Configuration

聲明當前類爲配置類，相當於xml形式的Spring配置。內部有@Component，表明這個類也是一個bean

package org.springframework.context.annotation;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.core.annotation.AliasFor;
import org.springframework.stereotype.Component;


@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component
public @interface Configuration {

	@AliasFor(annotation = Component.class)
	String value() default "";

}

@Bean

聲明當前方法的返回值爲一個bean，相當於xml配置中的bean標籤

package org.springframework.context.annotation;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

import org.springframework.beans.factory.annotation.Autowire;
import org.springframework.beans.factory.support.AbstractBeanDefinition;
import org.springframework.core.annotation.AliasFor;

@Target({ElementType.METHOD, ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Bean {


	@AliasFor("name")
	String[] value() default {};

	@AliasFor("value")
	String[] name() default {};

	@Deprecated
	Autowire autowire() default Autowire.NO;

	boolean autowireCandidate() default true;

	String initMethod() default "";

	String destroyMethod() default AbstractBeanDefinition.INFER_METHOD;

}

@Primary

當返回多個Bean時，使用@Primary註解表明當前Bean爲默認優先選擇,不可以同時設置多個

package org.springframework.context.annotation;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Primary {

}

舉個例子

@Primary
@Bean
public Queue MessageQueue() { 
     return new ActiveMQQueue("msgQue"); 
}

五、屬性注入

@Value

package org.springframework.beans.factory.annotation;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Target({ElementType.FIELD, ElementType.METHOD, ElementType.PARAMETER, ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Value {

	/**
	 * The actual value expression: for example {@code #{systemProperties.myProp}}.
	 */
	String value();

}

六、事務

@Transactional

7種事務的傳播機制

1. REQUIRED：默認機制，支持使用當前事務，如果當前事務不存在，創建一個新事務。

2. SUPPORTS：支持使用當前事務，如果當前事務不存在，則不使用事務。

3. MANDATORY：支持使用當前事務，如果當前事務不存在，則拋出Exception。

4. REQUIRES_NEW：創建一個新事務，如果當前事務存在，把當前事務掛起。

5. NOT_SUPPORTED：無事務執行，如果當前事務存在，把當前事務掛起。

6. NEVER：無事務執行，如果當前有事務，則拋出Exception。

7. NESTED：嵌套事務，如果當前事務存在，那麼在嵌套的事務中執行。如果當前事務不存在，則表現跟REQUIRED一樣。

4種隔離級別

事務隔離級別	髒讀	不可重複讀	幻讀
讀未提交(Read-Uncommitted)	是	是	是
不可重複讀(Read-Committed)	否	是	是
可重複讀(Repeatable-Read)	否	否	是
串行化(Serializable)	否	否	否

package org.springframework.transaction.annotation;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

import org.springframework.core.annotation.AliasFor;
import org.springframework.transaction.TransactionDefinition;

@Target({ElementType.METHOD, ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Inherited
@Documented
public @interface Transactional {

	@AliasFor("transactionManager")
	String value() default "";

	@AliasFor("value")
	String transactionManager() default "";

	Propagation propagation() default Propagation.REQUIRED;

	Isolation isolation() default Isolation.DEFAULT;

	int timeout() default TransactionDefinition.TIMEOUT_DEFAULT;

	boolean readOnly() default false;

	Class<? extends Throwable>[] rollbackFor() default {};

	String[] rollbackForClassName() default {};

	Class<? extends Throwable>[] noRollbackFor() default {};

	String[] noRollbackForClassName() default {};

}

七、映射

@RequestMapping

可以用在類上和方法上，用來映射web請求到某一個類或者方法上。

package org.springframework.web.bind.annotation;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

import org.springframework.core.annotation.AliasFor;

@Target({ElementType.METHOD, ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Mapping
public @interface RequestMapping {

	String name() default "";

	@AliasFor("path")
	String[] value() default {};

	@AliasFor("value")
	String[] path() default {};

	RequestMethod[] method() default {};

	String[] params() default {};

	String[] headers() default {};

	String[] consumes() default {};
	
	String[] produces() default {};

}

@GetMapping/@PostMapping/@PutMapping/@PatchMapping/@DeleteMapping

@GetMapping就是@RequestMapping中的RequestMethod爲GET。

其他註解類似。

package org.springframework.web.bind.annotation;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

import org.springframework.core.annotation.AliasFor;

@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@RequestMapping(method = RequestMethod.GET)
public @interface GetMapping

	

八、異步任務

@EnableAsync

開啓對異步任務的支持，放在啓動類上

@Async

在方法使用該註解來指明這是一個異步操作

注意：

@Async異步方法和調用異步方法的方法不能在同一個類中，@Transactional同樣，原因是@Async和@Transactional利用了動態代理機制。具體原因參考 https://blog.csdn.net/clementad/article/details/47339519。

異步方法和事務方法不能是private方法

九、元註解

元註解就是註解註解的註解0.0

@Target

描述註解的使用範圍，有下面10種，分別是

類或接口 / 成員變量 / 成員方法 / 方法參數 / 構造方法 / 局部變量 / 註解類 / 包 / 類型參數 / 使用類型的地方

package java.lang.annotation;

public enum ElementType {
    /** Class, interface (including annotation type), or enum declaration */
    TYPE,

    /** Field declaration (includes enum constants) */
    FIELD,

    /** Method declaration */
    METHOD,

    /** Formal parameter declaration */
    PARAMETER,

    /** Constructor declaration */
    CONSTRUCTOR,

    /** Local variable declaration */
    LOCAL_VARIABLE,

    /** Annotation type declaration */
    ANNOTATION_TYPE,

    /** Package declaration */
    PACKAGE,

    /**
     * Type parameter declaration
     *
     * @since 1.8
     */
    TYPE_PARAMETER,

    /**
     * Use of a type
     *
     * @since 1.8
     */
    TYPE_USE
}

@Retention

描述註解保留的時間範圍，有下面3種，分別是

源文件保留 / 編譯期保留（默認）/ 運行期保留

package java.lang.annotation;

public enum RetentionPolicy {
    /**
     * Annotations are to be discarded by the compiler.
     */
    SOURCE,

    /**
     * Annotations are to be recorded in the class file by the compiler
     * but need not be retained by the VM at run time.  This is the default
     * behavior.
     */
    CLASS,

    /**
     * Annotations are to be recorded in the class file by the compiler and
     * retained by the VM at run time, so they may be read reflectively.
     *
     * @see java.lang.reflect.AnnotatedElement
     */
    RUNTIME
}

@Documented

描述在使用 javadoc 工具爲類生成幫助文檔時是否要保留其註解信息。

@Inherited

使被它修飾的註解具有繼承性（如果某個類使用了被@Inherited修飾的註解，則其子類將自動具有該註解）。