@Value 用法

占位符

UserService.java

package io.github.jihch.service;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

@Component
public class UserService {

	@Value("${name}")
	private String test;
	
	public void test() {
		System.out.println(test);
	}
	
}

AppConfig.java

package io.github.jihch;

import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.PropertySource;

@ComponentScan("io.github.jihch")
@PropertySource("classpath:spring.properties")
public class AppConfig {

}

spring.properties

name=zhangsan

Test.java

package io.github.jihch;

import org.springframework.context.annotation.AnnotationConfigApplicationContext;

import io.github.jihch.service.UserService;

public class Test {

	public static void main(String[] args) {
		
		AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(AppConfig.class);
	
		UserService userService = applicationContext.getBean("userService", UserService.class);
		
		userService.test();
		
	}

}

输出：zhangsan 如果对应的 key 在 spring.properties 中不存在：

#name=zhangsan

则输出：${name}

普通字符串

如果是：@Value("name")：

package io.github.jihch.service;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

@Component
public class UserService {

	@Value("name")
	private String test;
	
	public void test() {
		System.out.println(test);
	}
	
}

那就直接把“name”作为一个字符串注入到字符串属性 test 中，输出：name

Spring EL

package io.github.jihch.service;

import org.springframework.stereotype.Component;

@Component("name")
public class OrderService {

}

package io.github.jihch.service;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

@Component
public class UserService {

	@Value("#{name}")
	private OrderService test;
	
	public void test() {
		System.out.println(test);
	}
	
}

输出：io.github.jihch.service.OrderService@6574a52c

这么用 @Value 就和 @Autowired、@Resource 一样给属性注入了 bean 对象，因为 @Value 注解里使用 # 就表示 SpEL（Spring Expression Language，Spring 表达式），

会作为一个 beanName 去定位 bean 对象，如果类型不匹配就会抛异常。

自定义注解

spring.properties

local.server.port=8080

LocalServerPort.java

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.Value;

@Target({ElementType.FIELD, ElementType.METHOD, ElementType.PARAMETER, ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Value("${local.server.port}")
public @interface LocalServerPort {

}

UserService.java

import org.springframework.stereotype.Component;

@Component
public class UserService {
	
	@LocalServerPort	
	private String test;

	public void test() {
		System.out.println(test);
	}
	
}

输出:8080