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[英]Caused by: java.lang.ClassNotFoundException: javax.servlet.http.HttpServlet
[英]byte-buddy throws java.lang.ClassNotFoundException: javax.servlet.http.HttpServlet
我正在嘗試使用基於Byte Buddy的Java代理來檢測對javax.servlet.http.HttpServlet的service()方法的調用。 我的代碼中的premain函數已正確調用,但檢測失敗並顯示堆棧跟蹤:
java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at sun.instrument.InstrumentationImpl.loadClassAndStartAgent(InstrumentationImpl.java:386)
at sun.instrument.InstrumentationImpl.loadClassAndCallPremain(InstrumentationImpl.java:401)
Caused by: java.lang.NoClassDefFoundError: javax/servlet/http/HttpServlet
at ub.jagent.ServletInstrumentation.instrument(ServletInstrumentation.java:24)
at ub.jagent.StackTracerAgent.premain(StackTracerAgent.java:75)
... 6 more
Caused by: java.lang.ClassNotFoundException: javax.servlet.http.HttpServlet
at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
... 8 more
FATAL ERROR in native method: processing of -javaagent failed
我使用代理構建器,如下所示:
AgentBuilder b = new AgentBuilder.Default().ignore(ElementMatchers.none())
.with(AgentBuilder.RedefinitionStrategy.RETRANSFORMATION)
.with(AgentBuilder.InitializationStrategy.NoOp.INSTANCE)
.with(AgentBuilder.TypeStrategy.Default.REDEFINE)
.type(ElementMatchers.isSubTypeOf(HttpServlet.class))
.transform((builder, type, classLoader) ->
builder.visit(Advice.to(ServletAdvice.class)
.on(ElementMatchers.named("service")
.and(ElementMatchers.takesArgument(0, HttpServletRequest.class))
.and(ElementMatchers.takesArgument(1, HttpServletResponse.class)))).installOn(inst);
我的Advice實施如下:
public class ServletAdvice {
@Advice.OnMethodEnter
public static void before(@Advice.This Object obj,
@Advice.Argument(value = 0) HttpServletRequest a1,
@Advice.Argument(value = 1) HttpServletResponse a2,
@Advice.Origin Method method)
{
System.out.println("\nRunning pre-method logic for " + obj.getClass().getCanonicalName() + ":" + method.getName() + "()");
<...etc...>
}
}
}
奇怪的是,當我在特定的Tomcat實現類上進行匹配時:
.type(ElementMatchers.named("org.glassfish.jersey.servlet.ServletContainer"))
...然后代理設置就可以了(盡管在檢測本身期間,Advice方法中對HttpServletRequest和HttpServletResponse的引用會觸發ClassNotFoundException)。
這是否意味着我必須在代理.jar文件本身中包括所有代理依賴項(包括Java Servlet API)?
我正在使用ByteBuddy 1.6.2,Apache Tomcat v8.0。
編輯修改后的工作代碼(在Rafael的幫助下)如下所示:
.type(ElementMatchers.isSubTypeOf(new TypeDescription.Latent("javax.servlet.GenericServlet", Modifier.PUBLIC | Modifier.ABSTRACT, TypeDescription.Generic.OBJECT, null)))
.transform(
new AgentBuilder.Transformer.ForAdvice()
.include(getClass().getClassLoader())
.advice(
ElementMatchers.named("service")
.and(ElementMatchers.takesArgument(0, ElementMatchers.named("javax.servlet.http.HttpServletRequest"))
.and(ElementMatchers.takesArgument(1, ElementMatchers.named( "javax.servlet.http.HttpServletResponse")),
ServletAdvice.class.getName())
);
我假設Byte Buddy用於解決建議的類加載器無法使用類型的servlet系列。 為了克服這個問題,Byte Buddy提供了一個特定的轉換器,可以為用戶和代理的類加載器解析建議類:
new AgentBuilder.Transformation.ForAdvice()
.include(getClass().getClassLoader())
.advice("your.pkg.ServletAdvice")
至於元素匹配器,則先使用類型常量匹配參數的名稱。
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