代码进口

上文【Spring源码阐明】Bean加载流程概览，较量具体地阐明白Spring上下文加载的代码进口，而且在AbstractApplicationContext的refresh要领中，点出了finishBeanFactoryInitialization要领完成了对付所有非懒加载的Bean的初始化。

finishBeanFactoryInitialization要领中挪用了DefaultListableBeanFactory的preInstantiateSingletons要领，本文针对preInstantiateSingletons举办阐明，解读一下Spring是如何初始化Bean实例工具出来的。

DefaultListableBeanFactory的preInstantiateSingletons要领

DefaultListableBeanFactory的preInstantiateSingletons要领，顾名思义，初始化所有的单例Bean，软件开发，看一下要领的界说：

public void preInstantiateSingletons() throws BeansException {
    if (this.logger.isInfoEnabled()) {
        this.logger.info("Pre-instantiating singletons in " + this);
    }
    synchronized (this.beanDefinitionMap) {
        // Iterate over a copy to allow for init methods which in turn register new bean definitions.
        // While this may not be part of the regular factory bootstrap, it does otherwise work fine.
        List<String> beanNames = new ArrayList<String>(this.beanDefinitionNames);
        for (String beanName : beanNames) {
            RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
            if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
                if (isFactoryBean(beanName)) {
                    final FactoryBean factory = (FactoryBean) getBean(FACTORY_BEAN_PREFIX + beanName);
                    boolean isEagerInit;
                    if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
                        isEagerInit = AccessController.doPrivileged(new PrivilegedAction<Boolean>() {
                            public Boolean run() {
                                return ((SmartFactoryBean) factory).isEagerInit();
                            }
                        }, getAccessControlContext());
                    }
                    else {
                        isEagerInit = (factory instanceof SmartFactoryBean &&
                                ((SmartFactoryBean) factory).isEagerInit());
                    }
                    if (isEagerInit) {
                        getBean(beanName);
                    }
                }
                else {
                    getBean(beanName);
                }
            }
        }
    }
}

前面的代码较量简朴，按照beanName拿到BeanDefinition（即Bean的界说）。由于此要领实例化的是所有非懒加载的单例Bean，因此要实例化Bean，劳务派遣管理系统，必需满意11行的三个界说：

（1）不是抽象的

（2）必需是单例的

（3）必需长短懒加载的

接着简朴看一下第12行~第29行的代码，这段代码主要做的是一件工作：首先判定一下Bean是否FactoryBean的实现，接着判定Bean是否SmartFactoryBean的实现，如果Bean是SmartFactoryBean的实现而且eagerInit（这个单词字面意思是盼愿加载，找不到一个好的词语去翻译，意思就是界说了这个Bean需要当即加载的意思）的话，会当即实例化这个Bean。Java开拓人员不需要存眷这段代码，因为SmartFactoryBean根基不会用到，我翻译一下Spring官网对付SmartFactoryBean的界说描写：

代码示例

为了后头的代码阐明利便，事先我界说一个Bean：

package org.xrq.action;

import org.springframework.beans.factory.BeanClassLoaderAware;
import org.springframework.beans.factory.BeanNameAware;
import org.springframework.beans.factory.InitializingBean;

public class MultiFunctionBean implements InitializingBean, BeanNameAware, BeanClassLoaderAware {

    private int    propertyA;

    private int    propertyB;

    public int getPropertyA() {
        return propertyA;
    }

    public void setPropertyA(int propertyA) {
        this.propertyA = propertyA;
    }

    public int getPropertyB() {
        return propertyB;
    }

    public void setPropertyB(int propertyB) {
        this.propertyB = propertyB;
    }

    public void initMethod() {
        System.out.println("Enter MultiFunctionBean.initMethod()");
    }

    @Override
    public void setBeanClassLoader(ClassLoader classLoader) {
        System.out.println("Enter MultiFunctionBean.setBeanClassLoader(ClassLoader classLoader)");
    }

    @Override
    public void setBeanName(String name) {
        System.out.println("Enter MultiFunctionBean.setBeanName(String name)");
    }

    @Override
    public void afterPropertiesSet() throws Exception {
        System.out.println("Enter MultiFunctionBean.afterPropertiesSet()");
    }

    @Override
    public String toString() {
        return "MultiFunctionBean [propertyA=" + propertyA + ", propertyB=" + propertyB + "]";
    }

}