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这篇文章主要讲解了“Java ASM使用logback日志级别动态切换的方法”，文中的讲解内容简单清晰，易于学习与理解，下面请大家跟着小编的思路慢慢深入，一起来研究和学习“Java ASM使用logback日志级别动态切换的方法”吧！
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：
单个生产环境上，有几百近千个微服务
日志级别切换不重启服务，要求即时生效果
由业务开发人员去修改代码或增加相关依赖配置等涉及面广，推动进度慢
后期动态实时过滤垃圾日志，减少io和磁盘空间成本
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
logback-core:核心代码模块
logback-classic:log4j的一个改良版本，同时实现了slf4j的接口
logback-access:访问模块与Servlet容器集成提供通过Http来访问日志的功能
ContextInitializer类是logback自动配置流程的逻辑实现
日志级别由Logger维护和使用。其成员变量Level正是由Logger维护
Logger中有filterAndLog_0_Or3Plus、filterAndLog_1、filterAndLog_2三个不同参数的过滤日志输出方法
Logger中的setLevel就是对日志级别的维护
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：
每次调整扫描间隔时间都要重启服务
90%以上的扫描都是无用功，因为生产上的日志级别不可能经常有切换需求，也不允许这么做
生效不实时，如果设定在一分钟或几分钟扫描一次，那么让日志级别调整后生效就不是即时生效的，不过这个可以忽略
该方案满足不了我们的垃圾日志丢弃的需求，比如根据某些关键字丢弃日志的输出。针对这种历史原因打印很多垃圾日志的情况，考虑到时间成本，不可能让业务研发去优化。
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的加载类
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
寻找目标程序
执行jar
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
效果
PS:如果出现校验失败(caused by: java.lang.verifyerror)，请配上jvm参数：-noverify
感谢各位的阅读，以上就是“Java ASM使用logback日志级别动态切换的方法”的内容了，经过本文的学习后，相信大家对Java ASM使用logback日志级别动态切换的方法这一问题有了更深刻的体会，具体使用情况还需要大家实践验证。这里是亿速云，小编将为大家推送更多相关知识点的文章，欢迎关注！
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