Spring Boot读取properties配置文件中的数据

Spring Boot最常用的3种读取properties配置文件中数据的方法：
1、使用@Value注解读取
读取properties配置文件时，默认读取的是application.properties。

application.properties：

demo.name=Name
demo.age=18
Java代码：

import org.springframework.beans.factory.annotation.Value;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class GatewayController {

@Value("${demo.name}")
private String name;

@Value("${demo.age}")
private String age;

@RequestMapping(value = "/gateway")
public String gateway() {
    return "get properties value by ''@Value'' :" +
            //1、使用@Value注解读取
            " name=" + name +
            " , age=" + age;
}

}
运行结果如下：

这里，如果要把

@Value("$demo.name")privateStringname;@Value("${demo.age}")
private String age;

部分放到一个单独的类A中进行读取，然后在类B中调用，则要把类A增加@Component注解，并在类B中使用@Autowired自动装配类A，代码如下。

类A：

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

@Component
public class ConfigBeanValue {

@Value("${demo.name}")
public String name;

@Value("${demo.age}")
public String age;

}
类B：

import cn.wbnull.springbootdemo.config.ConfigBeanValue;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class GatewayController {

@Autowired
private ConfigBeanValue configBeanValue;

@RequestMapping(value = "/gateway")
public String gateway() {
    return "get properties value by ''@Value'' :" +
            //1、使用@Value注解读取
            " name=" + configBeanValue.name +
            " , age=" + configBeanValue.age;
}

}
运行结果如下：

注意：如果@Value${}所包含的键名在application.properties配置文件中不存在的话，会抛出异常：

org.springframework.beans.factory.BeanCreationException: Error creating bean with name ‘configBeanValue’: Injection of autowired dependencies failed; nested exception is java.lang.IllegalArgumentException: Could not resolve placeholder ‘demo.name’ in value “${demo.name}”

2、使用Environment读取
application.properties：

demo.sex=男
demo.address=山东
Java代码：

import cn.wbnull.springbootdemo.config.ConfigBeanValue;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.core.env.Environment;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class GatewayController {

@Autowired
private ConfigBeanValue configBeanValue;

@Autowired
private Environment environment;

@RequestMapping(value = "/gateway")
public String gateway() {
    return "get properties value by ''@Value'' :" +
            //1、使用@Value注解读取
            " name=" + configBeanValue.name +
            " , age=" + configBeanValue.age +
            "<p>get properties value by ''Environment'' :" +
            //2、使用Environment读取
            " , sex=" + environment.getProperty("demo.sex") +
            " , address=" + environment.getProperty("demo.address");
}

}
运行，发现中文乱码：

这里，我们在application.properties做如下配置：

server.tomcat.uri-encoding=UTF-8
spring.http.encoding.charset=UTF-8
spring.http.encoding.enabled=true
spring.http.encoding.force=true
spring.messages.encoding=UTF-8
然后修改IntelliJ IDEA，File --> Settings --> Editor --> File Encodings ，将最下方Default encoding for properties files设置为UTF-8，并勾选Transparent native-to-ascii conversion。

重新运行结果如下：

3、使用@ConfigurationProperties注解读取
在实际项目中，当项目需要注入的变量值很多时，上述所述的两种方法工作量会变得比较大，这时候我们通常使用基于类型安全的配置方式，将properties属性和一个Bean关联在一起，即使用注解@ConfigurationProperties读取配置文件数据。

在src\main\resources下新建config.properties配置文件：

demo.phone=10086
demo.wife=self
创建ConfigBeanProp并注入config.properties中的值：

import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.context.annotation.PropertySource;
import org.springframework.stereotype.Component;

@Component
@ConfigurationProperties(prefix = “demo”)
@PropertySource(value = “config.properties”)
public class ConfigBeanProp {

private String phone;

private String wife;

public String getPhone() {
    return phone;
}

public void setPhone(String phone) {
    this.phone = phone;
}

public String getWife() {
    return wife;
}

public void setWife(String wife) {
    this.wife = wife;
}

}
@Component 表示将该类标识为Bean

@ConfigurationProperties(prefix = “demo”)用于绑定属性，其中prefix表示所绑定的属性的前缀。

@PropertySource(value = “config.properties”)表示配置文件路径。

使用时，先使用@Autowired自动装载ConfigBeanProp，然后再进行取值，示例如下：

import cn.wbnull.springbootdemo.config.ConfigBeanProp;
import cn.wbnull.springbootdemo.config.ConfigBeanValue;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.core.env.Environment;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class GatewayController {

@Autowired
private ConfigBeanValue configBeanValue;

@Autowired
private Environment environment;

@Autowired
private ConfigBeanProp configBeanProp;

@RequestMapping(value = "/gateway")
public String gateway() {
    return "get properties value by ''@Value'' :" +
            //1、使用@Value注解读取
            " name=" + configBeanValue.name +
            " , age=" + configBeanValue.age +
            "<p>get properties value by ''Environment'' :" +
            //2、使用Environment读取
            " sex=" + environment.getProperty("demo.sex") +
            " , address=" + environment.getProperty("demo.address") +
            "<p>get properties value by ''@ConfigurationProperties'' :" +
            //3、使用@ConfigurationProperties注解读取
            " phone=" + configBeanProp.getPhone() +
            " , wife=" + configBeanProp.getWife();
}

}
运行结果如下：

使用springboot读取配置文件中的数据一直为null的问题？

springboot获取配置文件的数据一直为null的原意可能是

1.类上未加@Component,@Configuration注解

2.在创建此类时使用new来创建的对象，而不是利用注入的方式来创建对象

转载自https://blog.youkuaiyun.com/dkbnull/article/details/81953190#commentBox