理解spring事务底层原理

以你之姓@ 2022-02-27 06:46 230阅读 0赞

事务是一种all or nothing的执行策略，常见数据库，这种策略遵从ACID原则，可以很好的保证业务的执行，spring事务底层可以使用tx命名空间实现，也可以通过Transactional注解的方式来实现，本文就讲下spring transactional注解底层的工作原理，要了解这个工作原理，首先要了解cglib的工作原理，这个可以参考文章：[https://blog.csdn.net/john1337/article/details/88762825][https_blog.csdn.net_john1337_article_details_88762825]

了解了cglib的基本工作原理后，spring transactional底层工作原理就很容易理解了，笔者就把这个运作原理涉及到的几个重要的相关类在这里列举出来，感兴趣的进行代码跟踪即可了解：

**DefaultAdvisorAutoProxyCreator ** 这是BeanPostProcessor，重要的其基类**AbstractAdvisorAutoProxyCreator**的**postProcessAfterInitialization**方法，这个方法内部生成了对应service的代理类，基本代理类代码类似下面：

private boolean CGLIB$BOUND;  
   public static Object CGLIB$FACTORY\_DATA;  
   private static final ThreadLocal CGLIB$THREAD\_CALLBACKS;  
   private static final Callback\[\] CGLIB$STATIC\_CALLBACKS;  
   private MethodInterceptor CGLIB$CALLBACK\_0;  
   private MethodInterceptor CGLIB$CALLBACK\_1;  
   private NoOp CGLIB$CALLBACK\_2;  
   private Dispatcher CGLIB$CALLBACK\_3;  
   private Dispatcher CGLIB$CALLBACK\_4;  
   private MethodInterceptor CGLIB$CALLBACK\_5;  
   private MethodInterceptor CGLIB$CALLBACK\_6;  
   private static Object CGLIB$CALLBACK\_FILTER;  
   private static final Method CGLIB$insert$0$Method;  
   private static final MethodProxy CGLIB$insert$0$Proxy;  
   private static final Object\[\] CGLIB$emptyArgs;  
   private static final Method CGLIB$selectByPrimaryKey$1$Method;  
   private static final MethodProxy CGLIB$selectByPrimaryKey$1$Proxy;  
   private static final Method CGLIB$updateByPrimaryKeySelective$2$Method;  
   private static final MethodProxy CGLIB$updateByPrimaryKeySelective$2$Proxy;  
   private static final Method CGLIB$updateByPrimaryKey$3$Method;  
   private static final MethodProxy CGLIB$updateByPrimaryKey$3$Proxy;  
   private static final Method CGLIB$insertSelective$4$Method;  
   private static final MethodProxy CGLIB$insertSelective$4$Proxy;  
   private static final Method CGLIB$deleteByPrimaryKey$5$Method;  
   private static final MethodProxy CGLIB$deleteByPrimaryKey$5$Proxy;  
   private static final Method CGLIB$equals$6$Method;  
   private static final MethodProxy CGLIB$equals$6$Proxy;  
   private static final Method CGLIB$toString$7$Method;  
   private static final MethodProxy CGLIB$toString$7$Proxy;  
   private static final Method CGLIB$hashCode$8$Method;  
   private static final MethodProxy CGLIB$hashCode$8$Proxy;  
   private static final Method CGLIB$clone$9$Method;  
   private static final MethodProxy CGLIB$clone$9$Proxy;

static void CGLIB$STATICHOOK249() \{  
      CGLIB$THREAD\_CALLBACKS = new ThreadLocal();  
      CGLIB$emptyArgs = new Object\[0\];  
      Class var0 = Class.forName("hello.service.bank.impl.SubBankServiceImpl$$EnhancerBySpringCGLIB$$8fea4d01");  
      Class var1;  
      Method\[\] var10000 = ReflectUtils.findMethods(new String\[\]\{"equals", "(Ljava/lang/Object;)Z", "toString", "()Ljava/lang/String;", "hashCode", "()I", "clone", "()Ljava/lang/Object;"\}, (var1 = Class.forName("java.lang.Object")).getDeclaredMethods());  
      CGLIB$equals$6$Method = var10000\[0\];  
      CGLIB$equals$6$Proxy = MethodProxy.create(var1, var0, "(Ljava/lang/Object;)Z", "equals", "CGLIB$equals$6");  
      CGLIB$toString$7$Method = var10000\[1\];  
      CGLIB$toString$7$Proxy = MethodProxy.create(var1, var0, "()Ljava/lang/String;", "toString", "CGLIB$toString$7");  
      CGLIB$hashCode$8$Method = var10000\[2\];  
      CGLIB$hashCode$8$Proxy = MethodProxy.create(var1, var0, "()I", "hashCode", "CGLIB$hashCode$8");  
      CGLIB$clone$9$Method = var10000\[3\];  
      CGLIB$clone$9$Proxy = MethodProxy.create(var1, var0, "()Ljava/lang/Object;", "clone", "CGLIB$clone$9");  
      var10000 = ReflectUtils.findMethods(new String\[\]\{"insert", "(Lhello/entity/bank/SubBank;)I", "selectByPrimaryKey", "(Ljava/lang/String;)Lhello/entity/bank/SubBank;", "updateByPrimaryKeySelective", "(Lhello/entity/bank/SubBank;)I", "updateByPrimaryKey", "(Lhello/entity/bank/SubBank;)I", "insertSelective", "(Lhello/entity/bank/SubBank;)I", "deleteByPrimaryKey", "(Ljava/lang/String;)I"\}, (var1 = Class.forName("hello.service.bank.impl.SubBankServiceImpl")).getDeclaredMethods());  
      CGLIB$insert$0$Method = var10000\[0\];  
      CGLIB$insert$0$Proxy = MethodProxy.create(var1, var0, "(Lhello/entity/bank/SubBank;)I", "insert", "CGLIB$insert$0");  
      CGLIB$selectByPrimaryKey$1$Method = var10000\[1\];  
      CGLIB$selectByPrimaryKey$1$Proxy = MethodProxy.create(var1, var0, "(Ljava/lang/String;)Lhello/entity/bank/SubBank;", "selectByPrimaryKey", "CGLIB$selectByPrimaryKey$1");  
      CGLIB$updateByPrimaryKeySelective$2$Method = var10000\[2\];  
      CGLIB$updateByPrimaryKeySelective$2$Proxy = MethodProxy.create(var1, var0, "(Lhello/entity/bank/SubBank;)I", "updateByPrimaryKeySelective", "CGLIB$updateByPrimaryKeySelective$2");  
      CGLIB$updateByPrimaryKey$3$Method = var10000\[3\];  
      CGLIB$updateByPrimaryKey$3$Proxy = MethodProxy.create(var1, var0, "(Lhello/entity/bank/SubBank;)I", "updateByPrimaryKey", "CGLIB$updateByPrimaryKey$3");  
      CGLIB$insertSelective$4$Method = var10000\[4\];  
      CGLIB$insertSelective$4$Proxy = MethodProxy.create(var1, var0, "(Lhello/entity/bank/SubBank;)I", "insertSelective", "CGLIB$insertSelective$4");  
      CGLIB$deleteByPrimaryKey$5$Method = var10000\[5\];  
      CGLIB$deleteByPrimaryKey$5$Proxy = MethodProxy.create(var1, var0, "(Ljava/lang/String;)I", "deleteByPrimaryKey", "CGLIB$deleteByPrimaryKey$5");  
   \}

final int CGLIB$insert$0(SubBank var1) \{  
      return super.insert(var1);  
   \}

public final int insert(SubBank var1) \{  
      try \{  
         **MethodInterceptor** var10000 = this.CGLIB$CALLBACK\_0;  
         if (this.CGLIB$CALLBACK\_0 == null) \{  
            CGLIB$BIND\_CALLBACKS(this);  
            var10000 = this.CGLIB$CALLBACK\_0;  
         \}

if (var10000 != null) \{  
            Object var4 = var10000.intercept(this, CGLIB$insert$0$Method, new Object\[\]\{var1\}, CGLIB$insert$0$Proxy);  
            return var4 == null ? 0 : ((Number)var4).intValue();  
         \} else \{  
            return super.insert(var1);  
         \}  
      \} catch (Error | RuntimeException var2) \{  
         throw var2;  
      \} catch (Throwable var3) \{  
         throw new UndeclaredThrowableException(var3);  
      \}  
   \}

这个就是cglib产生的代理类

CglibAopProxy  这个类getProxy创建了对应的cglib代理

DynamicAdvisedInterceptor  这个类实现了MethodInteceptor接口，每次Service调用接口时首先进入的就是DynamicAdvisedInterceptor这个类的intercept方法，该方法内部会判断每个要执行的方法是否有对应的advice，被Transactional注解的方法对应的默认advice就是TransactionInteceptor

TransactionInterceptor 事务增强类，重要的是invoke方法：

@Override  
    public Object invoke(final MethodInvocation invocation) throws Throwable \{  
        // Work out the target class: may be \{@code null\}.  
        // The TransactionAttributeSource should be passed the target class  
        // as well as the method, which may be from an interface.  
        Class<?> targetClass = (invocation.getThis() != null ? AopUtils.getTargetClass(invocation.getThis()) : null);

// Adapt to TransactionAspectSupport's invokeWithinTransaction...  
        return **invokeWithinTransaction**(invocation.getMethod(), targetClass, new InvocationCallback() \{  
            @Override  
            public Object proceedWithInvocation() throws Throwable \{  
                return invocation.proceed();  
            \}  
        \});  
    \}

[https_blog.csdn.net_john1337_article_details_88762825]: https://blog.csdn.net/john1337/article/details/88762825