如何使用 Javassist 进行字节码操作以解决链接错误？

Question

我已经发布了几个与 javassit 链接错误 spring Exception when running application on WebSphere with java 8 相关的问题。现在，在围绕这个主题和错误进行一些研究工作之后，我获得了一些有关使用 Javassist 进行字节码操作以解决链接错误的有用信息。

供您参考（已在此处的其他问题中发布此堆栈跟踪）

  [10/13/17 ] 00000089 webapp        E com.ibm.ws.webcontainer.webapp.WebApp logServletError SRVE0293E: [Servlet                                                                       Error]-[weblge]: java.lang.ExceptionInInitializerError
        at java.lang.J9VMInternals.ensureError(J9VMInternals.java:134)
        at java.lang.J9VMInternals.recordInitializationFailure(J9VMInternals.java:123)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:83)
        at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:57)
        at java.lang.reflect.Constructor.newInstance(Constructor.java:437)
        at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:163)
        at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:120)
        at org.springframework.web.context.ContextLoader.createWebApplicationContext(ContextLoader.java:345)
        at org.springframework.web.context.ContextLoader.initWebApplicationContext(ContextLoader.java:278)
        at org.springframework.web.context.ContextLoaderListener.contextInitialized(ContextLoaderListener.java:103)
        at com.ibm.ws.webcontainer.webapp.WebApp.notifyServletContextCreated(WebApp.java:1826)
        at com.ibm.ws.webcontainer.webapp.WebAppImpl.initialize(WebAppImpl.java:442)
        at com.ibm.ws.webcontainer.webapp.WebGroupImpl.addWebApplication(WebGroupImpl.java:88)
        at com.ibm.ws.webcontainer.VirtualHostImpl.addWebApplication(VirtualHostImpl.java:171)
        at com.ibm.ws.webcontainer.WSWebContainer.addWebApp(WSWebContainer.java:904)
        at com.ibm.ws.webcontainer.WSWebContainer.addWebApplication(WSWebContainer.java:789)
        at com.ibm.ws.webcontainer.component.WebContainerImpl.install(WebContainerImpl.java:427)
        at com.ibm.ws.webcontainer.component.WebContainerImpl.start(WebContainerImpl.java:719)
        at com.ibm.ws.runtime.component.ApplicationMgrImpl.start(ApplicationMgrImpl.java:1247)
        at com.ibm.ws.runtime.component.DeployedApplicationImpl.fireDeployedObjectStart(DeployedApplicationImpl.java:1514)
        at com.ibm.ws.runtime.component.DeployedModuleImpl.start(DeployedModuleImpl.java:704)
        at com.ibm.ws.runtime.component.DeployedApplicationImpl.start(DeployedApplicationImpl.java:1096)
        at com.ibm.ws.runtime.component.ApplicationMgrImpl.startApplication(ApplicationMgrImpl.java:799)
        at com.ibm.ws.runtime.component.ApplicationMgrImpl.run(ApplicationMgrImpl.java:2315)
        at com.ibm.ws.security.auth.ContextManagerImpl.runAs(ContextManagerImpl.java:5488)
        at com.ibm.ws.security.auth.ContextManagerImpl.runAsSystem(ContextManagerImpl.java:5614)
        at com.ibm.ws.security.core.SecurityContext.runAsSystem(SecurityContext.java:255)
        at com.ibm.ws.runtime.component.ApplicationMgrImpl.start(ApplicationMgrImpl.java:2320)
        at com.ibm.ws.runtime.component.CompositionUnitMgrImpl.start(CompositionUnitMgrImpl.java:436)
        at com.ibm.ws.runtime.component.CompositionUnitImpl.start(CompositionUnitImpl.java:123)
        at com.ibm.ws.runtime.component.CompositionUnitMgrImpl.start(CompositionUnitMgrImpl.java:379)
        at com.ibm.ws.runtime.component.CompositionUnitMgrImpl.access0(CompositionUnitMgrImpl.java:127)
        at com.ibm.ws.runtime.component.CompositionUnitMgrImpl$CUInitializer.run(CompositionUnitMgrImpl.java:985)
        at com.ibm.wsspi.runtime.component.WsComponentImpl$_AsynchInitializer.run(WsComponentImpl.java:524)
        at com.ibm.ws.util.ThreadPool$Worker.run(ThreadPool.java:1909)
Caused by: java.lang.IllegalStateException: javassist.CannotCompileException: by java.lang.LinkageError: org.springframework.aop.framework.ProxyCreatorSupport
        at org.springframework.aop.framework.JavassistApplicationContext.<clinit>(JavassistApplicationContext.java:36)
        ... 34 more
Caused by: javassist.CannotCompileException: by java.lang.LinkageError: org.springframework.aop.framework.ProxyCreatorSupport
        at javassist.ClassPool.toClass(ClassPool.java:1170)
        at javassist.ClassPool.toClass(ClassPool.java:1113)
        at javassist.ClassPool.toClass(ClassPool.java:1071)
        at javassist.CtClass.toClass(CtClass.java:1275)
        at org.springframework.aop.framework.JavassistApplicationContext.<clinit>(JavassistApplicationContext.java:34)
        ... 34 more
Caused by: java.lang.LinkageError: org.springframework.aop.framework.ProxyCreatorSupport
        at java.lang.ClassLoader.defineClassImpl(Native Method)
        at java.lang.ClassLoader.defineClass(ClassLoader.java:357)
        at java.lang.ClassLoader.defineClass(ClassLoader.java:293)
        at sun.reflect.GeneratedMethodAccessor17.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:55)
        at java.lang.reflect.Method.invoke(Method.java:508)
        at javassist.ClassPool.toClass2(ClassPool.java:1183)
        at javassist.ClassPool.toClass(ClassPool.java:1164)
        ... 38 more

当我尝试对 org.springframework.aop.framework.ProxyCreatorSupport

执行操作时，我在 java 文件上收到此错误

package org.spring.aop.framework;

import javassist.ClassPool;
import javassist.CtClass;
import javassist.CtConstructor;
import javassist.LoaderClassPath;
import org.springframework.web.context.support.XmlWebApplicationContext;

public class JavassistApplicationContext extends XmlWebApplicationContext {

    static {
        ClassPool classPool = ClassPool.getDefault();
        try {
            ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
            classPool.appendClassPath(new LoaderClassPath(classLoader));

            CtClass cc = classPool.get("org.spring.aop.framework.ProxyCreatorSupport");
            CtConstructor c = cc.getConstructors()[0];
            c.insertAfter("[=11=].aopProxyFactory = new org.spring.aop.framework.JavassistAopProxyFactory();");
            cc.toClass();
        } catch (Exception e) {
            throw new IllegalStateException(e);
        }
    }
}

在线 cc.toClass();，我收到此异常。我在 WebSphere 上尝试了不同的 class 加载程序方法来解决此异常并得到相同的错误。

现在我明白 linkage problem is occur when tries to modify the class already loaded by referenced classloader . 能够解决这个错误，我 should unload the class first from the reference classloader 我认为这很难。

所以我认为解决这个问题的唯一方法是通过任何 class 加载器在 class 加载器之前执行字节码操作。不是吗？
如何使用 java 代理将现有代码更改为字节码操作？有什么想法和建议吗？请不要重复提问。这只是上一个问题的参考工作。

Answer 1

您需要写 a Java agent and attach it dynamically to transform a class at load time. You can find a cool tutorial here 来说明如何操作。

请注意，此方法允许您在 class 由 JVM 加载时拦截它，并在加载实际完成后修改它。

如何使用 Javassist 进行字节码操作以解决链接错误？

How to do bytecode manipulation with Javassist for solving linkage errors?

java

spring

instrumentation

javassist