Spring事务的开启原理详解

作者: 必有卧槽
来源: 51数据库
2021-08-27

在事务配置类上声明@enabletransactionmanagement注解开启事务
在事务配置类上定义数据源
在事务配置类上定义事务管理器
在相关类或者方法上使用@transactional声明事务

代码如下：

@configuration
@enabletransactionmanagement
public class rootconfig{
 
 @bean
 public datasource datasource(){
  druiddatasource datasource = new druiddatasource();
  datasource.setxxx();
  ...
  
  return datasource;
 }
 
 @bean
 public platfromtransactionmanager txmanager(){
  return new datasourcetransactionmanager(datasource());
 }
}

@service
public class userservice{

 @autowired
 private userrepository userrepository;
 
 @transactional
 public void adduser(user user){
  userrepository.save(user);
 }
}

@enabletransactionmanagement开启事务原理解析

@enabletransactionmanagement源码如下：

@target(elementtype.type)
@retention(retentionpolicy.runtime)
@documented
@import(transactionmanagementconfigurationselector.class)
public @interface enabletransactionmanagement {
 boolean proxytargetclass() default false;
 advicemode mode() default advicemode.proxy;
 int order() default ordered.lowest_precedence;
}

可以看到，@enabletransactionmanagement接口类主要import了transactionmanagementconfigurationselector来实现其注入，而transactionmanagementconfigurationselector又主要使用selectimport方法来实现其注入，代码如下：

@override
public final string[] selectimports(annotationmetadata importingclassmetadata) {
 class<?> annotype = generictyperesolver.resolvetypeargument(getclass(), advicemodeimportselector.class);
 annotationattributes attributes = annotationconfigutils.attributesfor(importingclassmetadata, annotype);
 if (attributes == null) {
  throw new illegalargumentexception(string.format(
   "@%s is not present on importing class '%s' as expected",
   annotype.getsimplename(), importingclassmetadata.getclassname()));
 }

 advicemode advicemode = attributes.getenum(this.getadvicemodeattributename());
 //根据advicemode返回不同的类型，默认是advicemode.proxy。
 string[] imports = selectimports(advicemode);
 if (imports == null) {
  throw new illegalargumentexception(string.format("unknown advicemode: '%s'", advicemode));
 }
 return imports;
}

@override
protected string[] selectimports(advicemode advicemode) {
 switch (advicemode) {
  case proxy:
   return new string[] {autoproxyregistrar.class.getname(), proxytransactionmanagementconfiguration.class.getname()};
  case aspectj:
   return new string[] {transactionmanagementconfigutils.transaction_aspect_configuration_class_name};
  default:
   return null;
 }
}

其中主要功能点为根据advicemode选择创建不同的bean，advicemode的默认代理方式是proxy，jdk代理。所以返回的是autoproxyregistrar和proxytransactionmanagementconfiguration。

我们先分析autoproxyregistrar，autoproxyregistrar实现了importbeandefinitionregistrar，那在创建bean的时候会调用registerbeandefinitions方法。registerbeandefinitions方法的实现：

@override
public void registerbeandefinitions(annotationmetadata importingclassmetadata, beandefinitionregistry registry) {
 boolean candidatefound = false;
 set<string> annotypes = importingclassmetadata.getannotationtypes();
 for (string annotype : annotypes) {
  annotationattributes candidate = annotationconfigutils.attributesfor(importingclassmetadata, annotype);
  if (candidate == null) {
   continue;
  }
  object mode = candidate.get("mode");
  object proxytargetclass = candidate.get("proxytargetclass");
  if (mode != null && proxytargetclass != null && advicemode.class == mode.getclass() &&
    boolean.class == proxytargetclass.getclass()) {
   candidatefound = true;
   //只有@enabletransactionmanagement注解才会走到这里
   if (mode == advicemode.proxy) {
    aopconfigutils.registerautoproxycreatorifnecessary(registry);
    if ((boolean) proxytargetclass) {
     aopconfigutils.forceautoproxycreatortouseclassproxying(registry);
     return;
    }
   }
  }
 }
 //...
}

public static beandefinition registerautoproxycreatorifnecessary(beandefinitionregistry registry, object source) {
 return registerorescalateapcasrequired(infrastructureadvisorautoproxycreator.class, registry, source);
}

可以看到，它通过注册infrastructureadvisorautoproxycreator来启动spring aop。

接下来再看proxytransactionmanagementconfiguration的作用，代码如下：

@configuration
public class proxytransactionmanagementconfiguration extends abstracttransactionmanagementconfiguration {

 @bean(name = transactionmanagementconfigutils.transaction_advisor_bean_name)
 @role(beandefinition.role_infrastructure)
 public beanfactorytransactionattributesourceadvisor transactionadvisor() {
  beanfactorytransactionattributesourceadvisor advisor = new beanfactorytransactionattributesourceadvisor();
  advisor.settransactionattributesource(transactionattributesource());
  advisor.setadvice(transactioninterceptor());
  advisor.setorder(this.enabletx.<integer>getnumber("order"));
  return advisor;
 }

 @bean
 @role(beandefinition.role_infrastructure)
 public transactionattributesource transactionattributesource() {
  return new annotationtransactionattributesource();
 }

 @bean
 @role(beandefinition.role_infrastructure)
 public transactioninterceptor transactioninterceptor() {
  transactioninterceptor interceptor = new transactioninterceptor();
  interceptor.settransactionattributesource(transactionattributesource());
  if (this.txmanager != null) {
   interceptor.settransactionmanager(this.txmanager);
  }
  return interceptor;
 }

}

proxytransactionmanagementconfiguration是一个配置文件，注册了三个bean，beanfactorytransactionattributesourceadvisor、annotationtransactionattributesource、transactioninterceptor，而这三个类分别继承advisor、advice和pointcut。即切面所需组件。

总结

@enabletransactionmanagement利用autoproxyregistrar启动spring aop,使用proxytransactionmanagementconfiguration配置对应切面部件。

以上就是spring事务的简单实现步骤的详细内容，更多关于spring事务实现步骤的资料请关注其它相关文章！