掌握这些springboot的配置方式，让你工作效率翻个倍!

springboot的多种配置方式

java配置主要靠java类和一些注解，比较常用的注解有：
@Configuration ：声明一个类作为配置类，代替xml文件
@Bean ：声明在方法上，将方法的返回值加入Bean容器，代替标签
@Value ：基本类型或String属性注入
@PropertySource ：指定外部属性文件
后面以Druid连接池配置为例，数据库名称为springboot_test

方式一

<!--pom.xml -->
<dependency> 
    <groupId>com.alibaba</groupId> 		     	
    <artifactId>druid</artifactId> 
    <version>1.1.6</version> 
</dependency>
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <scope>runtime</scope>
</dependency>

# src/resources/jdbc.properties
jdbc.driverClassName=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://127.0.0.1:3306/bos
jdbc.username=root
jdbc.password=123456

//src\main\java\com\itheima\config\DruidConfig.java
@Configuration
@PropertySource("classpath:jdbc.properties")
public class DruidConfig {
	@Value("${jdbc.url}")
	String url;
	@Value("${jdbc.driverClassName}")
	String driverClassName;
	@Value("${jdbc.username}")
	String username;
	@Value("${jdbc.password}")
	String password;

	@Bean
	public DataSource dataSource() {
		DruidDataSource dataSource = new DruidDataSource();
		dataSource.setDriverClassName(driverClassName);
		dataSource.setUrl(url);
		dataSource.setUsername(username);
		dataSource.setPassword(password);
		return dataSource;
	}
}

解读：

@Configuration ：声明我们 DruidConfig是一个配置类
@PropertySource ：指定属性文件的路径是: classpath:jdbc.properties
@Value 为属性注入值（只能是基本类型或String）
@Bean将 dataSource() 方法声明为一个注册Bean的方法，Spring会自动调用该方法，将方法的返回值加入Spring容器中。

方式二

<!--pom.xml -->
<dependency>
     <groupId>com.alibaba</groupId>
     <artifactId>druid</artifactId>
     <version>1.1.6</version>
</dependency>
<dependency>
     <groupId>mysql</groupId>
     <artifactId>mysql-connector-java</artifactId>
     <scope>runtime</scope>
</dependency>
<!-- ============不添加在IDEA 会报红，但并不影响功能 ================= -->
<dependency>
     <groupId> org.springframework.boot </groupId>
     <artifactId>spring-boot-configuration-processor</artifactId>
     <optional>true</optional>
</dependency>
<!--============================================================== -->

# src/resources/application.properties
jdbc.driverClassName=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://127.0.0.1:3306/bos
jdbc.username=root
jdbc.password=123456

//src\main\java\com\itheima\config\DruidConfig.java
@ConfigurationProperties(prefix = "jdbc")
public class DruidProperties {
	private String url;
	private String driverClassName;
	private String username;
	private String password;

	public String getUrl() {
		return url;
	}

	public void setUrl(String url) {
		this.url = url;
	}

	public String getDriverClassName() {
		return driverClassName;
	}

	public void setDriverClassName(String driverClassName) {
		this.driverClassName = driverClassName;
	}

	public String getUsername() {
		return username;
	}

	public void setUsername(String username) {
		this.username = username;
	}

	public String getPassword() {
		return password;
	}

	public void setPassword(String password) {
		this.password = password;
	}
}

//src\main\java\com\itheima\config\DruidConfig.java
@Configuration
@EnableConfigurationProperties(DruidProperties.class)
public class DruidConfig {
	@Bean
	public DataSource dataSource(DruidProperties dp) {
		DruidDataSource dataSource = new DruidDataSource();
		dataSource.setDriverClassName(dp.getDriverClassName());
		dataSource.setUrl(dp.getUrl());
		dataSource.setUsername(dp.getUsername());
		dataSource.setPassword(dp.getPassword());
		return dataSource;
	}
}

解读：

@ConfifigurationProperties注解声明当前类为属性读取类，在类上定义各个属性，名称必须与属性文件中 jdbc. 后面部分一致。
@EnableConfigurationProperties()声明要使用的属性读取类，使用该类有三种注入方式

1. @Autowired注入

//src\main\java\com\itheima\config\DruidConfig.java
@Configuration
@EnableConfigurationProperties(DruidProperties.class)
public class DruidConfig {
   @Autowired
   private DruidProperties dp;
   @Bean
   public DataSource dataSource() {
   	DruidDataSource dataSource = new DruidDataSource();
   	//setter
   	return dataSource;
   }
}

2. 构造函数注入

```
//src\main\java\com\itheima\config\DruidConfig.java
@Configuration
@EnableConfigurationProperties(DruidProperties.class)
public class DruidConfig {
   	private DruidProperties dp; 
    public DruidConfig(DruidProperties dp){ this.dp = dp; }
	@Bean
	public DataSource dataSource() {
		DruidDataSource dataSource = new DruidDataSource();
		//setter
		return dataSource;
	}
}

```

3. 作为@Bean的方法参数注入(本例使用)

//src\main\java\com\itheima\config\DruidConfig.java
@Configuration
@EnableConfigurationPerProperties(DruidProperties.class)
public class DruidConfig {
 @Bean
 public DataSource dataSource(DruidProperties dp) {
 	DruidDataSource dataSource = new DruidDataSource();
 	//setter
 	return dataSource;
 }
}

方式二通过属性读取类解决了@Value不能读取对象属性(如user.friend.name)的问题，但似乎就更加麻烦了

方式三（推荐使用）

事实上，如果一段属性只有一个Bean需要使用，我们无需将其注入到一个类。

<!--pom.xml -->
<dependency>
     <groupId>com.alibaba</groupId>
     <artifactId>druid</artifactId>
     <version>1.1.6</version>
</dependency>
<dependency>
     <groupId>mysql</groupId>
     <artifactId>mysql-connector-java</artifactId>
     <scope>runtime</scope>
</dependency>
<!-- ============不添加在IDEA 会报红，但并不影响功能 ================= -->
<dependency>
     <groupId> org.springframework.boot </groupId>
     <artifactId>spring-boot-configuration-processor</artifactId>
     <optional>true</optional>
</dependency>
<!--============================================================== -->

# src/resources/application.properties
jdbc.driverClassName=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://127.0.0.1:3306/bos
jdbc.username=root
jdbc.password=123456

@Configuration
public class DruidConfig {
	@Bean
	@ConfigurationProperties(prefix = "jdbc")
	public DataSource dataSource() {
		return new DruidDataSource();
	}
}

方式四

<!--pom.xml -->
<dependency> 
    <groupId>com.alibaba</groupId> 		     	
    <artifactId>druid</artifactId> 
    <version>1.1.6</version> 
</dependency>
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <scope>runtime</scope>
</dependency>

# src/resources/application.properties
spring.datasource.type=com.alibaba.druid.pool.DruidDataSource
spring.datasource.driverClassName=com.mysql.jdbc.Driver
spring.datasource.url=jdbc:mysql://127.0.0.1:3306/bos
spring.datasource.username=root
spring.datasource.password=123456