Here is my sample non-working project。
它包含2个模块：
Wrap批注的定义。Wrap批注的主类。目录结构如下：
.
├── README.md
├── aop-app
│ ├── pom.xml
│ └── src
│ └── main
│ └── java
│ └── com
│ └── aop
│ └── app
│ ├── DynamicLoad.java
│ └── Main.java
└── aop-lib
├── pom.xml
└── src
└── main
└── java
└── com
└── aop
└── app
└── lib
├── Wrap.java
└── WrapDef.java
我试图通过如official docs中所述动态加载javaagent，通过加载时间编织（LTW）在aop-lib内使用方面aop-app（AOP建议库）方面。但这不起作用。
以下是Wrap.java
的内容@Target({ElementType.METHOD, ElementType.TYPE})
@Retention(value = RetentionPolicy.RUNTIME)
public @interface Wrap { }
以下是WrapDef.java
的内容@Aspect
public class WrapDef {
private static final Logger logger = LoggerFactory.getLogger(WrapDef.class);
public static boolean loaded = false;
@Around("@annotation( wrapAnnotation ) && execution(* *(..))")
public Object processSystemRequest(final ProceedingJoinPoint pjp, Wrap wrapAnnotation)
throws Throwable {
logger.debug("before wrap");
Object o = pjp.proceed();
logger.debug("after wrap");
return o;
}
static {
System.out.println("Loading");
WrapDef.loaded = true;
}
public static void reportLoaded() {
System.out.println("loaded : " + loaded);
}
}
以下是Main.java的内容：
public class Main {
private static final Logger logger = LoggerFactory.getLogger(Main.class);
@Wrap
public void myFunc(){
logger.debug("inside myFunc");
}
public static void main(String[] args) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException {
boolean dynamicLoad = Boolean.getBoolean("dynamicLoad");
if(dynamicLoad){
Main.isAdviceClassLoaded(); //To see if WrapDef.java is loaded or not.
if(!DynamicLoad.isAspectJAgentLoaded()) {
logger.error("AspectJ Not Loaded. Existing.");
System.exit(0);
}
Main.isAdviceClassLoaded(); //To see if WrapDef.java is loaded or not.
}
new Main().myFunc();
}
private static void isAdviceClassLoaded() throws NoSuchMethodException, InvocationTargetException, IllegalAccessException {
java.lang.reflect.Method m = ClassLoader.class.getDeclaredMethod("findLoadedClass", String.class);
m.setAccessible(true);
ClassLoader cl = ClassLoader.getSystemClassLoader();
Object test1 = m.invoke(cl, "com.aop.app.lib.WrapDef");
boolean loaded = test1 != null;
System.out.println("com.aop.app.lib.WrapDef Loaded : " + loaded);
}
}
使用javaagent作为cmd行arg，它可以很好地工作：
$ java -javaagent:deploy/lib/aspectjweaver-1.9.1.jar -classpath aop-app-1.0.jar:deploy/lib/* com.aop.app.Main
14:02:45.384 [main] DEBUG com.aop.app.lib.WrapDef - before wrap
14:02:45.391 [main] DEBUG com.aop.app.Main - inside myFunc
14:02:45.391 [main] DEBUG com.aop.app.lib.WrapDef - after wrap
但是，在动态加载javaagent的情况下，它会提供以下输出：
$ java -DdynamicLoad=true -DAGENT_PATH=deploy/lib/aspectjweaver-1.9.1.jar -classpath aop-app-1.0.jar:deploy/lib/* com.aop.app.Main
com.aop.app.lib.WrapDef Loaded : false //The WrapDef is NOT loaded before JAVAAGENT is Loaded - which is correct
java.lang.UnsupportedOperationException: AspectJ weaving agent was neither started via '-javaagent' (preMain) nor attached via 'VirtualMachine.loadAgent' (agentMain)
loading javaAgent deploy/lib/aspectjweaver-1.9.1.jar
loaded javaAgent deploy/lib/aspectjweaver-1.9.1.jar //The JAVAAGENT is Dynamically Loaded - which is correct
com.aop.app.lib.WrapDef Loaded : false //The WrapDef is STILL NOT loaded even AFTER JAVAAGENT is Loaded - THIS IS THE ISSUE
15:53:08.543 [main] DEBUG com.aop.app.Main - inside myFunc
official docs确实说了any classes loaded before attachment will not be woven。但是，与上面的输出相反，WrapDef类根本没有加载。
另外，请注意，我在aop-lib/pom.xml中使用aspectj-maven-plugin，具有以下选项：
<outxml>true</outxml> //creates META-INF/aop-ajc.xml
<showWeaveInfo>true</showWeaveInfo> //supposed to create <weaver options="-showWeaveInfo"/> BUT DOES NOT WORK
<verbose>true</verbose> //supposed to create <weaver options="-verbose"/> BUT DOES NOT WORK
因此，它将在META-INF/aop-ajc.xml内创建具有以下内容的aop-lib-1.0.jar：
<aspectj>
<aspects>
<aspect name="com.aop.app.lib.WrapDef"/>
</aspects>
</aspectj>
但与showWeaveInfo和verbose对应的其他标签未在META-INF/aop-ajc.xml中创建。这是另一件事，在这里不起作用。
如果您需要其他任何信息-我会提供。
感谢您的帮助。
答案 0 :(得分：2)
解释很简单：您正在类Main中直接测试编织代理，该类已经在之前加载，您从该类附加了那个代理。因此，您必须避免将要编织的类过早加载。我建议您将方法myFunc()（很糟糕的名称）放入另一个类。那怎么办？
package com.aop.app;
import com.aop.app.lib.Wrap;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class Application {
private static final Logger logger = LoggerFactory.getLogger(Application.class);
@Wrap
public void myFunc(){
logger.debug("inside myFunc");
}
public static void main(String[] args) {
new Application().myFunc();
}
}
然后在Main.main(..)的最后一行中，启动要编写的实际应用程序：
Application.main(null);
这将产生以下输出：
com.aop.app.lib.WrapDef Loaded : false
java.lang.UnsupportedOperationException: AspectJ weaving agent was neither started via '-javaagent' (preMain) nor attached via 'VirtualMachine.loadAgent' (agentMain)
loading javaAgent aop-app/target/deploy/lib/aspectjweaver-1.9.1.jar
loaded javaAgent aop-app/target/deploy/lib/aspectjweaver-1.9.1.jar
com.aop.app.lib.WrapDef Loaded : false
Loading
07:56:21.703 [main] DEBUG com.aop.app.lib.WrapDef - before wrap
07:56:21.716 [main] DEBUG com.aop.app.Application - inside myFunc
07:56:21.716 [main] DEBUG com.aop.app.lib.WrapDef - after wrap
P.S .：您真的认为方面库的用户在JVM命令行上指定两个属性而不是仅使用-javaagent:/path/to/aspectweaver.jar更容易吗？无论如何，您可能有使用动态Weaver附件的理由。从某种程度上来说，我很高兴有人使用我自己不久前添加到AspectJ中的功能。 ;-)