---
title: 'Spring boot @Value annotation'
disqus: hackmd
---
###### tags: `SpringBoot`

Spring boot @Value annotation
===

[TOC]

## 筆記目的

了解Spring @Value annotation該如何使用，並且將結果打印在console中。

為何要有這個註解是因為有時候你想要注入一些預設值，但是你並不想要寫死在java class中，你想要將他放入xxx.properties的檔案裡，統一管理

參考並改寫自:

* [菜鳥工程師](https://matthung0807.blogspot.com/2019/08/spring-boot-properties-file-value.html)
* [Spring value DB example](https://www.journaldev.com/21448/spring-value-annotation)
* [](https://)

第二個連結有以下程式碼請注意看

package com.journaldev.spring;

import java.sql.SQLException;

import org.springframework.context.annotation.AnnotationConfigApplicationContext;

public class SpringMainClass {

	public static void main(String[] args) throws SQLException {
		AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
		context.scan("com.journaldev.spring");
		context.refresh();
		System.out.println("Refreshing the spring context");
		DBConnection dbConnection = context.getBean(DBConnection.class);

		dbConnection.printDBConfigs();
		
		// close the spring context
		context.close();
	}

}

## 先備條件

準備兩個檔案application.properties 和 my-message.properties 將他們兩個都貼入
src/main/resources中

在application.properties放入
`my.food=pizza`
在my-message.properties放入

my.name=mike
my.address=asdf
my.postcode=97059
my.ticket-price=60

### 專案架構


## 程式碼部分

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.5.3</version>
		<relativePath /> <!-- lookup parent from repository -->
	</parent>
	<groupId>com.example</groupId>
	<artifactId>value</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>value</name>
	<description>Demo project for Spring Boot</description>
	<properties>
		<java.version>1.8</java.version>
	</properties>
	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter</artifactId>
		</dependency>

		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-test</artifactId>
			<scope>test</scope>
		</dependency>
		
	</dependencies>

	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
			</plugin>
		</plugins>
	</build>

</project>

Dog.java

package com.example.value;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;
@Component
public class Dog {
	@Value("${my.name}")
	private String name;
	@Value("${my.food}")
	private String weight;

	public void printinfo() {
		System.out.println(name);
		System.out.println(weight);
	}
	public Dog(   ) {
		
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public String getWeight() {
		return weight;
	}
	public void setWeight(String weight) {
		this.weight = weight;
	}
}

ValueApplication.java

package com.example.value;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.PropertySource;

@SpringBootApplication
@PropertySource(
	    value = { "classpath:my-message.properties" }, 
	    ignoreResourceNotFound = true,
	    encoding = "UTF-8"
	)
public class ValueApplication {

	public static void main(String[] args) {
		ApplicationContext appCtx = SpringApplication.run(ValueApplication.class, args);
	    Dog mydog = appCtx.getBean(Dog.class);
	    mydog.printinfo();
	    
//	    AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
//	    context.scan("com.example.value");
//	    context.refresh();
//	    Dog mydogcontext = context.getBean(Dog.class);
//		
//		mydogcontext.printinfo();
//		context.close();  
//		have error Error creating bean with name 'dog': Injection of autowired dependencies failed; nested exception is

	}
}

## 打印出來的結果


## 問題點

1. 翻了AIcampaign的程式碼，沒有發現使用 getBean 或是 AnnotationConfigApplicationContext 等字串

Ans 因為使用了autowired

2. ApplicationContext vs AnnotationConfigApplicationContext diff?

## Maybe是解法

[stackoverflow](https://stackoverflow.com/questions/28828748/read-file-properties-using-spring-annotations)