I. Introduction
The previous article Spring source code analysis (2) - IOC root class structure diagram sorted out the inheritance relationship of the entire Spring BeanFactory, and gained a basic understanding of the BeanFactory family.
This article continues with Spring source code analysis (1) - IOC demo to analyze the initialization process of ClassPathXmlApplicationContext.
2. Analysis of initialization process
ClassPathXmlApplicationContext process trace:
public class ClassPathXmlApplicationContext extends AbstractXmlApplicationContext {
......
/**
* Create a new ClassPathXmlApplicationContext, loading the definitions
* from the given XML file and automatically refreshing the context.
* @param configLocation resource location
* @throws BeansException if context creation failed
*/
public ClassPathXmlApplicationContext(String configLocation) throws BeansException {
this(new String[] {
configLocation}, true, null);
}
......
/**
* Create a new ClassPathXmlApplicationContext with the given parent,
* loading the definitions from the given XML files.
* @param configLocations array of resource locations
* @param refresh whether to automatically refresh the context,
* loading all bean definitions and creating all singletons.
* Alternatively, call refresh manually after further configuring the context.
* @param parent the parent context
* @throws BeansException if context creation failed
* @see #refresh()
*/
public ClassPathXmlApplicationContext(
String[] configLocations, boolean refresh, @Nullable ApplicationContext parent)
throws BeansException {
super(parent);
setConfigLocations(configLocations);
if (refresh) {
refresh();
}
}
......
It can be seen that
the initialization entry is the public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, @Nullable ApplicationContext parent) method;
this method does three things:
- super(parent); Set ApplicationContext;
- setConfigLocations(configLocations); Set the configuration file path;
- refresh(); load new configuration;
1. super(parent); sets the ApplicationContext; what is actually executed is the method of the AbstractApplicationContext class:
public abstract class AbstractApplicationContext extends DefaultResourceLoader
implements ConfigurableApplicationContext {
......
/**
* Create a new AbstractApplicationContext with no parent.
*/
public AbstractApplicationContext() {
this.resourcePatternResolver = getResourcePatternResolver();
}
/**
* Create a new AbstractApplicationContext with the given parent context.
* @param parent the parent context
*/
public AbstractApplicationContext(@Nullable ApplicationContext parent) {
this();
setParent(parent);
}
......
/**
* Set the parent of this application context.
* <p>The parent {@linkplain ApplicationContext#getEnvironment() environment} is
* {@linkplain ConfigurableEnvironment#merge(ConfigurableEnvironment) merged} with
* this (child) application context environment if the parent is non-{@code null} and
* its environment is an instance of {@link ConfigurableEnvironment}.
* @see ConfigurableEnvironment#merge(ConfigurableEnvironment)
*/
@Override
public void setParent(@Nullable ApplicationContext parent) {
this.parent = parent;
if (parent != null) {
Environment parentEnvironment = parent.getEnvironment();
if (parentEnvironment instanceof ConfigurableEnvironment configurableEnvironment) {
getEnvironment().merge(configurableEnvironment);
}
}
}
......
2. setConfigLocations(configLocations); Set the configuration file path; what is actually executed is the public void setConfigLocations(@Nullable String… locations) method of AbstractRefreshableConfigApplicationContext:
public abstract class AbstractRefreshableConfigApplicationContext extends AbstractRefreshableApplicationContext
implements BeanNameAware, InitializingBean {
......
/**
* Set the config locations for this application context.
* <p>If not set, the implementation may use a default as appropriate.
*/
public void setConfigLocations(@Nullable 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;
}
}
......
3. refresh(); loads the new configuration; what is actually executed is the refresh(…) method of AbstractApplicationContext:
public abstract class AbstractApplicationContext extends DefaultResourceLoader
implements ConfigurableApplicationContext {
......
@Override
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
StartupStep contextRefresh = this.applicationStartup.start("spring.context.refresh");
// 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);
StartupStep beanPostProcess = this.applicationStartup.start("spring.context.beans.post-process");
// Invoke factory processors registered as beans in the context.
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
registerBeanPostProcessors(beanFactory);
beanPostProcess.end();
// 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) {
if (logger.isWarnEnabled()) {
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;
}
finally {
// Reset common introspection caches in Spring's core, since we
// might not ever need metadata for singleton beans anymore...
resetCommonCaches();
contextRefresh.end();
}
}
}
......