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spring:@Value的使用方式

前言:

@Value是spring的赋值注解,在这里我们来了解它的使用方式,

比如@Value("#{lx}"),

   @Value("${lx}"),

   @Value("lx");

1.@Value("value值'')的用法

@Value("value值'')是直接把字符串(value值)直接赋值给当前字符串

2.@Value(“#{lx}”)

先解析spring表达式,将结果赋值给当前字段(解析spring表达式的结果可能是字符串或者是一个Bean对象)

3.@Value("${lx}"}

先进行占位符的替换,然后将替换后的字符串赋值给当前的字符段

根据操作系统变量,jvm环境变量,properties文件作为替换的来源

替换源

进行占位符替换

4.基于@Value做的扩展(创建注解)

4.1:@Value的源码

4.2:在properties里面添加LocalServerPort

4.3:创建LocalServerPort注解

4.4:使用@ LocalServerPort

5.源码

5.1 目录结构:

(用目录结构从下(properties)向上(LocalServerPort)开始)

依赖:

<dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-webmvc</artifactId>
            <version>5.1.10.RELEASE</version>
        </dependency>

5.2spring.properties

lx=hello word
LocalServerPort=8080

5.3:ValueTest

package com.lx;

import com.lx.service.UserService;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

public class ValueTest {
    public static void main(String[] args) {
        AnnotationConfigApplicationContext applicationContext=new AnnotationConfigApplicationContext(AppConfig.class);
        UserService userService1 = applicationContext.getBean("userService", UserService.class);
        userService1.test();
//        UserService userService=applicationContext.getBean("UserService",UserService.class);
//        userService.test();
    }
}

5.4:AppConfig

package com.lx;

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

@ComponentScan("com.lx")
@PropertySource("classpath:spring.properties")
public class AppConfig {

}

5.5:UserService

package com.lx.service;

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

@Component
public class UserService {
    @LocalServerPort
    public String test;
//    @Value("#{lx}")
//    private OrderService test;

//    @Value("${lx}")
//        @Value("value值")
//    public String test;
    public void test(){
        System.out.println(test);
    }
}

5.6:OrderService

package com.lx.service;

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

@Component("lx")
public class OrderService {

}

5.7:LocalServerPort

package com.lx.service;

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

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)
@Value("${LocalServerPort}")
public @interface LocalServerPort {
}
标签: spring java

本文转载自: https://blog.csdn.net/m0_53623945/article/details/125418628
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