每日一面 - Spring Boot 中的 ApplicationContext 的分层是什么意思？-阿里云开发者社区

每日一面 - Spring Boot 中的 ApplicationContext 的分层是什么意思？

2022-06-24 152

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简介： 每日一面 - Spring Boot 中的 ApplicationContext 的分层是什么意思？

ApplicationContext 是 spring 用来容纳管理 beans 以及其生命周期的容器。ApplicationContext 的分层规定了bean的界限以及可以复用的 bean。关于 ApplicationContext 层级可以参考官方文档(http://docs.spring.io/spring-boot/docs/current/reference/htmlsingle/#howto-build-an-application-context-hierarchy)，这里我们通过一个简单的例子来说明下 ApplicationContext 层级以及其中的bean界限，例如某些 bean 可以被多个 ApplicationContext 共享，同时某些 bean 只在某个 ApplicationContext 生效，不同 ApplicationContext 可以声明同名或者同类型的bean这样。我们将实现一个下图所示的 ApplicationContext 结构：

微信图片_20220624204625.jpg

我们会实现，一个 parent context 与三个对应 child context 的结构。

首先定义Parent context：

Bean类：

package com.test.spring.context.bean;
import lombok.Data;
import lombok.NoArgsConstructor;
@Data
@NoArgsConstructor
public class RootBean {
    private Stirng name;
}

Context类：

import com.hopegaming.scaffold.spring.context.bean.RootBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
@Configuration
@PropertySource(value = "classpath:/root.yaml", factory = YamlPropertyLoaderFactory.class)
public class RootContext {
    @Bean
    public RootBean getFatherBean() {
        RootBean rootBean = new RootBean();
        rootBean.setName("root");
        return rootBean;
    }
}

root.yml：

# 配置这些主要是将actuator相关接口暴露出来。
management:
  endpoint:
    health:
      show-details: always
  endpoints:
    jmx:
      exposure:
        exclude: '*'
    web:
      exposure:
        include: '*'

由于我们使用了yml，这里需要我们自定义一个YamlPropertyLoaderFactory用于加载yml配置：

package com.test.spring.context.config;
import org.springframework.boot.env.YamlPropertySourceLoader;
import org.springframework.core.env.PropertySource;
import org.springframework.core.io.support.DefaultPropertySourceFactory;
import org.springframework.core.io.support.EncodedResource;
import java.io.IOException;
public class YamlPropertyLoaderFactory extends DefaultPropertySourceFactory {
    @Override
    public PropertySource<?> createPropertySource(String name, EncodedResource resource) throws IOException {
        if (resource == null){
            return super.createPropertySource(name, resource);
        }
        return new YamlPropertySourceLoader().load(resource.getResource().getFilename(), resource.getResource()).get(0);
    }
}

定义child context的公共Bean类：

package com.test.spring.context.bean;
import lombok.Data;
import lombok.NoArgsConstructor;
@Data
@NoArgsConstructor
public class ChildBean {
    private RootBean fatherBean;
    private String name;
}

定义ChildContext1：

package com.test.spring.context.config.child1;
import com.hopegaming.scaffold.spring.context.bean.ChildBean;
import com.hopegaming.scaffold.spring.context.bean.RootBean;
import com.hopegaming.scaffold.spring.context.config.YamlPropertyLoaderFactory;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.PropertySource;
@SpringBootApplication(scanBasePackages = {"com.test.spring.context.controller"})
@PropertySource(value = "classpath:/bean-config-1.yaml", factory = YamlPropertyLoaderFactory.class)
public class ChildContext1 {
    @Bean
    public ChildBean getChildBean(@Value("${spring.application.name}") String name, RootBean fatherBean) {
        ChildBean childBean = new ChildBean();
        childBean.setFatherBean(fatherBean);
        childBean.setName(name);
        return childBean;
    }
}

bean-config-1.yaml：

server:
  port: 8080
spring:
  application:
    name: child1

接下来分别是ChildContext2，ChildContext3的：

package com.test.spring.context.config.child2;
import com.hopegaming.scaffold.spring.context.bean.ChildBean;
import com.hopegaming.scaffold.spring.context.bean.RootBean;
import com.hopegaming.scaffold.spring.context.config.YamlPropertyLoaderFactory;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.PropertySource;
@SpringBootApplication(scanBasePackages = {"com.test.spring.context.controller"})
@PropertySource(value = "classpath:/bean-config-2.yaml", factory = YamlPropertyLoaderFactory.class)
public class ChildContext2 {
    @Bean
    public ChildBean getChildBean(@Value("${spring.application.name}") String name, RootBean fatherBean) {
        ChildBean childBean = new ChildBean();
        childBean.setFatherBean(fatherBean);
        childBean.setName(name);
        return childBean;
    }
}
server:
  port: 8081
spring:
  application:
    name: child2
management:
  endpoint:
    health:
      show-details: always
  endpoints:
    jmx:
      exposure:
        exclude: '*'
    web:
      exposure:
        include: '*'
package com.test.spring.context.config.child3;
import com.hopegaming.scaffold.spring.context.bean.ChildBean;
import com.hopegaming.scaffold.spring.context.bean.RootBean;
import com.hopegaming.scaffold.spring.context.config.YamlPropertyLoaderFactory;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.PropertySource;
@SpringBootApplication(scanBasePackages = {"com.test.spring.context.controller"})
@PropertySource(value = "classpath:/bean-config-3.yaml", factory = YamlPropertyLoaderFactory.class)
public class ChildContext3 {
    @Bean
    public ChildBean getChildBean(@Value("${spring.application.name}") String name, RootBean fatherBean) {
        ChildBean childBean = new ChildBean();
        childBean.setFatherBean(fatherBean);
        childBean.setName(name);
        return childBean;
    }
}
server:
  port: 8082
spring:
  application:
    name: child3
management:
  endpoint:
    health:
      show-details: always
  endpoints:
    jmx:
      exposure:
        exclude: '*'
    web:
      exposure:
        include: '*'

测试接口TestController：

package com.test.spring.context.controller;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import java.util.Locale;
@RestController
public class TestController {
    @Autowired
    private ChildBean childBean;
    @RequestMapping("/test")
    public ChildBean getChildBean() {
        return childBean;
    }
}

启动类：

package com.test.spring.context;
import com.hopegaming.scaffold.spring.context.config.child1.ChildContext1;
import com.hopegaming.scaffold.spring.context.config.child2.ChildContext2;
import com.hopegaming.scaffold.spring.context.config.child3.ChildContext3;
import com.hopegaming.scaffold.spring.context.config.root.RootContext;
import org.springframework.boot.builder.SpringApplicationBuilder;
import org.springframework.context.ConfigurableApplicationContext;
public class ContextMain {
    public static void main(String[] args) {
        SpringApplicationBuilder appBuilder =
                new SpringApplicationBuilder()
                        .sources(RootContext.class)
                        //第一个子context用child，剩下的都用sibling
                        .child(ChildContext1.class)
                        .sibling(ChildContext2.class)
                        .sibling(ChildContext3.class);
        ConfigurableApplicationContext applicationContext = appBuilder.run();
    }
}

启动后，访问http://127.0.0.1:8080/test返回：

{"fatherBean":{"name":"root"},"name":"child1"}

访问http://127.0.0.1:8081/test返回：

{"fatherBean":{"name":"root"},"name":"child2"}

访问http://127.0.0.1:8082/test返回：

{"fatherBean":{"name":"root"},"name":"child3"}

访问http://127.0.0.1:8080/actuator/beans会有类似于下面的返回(省略了不关心的bean)：

{
  "contexts": {
    "application-1": {
      "beans": {
        "getChildBean": {
          "aliases": [],
          "scope": "singleton",
          "type": "com.hopegaming.scaffold.spring.context.bean.ChildBean",
          "resource": "com.hopegaming.scaffold.spring.context.config.child2.ChildContext2",
          "dependencies": [
            "getFatherBean"
          ]
        },
        "childContext2": {
          "aliases": [],
          "scope": "singleton",
          "type": "com.hopegaming.scaffold.spring.context.config.child2.ChildContext2$$EnhancerBySpringCGLIB$$26f80b15",
          "resource": null,
          "dependencies": []
        }
        .......
      },
      "parentId": "application"
    },
    "application": {
      "beans": {
        "getFatherBean": {
          "aliases": [],
          "scope": "singleton",
          "type": "com.hopegaming.scaffold.spring.context.bean.RootBean",
          "resource": "com.hopegaming.scaffold.spring.context.config.root.RootContext",
          "dependencies": []
        },
        "rootContext": {
          "aliases": [],
          "scope": "singleton",
          "type": "com.hopegaming.scaffold.spring.context.config.root.RootContext$$EnhancerBySpringCGLIB$$18d9c26f",
          "resource": null,
          "dependencies": []
        }
        .......
      },
      "parentId": null
    }
  }
}

通过这个例子，想必大家对于 ApplicationContext 层级有了一定的理解

每日一面 - Spring Boot 中的 ApplicationContext 的分层是什么意思？

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