Spring Boot-0-系统初始化器

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述

在Spring Boot项目的启动过程中,我们可以手动的去通过系统初始化器,往容器中设置系统变量,或者是进行一些其他的操作,本文将看一下系统初始化器的几种定义方式.

准备工作

首先新建一个空白的Spring Boot项目,启动测试没问题之后,开始下面的操作.

第一种方式

首先新建一个类 FirstInitializer 然后实现 ApplicationContextInitializer<ConfigurableApplicationContext> 然后实现 initialize 方法,具体代码如下: 

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@Order(1)
@Slf4j
public class FirstInitializer implements ApplicationContextInitializer<ConfigurableApplicationContext> {

    @Override
    public void initialize(ConfigurableApplicationContext applicationContext) {
        // 获取环境变量对象
        ConfigurableEnvironment environment = applicationContext.getEnvironment();

        Map<String, Object> map = new HashMap<>(1);
        map.put("k1", "v1");

        MapPropertySource mapPropertySource = new MapPropertySource("FirstInitializer", map);

        // 添加到环境变量中
        environment.getPropertySources().addLast(mapPropertySource);

        log.info("FirstInitializer done...");
    }
}

这里就是往环境变量中添加了一个属性k1,对应的值是v1,完成之后,还需要通过 spring.factories 文件来指定一下初始化器,否则这个类是不会被加载的

在 resource/META-INF/ 目录下创建 spring.factories 文件,内容如下:

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org.springframework.context.ApplicationContextInitializer=com.zhou.springboot.example.initializers.FirstInitializer

测试验证

到这里,这个系统初始化器就可以正常的被spring容器加载,然后我们写一个测试类去验证,创建 TestService ,
代码如下:

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@Service
public class TestService implements ApplicationContextAware {

    private ApplicationContext applicationContext;

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        this.applicationContext = applicationContext;
    }

    public String test(){
        return applicationContext.getEnvironment().getProperty("k1");
    }
}

然后再写一个controller去调用就好了,启动项目,先看一下启动日志,如下:

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  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.2.4.RELEASE)

2020-01-31 11:43:42.107  INFO 9188 --- [           main] c.z.s.e.initializers.FirstInitializer    : FirstInitializer done...
2020-01-31 11:43:42.158  INFO 9188 --- [           main] com.zhou.springboot.example.App          : Starting App on DESKTOP-B1V47DV with PID 9188 (D:\Demo\SpringBoot\spring-boot-example\build\classes\java\main started by Administrator in D:\Demo\SpringBoot\spring-boot-example)
2020-01-31 11:43:42.160  INFO 9188 --- [           main] com.zhou.springboot.example.App          : No active profile set, falling back to default profiles: default
2020-01-31 11:43:44.138  INFO 9188 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)
2020-01-31 11:43:44.153  INFO 9188 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]

.......................

这里可以看到,我们的初始化器是正常被执行了的,然后调用controller方法,返回如下:
image

返回正常,说明这个初始化器是OK的.

第二种方式

下面来看一下第二种方式, 新建一个类 SecondInitializer 代码是和上面的 FirstInitializer 一样的,复制过来修改一下就好,如下:

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@Order(2)
@Slf4j
public class SecondInitializer implements ApplicationContextInitializer<ConfigurableApplicationContext> {

    @Override
    public void initialize(ConfigurableApplicationContext applicationContext) {
        // 获取环境变量对象
        ConfigurableEnvironment environment = applicationContext.getEnvironment();

        Map<String, Object> map = new HashMap<>(1);
        map.put("k2", "v2");

        MapPropertySource mapPropertySource = new MapPropertySource("secondInitializer", map);

        // 添加到环境变量中
        environment.getPropertySources().addLast(mapPropertySource);

        log.info("SecondInitializer done...");
    }
}

然后这次要修改一下启动类,代码如下:

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@SpringBootApplication
public class App {
    public static void main(String[] args) {
        SpringApplication springApplication = new SpringApplication(App.class);
        springApplication.addInitializers(new SecondInitializer());
        springApplication.run(args);
    }
}

这里通过 SpringApplication 对象来添加初始化器,然后启动项目看一下启动日志,如下:

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 .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.2.4.RELEASE)

2020-01-31 13:24:43.569  INFO 12272 --- [           main] c.z.s.e.initializers.FirstInitializer    : FirstInitializer done...
2020-01-31 13:24:43.576  INFO 12272 --- [           main] c.z.s.e.initializers.SecondInitializer   : SecondInitializer done...
2020-01-31 13:24:43.602  INFO 12272 --- [           main] com.zhou.springboot.example.App          : Starting App on DESKTOP-B1V47DV with PID 12272 (D:\Demo\SpringBoot\spring-boot-example\build\classes\java\main started by Administrator in D:\Demo\SpringBoot\spring-boot-example)
2020-01-31 13:24:43.604  INFO 12272 --- [           main] com.zhou.springboot.example.App          : No active profile set, falling back to default profiles: default
2020-01-31 13:24:45.813  INFO 12272 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)

......................

通过日志可以看到两个初始化器都是被正常加载的,然后他们加载的顺序也是我们通过 @Order 指定的顺序,然后也可以通过上面写的controller方法去验证一下

第三种方式

下面来看第三种方式, 还是先创建一个类 ThirdInitializer ,代码和前面的一样,还是复制过来修改一哈,如下:

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@Order(3)
@Slf4j
public class ThirdInitializer implements ApplicationContextInitializer<ConfigurableApplicationContext> {

    @Override
    public void initialize(ConfigurableApplicationContext applicationContext) {
        // 获取环境变量对象
        ConfigurableEnvironment environment = applicationContext.getEnvironment();

        Map<String, Object> map = new HashMap<>(1);
        map.put("k3", "v3");

        MapPropertySource mapPropertySource = new MapPropertySource("thirdInitializer", map);

        // 添加到环境变量中
        environment.getPropertySources().addLast(mapPropertySource);

        log.info("ThirdInitializer done...");
    }
}

然后这里要通过 application.yml 去添加这个初始化器,如下:

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context:
  initializer:
    classes: com.zhou.springboot.example.initializers.ThirdInitializer

然后启动项目,看下输出日志,如下:

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 .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.2.4.RELEASE)

2020-01-31 13:38:15.059  INFO 15848 --- [           main] c.z.s.e.initializers.ThirdInitializer    : ThirdInitializer done...
2020-01-31 13:38:15.064  INFO 15848 --- [           main] c.z.s.e.initializers.FirstInitializer    : FirstInitializer done...
2020-01-31 13:38:15.064  INFO 15848 --- [           main] c.z.s.e.initializers.SecondInitializer   : SecondInitializer done...

这里可以看到,这个初始化器是被正常加载了,但是这里有个问题,我们在 ThirdInitializer 指定的 @Order(3) 正常来说,他应该是最后一个执行的,但是这里变成了第一个执行的,这里是因为,在 application 配置中指定的系统初始化器是优先于前两种方法的

总结

  • 三种方法的共同点都是要实现 ApplicationContextInitializer 接口
  • @Order 的值越小越先执行
  • application 配置文件指定的方式优先于其他方式