我需要创建一个Java代理，启用该代理后，它会将jar文件的路径作为参数，然后替换所有已加载的类，如果它们的名称匹配，则替换jar文件中的那个加载的类。
例如，我们有一个名为com.something.ClassTest的类的应用程序。现在，如果提到的jar(不在类路径中)具有与com.something.ClassTest完全相同的名称，我想将其替换为jar中的一个。
我有这个类的转换器，但不确定是否正确。我收到IOException，找不到消息类。
@Override
public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {
if(classNames.contains(className.replace("/", "."))) {
System.out.format("\n==> Found %s \n", className);
try {
Class c = urlClassLoader.loadClass(className.replace("/", "."));
InputStream is = urlClassLoader.getResourceAsStream(className.replace("/", "."));
System.out.println("Loaded class " + c);
ClassReader reader = new ClassReader(is);
ClassWriter writer = new ClassWriter(reader, ClassWriter.COMPUTE_FRAMES | ClassWriter.COMPUTE_MAXS);
byte[] content = writer.toByteArray();
System.out.println("Redifned " + new String(content));
System.out.println("Orig " + new String(classfileBuffer));
ClassDefinition cd = new ClassDefinition(c, content);
instrumentation.redefineClasses(cd);
return content;
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (UnmodifiableClassException e) {
e.printStackTrace();
}
}
return classfileBuffer;
}
我得到的错误是在ClassReader实例化的那一行。我猜这是因为urlClassloader在当前类加载器的层次结构下...但是我不知道我还能怎么做。
这是初始化加载的URL类的代码
public SimpleClassTransformer(Instrumentation instrumentation, String jarFileName) {
this.jarFileName = jarFileName;
if(jarFileName != null) {
JarFile jarFile = null;
try {
jarFile = new JarFile(this.jarFileName);
Enumeration e = jarFile.entries();
System.out.println("Jar file: " + this.jarFileName);
URL[] urls = { new URL("jar:file:" + this.jarFileName+"!/") };
urlClassLoader = URLClassLoader.newInstance(urls);
while (e.hasMoreElements()) {
JarEntry je = (JarEntry) e.nextElement();
if(je.isDirectory() || !je.getName().endsWith(".class")){
continue;
}
// -6 because of .class
String jarClassName = je.getName().substring(0,je.getName().length()-6);
jarClassName = jarClassName.replace('/', '.');
System.out.println("Adding class " + jarClassName);
this.classNames.add(jarClassName);
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
在premain()方法中实例化转换器的同时设置仪器。我试图避免使用Javassist。你能帮我这个忙吗？
这是我得到的异常(exception):
java.io.IOException: Class not found
at jdk.internal.org.objectweb.asm.ClassReader.readClass(ClassReader.java:484)
at jdk.internal.org.objectweb.asm.ClassReader.<init>(ClassReader.java:453)
at com.agent.SimpleClassTransformer.transform(SimpleClassTransformer.java:79)
at sun.instrument.TransformerManager.transform(TransformerManager.java:188)
at sun.instrument.InstrumentationImpl.transform(InstrumentationImpl.java:428)
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:760)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:467)
at java.net.URLClassLoader.access$100(URLClassLoader.java:73)
at java.net.URLClassLoader$1.run(URLClassLoader.java:368)
at java.net.URLClassLoader$1.run(URLClassLoader.java:362)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:361)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
at org.springframework.util.ClassUtils.forName(ClassUtils.java:250)
at org.springframework.beans.factory.support.AbstractBeanDefinition.resolveBeanClass(AbstractBeanDefinition.java:394)
at org.springframework.beans.factory.support.AbstractBeanFactory.doResolveBeanClass(AbstractBeanFactory.java:1397)
at org.springframework.beans.factory.support.AbstractBeanFactory.resolveBeanClass(AbstractBeanFactory.java:1344)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.determineTargetType(AbstractAutowireCapableBeanFactory.java:628)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.predictBeanType(AbstractAutowireCapableBeanFactory.java:597)
at org.springframework.beans.factory.support.AbstractBeanFactory.isFactoryBean(AbstractBeanFactory.java:1445)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.doGetBeanNamesForType(DefaultListableBeanFactory.java:445)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBeanNamesForType(DefaultListableBeanFactory.java:415)
at org.springframework.boot.autoconfigure.web.DispatcherServletAutoConfiguration$DefaultDispatcherServletCondition.checkServlets(DispatcherServletAutoConfiguration.java:141)
at org.springframework.boot.autoconfigure.web.DispatcherServletAutoConfiguration$DefaultDispatcherServletCondition.getMatchOutcome(DispatcherServletAutoConfiguration.java:131)
at org.springframework.boot.autoconfigure.condition.SpringBootCondition.matches(SpringBootCondition.java:47)
at org.springframework.context.annotation.ConditionEvaluator.shouldSkip(ConditionEvaluator.java:102)
at org.springframework.context.annotation.ConfigurationClassParser.processConfigurationClass(ConfigurationClassParser.java:203)
at org.springframework.context.annotation.ConfigurationClassParser.processMemberClasses(ConfigurationClassParser.java:336)
at org.springframework.context.annotation.ConfigurationClassParser.doProcessConfigurationClass(ConfigurationClassParser.java:248)
at org.springframework.context.annotation.ConfigurationClassParser.processConfigurationClass(ConfigurationClassParser.java:231)
at org.springframework.context.annotation.ConfigurationClassParser.processImports(ConfigurationClassParser.java:509)
at org.springframework.context.annotation.ConfigurationClassParser.processDeferredImportSelectors(ConfigurationClassParser.java:454)
at org.springframework.context.annotation.ConfigurationClassParser.parse(ConfigurationClassParser.java:185)
at org.springframework.context.annotation.ConfigurationClassPostProcessor.processConfigBeanDefinitions(ConfigurationClassPostProcessor.java:321)
at org.springframework.context.annotation.ConfigurationClassPostProcessor.postProcessBeanDefinitionRegistry(ConfigurationClassPostProcessor.java:243)
at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanDefinitionRegistryPostProcessors(PostProcessorRegistrationDelegate.java:273)
at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(PostProcessorRegistrationDelegate.java:98)
at org.springframework.context.support.AbstractApplicationContext.invokeBeanFactoryPostProcessors(AbstractApplicationContext.java:677)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:519)
at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.refresh(EmbeddedWebApplicationContext.java:118)
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:752)
at org.springframework.boot.SpringApplication.doRun(SpringApplication.java:347)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:295)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1112)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1101)
====编辑====
解决了url类加载器的问题后，我现在得到了这个错误，该错误在Spring尝试刷新其上下文时发生:
TestClass has been compiled by a more recent version of the Java Runtime (class file version 0.0), this version of the Java Runtime only recognizes class file versions up to 52.0
最佳答案
解决您的问题的另一种方法是使用背书目录。
将要加载的类保留在库中，并提供-Djava.endorsed.dirs=<directory_path>作为该程序的JVM参数。
在加载类时，JVM首先检查此目录中的类可用性，如果找不到，则它将检查应用程序类。
这完全可以正常工作，没有任何问题，也没有任何编码。