Java ASM使用logback日誌等級動態切換方法

背景

一切都有因果，所有事情，都有事件驅動。本方案的日誌等級切換是由這樣的背景下產生的：

• 單一生產環境上，有幾百近千個微服務

• #日誌等級切換不重啟服務，要求即時生效果

• 由業務開發人員去修改程式碼或增加相關依賴配置等涉及面廣，推動進度慢

• 後期動態即時過濾垃圾日誌，減少io和磁碟空間成本

logback簡介

在跟敵人發動戰爭之前，只有先發解敵方的情況，才能做到百戰百勝。要對logback的日誌等級做動態切換，首先至少對logback做個初步的了解、和看看它有沒有提供現成的實作方案。以下簡單介紹一下logback跟這次需求有關的內容。

logback是java的日誌開源元件，是log4j創辦人寫的，目前主要分為3個模組

• logback-core:核心程式碼模組

• logback-classic:log4j的一個改良版本，同時實作了slf4j的介面

• ##logback-access:存取模組與Servlet容器整合提供透過Http來存取日誌的功能

• ContextInitializer類別是logback自動配置流程的邏輯實作

##日誌等級由Logger維護和使用。其成員變數Level正是由Logger維護
Logger中有filterAndLog_0_Or3Plus、filterAndLog_1、filterAndLog_2三個不同參數的過濾日誌輸出方法
Logger中的setLevel就是對日誌等級的維護

#解決方案

在滿頭苦幹之前，先了解市面上的方案。是設計師們乃至產品大佬們尋求最優解決方案的思路。

方案一：logback自動掃描更新

這個方案是logback自帶現成的實現，只要開啟配置就可以實現所謂的日誌等級動態切換。設定方法：在logback的設定檔中，增加定時掃描器即可，如：

<configuration scan="true" scanPeriod="30 seconds" debug="false">

此方案可以不需要研發成本，維運人員自己配上並能使用。

它的缺點是：

每次調整掃描間隔時間都要重新啟動服務
90%以上的掃描都是無用功，因為生產上的日誌等級不可能經常有切換需求，也不允許這麼做
生效不實時，如果設定在一分鐘或幾分鐘掃描一次，那麼讓日誌等級調整後生效就不是即時生效的，不過這個可以忽略
該方案滿足不了我們的垃圾日誌丟棄的需求，例如根據某些關鍵字丟棄日誌的輸出。針對這種歷史原因列印許多垃圾日誌的情況，考慮到時間成本，不可能讓業務研發去優化。
方案二：ASM動態修改字節碼

當然，還有其它方案，如：自己定義介面api。來直接呼叫Logger中的setLevel方法，達到調整等級的目的；springboot的整合。

這些方案都不避免不了專主於業務開發角色的參與。

透過asm動態修改指令，方案除了能滿足調整日誌等級即時生效之外。還可以滿足過濾日誌的需求

具體實作如下，在這裡就不對asm做介紹了，不了解的同學，需要先去熟悉asm、java agent和jvm的指令：

一、idea創建maven工程

二、maven引入依賴

<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、寫attrach啟動類別

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、實作字碼轉換處理器

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、實作Logger元素的訪客

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、最後實作Logger關鍵方法的訪客

該訪客(類別)，實現日誌等級的切換，需要對Logger的三個日誌過濾方法進行指令的修改。原理是把指令行入參的日誌等級參數值覆寫其成員變數effectiveLevelInt的值，由於篇幅過大，只貼核心部分程式碼，請看下面：

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();分別對應filterAndLog_1、filterAndLog_2、filterAndLog_0_Or3Plus方法指令的修改。下面只貼modifyLogLevel_1的實作

/**
     * 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、最後再寫載入attach Agent的載入類別

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、打包執行

尋找目標程序

執行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:如果出現校驗失敗(caused by: java.lang.verifyerror)，請配上jvm參數：-noverify

以上是Java ASM使用logback日誌等級動態切換方法的詳細內容。更多資訊請關注PHP中文網其他相關文章！