spring-transaction源码分析(4)AspectJ和spring-aspects模块
AspectJ是Java语言实现的一个面向切面编程的扩展库，能够基于一定的语法编写Aspect代码，使用ajc编译器将其编译成.class文件，之后在Java程序编写或加载时将Aspect逻辑嵌入到指定的切面。
安装AspectJ
下载AspectJ
到官网下载安装包：
http://www.eclipse.org/downloads/download.php?file=/tools/aspectj/aspectj-1.9.6.jar
安装AspectJ
java -jar aspectj-1.9.6.jar
示例安装到D:\app\aspectj1.9目录下。
基础示例
目录结构
aspectj1.9
|-- bin
|-- ajc
|-- ajc.bat
|-- doc
|-- lib
|-- aspectjrt.jar
|-- aspectjtools.jar
|-- aspectjweaver.jar
官方示例
cd D:\app\aspectj1.9\doc\examples
set CLASSPATH="D:\app\aspectj1.9\lib\aspectjrt.jar"
set Path=D:\app\aspectj1.9\bin;%Path%
ajc -argfile tracing/tracelib.lst -outjar tracelib.jar
ajc -aspectpath tracelib.jar -argfile tracing/notrace.lst -outjar tracedapp.jar
java -classpath "%CLASSPATH%;tracedapp.jar;tracelib.jar" tracing.ExampleMain
spring-aspects模块
AdviceMode.ASPECTJ模式
当EnableTransactionManagement注解的mode属性设置为AdviceMode.ASPECTJ时，将不会再使用spring aop生成事务代理，而是使用AspectJ代理，即装配AnnotationTransactionAspect对象，AnnotationTransactionAspect是一个原生AspectJ组件，该组件使用AspectJ在类加载阶段为目标方法嵌入事务拦截逻辑以实现事务管理。
此时需要：
- 添加spring-aspects依赖
- 添加-javaagent:path/to/aspectjweaver.jar启动参数
AnnotationTransactionAspect
这个类在spring-aspects模块中。
AnnotationTransactionAspect.aj文件：
public aspect AnnotationTransactionAspect extends AbstractTransactionAspect {
public AnnotationTransactionAspect() {
super(new AnnotationTransactionAttributeSource(false));
}
private pointcut executionOfAnyPublicMethodInAtTransactionalType() :
execution(public * ((@Transactional *)+).*(..)) && within(@Transactional *);
private pointcut executionOfTransactionalMethod() :
execution(@Transactional * *(..));
protected pointcut transactionalMethodExecution(Object txObject) :
(executionOfAnyPublicMethodInAtTransactionalType() || executionOfTransactionalMethod() ) &&
this(txObject);
}
AbstractTransactionAspect.aj文件：
public abstract aspect AbstractTransactionAspect extends TransactionAspectSupport implements DisposableBean {
protected AbstractTransactionAspect(TransactionAttributeSource tas) {
setTransactionAttributeSource(tas);
}
@Override
public void destroy() {
clearTransactionManagerCache();
}
@SuppressAjWarnings("adviceDidNotMatch")
Object around(final Object txObject): transactionalMethodExecution(txObject) {
MethodSignature methodSignature = (MethodSignature) thisJoinPoint.getSignature();
// Adapt to TransactionAspectSupport's invokeWithinTransaction...
try {
return invokeWithinTransaction(methodSignature.getMethod(), txObject.getClass(),
new InvocationCallback() {
public Object proceedWithInvocation() throws Throwable {
return proceed(txObject);
}
});
} catch (RuntimeException | Error ex) {
throw ex;
} catch (Throwable thr) {
Rethrower.rethrow(thr);
throw new IllegalStateException("Should never get here", thr);
}
}
protected abstract pointcut transactionalMethodExecution(Object txObject);
}
这两个类使用aspectj语法声明了事务切入点和环绕通知。
该模块在构建时会使用aspectj的ajc编译器将aj文件编译成class文件。