1.@Value與@PropertySource注解

@Value注解：主要用于賦值，該值可以是取值配置文件中的，也可以直接賦值，也可以使用SpEl表達式進行計算的結果，抑或直接從環境變量中獲取。 該注解不能處理日期類賦值

1、基本數值 2、可以寫SpEL； #{} 3、可以寫${}；取出配置文件【properties】中的值（在運行環境變量里面的值）

? 原理是底層使用了后置處理器AutowiredAnnotationBeanPostProcessor。

* <p>Note that actual processing of the {@code @Value} annotation is performed * by a {@link org.springframework.beans.factory.config.BeanPostProcessor * BeanPostProcessor} which in turn means that you <em>cannot</em> use * {@code @Value} within * {@link org.springframework.beans.factory.config.BeanPostProcessor * BeanPostProcessor} or * {@link org.springframework.beans.factory.config.BeanFactoryPostProcessor BeanFactoryPostProcessor} * types. Please consult the javadoc for the {@link AutowiredAnnotationBeanPostProcessor} * class (which, by default, checks for the presence of this annotation).

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@PropertySource注解：主要用于加載配置文件，value值為classpath

等價于?<context:property-placeholder location="classpath:student.properties"/>

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2.實例

@PropertySource放置的位置問題：

1.若使用@Component方式注入對象，則@PropertySource防止在普通類Student或配置類中都可以

2.若使用@Bean方式注入Student對象，則@PropertySource必須放在配置類上加載

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方式一：使用@Component方式注入Student對象

/**** 使用@Value賦值；* 1、基本數值* 2、可以寫SpEL； #{}* 3、可以寫${}；取出配置文件【properties】中的值（在運行環境變量里面的值）*/ @PropertySource({"classpath:/student.properties"})//指定配置文件classPath @Component //此時使用的是@Component方式注入，則@PropertySource放在哪都可以 public class Student {@Value("張三")//直接賦值private String name;@Value("${stu.name}")//從配置文件中取值private String alias;@Value("${os.name}")//從容器中讀取環境變量private String system;@Value("#{33-12}")//使用SpEL 計算private Integer age; // @Value("${stu.birthDate}")//不能處理日期private Date birthDate;@Value("${stu.hasNickName}") //布爾值private Boolean hasNickName;@Overridepublic String toString() {return "Student{" +"name='" + name + '\'' +", alias='" + alias + '\'' +", system='" + system + '\'' +", age=" + age +", birthDate=" + birthDate +", hasNickName=" + hasNickName +'}';}public Boolean getHasNickName() {return hasNickName;}public void setHasNickName(Boolean hasNickName) {this.hasNickName = hasNickName;}public String getAlias() {return alias;}public void setAlias(String alias) {this.alias = alias;}public String getSystem() {return system;}public void setSystem(String system) {this.system = system;}public String getName() {return name;}public void setName(String name) {this.name = name;}public Integer getAge() {return age;}public void setAge(Integer age) {this.age = age;}public Date getBirthDate() {return birthDate;}public void setBirthDate(Date birthDate) {this.birthDate = birthDate;} }@Configuration @ComponentScan(basePackages = "com.java.model") //@PropertySource({"classpath:/student.properties"}) //放在這里也可以 public class PropertyValueConfig {}public class PropertyValueTest {public static void main(String[] args) {AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(PropertyValueConfig.class);Student s = applicationContext.getBean(Student.class);System.out.println(s);} }測試結果： Student{name='張三', alias='張三', system='Windows 7', age=21, birthDate=null, hasNickName=true}

方式二：使用@Bean方式注入Student對象

/**** 使用@Value賦值；* 1、基本數值* 2、可以寫SpEL； #{}* 3、可以寫${}；取出配置文件【properties】中的值（在運行環境變量里面的值）*/ public class Student {@Value("張三")//直接賦值private String name;@Value("${stu.name}")//從配置文件中取值private String alias;@Value("${os.name}")//從容器中讀取環境變量private String system;@Value("#{33-12}")//使用SpEL 計算private Integer age; // @Value("${stu.birthDate}")//不能處理日期private Date birthDate;@Value("${stu.hasNickName}") //布爾值private Boolean hasNickName;@Overridepublic String toString() {return "Student{" +"name='" + name + '\'' +", alias='" + alias + '\'' +", system='" + system + '\'' +", age=" + age +", birthDate=" + birthDate +", hasNickName=" + hasNickName +'}';}public Boolean getHasNickName() {return hasNickName;}public void setHasNickName(Boolean hasNickName) {this.hasNickName = hasNickName;}public String getAlias() {return alias;}public void setAlias(String alias) {this.alias = alias;}public String getSystem() {return system;}public void setSystem(String system) {this.system = system;}public String getName() {return name;}public void setName(String name) {this.name = name;}public Integer getAge() {return age;}public void setAge(Integer age) {this.age = age;}public Date getBirthDate() {return birthDate;}public void setBirthDate(Date birthDate) {this.birthDate = birthDate;} }@Configuration @PropertySource({"classpath:/student.properties"}) //此時只能放在這里加載 public class PropertyValueConfig {@Beanpublic Student student(){return new Student();} }public class PropertyValueTest {public static void main(String[] args) {AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(PropertyValueConfig.class);Student s = applicationContext.getBean(Student.class);System.out.println(s);} }測試結果： Student{name='張三', alias='張三', system='Windows 7', age=21, birthDate=null, hasNickName=true}

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3.EmbeddedValueResolverAware方式實現和@Value一樣的效果

EmbeddedValueResolverAware是一個String型的value解析器，想要通過這個獲取值的任何對象，都可以實現這個接口。

/*** Interface to be implemented by any object that wishes to be notified of a* {@code StringValueResolver} for the resolution of embedded definition values.** <p>This is an alternative to a full ConfigurableBeanFactory dependency via the* {@code ApplicationContextAware}/{@code BeanFactoryAware} interfaces.** @author Juergen Hoeller* @author Chris Beams* @since 3.0.3* @see org.springframework.beans.factory.config.ConfigurableBeanFactory#resolveEmbeddedValue(String)* @see org.springframework.beans.factory.config.ConfigurableBeanFactory#getBeanExpressionResolver()* @see org.springframework.beans.factory.config.EmbeddedValueResolver*/ public interface EmbeddedValueResolverAware extends Aware {/*** Set the StringValueResolver to use for resolving embedded definition values.*/void setEmbeddedValueResolver(StringValueResolver resolver);}

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使用方法如下：

@Configuration //@ComponentScan(basePackages = "com.java.model") @PropertySource({"classpath:/student.properties"})//指定配置文件classPath public class PropertyValueConfig implements EmbeddedValueResolverAware{@Beanpublic Student student(){System.out.println("EmbeddedValueResolverAware----->setEmbeddedValueResolver--->stu = "+stuName);return new Student();}private String stuName;@Overridepublic void setEmbeddedValueResolver(StringValueResolver resolver) {this.stuName = resolver.resolveStringValue("${stu.name}");} }

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總結

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