那些遇到过的问题

如何用 Java 检测用新的类替换一个类？

xbm*_*ono 6 java instrumentation bytecode

我需要创建一个 java 代理，当启用它时，它将获取 jar 文件的路径作为参数，然后如果它们的名称匹配，它将替换 jar 文件中的任何加载类。

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）有一个与 com.something.ClassTest 同名的类，我想用 jar 中的那个来替换它。

我有这个类转换器，但不确定这是否正确。我收到消息 Class not found 的 IOException。

    @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;
}
Run Code Online (Sandbox Code Playgroud)

我得到的错误是在 ClassReader 实例化的那一行。我猜这个错误是因为 urlClassloader 以某种方式在当前类加载器的层次结构下......但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();
        }

    }

}
Run Code Online (Sandbox Code Playgroud)

在 premain() 方法中实例化转换器时设置检测。我试图避免使用 Javassist。你能帮我解决这个问题吗？

这是我得到的例外： 

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)
Run Code Online (Sandbox Code Playgroud)

==== 编辑 ====

使用 url 类加载器修复问题后，我现在收到了 Spring 尝试刷新其上下文时发生的错误：

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
Run Code Online (Sandbox Code Playgroud)

xbm*_*ono 2

我设法解决了这个问题。如果有人遇到同样的问题，这里的问题是：

我正在使用 ClassReader 和 ClassWriter。由于某种原因，ClassWriter 正在填充字节代码，也许我的错误是将已编译的类传递给类编写器，但无论如何，以下代码：

    ClassReader reader = new ClassReader(is);
    ClassWriter writer = new ClassWriter(reader, ClassWriter.COMPUTE_FRAMES | ClassWriter.COMPUTE_MAXS);
    byte[] content = writer.toByteArray();
Run Code Online (Sandbox Code Playgroud)

替换为：

        InputStream is = urlClassLoader.getResourceAsStream(className + ".class");

        byte[] content = new byte[is.available()];
        is.read(content);

        System.out.println ("Original class version: " + ((classfileBuffer[6]&0xff)<<8 | (classfileBuffer[7]&0xff)));
        System.out.println ("Redefined class version: " + ((content[6]&0xff)<<8 | (content[7]&0xff)));
Run Code Online (Sandbox Code Playgroud)

正如您所看到的，我正在使用 InputStream 直接检索字节码。这解决了这个问题，如果您感兴趣的话，Spring 很好地检测到了差异并刷新了上下文。

====编辑====

我注意到在这里使用 URLClassLoader 并不可靠，因为由于某种原因，它可能返回应用程序本身中已加载的类，而不是 JAR 文件中的类。它是随机的，有时返回 jar 内的类，有时返回原始类，因此我决定删除 URLClassLoader 并在遍历 jar 文件时将类文件作为 InputStream 获取。这是我的变压器的最终代码，供需要它的任何人使用：

public class JarFileClassTransformer implements ClassFileTransformer {

private String jarFileName = null;
protected Map<String, InputStream> classNames = new HashMap<>();
static Instrumentation instrumentation = null;

/**
 * Constructor.
 * @param jarFileName
 */
public JarFileClassTransformer(String jarFileName) {
    this.jarFileName = jarFileName;

    File file  = new File(jarFileName);
    System.out.println("Jar file '" + this.jarFileName + "' " + (file.exists() ? "exists" : "doesn't exists!"));

    if(file.exists()) {
        try {
            JarFile jarFile = new JarFile(file);
            Enumeration e = jarFile.entries();

            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.put(jarClassName, jarFile.getInputStream(je));

            }
        } catch (IOException e) {
            e.printStackTrace();
        }

    }

}

@Override
public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {

    if(classNames.containsKey(className.replace("/", "."))) {
        System.out.format("\n==> Found %s to replace with the existing version\n", className);
        try {

            Class c = loader.loadClass(className.replace("/", "."));
            System.out.println("Existing class: " + c);
            InputStream is = classNames.get(className.replace("/", "."));

            byte[] content = new byte[is.available()];
            is.read(content);

            System.out.println("Original class version: " + ((classfileBuffer[6]&0xff)<<8 | (classfileBuffer[7]&0xff)));
            System.out.println("Redefined class version: " + ((content[6]&0xff)<<8 | (content[7]&0xff)));

            System.out.println("Original bytecode: " + new String(classfileBuffer));
            System.out.println("Redefined byte code: " + new String(content));
            ClassDefinition cd = new ClassDefinition(c, content);
            instrumentation.redefineClasses(cd);

            return content;
        } catch (Throwable e) {
            e.printStackTrace();

        }

    }
    return classfileBuffer;
}
Run Code Online (Sandbox Code Playgroud)

}

归档时间：

查看次数：

3379 次

最近记录：

9 年，6 月 前
相关归档
比较Java枚举成员:==或equals()？ 1645
Mockito.any()传递与泛型的接口 145
为什么String.split需要管道分隔符进行转义？ 140
如何在Java中获取文件大小 118
Mockito,JUnit和Spring 75
由于java中的继承而创建了多少个对象？ 54
我可以在Java 8中复制Stream吗？ 54
如果父项的实例,instanceof是否返回true？ 46
我收到了这个警告:非varargs调用varargs方法,最后一个参数的参数类型不精确; 45
配置项目“:app”时出现问题。在 react-native 中并给出一些字节码作为错误 5
难疑归档
Python有一个字符串'contains'子串方法吗？ 3601
从Git中的分支中删除提交 3035
不区分大小写'包含(字符串)' 2785
如何使用Curl从终端/命令行发布JSON数据到测试Spring REST？ 2606
如何将列表拆分为大小均匀的块？ 2068
如何修复java.lang.UnsupportedClassVersionError:不支持的major.minor版本 1532
如何确定Python变量的类型？ 1437
如何从其他线程更新GUI？ 1331
我如何修剪空白？ 1035
如何在psql中切换数据库？ 1029