深入浅出Spring（25）

参考链接

官方文档

这些问题你都知道吗?

1. @Value的用法
2. @Value数据来源
3. @Value动态刷新的问题

@Value的用法

源码

@Target({ElementType.FIELD, ElementType.METHOD, ElementType.PARAMETER, ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Value {
	String value();
}
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修饰范围：字段，方法，方法参数，注解。

案例1 解析默认配置文件内容

@Component
public class DbConfig {

    @Value("${jdbc.url}")
    private String url;

    @Value("${jdbc.username}")
    private String username;

    @Value("${jdbc.password}")
    private String password;
    
	//省略
｝
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如果application.yml和properties同时存在会解析properties。

案例2 指定配置文件解析

valued1.properties

jdbc.url=v1Url
jdbc.username=v1Name
jdbc.password=v1password
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@Component
@PropertySource("classpath:valued1.properties")
public class DbConfig {

    @Value("${jdbc.url}")
    private String url;

    @Value("${jdbc.username}")
    private String username;

    @Value("${jdbc.password}")
    private String password;

	//省略
}
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PropertySource

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Repeatable(PropertySources.class)
public @interface PropertySource {

	String name() default "";

	String[] value();

	boolean ignoreResourceNotFound() default false;

	String encoding() default "";
	
	Class<? extends PropertySourceFactory> factory() default PropertySourceFactory.class;
}
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修饰在类型上，有@Repeatable重复使用注解。
既然允许重复，我们修改新增一个配置文件 valued2.properties

jdbc.url=v2
jdbc.username=v2name
jdbc.password=v3name
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在DbConfig上面，并且修改顺序查看输出验证以哪一个配置文件为准。

@PropertySource("classpath:valued2.properties")
@PropertySource("classpath:valued1.properties")
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经过测试，以最下面一个读取的配置文件为准。

@Value数据来源

省略 get、set、tostring

@Component
public class MailConfig {

    @Value("${mail.host}")
    private String host;

    @Value("${mail.username}")
    private String username;

    @Value("${mail.password}")
    private String password;
}
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配置类

@Configuration
@ComponentScan
public class Client {
    public static void main(String[] args) {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
        java.util.Map<String, Object> mailInfoFromDb = getMailInfoFromDb();
        MapPropertySource mailPropertySource = new MapPropertySource("mail", mailInfoFromDb);
        context.getEnvironment().getPropertySources().addFirst(mailPropertySource);
        context.register(Client.class);
        context.refresh();
        MailConfig mailConfig = context.getBean(MailConfig.class);
        System.out.println(mailConfig);
    }

    public static Map<String, Object> getMailInfoFromDb() {
        Map<String, Object> result = new HashMap<>();
        result.put("mail.host", "smtp.qq.com");
        result.put("mail.username", "路人");
        result.put("mail.password", "123");
        return result;
    }
}
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org.springframework.beans.factory.config.scope

深入浅出Spring注解@Scope、@DependsOn、@ImportResource、@Lazy

在这篇中我们没有说 ScopedProxyMode proxyMode() default ScopedProxyMode.DEFAULT，这个参数为TARGET_CLASS的作用。

先来看一下枚举上的注释 Create a class-based proxy (uses CGLIB). 创建一个基于CGLIB代理的类。

org.springframework.cloud.context.config.annotation.RefreshScope

package org.springframework.cloud.context.config.annotation;

@Target({ ElementType.TYPE, ElementType.METHOD })
@Retention(RetentionPolicy.RUNTIME)
@Scope("refresh")
@Documented
public @interface RefreshScope {

	ScopedProxyMode proxyMode() default ScopedProxyMode.TARGET_CLASS;
}
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我们在nacos中就使用了这个注解实现配置文件更新后刷新。

org.springframework.beans.factory.config.Scope 接口

public interface Scope {
	//获取对象
	Object get(String name, ObjectFactory<?> objectFactory);
	//删除对象
	@Nullable
	Object remove(String name);
	//注册销毁回调
	void registerDestructionCallback(String name, Runnable callback);
	//根据给定的key解析上下文
	@Nullable
	Object resolveContextualObject(String key);
	
	@Nullable
	String getConversationId();
}
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实现@Value动态刷新

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

    ScopedProxyMode proxyMode() default ScopedProxyMode.TARGET_CLASS;

}
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public class MyRefreshScopeConfig implements org.springframework.beans.factory.config.Scope {

    @Override
    public Object get(String name, ObjectFactory<?> objectFactory) {
        System.out.println("BeanMyScope >>>>>>>>> get:" + name);
        return objectFactory.getObject(); //@3
    }

    @Override
    public Object remove(String name) {
        return null;
    }

    @Override
    public void registerDestructionCallback(String name, Runnable callback) {

    }

    @Override
    public Object resolveContextualObject(String key) {
        return null;
    }

    @Override
    public String getConversationId() {
        return null;
    }
}

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@Component
@MyRefreshScope
public class User {

    private String username;

    public User() {
        System.out.println("---------创建User对象" + this);
        this.username = UUID.randomUUID().toString();
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

}
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@ComponentScan
@Configuration
public class Client {

    public static void main(String[] args) {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
        context.getBeanFactory().registerScope("MyRefreshScope", new MyRefreshScopeConfig());
        context.register(Client.class);
        context.refresh();

        System.out.println("从容器中获取User对象");
        User user = context.getBean(User.class);
        System.out.println("user对象的class为：" + user.getClass());

        System.out.println("多次调用user的getUsername感受一下效果\n");
        for (int i = 1; i <= 3; i++) {
            System.out.println(String.format("********\n第%d次开始调用getUsername", i));
            System.out.println(user.getUsername());
            System.out.println(String.format("第%d次调用getUsername结束\n********\n", i));
        }
    }
}
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从容器中获取User对象
user对象的class为：class com.example.lurenjia.spring.c24.d3.User$$EnhancerBySpringCGLIB$$4e23e0c6
多次调用user的getUsername感受一下效果

********
第1次开始调用getUsername
BeanMyScope >>>>>>>>> get:scopedTarget.user
---------创建User对象com.example.lurenjia.spring.c24.d3.User@3e58a80e
adb8ff42-e42c-4949-9662-79bd40bbb063
第1次调用getUsername结束
********

********
第2次开始调用getUsername
BeanMyScope >>>>>>>>> get:scopedTarget.user
---------创建User对象com.example.lurenjia.spring.c24.d3.User@9597028
fb145915-a3bf-40e3-8c51-c987f9756b05
第2次调用getUsername结束
********

********
第3次开始调用getUsername
BeanMyScope >>>>>>>>> get:scopedTarget.user
---------创建User对象com.example.lurenjia.spring.c24.d3.User@6069db50
a918c35d-0bff-4148-8d17-4dcfc2b29a77
第3次调用getUsername结束
********


进程已结束，退出代码为 0

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官方文档用法

https://docs.spring.io/spring-framework/docs/current/reference/html/core.html#beans-value-annotations

官方示例一：注入catalog.name

@Component
public class MovieRecommender {

    private final String catalog;

    public MovieRecommender(@Value("${catalog.name}") String catalog) {
        this.catalog = catalog;
    }
}
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