一切皆有因果，所有事情，都有事件驱动。本方案的日志级别切换是由这样的背景下产生的：
在跟敌人发起战争之前，只有先发解敌方的情况，才能做到百战百胜。要想对logback的日志级别做动态切换，首先至少对logback做个初步的了解、和看看它有没有提供现成的实现方案。下面简单介绍一下logback跟这次需求有关的内容。
logback是java的日志开源组件，是log4j创始人写的，目前主要分为3个模块
slf4j的接口
在满头苦干之前，先了解市面上的方案。是设计师们乃至产品大佬们寻求最优解决方案的思路。
这个方案是logback自带现成的实现，只要开启配置就可以实现所谓的日志级别动态切换。配置方法：在logback的配置文件中，增加定时扫描器即可，如：
<configuration scan="true" scanPeriod="30 seconds" debug="false">
该方案可以不需要研发成本，运维人员自己配上并能使用。
它的缺点是：
当然，还有其它方案，如：自己定义接口api。来直接调用Logger中的setLevel方法，达到调整级别的目的；springboot的集成。
这些方案都不避免不了专主于业务开发角色的参与。
通过asm动态修改指令，该方案除了能满足调整日志级别即时生效之外。还可以满足过滤日志的需求
具体实现如下，在这里就不对asm做介绍了，不了解的同学，需要先去熟悉asm、java agent和jvm的指令：
一、idea创建maven工程
二、maven引入依赖
<dependencies> <dependency> <groupId>org.ow2.asm</groupId> <artifactId>asm</artifactId> <version>7.1</version> </dependency> <dependency> <artifactId>asm-commons</artifactId> <groupId>org.ow2.asm</groupId> <version>7.1</version> </dependency> <dependency> <groupId>com.sun</groupId> <artifactId>tools</artifactId> <version>1.8</version> <scope>system</scope> <systemPath>/Library/Java/JavaVirtualMachines/jdk1.8.0_191.jdk/Contents/Home/lib/tools.jar</systemPath> </dependency> </dependencies><build> <plugins> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-jar-plugin</artifactId> <version>3.2.0</version> <configuration> <archive> <manifestEntries> <!-- 主程序启动类 --> <Agent-Class> agent.LogbackAgentMain </Agent-Class> <!-- 允许重新定义类 --> <Can-Redefine-Classes>true</Can-Redefine-Classes> <!-- 允许转换并重新加载类 --> <Can-Retransform-Classes>true</Can-Retransform-Classes> </manifestEntries> </archive> </configuration> </plugin> <plugin> <artifactId>maven-compiler-plugin</artifactId> <configuration> <source>1.8</source> <target>1.8</target> <encoding>UTF-8</encoding> <compilerArguments> <verbose /> <!-- 将jdk的依赖jar打入项目中--> <bootclasspath>${java.home}/lib/rt.jar</bootclasspath> </compilerArguments> </configuration> </plugin> </plugins></build>
三、编写attrach启动类
package agent;import java.lang.instrument.Instrumentation;import java.lang.instrument.UnmodifiableClassException;/** * @author dengbp * @ClassName LogbackAgentMain * @Description attach 启动器 * @date 3/25/22 6:27 PM */public class LogbackAgentMain { private static String FILTER_CLASS = "ch.qos.logback.classic.Logger"; public static void agentmain(String agentArgs, Instrumentation inst) throws UnmodifiableClassException { System.out.println("agentArgs:" + agentArgs); inst.addTransformer(new LogBackFileTransformer(agentArgs), true); Class[] classes = inst.getAllLoadedClasses(); for (int i = 0; i < classes.length; i++) { if (FILTER_CLASS.equals(classes[i].getName())) { System.out.println("----重新加载Logger开始----"); inst.retransformClasses(classes[i]); System.out.println("----重新加载Logger完毕----"); break; } } }}
四、实现字节码转换处理器
package agent;import jdk.internal.org.objectweb.asm.ClassReader;import jdk.internal.org.objectweb.asm.ClassVisitor;import jdk.internal.org.objectweb.asm.ClassWriter;import java.lang.instrument.ClassFileTransformer;import java.security.ProtectionDomain;/** * @author dengbp * @ClassName LogBackFileTransformer * @Description 字节码文件转换器 * @date 3/25/22 6:25 PM */public class LogBackFileTransformer implements ClassFileTransformer { private final String level; private static String CLASS_NAME = "ch/qos/logback/classic/Logger"; public LogBackFileTransformer(String level) { this.level = level; } @Override public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) { if (!CLASS_NAME.equals(className)) { return classfileBuffer; } ClassReader cr = new ClassReader(classfileBuffer); ClassWriter cw = new ClassWriter(cr, ClassWriter.COMPUTE_FRAMES); ClassVisitor cv1 = new LogBackClassVisitor(cw, level); /*ClassVisitor cv2 = new LogBackClassVisitor(cv1);*/ // asm框架使用到访问模式和责任链模式 // ClassReader 只需要 accept 责任链中的头节点处的 ClassVisitor即可 cr.accept(cv1, ClassReader.SKIP_FRAMES | ClassReader.SKIP_DEBUG); System.out.println("end..."); return cw.toByteArray(); }}
五、实现Logger元素的访问者
package agent;import jdk.internal.org.objectweb.asm.ClassVisitor;import jdk.internal.org.objectweb.asm.MethodVisitor;import org.objectweb.asm.Opcodes;/** * @author dengbp * @ClassName LogBackClassVisitor * @Description Logger类元素访问者 * @date 3/25/22 5:01 PM */public class LogBackClassVisitor extends ClassVisitor { private final String level; /** * asm版本 */ private static final int ASM_VERSION = Opcodes.ASM4; public LogBackClassVisitor(ClassVisitor classVisitor, String level) { super(ASM_VERSION, classVisitor); this.level = level; } @Override public MethodVisitor visitMethod(int access, String name, String descriptor, String signature, String[] exceptions) { MethodVisitor mv = super.visitMethod(access, name, descriptor, signature, exceptions); return new LogFilterMethodVisitor(api, mv, access, name, descriptor, level); }}
六、最后实现Logger关键方法的访问者
该访问者(类)，实现日志级别的切换，需要对Logger的三个日志过滤方法进行指令的修改。原理是把命令行入参的日志级别参数值覆盖其成员变量effectiveLevelInt的值，由于篇幅过大，只贴核心部分代码，请看下面：
package agent;import jdk.internal.org.objectweb.asm.Label;import jdk.internal.org.objectweb.asm.MethodVisitor;import jdk.internal.org.objectweb.asm.commons.AdviceAdapter;import org.objectweb.asm.Opcodes;/** * @author dengbp * @ClassName LogFilterMethodVisitor * @Description Logger类日志过滤方法元素访问者 * @date 3/25/22 5:01 PM */public class LogFilterMethodVisitor extends AdviceAdapter { private String methodName; private final String level; private static final String filterAndLog_1 = "filterAndLog_1"; private static final String filterAndLog_2 = "filterAndLog_2"; private static final String filterAndLog_0_Or3Plus = "filterAndLog_0_Or3Plus"; protected LogFilterMethodVisitor(int api, MethodVisitor methodVisitor, int access, String name, String descriptor, String level) { super(api, methodVisitor, access, name, descriptor); this.methodName = name; this.level = level; } /** * Description 在访问方法的头部时被访问 * @param * @return void * @Author dengbp * @Date 3:36 PM 4/1/22 **/ @Override public void visitCode() { System.out.println("visitCode method"); super.visitCode(); } @Override protected void onMethodEnter() { System.out.println("开始重写日志级别为："+level); System.out.println("----准备修改方法----"); if (filterAndLog_1.equals(methodName)) { modifyLogLevel_1(); } if (filterAndLog_2.equals(methodName)) { modifyLogLevel_2(); } if (filterAndLog_0_Or3Plus.equals(methodName)) { modifyLogLevel_3(); } System.out.println("重写日志级别成功...."); }
其中modifyLogLevel_1(); modifyLogLevel_2();modifyLogLevel_3();分别对应filterAndLog_1、filterAndLog_2、filterAndLog_0_Or3Plus方法指令的修改。下面只贴modifyLogLevel_1的实现
/** * Description 修改目标方法：filterAndLog_1 * @param * @return void * @Author dengbp * @Date 2:20 PM 3/31/22 **/ private void modifyLogLevel_1(){ Label l0 = new Label(); mv.visitLabel(l0); mv.visitLineNumber(390, l0); mv.visitVarInsn(Opcodes.ALOAD, 0); mv.visitLdcInsn(level); mv.visitMethodInsn(Opcodes.INVOKESTATIC, "ch/qos/logback/classic/Level", "toLevel", "(Ljava/lang/String;)Lch/qos/logback/classic/Level;", false); mv.visitFieldInsn(Opcodes.GETFIELD, "ch/qos/logback/classic/Level", "levelInt", "I"); mv.visitFieldInsn(Opcodes.PUTFIELD, "ch/qos/logback/classic/Logger", "effectiveLevelInt", "I"); Label l1 = new Label(); mv.visitLabel(l1); mv.visitLineNumber(392, l1); mv.visitVarInsn(Opcodes.ALOAD, 0); mv.visitFieldInsn(Opcodes.GETFIELD, "ch/qos/logback/classic/Logger", "loggerContext", "Lch/qos/logback/classic/LoggerContext;"); mv.visitVarInsn(Opcodes.ALOAD, 2); mv.visitVarInsn(Opcodes.ALOAD, 0); mv.visitVarInsn(Opcodes.ALOAD, 3); mv.visitVarInsn(Opcodes.ALOAD, 4); mv.visitVarInsn(Opcodes.ALOAD, 5); mv.visitVarInsn(Opcodes.ALOAD, 6); mv.visitMethodInsn(Opcodes.INVOKEVIRTUAL, "ch/qos/logback/classic/LoggerContext", "getTurboFilterChainDecision_1", "(Lorg/slf4j/Marker;Lch/qos/logback/classic/Logger;Lch/qos/logback/classic/Level;Ljava/lang/String;Ljava/lang/Object;Ljava/lang/Throwable;)Lch/qos/logback/core/spi/FilterReply;", false); mv.visitVarInsn(Opcodes.ASTORE, 7); Label l2 = new Label(); mv.visitLabel(l2); mv.visitLineNumber(394, l2); mv.visitVarInsn(Opcodes.ALOAD, 7); mv.visitFieldInsn(Opcodes.GETSTATIC, "ch/qos/logback/core/spi/FilterReply", "NEUTRAL", "Lch/qos/logback/core/spi/FilterReply;"); Label l3 = new Label(); mv.visitJumpInsn(Opcodes.IF_ACMPNE, l3); Label l4 = new Label(); mv.visitLabel(l4); mv.visitLineNumber(395, l4); mv.visitVarInsn(Opcodes.ALOAD, 0); mv.visitFieldInsn(Opcodes.GETFIELD, "ch/qos/logback/classic/Logger", "effectiveLevelInt", "I"); mv.visitVarInsn(Opcodes.ALOAD, 3); mv.visitFieldInsn(Opcodes.GETFIELD, "ch/qos/logback/classic/Level", "levelInt", "I"); Label l5 = new Label(); mv.visitJumpInsn(Opcodes.IF_ICMPLE, l5); Label l6 = new Label(); mv.visitLabel(l6); mv.visitLineNumber(396, l6); mv.visitInsn(Opcodes.RETURN); mv.visitLabel(l3); mv.visitLineNumber(398, l3); mv.visitFrame(Opcodes.F_APPEND, 1, new Object[]{"ch/qos/logback/core/spi/FilterReply"}, 0, null); mv.visitVarInsn(Opcodes.ALOAD, 7); mv.visitFieldInsn(Opcodes.GETSTATIC, "ch/qos/logback/core/spi/FilterReply", "DENY", "Lch/qos/logback/core/spi/FilterReply;"); mv.visitJumpInsn(Opcodes.IF_ACMPNE, l5); Label l7 = new Label(); mv.visitLabel(l7); mv.visitLineNumber(399, l7); mv.visitInsn(Opcodes.RETURN); mv.visitLabel(l5); mv.visitLineNumber(402, l5); mv.visitFrame(Opcodes.F_SAME, 0, null, 0, null); mv.visitVarInsn(Opcodes.ALOAD, 0); mv.visitVarInsn(Opcodes.ALOAD, 1); mv.visitVarInsn(Opcodes.ALOAD, 2); mv.visitVarInsn(Opcodes.ALOAD, 3); mv.visitVarInsn(Opcodes.ALOAD, 4); mv.visitInsn(Opcodes.ICONST_1); mv.visitTypeInsn(Opcodes.ANEWARRAY, "java/lang/Object"); mv.visitInsn(Opcodes.DUP); mv.visitInsn(Opcodes.ICONST_0); mv.visitVarInsn(Opcodes.ALOAD, 5); mv.visitInsn(Opcodes.AASTORE); mv.visitVarInsn(Opcodes.ALOAD, 6); mv.visitMethodInsn(Opcodes.INVOKESPECIAL, "ch/qos/logback/classic/Logger", "buildLoggingEventAndAppend", "(Ljava/lang/String;Lorg/slf4j/Marker;Lch/qos/logback/classic/Level;Ljava/lang/String;[Ljava/lang/Object;Ljava/lang/Throwable;)V", false); Label l8 = new Label(); mv.visitLabel(l8); mv.visitLineNumber(403, l8); mv.visitInsn(Opcodes.RETURN); Label l9 = new Label(); mv.visitLabel(l9); mv.visitLocalVariable("this", "Lch/qos/logback/classic/Logger;", null, l0, l9, 0); mv.visitLocalVariable("localFQCN", "Ljava/lang/String;", null, l0, l9, 1); mv.visitLocalVariable("marker", "Lorg/slf4j/Marker;", null, l0, l9, 2); mv.visitLocalVariable("level", "Lch/qos/logback/classic/Level;", null, l0, l9, 3); mv.visitLocalVariable("msg", "Ljava/lang/String;", null, l0, l9, 4); mv.visitLocalVariable("param", "Ljava/lang/Object;", null, l0, l9, 5); mv.visitLocalVariable("t", "Ljava/lang/Throwable;", null, l0, l9, 6); mv.visitLocalVariable("decision", "Lch/qos/logback/core/spi/FilterReply;", null, l2, l9, 7); mv.visitMaxs(9, 8); mv.visitEnd(); }
七、最后再编写加载attach Agent的启动类
import com.sun.tools.attach.VirtualMachine;import java.io.IOException;import java.io.UnsupportedEncodingException;/** * @author dengbp * @ClassName MyAttachMain * @Description jar 执行命令： * @date 3/25/22 4:12 PM */public class MyAttachMain { private static final int ARGS_SIZE = 2; public static void main(String[] args) { if (args == null || args.length != ARGS_SIZE) { System.out.println("请输入进程id和日志级别(ALL、TRACE、DEBUG、INFO、WARN、ERROR、OFF),如：31722 info"); return; } VirtualMachine vm = null; try { System.out.println("修改的进程id:" + args[0]); vm = VirtualMachine.attach(args[0]); System.out.println("调整日志级别为：" + args[1]); vm.loadAgent(getJar(), args[1]); } catch (Exception e) { e.printStackTrace(); } finally { if (vm != null) { try { vm.detach(); } catch (IOException e) { e.printStackTrace(); } } } } private static String getJar() throws UnsupportedEncodingException { String jarFilePath = MyAttachMain.class.getProtectionDomain().getCodeSource().getLocation().getFile(); jarFilePath = java.net.URLDecoder.decode(jarFilePath, "UTF-8"); int beginIndex = 0; int endIndex = jarFilePath.length(); if (jarFilePath.contains(".jar")) { endIndex = jarFilePath.indexOf(".jar") + 4; } if (jarFilePath.startsWith("file:")) { beginIndex = jarFilePath.indexOf("file:") + 5; } jarFilePath = jarFilePath.substring(beginIndex, endIndex); System.out.println("jar path:" + jarFilePath); return jarFilePath; }}
八、打包执行
java -Xbootclasspath/a:/Library/Java/JavaVirtualMachines/jdk1.8.0_191.jdk/Contents/Home/lib/tools.jar -cp change-log-agent-1.0.1.jar MyAttachMain 52433 DEBUG
java -Xbootclasspath/a:/Library/Java/JavaVirtualMachines/jdk1.8.0_191.jdk/Contents/Home/lib/tools.jar -cp change-log-agent-1.0.1.jar MyAttachMain 52433 ERROR
java -Xbootclasspath/a:/Library/Java/JavaVirtualMachines/jdk1.8.0_191.jdk/Contents/Home/lib/tools.jar -cp change-log-agent-1.0.1.jar MyAttachMain 52433 INFO
PS:如果出现校验失败(caused by: java.lang.verifyerror)，请配上jvm参数：-noverify
通过attach探针动态修改指令技术，可以在服务不停的情况下，实现部分代码的热部署； 也可以对代码的增强处理。下一期：代码热部署工具
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