Spring 事务源码深度剖析
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源码环境
IDEA：2022.2.2
Spring 版本：5.2.x
备注：建议先熟悉下AOP原理，可参考文章：【Spring 源码之 AOP 流程分析】。
文末有彩蛋！
Sping 框架中的事务管理是其核心特性之一，是基于AOP实现的，开发者在方法执行前后定义一系列操作，以确保数据完整性和一致性。
Srping 提供了声明式事务和编程式事务两种管理方式，本文通过声明式事务（注解）方式深入剖析Spring 事务源码，了解其核心机制，帮助更好的理解和应用Spring 事务。
示例（注解方式）
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TxConfig：配置类
// 配置类 @Configuration @PropertySource("classpath:db.properties") @EnableTransactionManagement @ComponentScan(basePackages = "com.wl.anination.tx") public class TxConfig { @Value("¨E123Ejdbc.driverClassName¨E125E")privateStringdriverClassname@Value("{jdbc.driverClassName}") private String driverClassname; @Value("<span class="katex-html" aria-hidden="true" style="font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"><span class="strut" style="height:1em;vertical-align:-0.25em;" style="font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">¨<span class="mord mathit" style="margin-right:0.05764em;" style="font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">E123<span class="mord mathit" style="margin-right:0.05764em;" style="font-size: inherit;color: inherit;line-height: 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MyService：业务方法
// 调用dao插入一条记录 @Component public class MyService { @Autowired MyDao myDao; @Transactional(rollbackFor = Exception.class) public void insert(String name){ myDao.insert(name); int a = 0; int b = 1 / a; } } -
MyDao：数据库交互
// 插入一条记录 @Component public class MyDao { @Autowired JdbcTemplate jdbcTemplate; public void insert(String name){ jdbcTemplate.update("insert into test (name) values (?)",name); } }
启用事务管理主要的操作？
-
@EnableTransactionManagement
启用事务管理的注解，扫描带有@Transaction 注解的方法，并在这些方法织入事务管理逻辑。
-
PlatformTransactionManager
事务管理核心接口，开启事务、提交事务和回滚事务。
-
@Transactional
可用在接口、类、类方法。
作用方法：方法配置事务属性
作用类：表示该类的public方法都配置事务属性
作用接口：不推荐，动态代理下此注解会失效
下面我们将从源码出发，分析事务是如何实现的。
源码分析：需要先了解AOP源码
@EnableTransactionManagement
此注解会通过@Import 导入TransactionManagementConfigurationSelector类
public class TransactionManagementConfigurationSelector extends AdviceModeImportSelector<EnableTransactionManagement> {
@Override
protected String[] selectImports(AdviceMode adviceMode) {
switch (adviceMode) {
case PROXY:
return new String[] {AutoProxyRegistrar.class.getName(),
ProxyTransactionManagementConfiguration.class.getName()};
case ASPECTJ:
return new String[] {determineTransactionAspectClass()};
default:
return null;
}
}
private String determineTransactionAspectClass() {
return (ClassUtils.isPresent("javax.transaction.Transactional", getClass().getClassLoader()) ?
TransactionManagementConfigUtils.JTA_TRANSACTION_ASPECT_CONFIGURATION_CLASS_NAME :
TransactionManagementConfigUtils.TRANSACTION_ASPECT_CONFIGURATION_CLASS_NAME);
}
}
adviceMode默认proxy，会容器职工添加AutoProxyRegistrar 和 ProxyTransactionManagementConfiguration，解析其会相应添加其他类
AutoProxyRegistrar
-
InfrashtructureAdvisorProxyCreator
AOP 通知器检测实例方法是否有事务注解
ProxyTransactionManagementConfiguration
-
internalTransactionAdvisor:BeanFactoryTransactionAttributeSourceAdvisor，事务增强器
实现类BeanFactoryTransactionAttributeSourceAdvisor，事务增强器，注入了transactionAttributeSource，TransactionInterceptor
-
transactionAttributeSource:AnnotationTransactionAttributeSource
实现类AnnotationTransactionAttributeSource，事务解析器，解析@Transation配置的属性
-
transactionInterceptor:TransactionInterceptor
事务拦截器，依赖注入了TransactionAttributeSource，实现MethodInterceptor的invoke。
创建对象时，同AOP ，myService ， 在之后后置处理器时，找到增强器，canApply先判断类是否有注解
SpringTransactionAnnotationParser.isCandidateClass()方法判断类是否有Transactional注解
public boolean isCandidateClass(Class<?> targetClass) {
return AnnotationUtils.isCandidateClass(targetClass, Transactional.class);
}
再循环遍历方法是否有注解属性，注解属性解析结果不为空就表示有注解，及需要被代理，这里先获取类注解属性信息，再获取方法的。
myService生成代理类后调用insert，其实直接调用（同AOP逻辑）DynamicAdvisedInterceptor，事务没有ExposeInvocationInterceptor，直接调用TransactionInterceptor.invoke()方法，调用父类invokeWithinTransaction方法
protected Object invokeWithinTransaction(Method method, @Nullable Class<?> targetClass,
final InvocationCallback invocation) throws Throwable {
// 获取事务源对象
// If the transaction attribute is null, the method is non-transactional.
TransactionAttributeSource tas = getTransactionAttributeSource();
// 当前方法事务属性
final TransactionAttribute txAttr = (tas != null ? tas.getTransactionAttribute(method, targetClass) : null);
// 获取事务管理器对象
final TransactionManager tm = determineTransactionManager(txAttr);
if (this.reactiveAdapterRegistry != null && tm instanceof ReactiveTransactionManager) {
ReactiveTransactionSupport txSupport = this.transactionSupportCache.computeIfAbsent(method, key -> {
if (KotlinDetector.isKotlinType(method.getDeclaringClass()) && KotlinDelegate.isSuspend(method)) {
throw new TransactionUsageException(
"Unsupported annotated transaction on suspending function detected: " + method +
". Use TransactionalOperator.transactional extensions instead.");
}
ReactiveAdapter adapter = this.reactiveAdapterRegistry.getAdapter(method.getReturnType());
if (adapter == null) {
throw new IllegalStateException("Cannot apply reactive transaction to non-reactive return type: " +
method.getReturnType());
}
return new ReactiveTransactionSupport(adapter);
});
return txSupport.invokeWithinTransaction(
method, targetClass, invocation, txAttr, (ReactiveTransactionManager) tm);
}
PlatformTransactionManager ptm = asPlatformTransactionManager(tm);
// 连接点标识 类+方法
final String joinpointIdentification = methodIdentification(method, targetClass, txAttr);
// 声明式事务
if (txAttr == null || !(ptm instanceof CallbackPreferringPlatformTransactionManager)) {
// Standard transaction demarcation with getTransaction and commit/rollback calls.
// 创建TransactionInfo
TransactionInfo txInfo = createTransactionIfNecessary(ptm, txAttr, joinpointIdentification);
Object retVal;
try {
// This is an around advice: Invoke the next interceptor in the chain.
// This will normally result in a target object being invoked.
// 执行增强的方法
retVal = invocation.proceedWithInvocation();
}
catch (Throwable ex) {
// target invocation exception
// 异常回滚
completeTransactionAfterThrowing(txInfo, ex);
throw ex;
}
finally {
// 清除事务信息，恢复线程私有的旧事务
cleanupTransactionInfo(txInfo);
}
if (retVal != null && vavrPresent && VavrDelegate.isVavrTry(retVal)) {
// Set rollback-only in case of Vavr failure matching our rollback rules...
TransactionStatus status = txInfo.getTransactionStatus();
if (status != null && txAttr != null) {
retVal = VavrDelegate.evaluateTryFailure(retVal, txAttr, status);
}
}
// 事务提交，连接释放、恢复、挂起事务相关操作
commitTransactionAfterReturning(txInfo);
return retVal;
}
else {
// 编程式事务处理
Object result;
final ThrowableHolder throwableHolder = new ThrowableHolder();
// It's a CallbackPreferringPlatformTransactionManager: pass a TransactionCallback in.
try {
result = ((CallbackPreferringPlatformTransactionManager) ptm).execute(txAttr, status -> {
TransactionInfo txInfo = prepareTransactionInfo(ptm, txAttr, joinpointIdentification, status);
try {
Object retVal = invocation.proceedWithInvocation();
if (retVal != null && vavrPresent && VavrDelegate.isVavrTry(retVal)) {
// Set rollback-only in case of Vavr failure matching our rollback rules...
retVal = VavrDelegate.evaluateTryFailure(retVal, txAttr, status);
}
return retVal;
}
catch (Throwable ex) {
if (txAttr.rollbackOn(ex)) {
// A RuntimeException: will lead to a rollback.
if (ex instanceof RuntimeException) {
throw (RuntimeException) ex;
}
else {
throw new ThrowableHolderException(ex);
}
}
else {
// A normal return value: will lead to a commit.
throwableHolder.throwable = ex;
return null;
}
}
finally {
cleanupTransactionInfo(txInfo);
}
});
}
catch (ThrowableHolderException ex) {
throw ex.getCause();
}
catch (TransactionSystemException ex2) {
if (throwableHolder.throwable != null) {
logger.error("Application exception overridden by commit exception", throwableHolder.throwable);
ex2.initApplicationException(throwableHolder.throwable);
}
throw ex2;
}
catch (Throwable ex2) {
if (throwableHolder.throwable != null) {
logger.error("Application exception overridden by commit exception", throwableHolder.throwable);
}
throw ex2;
}
// Check result state: It might indicate a Throwable to rethrow.
if (throwableHolder.throwable != null) {
throw throwableHolder.throwable;
}
return result;
}
}
执行逻辑比较清晰，创建事务、执行源方法，异常回滚，正常就提交
创建事务createTransactionIfNecessary
这块就涉及到了Spring 事务重要特性：Spring 事务传播特性
此方法直接调tm.getTransaction(txAttr)，
public final TransactionStatus getTransaction(@Nullable TransactionDefinition definition)
throws TransactionException {
// 如果没有事务定义信息则使用默认的事务管理器定义信息
// Use defaults if no transaction definition given.
TransactionDefinition def = (definition != null ? definition : TransactionDefinition.withDefaults());
// 获取事务
Object transaction = doGetTransaction();
boolean debugEnabled = logger.isDebugEnabled();
// 当前线程是否存在事务，判断依据为当前线程记录的连接不为空且连接中的transactionActive属性不为空
if (isExistingTransaction(transaction)) {
// Existing transaction found -> check propagation behavior to find out how to behave.
// 当前线程已经存在事务
return handleExistingTransaction(def, transaction, debugEnabled);
}
// 事务超时设置验证
// Check definition settings for new transaction.
if (def.getTimeout() < TransactionDefinition.TIMEOUT_DEFAULT) {
throw new InvalidTimeoutException("Invalid transaction timeout", def.getTimeout());
}
// 如果当前线程不存在事务，但是Propagation却被声明为PROPAGATION_MANDATORY抛出异常
// No existing transaction found -> check propagation behavior to find out how to proceed.
if (def.getPropagationBehavior() == TransactionDefinition.PROPAGATION_MANDATORY) {
throw new IllegalTransactionStateException(
"No existing transaction found for transaction marked with propagation 'mandatory'");
}
// PROPAGATION_REQUIRED，PROPAGATION_REQUIRES_NEW，PROPAGATION_NESTED都需要新建事务
else if (def.getPropagationBehavior() == TransactionDefinition.PROPAGATION_REQUIRED ||
def.getPropagationBehavior() == TransactionDefinition.PROPAGATION_REQUIRES_NEW ||
def.getPropagationBehavior() == TransactionDefinition.PROPAGATION_NESTED) {
//没有当前事务的话，REQUIRED，REQUIRES_NEW，NESTED挂起的是空事务，然后创建一个新事务
SuspendedResourcesHolder suspendedResources = suspend(null);
if (debugEnabled) {
logger.debug("Creating new transaction with name [" + def.getName() + "]: " + def);
}
try {
// 开启事务
return startTransaction(def, transaction, debugEnabled, suspendedResources);
}
catch (RuntimeException | Error ex) {
// 恢复挂起的事务
resume(null, suspendedResources);
throw ex;
}
}
else {
// 创建一个空的事务
// Create "empty" transaction: no actual transaction, but potentially synchronization.
if (def.getIsolationLevel() != TransactionDefinition.ISOLATION_DEFAULT && logger.isWarnEnabled()) {
logger.warn("Custom isolation level specified but no actual transaction initiated; " +
"isolation level will effectively be ignored: " + def);
}
boolean newSynchronization = (getTransactionSynchronization() == SYNCHRONIZATION_ALWAYS);
return prepareTransactionStatus(def, null, true, newSynchronization, debugEnabled, null);
}
}
startTransaction：开启事务
private TransactionStatus startTransaction(TransactionDefinition definition, Object transaction,
boolean debugEnabled, @Nullable SuspendedResourcesHolder suspendedResources) {
boolean newSynchronization = (getTransactionSynchronization() != SYNCHRONIZATION_NEVER);
// 创建新的事务
DefaultTransactionStatus status = newTransactionStatus(
definition, transaction, true, newSynchronization, debugEnabled, suspendedResources);
// 开启事务和连接
doBegin(transaction, definition);
prepareSynchronization(status, definition);
return status;
}
doBegin：开启事务和连接
protected void doBegin(Object transaction, TransactionDefinition definition) {
DataSourceTransactionObject txObject = (DataSourceTransactionObject) transaction;
Connection con = null;
try {
if (!txObject.hasConnectionHolder() ||
txObject.getConnectionHolder().isSynchronizedWithTransaction()) {
// 根据数据源获取数据库连接对象
Connection newCon = obtainDataSource().getConnection();
if (logger.isDebugEnabled()) {
logger.debug("Acquired Connection [" + newCon + "] for JDBC transaction");
}
// 连接包装成ConnectionHolder
txObject.setConnectionHolder(new ConnectionHolder(newCon), true);
}
// 标记是同步事务
txObject.getConnectionHolder().setSynchronizedWithTransaction(true);
con = txObject.getConnectionHolder().getConnection();
// 为当前事务设置隔离级别
Integer previousIsolationLevel = DataSourceUtils.prepareConnectionForTransaction(con, definition);
// 设置先前隔离级别
txObject.setPreviousIsolationLevel(previousIsolationLevel);
txObject.setReadOnly(definition.isReadOnly());
// Switch to manual commit if necessary. This is very expensive in some JDBC drivers,
// so we don't want to do it unnecessarily (for example if we've explicitly
// configured the connection pool to set it already).
if (con.getAutoCommit()) {
// 需要恢复自动提交
txObject.setMustRestoreAutoCommit(true);
if (logger.isDebugEnabled()) {
logger.debug("Switching JDBC Connection [" + con + "] to manual commit");
}
// 关闭自动提交
con.setAutoCommit(false);
}
prepareTransactionalConnection(con, definition);
txObject.getConnectionHolder().setTransactionActive(true);
int timeout = determineTimeout(definition);
if (timeout != TransactionDefinition.TIMEOUT_DEFAULT) {
txObject.getConnectionHolder().setTimeoutInSeconds(timeout);
}
// Bind the connection holder to the thread.
// 把数据源作为key，数据库连接为value设置到线程中
if (txObject.isNewConnectionHolder()) {
TransactionSynchronizationManager.bindResource(obtainDataSource(), txObject.getConnectionHolder());
}
}
catch (Throwable ex) {
// 释放连接
if (txObject.isNewConnectionHolder()) {
DataSourceUtils.releaseConnection(con, obtainDataSource());
txObject.setConnectionHolder(null, false);
}
throw new CannotCreateTransactionException("Could not open JDBC Connection for transaction", ex);
}
}
异常回滚
主要是规则处理，判断是否可以回滚,回滚调用processRollback();
/**
* unexpected这个一般是false，除非是设置rollback-only=true，才是true，表示是全局的回滚标记。首先会进行回滚前回调，
* 然后判断是否设置了保存点，比如NESTED会设置，要先回滚到保存点。如果状态是新的事务，那就进行回滚，如果不是新的，就设置一个回滚标记，
* 内部是设置连接持有器回滚标记。然后回滚完成回调，根据事务状态信息，完成后数据清除,和线程的私有资源解绑，
* 重置连接自动提交，隔离级别，是否只读，释放连接，恢复挂起事务等
*
* Process an actual rollback.
* The completed flag has already been checked.
* @param status object representing the transaction
* @throws TransactionException in case of rollback failure
*/
private void processRollback(DefaultTransactionStatus status, boolean unexpected) {
try {
// 意外的回滚
boolean unexpectedRollback = unexpected;
try {
// 回滚完成前回调
triggerBeforeCompletion(status);
// 有保存点回滚到保存点
if (status.hasSavepoint()) {
if (status.isDebug()) {
logger.debug("Rolling back transaction to savepoint");
}
status.rollbackToHeldSavepoint();
}
// 当前状态是一个新事务
else if (status.isNewTransaction()) {
if (status.isDebug()) {
logger.debug("Initiating transaction rollback");
}
// 进行回滚
doRollback(status);
}
else {
// Participating in larger transaction
if (status.hasTransaction()) {
if (status.isLocalRollbackOnly() || isGlobalRollbackOnParticipationFailure()) {
if (status.isDebug()) {
logger.debug("Participating transaction failed - marking existing transaction as rollback-only");
}
//设置连接要回滚标记，也就是全局回滚
doSetRollbackOnly(status);
}
else {
if (status.isDebug()) {
logger.debug("Participating transaction failed - letting transaction originator decide on rollback");
}
}
}
else {
logger.debug("Should roll back transaction but cannot - no transaction available");
}
// Unexpected rollback only matters here if we're asked to fail early
if (!isFailEarlyOnGlobalRollbackOnly()) {
unexpectedRollback = false;
}
}
}
catch (RuntimeException | Error ex) {
triggerAfterCompletion(status, TransactionSynchronization.STATUS_UNKNOWN);
throw ex;
}
// 回滚完成后回调
triggerAfterCompletion(status, TransactionSynchronization.STATUS_ROLLED_BACK);
// Raise UnexpectedRollbackException if we had a global rollback-only marker
if (unexpectedRollback) {
throw new UnexpectedRollbackException(
"Transaction rolled back because it has been marked as rollback-only");
}
}
finally {
// 根据事务状态信息，完成后数据清除，和线程的私有资源解绑，重置连接自动提交，隔离级别，是否只读，释放连接，恢复挂起事务等
cleanupAfterCompletion(status);
}
}
正常提交
提交事务，就算没有异常，但是提交的时候也可能会回滚，因为有内层事务可能会标记回滚。所以这里先判断是否状态是否需要本地回滚，
也就是设置回滚标记为全局回滚，不会进行回滚，再判断是否需要全局回滚，就是真的执行回滚。但是这里如果是发现有全局回滚，还要进行提交，就会报异常
public final void commit(TransactionStatus status) throws TransactionException {
if (status.isCompleted()) {
throw new IllegalTransactionStateException(
"Transaction is already completed - do not call commit or rollback more than once per transaction");
}
DefaultTransactionStatus defStatus = (DefaultTransactionStatus) status;
// 如果在事务链中已经被标记回滚，那么不会尝试提交事务，直接回滚
if (defStatus.isLocalRollbackOnly()) {
if (defStatus.isDebug()) {
logger.debug("Transactional code has requested rollback");
}
// 不可预期的回滚
processRollback(defStatus, false);
return;
}
// 设置了全局回滚
if (!shouldCommitOnGlobalRollbackOnly() && defStatus.isGlobalRollbackOnly()) {
if (defStatus.isDebug()) {
logger.debug("Global transaction is marked as rollback-only but transactional code requested commit");
}
// 可预期的回滚，可能会报异常
processRollback(defStatus, true);
return;
}
// 处理事务提交
processCommit(defStatus);
}
处理提交，先处理保存点，然后处理新事务，如果不是新事务不会真正提交，要等外层是新事务的才提交，
最后根据条件执行数据清除,线程的私有资源解绑，重置连接自动提交，隔离级别，是否只读，释放连接，恢复挂起事务等
private void processCommit(DefaultTransactionStatus status) throws TransactionException {
try {
boolean beforeCompletionInvoked = false;
try {
boolean unexpectedRollback = false;
// 空方法
prepareForCommit(status);
// 添加的TransactionSynchronization中的对应方法的调用
triggerBeforeCommit(status);
// 提交完成前回调
triggerBeforeCompletion(status);
beforeCompletionInvoked = true;
// 有保存点
if (status.hasSavepoint()) {
if (status.isDebug()) {
logger.debug("Releasing transaction savepoint");
}
//是否有全局回滚标记
unexpectedRollback = status.isGlobalRollbackOnly();
// 如果存在保存点则清除保存点信息
status.releaseHeldSavepoint();
}
//当前状态是新事务
else if (status.isNewTransaction()) {
if (status.isDebug()) {
logger.debug("Initiating transaction commit");
}
unexpectedRollback = status.isGlobalRollbackOnly();
// 如果是独立的事务则直接提交
doCommit(status);
}
else if (isFailEarlyOnGlobalRollbackOnly()) {
unexpectedRollback = status.isGlobalRollbackOnly();
}
// Throw UnexpectedRollbackException if we have a global rollback-only
// marker but still didn't get a corresponding exception from commit.
// 有全局回滚标记就报异常
if (unexpectedRollback) {
throw new UnexpectedRollbackException(
"Transaction silently rolled back because it has been marked as rollback-only");
}
}
catch (UnexpectedRollbackException ex) {
// can only be caused by doCommit
triggerAfterCompletion(status, TransactionSynchronization.STATUS_ROLLED_BACK);
throw ex;
}
catch (TransactionException ex) {
// can only be caused by doCommit
if (isRollbackOnCommitFailure()) {
doRollbackOnCommitException(status, ex);
}
else {
triggerAfterCompletion(status, TransactionSynchronization.STATUS_UNKNOWN);
}
throw ex;
}
catch (RuntimeException | Error ex) {
if (!beforeCompletionInvoked) {
triggerBeforeCompletion(status);
}
// 提交过程中出现异常则回滚
doRollbackOnCommitException(status, ex);
throw ex;
}
// Trigger afterCommit callbacks, with an exception thrown there
// propagated to callers but the transaction still considered as committed.
try {
// 提交后回调
triggerAfterCommit(status);
}
finally {
// 提交后清除线程私有同步状态
triggerAfterCompletion(status, TransactionSynchronization.STATUS_COMMITTED);
}
}
finally {
//根据条件，完成后数据清除,和线程的私有资源解绑，重置连接自动提交，隔离级别，是否只读，释放连接，恢复挂起事务等
cleanupAfterCompletion(status);
}
}
回滚后的处理工作，如果是新的事务同步状态的话，要把线程的同步状态清除了，
如果是新事务的话，进行数据清除,线程的私有资源解绑，重置连接自动提交，隔离级别，是否只读，释放连接等。
如果有挂起的事务，还要把这个事务给恢复，其实就是把属性设置回去
private void cleanupAfterCompletion(DefaultTransactionStatus status) {
// 设置完成状态
status.setCompleted();
if (status.isNewSynchronization()) {
// 线程同步状态清除
TransactionSynchronizationManager.clear();
}
// 如果是新事务的话，进行数据清除，线程的私有资源解绑，重置连接自动提交，隔离级别，是否只读，释放连接等
if (status.isNewTransaction()) {
doCleanupAfterCompletion(status.getTransaction());
}
// 有挂起的事务要恢复
if (status.getSuspendedResources() != null) {
if (status.isDebug()) {
logger.debug("Resuming suspended transaction after completion of inner transaction");
}
Object transaction = (status.hasTransaction() ? status.getTransaction() : null);
// 结束之前事务的挂起状态
resume(transaction, (SuspendedResourcesHolder) status.getSuspendedResources());
}
}
事务失效场景
-
访问权限：非public方法，spring aop代理只适用public
-
方法final修饰：代理需要重写此方法
-
方法内部调用：不走代理类
-
异常类型不被事务属性捕获
-
事务传播特性不正确
-
数据库本身不支持事务
-
未进行Spring 事务管理
-
异常被捕获未抛出
Spring 事务传播类型
-
支持外层事务
- REQUIRED：使用当前事务，如果没有就创建一个，默认
- SUPPORTS：有事务就用，没有就以非事务运行
- MANDATORY：有事务就用当前事务，没有抛异常
-
不支持外层事务
- REQUIRED_NEW：有事务挂起，创建一个新的
- NOT_SUPPORTED：不需要事务，有就挂起
- NEVER：不要事务，有就抛异常
-
嵌套事务
- NESTED:如果存在事务，会创建保存点，不存在创建一个事务
彩蛋
跟代码过程中，发现@Configuration的类都被动态代理
Config1 定义如下
@Configuration
public class Config1 {
}
为什么要被代理？
原因：如下图，注入A对象会创建一次A，注入B时调用方法a()不在生成A对象。
Spring 如何做的？
每次调用方法时，调用代理类方法，这块调用前先去容器取对象，调用a() 就能取到a对象就不再执行a方法
演示不被代理的情况
通过改源码（ConfigurationClassPostProcessor 搜 postProcessBeanFactory方法中注释掉enhanceConfigurationClasses(beanFactory) 调用），使Config1不被代理，A 对象被创建2次
来自公众号：一个程序猿的笔记
转载自:https://juejin.cn/post/7372393716093763635