摘要：本文通過講解如何解析application.properties屬性，介紹了幾個註解的運用@Value @ConfigurationProperties @EnableConfigurationProperties @Autowired @ConditionalOnProperty

1 準備

1.1 搭建springboot

1.2 寫一個controller類

package com.gbm.controller;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
 
import org.springframework.web.bind.annotation.ResponseBody;

/**
 * Created by Administrator on 2019/2/20.
 */

@Controller
public class IndexController {
    @RequestMapping("/index")
    @ResponseBody
    public String index() {
        return "我愛北京天安門！";
    }
}

2 幾種獲取屬性值方式

　　配置application.properties

value.local.province=Zhejiang
value.local.city=Hangzhou

complex.other.province=Jiangsu
complex.other.city=Suzhou
complex.other.flag=false

2.1 使用註解@Value("${xxx}")獲取指定屬性值

2.1.1 在controller類中獲取屬性值

package com.gbm.controller;

import org.springframework.beans.factory.annotation.Value;
 
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;

/**
 * Created by Administrator on 2019/2/20.
 */

@Controller
public class IndexController {
    @Value("${value.local.province}")
    private String province;

    @Value("${value.local.city}")
    private String city;

    @RequestMapping("/index")
    @ResponseBody
    public String index() {
        StringBuffer sb = new StringBuffer();
        sb.append(this.city);
        sb.append(",");
        sb.append(this.province);
        sb.append(" ");
        return sb.toString();
    }
}

2.1.2 任何瀏覽器上運行 http://localhost:8080/index，結果如下　　

2.2 使用註解@ConfigurationProperties(prefix = "xxx")獲得前綴相同的一組屬性，並轉換成bean對象

2.2.1 寫一個實體類

package com.gbm.models;

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

/**
 * Created by Administrator on 2019/2/21.
 */
@Component
@ConfigurationProperties(prefix = "complex.other")
public class Complex {
    private String province;
    private String city;
    private Boolean flag;

    public String getProvince() {
        return province;
    }

    public void setProvince(String province) {
        this.province = province;
    }

    public String getCity() {
        return city;
    }

    public void setCity(String city) {
        this.city = city;
    }

    public Boolean getFlag() {
        return flag;
    }

    public void setFlag(Boolean flag) {
        this.flag = flag;
    }

    @Override
    public String toString() {
        return "Complex{" +
                "province=‘" + province + ‘\‘‘ +
                ", city=‘" + city + ‘\‘‘ +
                ", flag=" + flag +
                ‘}‘;
    }
}

2.2.2 在controller類中獲取屬性值

package com.gbm.controller;

import com.gbm.models.Complex;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;

/**
 * Created by Administrator on 2019/2/20.
 */

@Controller
public class IndexController {
    @Autowired
    private Complex complex;

    @RequestMapping("/index")
    @ResponseBody
    public String index() {
        return complex.toString();
    }
}

2.2.3 在SpringBootApplication中使Configuration生效

package com.gbm.myspingboot;

import com.gbm.models.Complex;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.ComponentScans;

@SpringBootApplication
@ComponentScans({@ComponentScan("com.gbm.controller"), @ComponentScan("com.gbm.models")})
@EnableConfigurationProperties(Complex.class)
@ConditionalOnProperty(value = "complex.other.town", matchIfMissing = true)
public class MyspingbootApplication {

    public static void main(String[] args) {
        SpringApplication.run(MyspingbootApplication.class, args);
    }
}

2.2.4 任何瀏覽器上運行 http://localhost:8080/index，結果如下　

3 總結

　　關於解析application.properties文件，最重要的是對註解的使用，本文主要涉及到如下幾個註解的運用

　　@Value("${xxx}")——獲取指定屬性值

　　@ConfigurationProperties(prefix = "xxx")——獲得前綴相同的一組屬性，並轉換成bean對象

　　@EnableConfigurationProperties(xxx.class)——使Configuration生效，並從IOC容器中獲取bean

　　@Autowired——自動註入set和get方法

　　@ConditionalOnProperty(value = "complex.other.town", matchIfMissing = true)——缺少該property時是否可以加載，如果是true，沒有該property也會正常加載；如果是false則會拋出異常。例如

package com.gbm.myspingboot;

import com.gbm.models.Complex;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.ComponentScans;

@SpringBootApplication
@ComponentScans({@ComponentScan("com.gbm.controller"), @ComponentScan("com.gbm.models")})
@EnableConfigurationProperties(Complex.class)
@ConditionalOnProperty(value = "complex.other.town", matchIfMissing = false)
public class MyspingbootApplication {

    public static void main(String[] args) {
        SpringApplication.run(MyspingbootApplication.class, args);
    }
}

Error starting ApplicationContext. To display the conditions report re-run your application with ‘debug‘ enabled.
2019-02-21 23:30:56.532 ERROR 3152 --- [           main] o.s.boot.SpringApplication               : Application run failed

Spring系列之——springboot解析resources.application.properties文件