Spring源码解读（一）

前期准备

首先搭建一个简单的Spring Demo工程

项目目录结构如下图所示：

applicationContect.xml (可以取其他文件名，只要在加载配置文件时指定文件路径)

<?xml version="1.0" encoding="UTF-8"?>

<beans

    xmlns="http://www.springframework.org/schema/beans"

    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

    xmlns:p="http://www.springframework.org/schema/p"

    xmlns:aop="http://www.springframework.org/schema/aop"

    xsi:schemaLocation="http://www.springframework.org/schema/beans

        http://www.springframework.org/schema/beans/spring-beans-3.0.xsd

        http://www.springframework.org/schema/aop

        http://www.springframework.org/schema/aop/spring-aop-3.0.xsd">

    <bean id="chinese" class="com.bean.ChineseImpl">

        <property name="name">

            <value>小明</value>

        </property>

        <property name="age">

            <value>10</value>

        </property>

    </bean>

    <bean id="american" class="com.bean.AmericanImpl">

        <property name="name">

            <value>Tom</value>

        </property>

        <property name="age">

            <value>15</value>

        </property>

    </bean>

</beans>

Person.java

package com.bean;

public interface Person{

    public void Speak();

}

ChineseImpl.java

package com.bean;

public class ChineseImpl implements Person{

    private String name;

    private int age;

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

    public int getAge() {

        return age;

    }

    public void setAge(int age) {

        this.age = age;

    }

    @Override

    public void Speak() {

        // TODO Auto-generated method stub

        System.out.println("I'm Chinese,My name is "+this.name+",I'm "+this.age+" years old!");

    }

}

AmericanImpl.java

package com.bean;

public class AmericanImpl implements Person{

    private String name;

    private int age;

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

    public int getAge() {

        return age;

    }

    public void setAge(int age) {

        this.age = age;

    }

    @Override

    public void Speak() {

        // TODO Auto-generated method stub

        System.out.println("I'm American,My name is "+this.name+",I'm "+this.age+" years old!");

    }

}

Test.java

package com.spring;

import org.springframework.context.ApplicationContext;

import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.bean.Person;

public class Test {

    public static void main(String[] args) {

        ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");

        Person person = (Person) context.getBean("chinese");

        person.Speak();

        person = (Person) context.getBean("american");

        person.Speak();

    }

}

下面将按照Spring初始化的过程：

构造函数

ClassPathXmlApplicationContext构造函数(ClassPathXmlApplicationContext[只能读放在web-info/classes目录下的配置文件],FileSystemXmlApplicationContext读具体路径)

    public ClassPathXmlApplicationContext(String configLocation) throws BeansException {

        this(new String[] {configLocation}, true, null);

    }

根据传入参数的不同，调用不同的构造函数，最终调用以下构造函数

    public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent)

            throws BeansException {

        super(parent);

        setConfigLocations(configLocations);

        if (refresh) {

            refresh();

        }

    }

设置配置文件路径

即AbstractRefreshableConfigApplicationContext.setConfigLocations

    public void setConfigLocations(String... locations) {

        if (locations != null) {

            Assert.noNullElements(locations, "Config locations must not be null");

            this.configLocations = new String[locations.length];

            for (int i = 0; i < locations.length; i++) {

                this.configLocations[i] = resolvePath(locations[i]).trim();

            }

        }

        else {

            this.configLocations = null;

        }

    }

resolvePath:

    protected String resolvePath(String path) {

        return getEnvironment().resolveRequiredPlaceholders(path);

    }

此方法的目的在于将占位符(placeholder)解析成实际的地址。比如可以这么写: new ClassPathXmlApplicationContext("classpath:config.xml");那么classpath:就是需要被解析的

refesh()

Spring bean解析就在此方法，所以单独提出来。

AbstractApplicationContext.refresh:

@Override

    public void refresh() throws BeansException, IllegalStateException {

        synchronized (this.startupShutdownMonitor) {

            // Prepare this context for refreshing.

            prepareRefresh();

            // Tell the subclass to refresh the internal bean factory.

            ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

            // Prepare the bean factory for use in this context.

            prepareBeanFactory(beanFactory);

            try {

                // Allows post-processing of the bean factory in context subclasses.

                postProcessBeanFactory(beanFactory);

                // Invoke factory processors registered as beans in the context.

                invokeBeanFactoryPostProcessors(beanFactory);

                // Register bean processors that intercept bean creation.

                registerBeanPostProcessors(beanFactory);

                // Initialize message source for this context.

                initMessageSource();

                // Initialize event multicaster for this context.

                initApplicationEventMulticaster();

                // Initialize other special beans in specific context subclasses.

                onRefresh();

                // Check for listener beans and register them.

                registerListeners();

                // Instantiate all remaining (non-lazy-init) singletons.

                finishBeanFactoryInitialization(beanFactory);

                // Last step: publish corresponding event.

                finishRefresh();

            }

            catch (BeansException ex) {

                logger.warn("Exception encountered during context initialization - cancelling refresh attempt", ex);

                // Destroy already created singletons to avoid dangling resources.

                destroyBeans();

                // Reset 'active' flag.

                cancelRefresh(ex);

                // Propagate exception to caller.

                throw ex;

            }

        }

    }

prepareRefresh

    protected void prepareRefresh() {

        this.startupDate = System.currentTimeMillis();

        this.active.set(true);

        if (logger.isInfoEnabled()) {

            logger.info("Refreshing " + this);

        }

        // Initialize any placeholder property sources in the context environment

        initPropertySources();

        // Validate that all properties marked as required are resolvable

        // see ConfigurablePropertyResolver#setRequiredProperties

        getEnvironment().validateRequiredProperties();

    }

属性校验

AbstractEnvironment.validateRequiredProperties:

    @Override

    public void validateRequiredProperties() throws MissingRequiredPropertiesException {

        this.propertyResolver.validateRequiredProperties();

    }

AbstractPropertyResolver.validateRequiredProperties:

    @Override

    public void validateRequiredProperties() {

        MissingRequiredPropertiesException ex = new MissingRequiredPropertiesException();

        for (String key : this.requiredProperties) {

            if (this.getProperty(key) == null) {

                ex.addMissingRequiredProperty(key);

            }

        }

        if (!ex.getMissingRequiredProperties().isEmpty()) {

            throw ex;

        }

    }

requiredProperties是通过setRequiredProperties方法设置的，保存在一个list里面，默认是空的，也就是不需要校验任何属性

BeanFactory创建

由 refesh() 中的 obtainFreshBeanFactory 调用 AbstractRefreshableApplicationContext.refreshBeanFactory:

    @Override

    protected final void refreshBeanFactory() throws BeansException {
　　　　　//如果存在就销毁

        if (hasBeanFactory()) {

            destroyBeans();

            closeBeanFactory();

        }

        try {

            DefaultListableBeanFactory beanFactory = createBeanFactory();

            beanFactory.setSerializationId(getId());

            customizeBeanFactory(beanFactory);

            loadBeanDefinitions(beanFactory);

            synchronized (this.beanFactoryMonitor) {

                this.beanFactory = beanFactory;

            }

        }

        catch (IOException ex) {

            throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);

        }

    }

BeanFactory定制

AbstractRefreshableApplicationContext.customizeBeanFactory方法用于给子类提供一个自由配置的机会，默认实现:

protected void customizeBeanFactory(DefaultListableBeanFactory beanFactory) {

        if (this.allowBeanDefinitionOverriding != null) {

            beanFactory.setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);

        }

        if (this.allowCircularReferences != null) {

            beanFactory.setAllowCircularReferences(this.allowCircularReferences);

        }

    }

Bean加载

AbstractXmlApplicationContext.loadBeanDefinitions，这个便是核心的bean加载了:

protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {

        // Create a new XmlBeanDefinitionReader for the given BeanFactory.

        XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);

        // Configure the bean definition reader with this context's

        // resource loading environment.

        beanDefinitionReader.setEnvironment(this.getEnvironment());

        beanDefinitionReader.setResourceLoader(this);

        beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));

        // Allow a subclass to provide custom initialization of the reader,

        // then proceed with actually loading the bean definitions.

        initBeanDefinitionReader(beanDefinitionReader);

        loadBeanDefinitions(beanDefinitionReader);

    }

巴特西

Spring源码解读（一）

prepareRefresh

属性校验

BeanFactory定制

Bean加载

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