自定义《自动装配》

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引言：

Spring 传统项目配置http编码：

<filter>
     <filter-name>CharacterEncoding</filter-name>
     <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
     <init-param>
         <param-name>encoding</param-name>
         <param-value>UTF-8</param-value>
     </init-param>
     <init-param>
         <param-name>forceEncoding</param-name>
         <param-value>true</param-value>
     </init-param>
 </filter>

Spring Boot中没有配置，因使用自动配置帮我们设置好，那么到底是怎么自动配置的呢，下面我通过自定义自动配置来更进一步的了解它的原理。

正文

1. 使用maven将我们要配置的类打成jar文件在本地仓库中，然后创建Spring Boot 项目使用验证。
2. 话不多说，上代码

pom.xml

<dependencies>
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-autoconfigure</artifactId>
    <version>1.5.4.RELEASE</version>
  </dependency>
  <dependency>
    <groupId>junit</groupId>
    <artifactId>junit</artifactId>
    <version>4.12</version>
  </dependency>
</dependencies>

HelloServiceProper

//设置读取application.properties文件中的前缀
@ConfigurationProperties(prefix = "hello")
public class HelloServiceProper {
    private static final String MSG  = "world";
    private String msg = MSG;

    public String getMsg() {
        return msg;
    }

    public void setMsg(String msg) {
        this.msg = msg;
    }
}

HelloService
自动装配的类

public class HelloService {
    private String msg;

    public String sayHello(){
        return "Hello" + msg;
    }

    public String getMsg() {
        return msg;
    }

    public void setMsg(String msg) {
        this.msg = msg;
    }
}

HelloConfig
类加载

//项目启动时加载
@Configuration
//加载读取spring.factories文件
@EnableConfigurationProperties(HelloServiceProper.class)
//加载类别（当前路径加载类）
@ConditionalOnClass(HelloService.class)
@ConditionalOnProperty(prefix = "hello",value = "enabled", matchIfMissing = true)
public class HelloServiceConfig {

    @Autowired
    private HelloServiceProper helloServiceProper;
    @Bean
    @ConditionalOnMissingBean(HelloService.class)
    public HelloService helloService(){
        HelloService helloService = new HelloService();
        helloService.setMsg(helloServiceProper.getMsg());
        return helloService;

    }

}

spring.factories

org.springframework.boot.autoconfigure.EnableAutoConfiguration=com.ralap.auto.HelloServiceConfig

3. 使用自定义配置
   启动类

@RestController
@SpringBootApplication
public class UseautoApplication {


    @Autowired
    private HelloService helloService;

    @GetMapping("/hello")
    public String hello(){
        return helloService.sayHello();
    }

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

application.properties

hello.msg=hjx

4. 效果

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