spring-core源码解析-(1)
基本
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:
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:
/** 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";
@Override
protected 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:
@Override
public 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:
@Override
public 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
PropertySourcesPropertyResolver继承体系(排除Environment分支):
此接口正是用来解析PropertyResource。
解析
AbstractPropertyResolver.resolveRequiredPlaceholders:
@Override
public 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:
@Override
protected 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;
}
很明显了，就是从System.getProperty和System.getenv获取，但是由于环境变量是无法自定义的，所以其实此处只能通过System.setProperty指定。
注意，classpath:XXX这种写法的classpath前缀到目前为止还没有被处理。
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