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1. spring5.0源码讲解-bean的加载过程|一

#spring-core源码解析-(1)

基本
- ClassPathXmlApplicationContext
  - 构造器
  - 设置配置文件路径
    - Environment接口
      - Profile
      - Property
    - Environment构造器
      - PropertySources接口
      - PropertySource接口
    - 路径Placeholder处理
      - PropertyResolver接口
      - 解析

基础

本部分从最基本的Spring开始。配置文件:

<?xml version="1.0" encoding="UTF-8"?>    <beans>        <bean class="base.SimpleBean"></bean></beans>

启动代码:

public static void main(String[] args) {    ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("config.xml");    SimpleBean bean = context.getBean(SimpleBean.class);    bean.send();    context.close();}

SimpleBean:

public class SimpleBean {    public void send() {        System.out.println("I am send method from SimpleBean!");    }}

ClassPathXmlApplicationContext

整个继承体系如下:

ResourceLoader代表了加载资源的一种方式，正是策略模式的实现。

构造器源码:

public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent) {    super(parent);    setConfigLocations(configLocations);    //默认true    if (refresh) {        refresh();    }}

构造器

首先看父类构造器，沿着继承体系一直向上调用，直到AbstractApplicationContext:

public AbstractApplicationContext(ApplicationContext parent) {    this();    setParent(parent);}public AbstractApplicationContext() {    this.resourcePatternResolver = getResourcePatternResolver();}

getResourcePatternResolver:

protected ResourcePatternResolver getResourcePatternResolver() {    return new PathMatchingResourcePatternResolver(this);}

PathMatchingResourcePatternResolver支持Ant风格的路径解析。

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。

getEnvironment方法来自于ConfigurableApplicationContext接口，源码很简单，如果为空就调用createEnvironment创建一个。AbstractApplicationContext.createEnvironment:

protected ConfigurableEnvironment createEnvironment() {    return new StandardEnvironment();}

Environment接口

StandardEnvironment继承体系:

Environmen接口**代表了当前应用所处的环境。**从此接口的方法可以看出，其主要和profile、Property相关。

Profile

Spring Profile特性是从3.1开始的，其主要是为了解决这样一种问题: 线上环境和测试环境使用不同的配置或是数据库或是其它。有了Profile便可以在不同环境之间无缝切换。**Spring容器管理的所有bean都是和一个profile绑定在一起的。**使用了Profile的配置文件示例:

<beans profile="develop">      <context:property-placeholder location="classpath*:jdbc-develop.properties"/>  </beans>  <beans profile="production">      <context:property-placeholder location="classpath*:jdbc-production.properties"/>  </beans>  <beans profile="test">      <context:property-placeholder location="classpath*:jdbc-test.properties"/>  </beans>

在启动代码中可以用如下代码设置活跃(当前使用的)Profile:

context.getEnvironment().setActiveProfiles("dev");

当然使用的方式还有很多(比如注解)，参考:

spring3.1 profile 配置不同的环境

Spring Profiles example

Property

这里的Property指的是程序运行时的一些参数，引用注释:

properties files, JVM system properties, system environment variables, JNDI, servlet context parameters, ad-hoc Properties objects,Maps, and so on.

Environment构造器

private final MutablePropertySources propertySources = new MutablePropertySources(this.logger);public AbstractEnvironment() {    customizePropertySources(this.propertySources);}

PropertySources接口

继承体系:

此接口实际上是PropertySource的容器，默认的MutablePropertySources实现内部含有一个CopyOnWriteArrayList作为存储载体。

StandardEnvironment.customizePropertySources:此接口实际上是PropertySource的容器，默认的MutablePropertySources实现内部含有一个CopyOnWriteArrayList作为存储载体。

StandardEnvironment.customizePropertySources:

/** System environment property source name: {@value} */public static final String SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME = "systemEnvironment";/** JVM system properties property source name: {@value} */public static final String SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME = "systemProperties";@Overrideprotected void customizePropertySources(MutablePropertySources propertySources) {    propertySources.addLast(new MapPropertySource        (SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME, getSystemProperties()));    propertySources.addLast(new SystemEnvironmentPropertySource        (SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME, getSystemEnvironment()));}

PropertySource接口

PropertySource接口代表了键值对的Property来源。继承体系：

AbstractEnvironment.getSystemProperties:

@Overridepublic Map<String, Object> getSystemProperties() {    try {        return (Map) System.getProperties();    }    catch (AccessControlException ex) {        return (Map) new ReadOnlySystemAttributesMap() {            @Override            protected String getSystemAttribute(String attributeName) {                try {                    return System.getProperty(attributeName);                }                catch (AccessControlException ex) {                    if (logger.isInfoEnabled()) {                        logger.info(format("Caught AccessControlException when accessing system " +                                "property [%s]; its value will be returned [null]. Reason: %s",                                attributeName, ex.getMessage()));                    }                    return null;                }            }        };    }}

这里的实现很有意思，如果安全管理器阻止获取全部的系统属性，那么会尝试获取单个属性的可能性，如果还不行就抛异常了。

getSystemEnvironment方法也是一个套路，不过最终调用的是System.getenv，可以获取jvm和OS的一些版本信息。

路径Placeholder处理

AbstractEnvironment.resolveRequiredPlaceholders:

@Overridepublic String resolveRequiredPlaceholders(String text) throws IllegalArgumentException {    //text即配置文件路径，比如classpath:config.xml    return this.propertyResolver.resolveRequiredPlaceholders(text);}

propertyResolver是一个PropertySourcesPropertyResolver对象:

private final ConfigurablePropertyResolver propertyResolver =            new PropertySourcesPropertyResolver(this.propertySources);

PropertyResolver接口

PropertyResolver继承体系(排除Environment分支):

此接口正是用来解析PropertyResource。

解析

AbstractPropertyResolver.resolveRequiredPlaceholders:

@Overridepublic String resolveRequiredPlaceholders(String text) throws IllegalArgumentException {    if (this.strictHelper == null) {        this.strictHelper = createPlaceholderHelper(false);    }    return doResolvePlaceholders(text, this.strictHelper);}

private PropertyPlaceholderHelper createPlaceholderHelper(boolean ignoreUnresolvablePlaceholders) {    //三个参数分别是${, }, :    return new PropertyPlaceholderHelper(this.placeholderPrefix, this.placeholderSuffix,        this.valueSeparator, ignoreUnresolvablePlaceholders);}

doResolvePlaceholders：

private String doResolvePlaceholders(String text, PropertyPlaceholderHelper helper) {    //PlaceholderResolver接口依然是策略模式的体现    return helper.replacePlaceholders(text, new PropertyPlaceholderHelper.PlaceholderResolver() {        @Override        public String resolvePlaceholder(String placeholderName) {            return getPropertyAsRawString(placeholderName);        }    });}

其实代码执行到这里的时候还没有进行xml配置文件的解析，那么这里的解析placeHolder是什么意思呢，原因在于可以这么写:

System.setProperty("spring", "classpath");ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("${spring}:config.xml");SimpleBean bean = context.getBean(SimpleBean.class);

这样就可以正确解析。placeholder的替换其实就是字符串操作，这里只说一下正确的属性是怎么来的。实现的关键在于PropertySourcesPropertyResolver.getProperty:

@Overrideprotected String getPropertyAsRawString(String key) {    return getProperty(key, String.class, false);}protected <T> T getProperty(String key, Class<T> targetValueType, boolean resolveNestedPlaceholders) {    if (this.propertySources != null) {        for (PropertySource<?> propertySource : this.propertySources) {            Object value = propertySource.getProperty(key);            return value;        }    }    return null;}