IOC 容器启动过程 1 - prepareRefresh ()

知道了IOC启动的需要多个阶段，接下来学习下第一个阶段 AbstractApplicationContext # prepareRefresh() 都干了啥！

工作内容

这个阶段主要是准备工作：

• 设置启动日期，启动标志；
• 给子类扩展点，自定义处理环境变量；
• 验证环境变量是否都已经准备好了；
• 处理事件监听器们；

spring-web | org.springframework.context.support.AbstractApplicationContext#refresh

protected void prepareRefresh() {
  // 记录启动时间，设置状态表示开始启动
  // Switch to active.
  this.startupDate = System.currentTimeMillis();
  this.closed.set(false);
  this.active.set(true);
  if (logger.isDebugEnabled()) {
    if (logger.isTraceEnabled()) {
      logger.trace("Refreshing " + this);
    }
    else {
      logger.debug("Refreshing " + getDisplayName());
    }
  }
  // 留给子类自定义处理
  initPropertySources();
  // 检测下需要验证的属性是否都已经正确的放入当前环境中
  getEnvironment().validateRequiredProperties();
  // 准备相关监听器
  if (this.earlyApplicationListeners == null) {
    this.earlyApplicationListeners = new LinkedHashSet<>(this.applicationListeners);
  }
  else {
    // Reset local application listeners to pre-refresh state.
    this.applicationListeners.clear();
    this.applicationListeners.addAll(this.earlyApplicationListeners);
  }
  this.earlyApplicationEvents = new LinkedHashSet<>();
}

代码验证环境变量

可以重写这个 initPropertySources() 来测试下工作。
准备个 bean.xml 及对应的实体

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN 2.0//EN" 
"https://www.springframework.org/dtd/spring-beans-2.0.dtd">
<beans>
    <bean id="user" class="cn.lichenghao.entity.User">
        <property name="name">
            <value>Rod</value>
        </property>
        <property name="age">
            <value>31</value>
        </property>
    </bean>
</beans>

测试用对象。

package cn.lichenghao.entity;
public class User {
    private String name;
    private String age;
    public User() {
        System.out.println("User construct run~~~");
    }
    public User(String name, String age) {
        this.name = name;
        this.age = age;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getAge() {
        return age;
    }
    public void setAge(String age) {
        this.age = age;
    }
    @Override
    public String toString() {
        return "User{" +
                "name='" + name + '\'' +
                ", age='" + age + '\'' +
                '}';
    }
    public void sayHello() {
        System.out.println("hello world!");
    }
}

然后先加载测试。

/**
 * 编译后的第一个Hello World
 *
 * @author chenghao.li
 */
public class App {
  public static void main(String[] args) {
    // 根据配置文件加载bean
    ClassPathXmlApplicationContext classPathXmlApplicationContext 
        = new ClassPathXmlApplicationContext("bean.xml");
    User bean = classPathXmlApplicationContext.getBean(User.class);
    bean.sayHello();
  }
}

自定义个context。

/**
 * 自定义
 *
 * @author chenghao.li
 */
public class MyApplicationContext extends ClassPathXmlApplicationContext {
  public MyApplicationContext(String configLocation) throws BeansException {
    super(configLocation);
  }
  @Override
  protected void initPropertySources() {
    getEnvironment().setRequiredProperties("ABC");
    super.initPropertySources();
  }
}

再测试下。

/**
 * 编译后的第一个Hello World
 *
 * @author chenghao.li
 */
public class App {
    public static void main(String[] args) {
        // 自定义加载
        MyApplicationContext myApplicationContext = new MyApplicationContext("bean.xml");
        User mybean = myApplicationContext.getBean(User.class);
        mybean.sayHello();
    }
}

这个时候就会报错，因为我们的系统环境变量中并没有 ABC。

Exception in thread "main" org.springframework.core.env.MissingRequiredPropertiesException: 
    The following properties were declared as required but could not be resolved: [ABC]

添加个环境变量 ABC，再进行测试。

/**
 * 编译后的第一个Hello World
 *
 * @author chenghao.li
 */
public class App {
    public static void main(String[] args) {
    System.setProperty("ABC", "1234");
        // 自定义加载
        MyApplicationContext myApplicationContext = new MyApplicationContext("bean.xml");
        User mybean = myApplicationContext.getBean(User.class);
        mybean.sayHello();
    }
}