JAVA找出哪个类import了不存在的类1. 背景在JAVA中一个类A,import 另外的一个类B.然后在容器启动时,只会提示B类不存在,不会出现任何A类相关的信息 Tomcat中错误信息如下,测试代码使用org.slf4j.Logger说明 ,部分错误信息如下at java.lang.Thread.run(Thread.java:748) Caused by: java.lang.NoClassDefFoundError: Lorg/slf4j/Logger; at java.lang.Class.getDeclaredFields0(Native Method) at java.lang.Class.privateGetDeclaredFields(Class.java:2583) ... 10 more Caused by: java.lang.ClassNotFoundException: org.slf4j.Logger at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1360) at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1182) ... 23 more2. 日志能解决吗在容器TOMCAT为类WebappClassLoaderBase开启详细日志,在/conf/logging.properties 添加如下日志org.apache.catalina.loader.WebappClassLoaderBase.level FINE加上日志以后,输出内容如下org.apache.catalina.loader.WebappClassLoaderBase.loadClass Loading class from local repository org.apache.catalina.loader.WebappClassLoaderBase.loadClass loadClass(dxxs.BTestClass, false) org.apache.catalina.loader.WebappClassLoaderBase.loadClass Searching local repositories org.apache.catalina.loader.WebappClassLoaderBase.findClass findClass(dxxs.BTestClass) org.apache.catalina.loader.WebappClassLoaderBase.loadClass Loading class from local repository org.apache.catalina.loader.WebappClassLoaderBase.loadClass loadClass(org.slf4j.Logger, false) org.apache.catalina.loader.WebappClassLoaderBase.loadClass Searching local repositories org.apache.catalina.loader.WebappClassLoaderBase.findClass findClass(org.slf4j.Logger) org.apache.catalina.loader.WebappClassLoaderBase.findClass -- Returning ClassNotFoundException从日志输出上来看,只是知道dxxs.BTestClass后就加载org.slf4j.Logger,但并不能确定就是dxxs.BTestClass导致的3. 分析字节码能解决吗通过日志分析,感觉上是可以,但是不能确定.所以为了确定,采用 Java Agent 方式分析,当前加载的class是否引用了当前环境不存在的class在TOMCAT启动时,配置参数,在启动时,注入编写jarset JAVA_OPTS%JAVA_OPTS% -javaagent:%CATALINA_HOME%\lib\class-load-monitor-agent.jar%CATALINA_HOME%\conf\agent-config.properties再次启动后,对应输出内容如下[ClassLoadMonitor] [ClassLoadMonitor] FOUND REFERENCE TO MISSING CLASS: [ClassLoadMonitor] Source class: dxxs.BTestClass [ClassLoadMonitor] Missing class: org.slf4j.Logger [ClassLoadMonitor] ClassLoader: ParallelWebappClassLoader context: test delegate: false ---------- Parent Classloader: java.net.URLClassLoader87aac27 [ClassLoadMonitor] Thread: localhost-startStop-1这次从日志中,可以明确知道dxxs.BTestClass引用了类org.slf4j.Logger,而当前环境中却不存在org.slf4j.Logger.由此问题解决4. 如何实现构建配置,实现javaagent,需要在MANIFEST.MF文件中配置Premain-Class和Agent-Class,所有当前pom.xml构建配置信息如下plugin groupIdorg.apache.maven.plugins/groupId artifactIdmaven-jar-plugin/artifactId version3.2.0/version configuration archive manifestEntries Premain-Classcom.example.ClassLoadMonitorAgent/Premain-Class Agent-Classcom.example.ClassLoadMonitorAgent/Agent-Class Can-Redefine-Classestrue/Can-Redefine-Classes Can-Retransform-Classestrue/Can-Retransform-Classes /manifestEntries /archive /configuration /plugin这个代码中实现两个方法public static void premain(String agentArgs, Instrumentation inst); public static void agentmain(String agentArgs, Instrumentation inst)添加类加载转换器inst.addTransformer(new ClassFileTransformer() { Override public byte[] transform(ClassLoader loader, String className, Class? classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException { if (className ! null classfileBuffer ! null) { String fullClassName className.replace(/, .); if (!checkedClasses.contains(fullClassName)) { checkedClasses.add(fullClassName); analyzeBytecode(fullClassName, classfileBuffer, loader); } } return classfileBuffer; } }, true);核心分析类分析代码analyzeBytecode关于常量池信息参考,可以查看地址docs.oracle.com/javase/spec…private static void analyzeBytecode(String className, byte[] bytecode, ClassLoader loader) { try { DataInputStream dis new DataInputStream(new ByteArrayInputStream(bytecode)); int magic dis.readInt(); if (magic ! 0xCAFEBABE) { return; } dis.readShort(); dis.readShort(); int constantPoolCount dis.readShort(); String[] utf8Pool new String[constantPoolCount]; int[] classRefIndices new int[constantPoolCount]; int classRefCount 0; for (int i 1; i constantPoolCount; i) { byte tag dis.readByte(); switch (tag) { case 1: // UTF8 utf8Pool[i] dis.readUTF(); break; case 7: // Class int nameIndex dis.readShort(); classRefIndices[classRefCount] nameIndex; break; case 8: // String dis.readShort(); break; case 9: // Fieldref case 10: // Methodref case 11: // InterfaceMethodref case 12: // NameAndType dis.readShort(); dis.readShort(); break; case 3: // Integer case 4: // Float dis.readInt(); break; case 5: // Long case 6: // Double dis.readLong(); i; break; case 15: // MethodHandle dis.readByte(); dis.readShort(); break; case 16: // MethodType dis.readShort(); break; case 18: // InvokeDynamic dis.readShort(); dis.readShort(); break; default: break; } } for (int i 0; i classRefCount; i) { int utf8Index classRefIndices[i]; if (utf8Index 0 utf8Index constantPoolCount utf8Pool[utf8Index] ! null) { // 小游戏 地心侠士 // 获取到当前class文件中引用类名 String referencedClass utf8Pool[utf8Index].replace(/, .); // className 配置是要检查的的类名 checkReference(className, referencedClass, loader); } } // 小游戏 地心侠士 // 检查class文件,其他地方是否包含丢失的class scanForClassReferences(className, bytecode, loader); } catch (Exception e) { } } private static void scanForClassReferences(String className, byte[] bytecode, ClassLoader loader) { // 公众号: 小满小慢 for (String missingClass : missingClasses) { String internalName missingClass.replace(., /); String descriptorFormat L internalName ;; if (containsClassReference(bytecode, internalName) || containsClassReference(bytecode, descriptorFormat)) { logClassReference(className, missingClass, loader); } } }如何使用?生成配置文件agent-config.properties配置内容如下:# 小游戏 地心侠士 # 公众号 小满小漫 精心制作 # 配置需要监控的不存在的类多个类用逗号或分号分隔 missingClassesorg.slf4j.Logger修改启动参数 在catalina.bat文件中添加,agent配置信息,修改内容如下set JAVA_OPTS%JAVA_OPTS% -javaagent:%CATALINA_HOME%\lib\class-load-monitor-agent-1.0-SNAPSHOT.jar%CATAL