Spring boot源码探险
Application启动流程
我们知道SpringBoot是通过Application进行启动的，所以我没来看看具体的启动流程是怎样的。一般的启动是这样的：
public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}
其中Application是启动入口所在的类。这个方法进入之后是
/**
* Static helper that can be used to run a {@link SpringApplication} from the
* specified source using default settings.
* @param primarySource the primary source to load
* @param args the application arguments (usually passed from a Java main method)
* @return the running {@link ApplicationContext}
*/
public static ConfigurableApplicationContext run(Class<?> primarySource,
String... args) {
return run(new Class<?>[] { primarySource }, args);
}
/**
* Static helper that can be used to run a {@link SpringApplication} from the
* specified sources using default settings and user supplied arguments.
* @param primarySources the primary sources to load
* @param args the application arguments (usually passed from a Java main method)
* @return the running {@link ApplicationContext}
*/
public static ConfigurableApplicationContext run(Class<?>[] primarySources,
String[] args) {
return new SpringApplication(primarySources).run(args);
}
这只是一个简单的静态方法，它内部会创建一个SpringApplication的实例，并调用实例的run方法。
我们看一下构造器里具体干了什么：
/**
* Create a new {@link SpringApplication} instance. The application context will load
* beans from the specified primary sources (see {@link SpringApplication class-level}
* documentation for details. The instance can be customized before calling
* {@link #run(String...)}.
* @param primarySources the primary bean sources
* @see #run(Class, String[])
* @see #SpringApplication(ResourceLoader, Class...)
* @see #setSources(Set)
*/
public SpringApplication(Class<?>... primarySources) {
this(null, primarySources);
}
/**
* Create a new {@link SpringApplication} instance. The application context will load
* beans from the specified primary sources (see {@link SpringApplication class-level}
* documentation for details. The instance can be customized before calling
* {@link #run(String...)}.
* @param resourceLoader the resource loader to use
* @param primarySources the primary bean sources
* @see #run(Class, String[])
* @see #setSources(Set)
*/
@SuppressWarnings({ "unchecked", "rawtypes" })
public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
this.resourceLoader = resourceLoader;
Assert.notNull(primarySources, "PrimarySources must not be null");
this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
//检测是否是web应用
this.webApplicationType = WebApplicationType.deduceFromClasspath();
//之后从spring.factories中加载需要创建哪些ApplicationContextInitializer实例
setInitializers((Collection) getSpringFactoriesInstances(
ApplicationContextInitializer.class));
//之后从spring.factories中加载需要创建哪些ApplicationListener实例
setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
this.mainApplicationClass = deduceMainApplicationClass();
}
我们来看一下Spring是如何判断应用是否是Web应用的。
private static final String[] SERVLET_INDICATOR_CLASSES = { "javax.servlet.Servlet",
"org.springframework.web.context.ConfigurableWebApplicationContext" };
private static final String WEBMVC_INDICATOR_CLASS = "org.springframework."
+ "web.servlet.DispatcherServlet";
private static final String WEBFLUX_INDICATOR_CLASS = "org."
+ "springframework.web.reactive.DispatcherHandler";
private static final String JERSEY_INDICATOR_CLASS = "org.glassfish.jersey.servlet.ServletContainer";
private static final String SERVLET_APPLICATION_CONTEXT_CLASS = "org.springframework.web.context.WebApplicationContext";
private static final String REACTIVE_APPLICATION_CONTEXT_CLASS = "org.springframework.boot.web.reactive.context.ReactiveWebApplicationContext";
static WebApplicationType deduceFromClasspath() {
if (ClassUtils.isPresent(WEBFLUX_INDICATOR_CLASS, null)
&& !ClassUtils.isPresent(WEBMVC_INDICATOR_CLASS, null)
&& !ClassUtils.isPresent(JERSEY_INDICATOR_CLASS, null)) {
return WebApplicationType.REACTIVE;
}
//如果没有出现WEBFLUX，且没有出现javax.servlet.Servlet或org.springframework.web.context.ConfigurableWebApplicationContext才会认为不是WEB应用
for (String className : SERVLET_INDICATOR_CLASSES) {
if (!ClassUtils.isPresent(className, null)) {
return WebApplicationType.NONE;
}
}
return WebApplicationType.SERVLET;
}
以及是如何找到main方法所在的类型的。
private Class<?> deduceMainApplicationClass() {
try {
//这里利用了创建异常对象时，JVM会填充它的栈轨迹
StackTraceElement[] stackTrace = new RuntimeException().getStackTrace();
//不断退栈，找到第一个main方法，但是这当然不一定对
for (StackTraceElement stackTraceElement : stackTrace) {
if ("main".equals(stackTraceElement.getMethodName())) {
return Class.forName(stackTraceElement.getClassName());
}
}
}
catch (ClassNotFoundException ex) {
// Swallow and continue
}
return null;
}
接下来看一下SpringApplication的run方法，它会贯穿整个Spring容器的生命周期。
/**
* Run the Spring application, creating and refreshing a new
* {@link ApplicationContext}.
* @param args the application arguments (usually passed from a Java main method)
* @return a running {@link ApplicationContext}
*/
public ConfigurableApplicationContext run(String... args) {
//创建一个计时器
StopWatch stopWatch = new StopWatch();
stopWatch.start();
ConfigurableApplicationContext context = null;
Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
configureHeadlessProperty();
//创建监听器
SpringApplicationRunListeners listeners = getRunListeners(args);
listeners.starting();
try {
//创建应用参数
ApplicationArguments applicationArguments = new DefaultApplicationArguments(
args);
//创建环境
ConfigurableEnvironment environment = prepareEnvironment(listeners,
applicationArguments);
configureIgnoreBeanInfo(environment);
//输出banner
Banner printedBanner = printBanner(environment);
//创建上下文
context = createApplicationContext();
exceptionReporters = getSpringFactoriesInstances(
SpringBootExceptionReporter.class,
new Class[] { ConfigurableApplicationContext.class }, context);
prepareContext(context, environment, listeners, applicationArguments,
printedBanner);
refreshContext(context);
afterRefresh(context, applicationArguments);
stopWatch.stop();
if (this.logStartupInfo) {
new StartupInfoLogger(this.mainApplicationClass)
.logStarted(getApplicationLog(), stopWatch);
}
listeners.started(context);
callRunners(context, applicationArguments);
}
catch (Throwable ex) {
handleRunFailure(context, ex, exceptionReporters, listeners);
throw new IllegalStateException(ex);
}
try {
listeners.running(context);
}
catch (Throwable ex) {
handleRunFailure(context, ex, exceptionReporters, null);
throw new IllegalStateException(ex);
}
return context;
}
还是比较复杂的，第一步好像启动了一个stopwatch对象，我们先来看看stopwatch是个啥。
/**
* Simple stop watch, allowing for timing of a number of tasks,
* exposing total running time and running time for each named task.
*
* <p>Conceals use of {@code System.currentTimeMillis()}, improving the
* readability of application code and reducing the likelihood of calculation errors.
*
* <p>Note that this object is not designed to be thread-safe and does not
* use synchronization.
*
* <p>This class is normally used to verify performance during proof-of-concepts
* and in development, rather than as part of production applications.
*
* @author Rod Johnson
* @author Juergen Hoeller
* @author Sam Brannen
* @since May 2, 2001
*/
public class StopWatch {
/**
* Construct a new stop watch. Does not start any task.
*/
public StopWatch() {
this("");
}
/**
* Construct a new stop watch with the given id.
* Does not start any task.
* @param id identifier for this stop watch.
* Handy when we have output from multiple stop watches
* and need to distinguish between them.
*/
public StopWatch(String id) {
this.id = id;
}
}
看类上的注释应该就是一个简单的检验性能的计时器。
接下来会创建listener，并启动他们。具体的代码如下：
private SpringApplicationRunListeners getRunListeners(String[] args) {
//参数为SpringApplication和String数组
Class<?>[] types = new Class<?>[] { SpringApplication.class, String[].class };
return new SpringApplicationRunListeners(logger, getSpringFactoriesInstances(
SpringApplicationRunListener.class, types, this, args));
}
private <T> Collection<T> getSpringFactoriesInstances(Class<T> type,
Class<?>[] parameterTypes, Object... args) {
ClassLoader classLoader = getClassLoader();
// Use names and ensure unique to protect against duplicates
//获取工厂类名
Set<String> names = new LinkedHashSet<>(
SpringFactoriesLoader.loadFactoryNames(type, classLoader));
//将工厂进行实例化
List<T> instances = createSpringFactoriesInstances(type, parameterTypes,
classLoader, args, names);
//根据类上的Order或Priority标记进行排序
AnnotationAwareOrderComparator.sort(instances);
return instances;
}
先看SpringFactoriesLoader.loadFactoryNames(type, classLoader));。
/**
* Load the fully qualified class names of factory implementations of the
* given type from {@value #FACTORIES_RESOURCE_LOCATION}, using the given
* class loader.
* @param factoryClass the interface or abstract class representing the factory
* @param classLoader the ClassLoader to use for loading resources; can be
* {@code null} to use the default
* @throws IllegalArgumentException if an error occurs while loading factory names
* @see #loadFactories
*/
public static List<String> loadFactoryNames(Class<?> factoryClass, @Nullable ClassLoader classLoader) {
String factoryClassName = factoryClass.getName();
return loadSpringFactories(classLoader).getOrDefault(factoryClassName, Collections.emptyList());
}
private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) {
MultiValueMap<String, String> result = cache.get(classLoader);
if (result != null) {
return result;
}
try {
Enumeration<URL> urls = (classLoader != null ?
classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :
ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));
result = new LinkedMultiValueMap<>();
while (urls.hasMoreElements()) {
URL url = urls.nextElement();
UrlResource resource = new UrlResource(url);
Properties properties = PropertiesLoaderUtils.loadProperties(resource);
for (Map.Entry<?, ?> entry : properties.entrySet()) {
String factoryClassName = ((String) entry.getKey()).trim();
for (String factoryName : StringUtils.commaDelimitedListToStringArray((String) entry.getValue())) {
result.add(factoryClassName, factoryName.trim());
}
}
}
cache.put(classLoader, result);
return result;
}
catch (IOException ex) {
throw new IllegalArgumentException("Unable to load factories from location [" +
FACTORIES_RESOURCE_LOCATION + "]", ex);
}
}
其中loadSpringFactories方法会从spring.factories文件中加载属性配置信息。下面给一个mybatis-spring-boot-autoconfigure包里的spring.factories的配置。
# Auto Configure
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
org.mybatis.spring.boot.autoconfigure.MybatisAutoConfiguration
而spring.factories文件实际上是Spring内部的SPI机制，Spring从Jar包中这个文件中获取哪些类要进行自动配置。
回到之前的源码。让我们来看看具体是如何通过工厂类的全限定类名实例化工厂对象的。
@SuppressWarnings("unchecked")
private <T> List<T> createSpringFactoriesInstances(Class<T> type,
Class<?>[] parameterTypes, ClassLoader classLoader, Object[] args,
Set<String> names) {
List<T> instances = new ArrayList<>(names.size());
for (String name : names) {
try {
//通过反射拿到类对象
Class<?> instanceClass = ClassUtils.forName(name, classLoader);
Assert.isAssignable(type, instanceClass);
//获得一个构造器
Constructor<?> constructor = instanceClass
.getDeclaredConstructor(parameterTypes);
//这里创建实例
T instance = (T) BeanUtils.instantiateClass(constructor, args);
instances.add(instance);
}
catch (Throwable ex) {
throw new IllegalArgumentException(
"Cannot instantiate " + type + " : " + name, ex);
}
}
return instances;
}
我们需要看下实例是怎么创建的：
/**
* Convenience method to instantiate a class using the given constructor.
* <p>Note that this method tries to set the constructor accessible if given a
* non-accessible (that is, non-public) constructor, and supports Kotlin classes
* with optional parameters and default values.
* @param ctor the constructor to instantiate
* @param args the constructor arguments to apply (use {@code null} for an unspecified
* parameter if needed for Kotlin classes with optional parameters and default values)
* @return the new instance
* @throws BeanInstantiationException if the bean cannot be instantiated
* @see Constructor#newInstance
*/
public static <T> T instantiateClass(Constructor<T> ctor, Object... args) throws BeanInstantiationException {
Assert.notNull(ctor, "Constructor must not be null");
try {
ReflectionUtils.makeAccessible(ctor);
return (KotlinDetector.isKotlinReflectPresent() && KotlinDetector.isKotlinType(ctor.getDeclaringClass()) ?
KotlinDelegate.instantiateClass(ctor, args) : ctor.newInstance(args));
}
catch (InstantiationException ex) {
throw new BeanInstantiationException(ctor, "Is it an abstract class?", ex);
}
catch (IllegalAccessException ex) {
throw new BeanInstantiationException(ctor, "Is the constructor accessible?", ex);
}
catch (IllegalArgumentException ex) {
throw new BeanInstantiationException(ctor, "Illegal arguments for constructor", ex);
}
catch (InvocationTargetException ex) {
throw new BeanInstantiationException(ctor, "Constructor threw exception", ex.getTargetException());
}
}
可以看到实例化对kotlin类型似乎有特殊处理，但是对于java类型只是简单的用反射创建了实例。
接下来会创建环境：
private ConfigurableEnvironment prepareEnvironment(
SpringApplicationRunListeners listeners,
ApplicationArguments applicationArguments) {
// Create and configure the environment
ConfigurableEnvironment environment = getOrCreateEnvironment();
configureEnvironment(environment, applicationArguments.getSourceArgs());
listeners.environmentPrepared(environment);
bindToSpringApplication(environment);
if (!this.isCustomEnvironment) {
environment = new EnvironmentConverter(getClassLoader())
.convertEnvironmentIfNecessary(environment, deduceEnvironmentClass());
}
ConfigurationPropertySources.attach(environment);
return environment;
}
其中的getOrCreateEnvironment会按需创建一个环境对象。
//根据WEB环境创建不同的环境
private ConfigurableEnvironment getOrCreateEnvironment() {
if (this.environment != null) {
return this.environment;
}
switch (this.webApplicationType) {
case SERVLET:
return new StandardServletEnvironment();
case REACTIVE:
return new StandardReactiveWebEnvironment();
default:
return new StandardEnvironment();
}
}
ClassUtils
一些静态成员
/**
* Map with primitive wrapper type as key and corresponding primitive
* type as value, for example: Integer.class -> int.class.
*/
private static final Map<Class<?>, Class<?>> primitiveWrapperTypeMap = new IdentityHashMap<>(8);
/**
* Map with primitive type as key and corresponding wrapper
* type as value, for example: int.class -> Integer.class.
*/
private static final Map<Class<?>, Class<?>> primitiveTypeToWrapperMap = new IdentityHashMap<>(8);
/**
* Map with primitive type name as key and corresponding primitive
* type as value, for example: "int" -> "int.class".
*/
private static final Map<String, Class<?>> primitiveTypeNameMap = new HashMap<>(32);
/**
* Map with common Java language class name as key and corresponding Class as value.
* Primarily for efficient deserialization of remote invocations.
*/
private static final Map<String, Class<?>> commonClassCache = new HashMap<>(64);
/**
* Common Java language interfaces which are supposed to be ignored
* when searching for 'primary' user-level interfaces.
*/
private static final Set<Class<?>> javaLanguageInterfaces;
这些静态成员的初始化：
static {
//8种包装类型转原生类型
primitiveWrapperTypeMap.put(Boolean.class, boolean.class);
primitiveWrapperTypeMap.put(Byte.class, byte.class);
primitiveWrapperTypeMap.put(Character.class, char.class);
primitiveWrapperTypeMap.put(Double.class, double.class);
primitiveWrapperTypeMap.put(Float.class, float.class);
primitiveWrapperTypeMap.put(Integer.class, int.class);
primitiveWrapperTypeMap.put(Long.class, long.class);
primitiveWrapperTypeMap.put(Short.class, short.class);
// Map entry iteration is less expensive to initialize than forEach with lambdas
for (Map.Entry<Class<?>, Class<?>> entry : primitiveWrapperTypeMap.entrySet()) {
//原生类型转包装类型
primitiveTypeToWrapperMap.put(entry.getValue(), entry.getKey());
//将保证类型作为公共类
registerCommonClasses(entry.getKey());
}
Set<Class<?>> primitiveTypes = new HashSet<>(32);
primitiveTypes.addAll(primitiveWrapperTypeMap.values());
Collections.addAll(primitiveTypes, boolean[].class, byte[].class, char[].class,
double[].class, float[].class, int[].class, long[].class, short[].class);
primitiveTypes.add(void.class);
//初始化原生类型名转原生类型
for (Class<?> primitiveType : primitiveTypes) {
primitiveTypeNameMap.put(primitiveType.getName(), primitiveType);
}
//一些公共类
registerCommonClasses(Boolean[].class, Byte[].class, Character[].class, Double[].class,
Float[].class, Integer[].class, Long[].class, Short[].class);
registerCommonClasses(Number.class, Number[].class, String.class, String[].class,
Class.class, Class[].class, Object.class, Object[].class);
registerCommonClasses(Throwable.class, Exception.class, RuntimeException.class,
Error.class, StackTraceElement.class, StackTraceElement[].class);
registerCommonClasses(Enum.class, Iterable.class, Iterator.class, Enumeration.class,
Collection.class, List.class, Set.class, Map.class, Map.Entry.class, Optional.class);
//java语言的一些特殊接口
Class<?>[] javaLanguageInterfaceArray = {Serializable.class, Externalizable.class,
Closeable.class, AutoCloseable.class, Cloneable.class, Comparable.class};
registerCommonClasses(javaLanguageInterfaceArray);
javaLanguageInterfaces = new HashSet<>(Arrays.asList(javaLanguageInterfaceArray));
}
/**
* Register the given common classes with the ClassUtils cache.
*/
private static void registerCommonClasses(Class<?>... commonClasses) {
for (Class<?> clazz : commonClasses) {
commonClassCache.put(clazz.getName(), clazz);
}
}
下面我们来看一下forName方法，用于找到某个全限定名称对应的类。
/**
* Replacement for {@code Class.forName()} that also returns Class instances
* for primitives (e.g. "int") and array class names (e.g. "String[]").
* Furthermore, it is also capable of resolving inner class names in Java source
* style (e.g. "java.lang.Thread.State" instead of "java.lang.Thread$State").
* @param name the name of the Class
* @param classLoader the class loader to use
* (may be {@code null}, which indicates the default class loader)
* @return a class instance for the supplied name
* @throws ClassNotFoundException if the class was not found
* @throws LinkageError if the class file could not be loaded
* @see Class#forName(String, boolean, ClassLoader)
*/
public static Class<?> forName(String name, @Nullable ClassLoader classLoader)
throws ClassNotFoundException, LinkageError {
Assert.notNull(name, "Name must not be null");
//试试看是不是原生类型
Class<?> clazz = resolvePrimitiveClassName(name);
//先尝试从缓存中拿
if (clazz == null) {
clazz = commonClassCache.get(name);
}
if (clazz != null) {
return clazz;
}
//数组类型的话特殊处理
// "java.lang.String[]" style arrays
if (name.endsWith(ARRAY_SUFFIX)) {
String elementClassName = name.substring(0, name.length() - ARRAY_SUFFIX.length());
//递归找到数组元素类型
Class<?> elementClass = forName(elementClassName, classLoader);
//通过Array.newInstance动态创建数组对象
return Array.newInstance(elementClass, 0).getClass();
}
//java语言规范的数组风格
// "[Ljava.lang.String;" style arrays
if (name.startsWith(NON_PRIMITIVE_ARRAY_PREFIX) && name.endsWith(";")) {
String elementName = name.substring(NON_PRIMITIVE_ARRAY_PREFIX.length(), name.length() - 1);
Class<?> elementClass = forName(elementName, classLoader);
return Array.newInstance(elementClass, 0).getClass();
}
//内部数组，特殊处理
// "[[I" or "[[Ljava.lang.String;" style arrays
if (name.startsWith(INTERNAL_ARRAY_PREFIX)) {
String elementName = name.substring(INTERNAL_ARRAY_PREFIX.length());
Class<?> elementClass = forName(elementName, classLoader);
return Array.newInstance(elementClass, 0).getClass();
}
ClassLoader clToUse = classLoader;
if (clToUse == null) {
clToUse = getDefaultClassLoader();
}
try {
//通过classLoader加载类
return Class.forName(name, false, clToUse);
}
catch (ClassNotFoundException ex) {
//找不到，可能是内部类，比如pack.Out.In，其实际的值应该是pack.Out$In
int lastDotIndex = name.lastIndexOf(PACKAGE_SEPARATOR);
if (lastDotIndex != -1) {
String innerClassName =
name.substring(0, lastDotIndex) + INNER_CLASS_SEPARATOR + name.substring(lastDotIndex + 1);
try {
return Class.forName(innerClassName, false, clToUse);
}
catch (ClassNotFoundException ex2) {
// Swallow - let original exception get through
}
}
//真的找不到
throw ex;
}
}
获取默认的ClassLoader：
/**
* Return the default ClassLoader to use: typically the thread context
* ClassLoader, if available; the ClassLoader that loaded the ClassUtils
* class will be used as fallback.
* <p>Call this method if you intend to use the thread context ClassLoader
* in a scenario where you clearly prefer a non-null ClassLoader reference:
* for example, for class path resource loading (but not necessarily for
* {@code Class.forName}, which accepts a {@code null} ClassLoader
* reference as well).
* @return the default ClassLoader (only {@code null} if even the system
* ClassLoader isn't accessible)
* @see Thread#getContextClassLoader()
* @see ClassLoader#getSystemClassLoader()
*/
@Nullable
public static ClassLoader getDefaultClassLoader() {
ClassLoader cl = null;
try {
//取上下文类加载器
cl = Thread.currentThread().getContextClassLoader();
}
catch (Throwable ex) {
// Cannot access thread context ClassLoader - falling back...
}
if (cl == null) {
// No thread context class loader -> use class loader of this class.
cl = ClassUtils.class.getClassLoader();
if (cl == null) {
// getClassLoader() returning null indicates the bootstrap ClassLoader
try {
cl = ClassLoader.getSystemClassLoader();
}
catch (Throwable ex) {
// Cannot access system ClassLoader - oh well, maybe the caller can live with null...
}
}
}
return cl;
}
isPresent方法用来判断某个类是否出现。
/**
* Determine whether the {@link Class} identified by the supplied name is present
* and can be loaded. Will return {@code false} if either the class or
* one of its dependencies is not present or cannot be loaded.
* @param className the name of the class to check
* @param classLoader the class loader to use
* (may be {@code null} which indicates the default class loader)
* @return whether the specified class is present (including all of its
* superclasses and interfaces)
* @throws IllegalStateException if the corresponding class is resolvable but
* there was a readability mismatch in the inheritance hierarchy of the class
* (typically a missing dependency declaration in a Jigsaw module definition
* for a superclass or interface implemented by the class to be checked here)
*/
public static boolean isPresent(String className, @Nullable ClassLoader classLoader) {
try {
//如果出现就不会抛出异常，否则会抛出ClassNotFound异常
forName(className, classLoader);
return true;
}
catch (IllegalAccessError err) {
throw new IllegalStateException("Readability mismatch in inheritance hierarchy of class [" +
className + "]: " + err.getMessage(), err);
}
catch (Throwable ex) {
// Typically ClassNotFoundException or NoClassDefFoundError...
return false;
}
}
接下来会创建上下文。
/**
* Strategy method used to create the {@link ApplicationContext}. By default this
* method will respect any explicitly set application context or application context
* class before falling back to a suitable default.
* @return the application context (not yet refreshed)
* @see #setApplicationContextClass(Class)
*/
protected ConfigurableApplicationContext createApplicationContext() {
Class<?> contextClass = this.applicationContextClass;
if (contextClass == null) {
try {
//根据类应用型创建上下文
switch (this.webApplicationType) {
case SERVLET:
contextClass = Class.forName(DEFAULT_SERVLET_WEB_CONTEXT_CLASS);
break;
case REACTIVE:
contextClass = Class.forName(DEFAULT_REACTIVE_WEB_CONTEXT_CLASS);
break;
default:
contextClass = Class.forName(DEFAULT_CONTEXT_CLASS);
}
}
catch (ClassNotFoundException ex) {
throw new IllegalStateException(
"Unable create a default ApplicationContext, "
+ "please specify an ApplicationContextClass",
ex);
}
}
return (ConfigurableApplicationContext) BeanUtils.instantiateClass(contextClass);
}
初始化顺序
Spring中利用Order和Priority注解来决定实例的初始化优先级，优先级较大的实例会先被初始化（没有打标记的则认为优先级最低）。
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE, ElementType.METHOD, ElementType.FIELD})
@Documented
public @interface Order {
/**
* The order value.
* <p>Default is {@link Ordered#LOWEST_PRECEDENCE}.
* @see Ordered#getOrder()
*/
int value() default Ordered.LOWEST_PRECEDENCE;
}
/**
* {@code Ordered} is an interface that can be implemented by objects that
* should be <em>orderable</em>, for example in a {@code Collection}.
*
* <p>The actual {@link #getOrder() order} can be interpreted as prioritization,
* with the first object (with the lowest order value) having the highest
* priority.
*
* <p>Note that there is also a <em>priority</em> marker for this interface:
* {@link PriorityOrdered}. Order values expressed by {@code PriorityOrdered}
* objects always apply before same order values expressed by <em>plain</em>
* {@link Ordered} objects.
*
* <p>Consult the Javadoc for {@link OrderComparator} for details on the
* sort semantics for non-ordered objects.
*
* @author Juergen Hoeller
* @author Sam Brannen
* @since 07.04.2003
* @see PriorityOrdered
* @see OrderComparator
* @see org.springframework.core.annotation.Order
* @see org.springframework.core.annotation.AnnotationAwareOrderComparator
*/
public interface Ordered {
/**
* Useful constant for the highest precedence value.
* @see java.lang.Integer#MIN_VALUE
*/
int HIGHEST_PRECEDENCE = Integer.MIN_VALUE;
/**
* Useful constant for the lowest precedence value.
* @see java.lang.Integer#MAX_VALUE
*/
int LOWEST_PRECEDENCE = Integer.MAX_VALUE;
/**
* Get the order value of this object.
* <p>Higher values are interpreted as lower priority. As a consequence,
* the object with the lowest value has the highest priority (somewhat
* analogous to Servlet {@code load-on-startup} values).
* <p>Same order values will result in arbitrary sort positions for the
* affected objects.
* @return the order value
* @see #HIGHEST_PRECEDENCE
* @see #LOWEST_PRECEDENCE
*/
int getOrder();
}
OrderComparator是一个简单的根据Order比较的实现类。
public class OrderComparator implements Comparator<Object> {
/**
* Shared default instance of {@code OrderComparator}.
*/
public static final OrderComparator INSTANCE = new OrderComparator();
/**
* Build an adapted order comparator with the given source provider.
* @param sourceProvider the order source provider to use
* @return the adapted comparator
* @since 4.1
*/
public Comparator<Object> withSourceProvider(OrderSourceProvider sourceProvider) {
return (o1, o2) -> doCompare(o1, o2, sourceProvider);
}
@Override
public int compare(@Nullable Object o1, @Nullable Object o2) {
return doCompare(o1, o2, null);
}
private int doCompare(@Nullable Object o1, @Nullable Object o2, @Nullable OrderSourceProvider sourceProvider) {
//没有实现PriorityOrdered接口，认为是最低优先级的
boolean p1 = (o1 instanceof PriorityOrdered);
boolean p2 = (o2 instanceof PriorityOrdered);
if (p1 && !p2) {
return -1;
}
else if (p2 && !p1) {
return 1;
}
//如果两者都没有实现PriorityOrdered或都实现了这个接口
int i1 = getOrder(o1, sourceProvider);
int i2 = getOrder(o2, sourceProvider);
return Integer.compare(i1, i2);
}
/**
* Determine the order value for the given object.
* <p>The default implementation checks against the given {@link OrderSourceProvider}
* using {@link #findOrder} and falls back to a regular {@link #getOrder(Object)} call.
* @param obj the object to check
* @return the order value, or {@code Ordered.LOWEST_PRECEDENCE} as fallback
*/
private int getOrder(@Nullable Object obj, @Nullable OrderSourceProvider sourceProvider) {
Integer order = null;
if (obj != null && sourceProvider != null) {
Object orderSource = sourceProvider.getOrderSource(obj);
if (orderSource != null) {
if (orderSource.getClass().isArray()) {
Object[] sources = ObjectUtils.toObjectArray(orderSource);
for (Object source : sources) {
order = findOrder(source);
if (order != null) {
break;
}
}
}
else {
order = findOrder(orderSource);
}
}
}
//如果没有提供sourceProvider，就通过下面方法拿到优先级
return (order != null ? order : getOrder(obj));
}
/**
* Determine the order value for the given object.
* <p>The default implementation checks against the {@link Ordered} interface
* through delegating to {@link #findOrder}. Can be overridden in subclasses.
* @param obj the object to check
* @return the order value, or {@code Ordered.LOWEST_PRECEDENCE} as fallback
*/
protected int getOrder(@Nullable Object obj) {
if (obj != null) {
Integer order = findOrder(obj);
if (order != null) {
return order;
}
}
//默认给最低优先级
return Ordered.LOWEST_PRECEDENCE;
}
/**
* Find an order value indicated by the given object.
* <p>The default implementation checks against the {@link Ordered} interface.
* Can be overridden in subclasses.
* @param obj the object to check
* @return the order value, or {@code null} if none found
*/
@Nullable
//直接拿到order
protected Integer findOrder(Object obj) {
return (obj instanceof Ordered ? ((Ordered) obj).getOrder() : null);
}
/**
* Determine a priority value for the given object, if any.
* <p>The default implementation always returns {@code null}.
* Subclasses may override this to give specific kinds of values a
* 'priority' characteristic, in addition to their 'order' semantics.
* A priority indicates that it may be used for selecting one object over
* another, in addition to serving for ordering purposes in a list/array.
* @param obj the object to check
* @return the priority value, or {@code null} if none
* @since 4.1
*/
@Nullable
public Integer getPriority(Object obj) {
return null;
}
}
下面看一个子类AnnotationAwareOrderComparator，它会从注解中取得优先级，而不需要类一定实现Ordered接口。
/**
* {@code AnnotationAwareOrderComparator} is an extension of
* {@link OrderComparator} that supports Spring's
* {@link org.springframework.core.Ordered} interface as well as the
* {@link Order @Order} and {@link javax.annotation.Priority @Priority}
* annotations, with an order value provided by an {@code Ordered}
* instance overriding a statically defined annotation value (if any).
*
* <p>Consult the Javadoc for {@link OrderComparator} for details on the
* sort semantics for non-ordered objects.
*
* @author Juergen Hoeller
* @author Oliver Gierke
* @author Stephane Nicoll
* @since 2.0.1
* @see org.springframework.core.Ordered
* @see org.springframework.core.annotation.Order
* @see javax.annotation.Priority
*/
public class AnnotationAwareOrderComparator extends OrderComparator {
/**
* This implementation checks for {@link Order @Order} or
* {@link javax.annotation.Priority @Priority} on various kinds of
* elements, in addition to the {@link org.springframework.core.Ordered}
* check in the superclass.
*/
@Override
@Nullable
protected Integer findOrder(Object obj) {
// Check for regular Ordered interface
Integer order = super.findOrder(obj);
if (order != null) {
return order;
}
// Check for @Order and @Priority on various kinds of elements
if (obj instanceof Class) {
return OrderUtils.getOrder((Class<?>) obj);
}
else if (obj instanceof Method) {
Order ann = AnnotationUtils.findAnnotation((Method) obj, Order.class);
if (ann != null) {
return ann.value();
}
}
else if (obj instanceof AnnotatedElement) {
Order ann = AnnotationUtils.getAnnotation((AnnotatedElement) obj, Order.class);
if (ann != null) {
return ann.value();
}
}
else {
order = OrderUtils.getOrder(obj.getClass());
if (order == null && obj instanceof DecoratingProxy) {
order = OrderUtils.getOrder(((DecoratingProxy) obj).getDecoratedClass());
}
}
return order;
}
}
转换器
转换器接口：
/**
* A service interface for type conversion. This is the entry point into the convert system.
* Call {@link #convert(Object, Class)} to perform a thread-safe type conversion using this system.
*
* @author Keith Donald
* @author Phillip Webb
* @since 3.0
*/
public interface ConversionService {
/**
* Return {@code true} if objects of {@code sourceType} can be converted to the {@code targetType}.
* <p>If this method returns {@code true}, it means {@link #convert(Object, Class)} is capable
* of converting an instance of {@code sourceType} to {@code targetType}.
* <p>Special note on collections, arrays, and maps types:
* For conversion between collection, array, and map types, this method will return {@code true}
* even though a convert invocation may still generate a {@link ConversionException} if the
* underlying elements are not convertible. Callers are expected to handle this exceptional case
* when working with collections and maps.
* @param sourceType the source type to convert from (may be {@code null} if source is {@code null})
* @param targetType the target type to convert to (required)
* @return {@code true} if a conversion can be performed, {@code false} if not
* @throws IllegalArgumentException if {@code targetType} is {@code null}
*/
boolean canConvert(@Nullable Class<?> sourceType, Class<?> targetType);
/**
* Return {@code true} if objects of {@code sourceType} can be converted to the {@code targetType}.
* The TypeDescriptors provide additional context about the source and target locations
* where conversion would occur, often object fields or property locations.
* <p>If this method returns {@code true}, it means {@link #convert(Object, TypeDescriptor, TypeDescriptor)}
* is capable of converting an instance of {@code sourceType} to {@code targetType}.
* <p>Special note on collections, arrays, and maps types:
* For conversion between collection, array, and map types, this method will return {@code true}
* even though a convert invocation may still generate a {@link ConversionException} if the
* underlying elements are not convertible. Callers are expected to handle this exceptional case
* when working with collections and maps.
* @param sourceType context about the source type to convert from
* (may be {@code null} if source is {@code null})
* @param targetType context about the target type to convert to (required)
* @return {@code true} if a conversion can be performed between the source and target types,
* {@code false} if not
* @throws IllegalArgumentException if {@code targetType} is {@code null}
*/
boolean canConvert(@Nullable TypeDescriptor sourceType, TypeDescriptor targetType);
/**
* Convert the given {@code source} to the specified {@code targetType}.
* @param source the source object to convert (may be {@code null})
* @param targetType the target type to convert to (required)
* @return the converted object, an instance of targetType
* @throws ConversionException if a conversion exception occurred
* @throws IllegalArgumentException if targetType is {@code null}
*/
@Nullable
<T> T convert(@Nullable Object source, Class<T> targetType);
/**
* Convert the given {@code source} to the specified {@code targetType}.
* The TypeDescriptors provide additional context about the source and target locations
* where conversion will occur, often object fields or property locations.
* @param source the source object to convert (may be {@code null})
* @param sourceType context about the source type to convert from
* (may be {@code null} if source is {@code null})
* @param targetType context about the target type to convert to (required)
* @return the converted object, an instance of {@link TypeDescriptor#getObjectType() targetType}
* @throws ConversionException if a conversion exception occurred
* @throws IllegalArgumentException if targetType is {@code null},
* or {@code sourceType} is {@code null} but source is not {@code null}
*/
@Nullable
Object convert(@Nullable Object source, @Nullable TypeDescriptor sourceType, TypeDescriptor targetType);
}
转换器注册中心接口：
/**
* For registering converters with a type conversion system.
*
* @author Keith Donald
* @author Juergen Hoeller
* @since 3.0
*/
public interface ConverterRegistry {
/**
* Add a plain converter to this registry.
* The convertible source/target type pair is derived from the Converter's parameterized types.
* @throws IllegalArgumentException if the parameterized types could not be resolved
*/
void addConverter(Converter<?, ?> converter);
/**
* Add a plain converter to this registry.
* The convertible source/target type pair is specified explicitly.
* <p>Allows for a Converter to be reused for multiple distinct pairs without
* having to create a Converter class for each pair.
* @since 3.1
*/
<S, T> void addConverter(Class<S> sourceType, Class<T> targetType, Converter<? super S, ? extends T> converter);
/**
* Add a generic converter to this registry.
*/
void addConverter(GenericConverter converter);
/**
* Add a ranged converter factory to this registry.
* The convertible source/target type pair is derived from the ConverterFactory's parameterized types.
* @throws IllegalArgumentException if the parameterized types could not be resolved
*/
void addConverterFactory(ConverterFactory<?, ?> factory);
/**
* Remove any converters from {@code sourceType} to {@code targetType}.
* @param sourceType the source type
* @param targetType the target type
*/
void removeConvertible(Class<?> sourceType, Class<?> targetType);
}
将上面两个接口合并后可以得到：
/**
* Configuration interface to be implemented by most if not all {@link ConversionService}
* types. Consolidates the read-only operations exposed by {@link ConversionService} and
* the mutating operations of {@link ConverterRegistry} to allow for convenient ad-hoc
* addition and removal of {@link org.springframework.core.convert.converter.Converter
* Converters} through. The latter is particularly useful when working against a
* {@link org.springframework.core.env.ConfigurableEnvironment ConfigurableEnvironment}
* instance in application context bootstrapping code.
*
* @author Chris Beams
* @since 3.1
* @see org.springframework.core.env.ConfigurablePropertyResolver#getConversionService()
* @see org.springframework.core.env.ConfigurableEnvironment
* @see org.springframework.context.ConfigurableApplicationContext#getEnvironment()
*/
public interface ConfigurableConversionService extends ConversionService, ConverterRegistry {
}
GenericConverter是一种更加复杂的转换器接口。
/**
* Generic converter interface for converting between two or more types.
*
* <p>This is the most flexible of the Converter SPI interfaces, but also the most complex.
* It is flexible in that a GenericConverter may support converting between multiple source/target
* type pairs (see {@link #getConvertibleTypes()}. In addition, GenericConverter implementations
* have access to source/target {@link TypeDescriptor field context} during the type conversion
* process. This allows for resolving source and target field metadata such as annotations and
* generics information, which can be used to influence the conversion logic.
*
* <p>This interface should generally not be used when the simpler {@link Converter} or
* {@link ConverterFactory} interface is sufficient.
*
* <p>Implementations may additionally implement {@link ConditionalConverter}.
*
* @author Keith Donald
* @author Juergen Hoeller
* @since 3.0
* @see TypeDescriptor
* @see Converter
* @see ConverterFactory
* @see ConditionalConverter
*/
public interface GenericConverter {
/**
* Return the source and target types that this converter can convert between.
* <p>Each entry is a convertible source-to-target type pair.
* <p>For {@link ConditionalConverter conditional converters} this method may return
* {@code null} to indicate all source-to-target pairs should be considered.
*/
@Nullable
Set<ConvertiblePair> getConvertibleTypes();
/**
* Convert the source object to the targetType described by the {@code TypeDescriptor}.
* @param source the source object to convert (may be {@code null})
* @param sourceType the type descriptor of the field we are converting from
* @param targetType the type descriptor of the field we are converting to
* @return the converted object
*/
@Nullable
Object convert(@Nullable Object source, TypeDescriptor sourceType, TypeDescriptor targetType);
/**
* Holder for a source-to-target class pair.
*/
final class ConvertiblePair {
private final Class<?> sourceType;
private final Class<?> targetType;
/**
* Create a new source-to-target pair.
* @param sourceType the source type
* @param targetType the target type
*/
public ConvertiblePair(Class<?> sourceType, Class<?> targetType) {
Assert.notNull(sourceType, "Source type must not be null");
Assert.notNull(targetType, "Target type must not be null");
this.sourceType = sourceType;
this.targetType = targetType;
}
public Class<?> getSourceType() {
return this.sourceType;
}
public Class<?> getTargetType() {
return this.targetType;
}
@Override
public boolean equals(@Nullable Object other) {
if (this == other) {
return true;
}
if (other == null || other.getClass() != ConvertiblePair.class) {
return false;
}
ConvertiblePair otherPair = (ConvertiblePair) other;
return (this.sourceType == otherPair.sourceType && this.targetType == otherPair.targetType);
}
@Override
public int hashCode() {
return (this.sourceType.hashCode() * 31 + this.targetType.hashCode());
}
@Override
public String toString() {
return (this.sourceType.getName() + " -> " + this.targetType.getName());
}
}
}
来看一个ConfigurableConversionService的基础实现类：
ConcurrentReferenceHashMap
ConcurrentReferenceHashMap是Spring中实现的一个支持并发的哈希表，其与ConcurrentHashMap的区别在于前者还支持设置key和Value的引用类型（可以是弱引用或软引用）。
refresh
Spring的启动中会调用refreshContext方法来刷新容器。
/**
* Run the Spring application, creating and refreshing a new
* {@link ApplicationContext}.
* @param args the application arguments (usually passed from a Java main method)
* @return a running {@link ApplicationContext}
*/
public ConfigurableApplicationContext run(String... args) {
StopWatch stopWatch = new StopWatch();
stopWatch.start();
ConfigurableApplicationContext context = null;
Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
configureHeadlessProperty();
SpringApplicationRunListeners listeners = getRunListeners(args);
listeners.starting();
try {
ApplicationArguments applicationArguments = new DefaultApplicationArguments(
args);
ConfigurableEnvironment environment = prepareEnvironment(listeners,
applicationArguments);
configureIgnoreBeanInfo(environment);
Banner printedBanner = printBanner(environment);
context = createApplicationContext();
exceptionReporters = getSpringFactoriesInstances(
SpringBootExceptionReporter.class,
new Class[] { ConfigurableApplicationContext.class }, context);
prepareContext(context, environment, listeners, applicationArguments,
printedBanner);
//刷新容器
refreshContext(context);
afterRefresh(context, applicationArguments);
stopWatch.stop();
if (this.logStartupInfo) {
new StartupInfoLogger(this.mainApplicationClass)
.logStarted(getApplicationLog(), stopWatch);
}
listeners.started(context);
callRunners(context, applicationArguments);
}
catch (Throwable ex) {
handleRunFailure(context, ex, exceptionReporters, listeners);
throw new IllegalStateException(ex);
}
try {
listeners.running(context);
}
catch (Throwable ex) {
handleRunFailure(context, ex, exceptionReporters, null);
throw new IllegalStateException(ex);
}
return context;
}
看一下具体的代码。第一步就是刷新操作。刷新完后向JVM注册Shutdown构子。
private void refreshContext(ConfigurableApplicationContext context) {
refresh(context);
if (this.registerShutdownHook) {
try {
context.registerShutdownHook();
}
catch (AccessControlException ex) {
// Not allowed in some environments.
}
}
}
具体的刷新。
/**
* Refresh the underlying {@link ApplicationContext}.
* @param applicationContext the application context to refresh
*/
protected void refresh(ApplicationContext applicationContext) {
Assert.isInstanceOf(AbstractApplicationContext.class, applicationContext);
((AbstractApplicationContext) applicationContext).refresh();
}
实际上调用的是上下文的刷新操作。
可以发现AbstractApplicationContext有三个实现类，我们随意选取一个ServletWebServerApplicationContext来看看具体做了什么。
/** Synchronization monitor for the "refresh" and "destroy". */
private final Object startupShutdownMonitor = new Object();
@Override
public void refresh() throws BeansException, IllegalStateException {
//startupShutdownMonitor对监视器加个锁
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) {
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();
}
}
}