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這篇文章主要講解了“Java ASM使用logback日志級別動態切換的方法”，文中的講解內容簡單清晰，易于學習與理解，下面請大家跟著小編的思路慢慢深入，一起來研究和學習“Java ASM使用logback日志級別動態切換的方法”吧！
一切皆有因果，所有事情，都有事件驅動。本方案的日志級別切換是由這樣的背景下產生的：
單個生產環境上，有幾百近千個微服務
日志級別切換不重啟服務，要求即時生效果
由業務開發人員去修改代碼或增加相關依賴配置等涉及面廣，推動進度慢
后期動態實時過濾垃圾日志，減少io和磁盤空間成本
在跟敵人發起戰爭之前，只有先發解敵方的情況，才能做到百戰百勝。要想對logback的日志級別做動態切換，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現方案。下面簡單介紹一下logback跟這次需求有關的內容。
logback是java的日志開源組件，是log4j創始人寫的，目前主要分為3個模塊
logback-core:核心代碼模塊
logback-classic:log4j的一個改良版本，同時實現了slf4j的接口
logback-access:訪問模塊與Servlet容器集成提供通過Http來訪問日志的功能
ContextInitializer類是logback自動配置流程的邏輯實現
日志級別由Logger維護和使用。其成員變量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志輸出方法
Logger中的setLevel就是對日志級別的維護
在滿頭苦干之前，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。
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志級別動態切換。配置方法：在logback的配置文件中，增加定時掃描器即可，如：
<configuration scan="true" scanPeriod="30 seconds" debug="false">
該方案可以不需要研發成本，運維人員自己配上并能使用。
它的缺點是：
每次調整掃描間隔時間都要重啟服務
90%以上的掃描都是無用功，因為生產上的日志級別不可能經常有切換需求，也不允許這么做
生效不實時，如果設定在一分鐘或幾分鐘掃描一次，那么讓日志級別調整后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志丟棄的需求，比如根據某些關鍵字丟棄日志的輸出。針對這種歷史原因打印很多垃圾日志的情況，考慮到時間成本，不可能讓業務研發去優化。
當然，還有其它方案，如：自己定義接口api。來直接調用Logger中的setLevel方法，達到調整級別的目的；springboot的集成。
這些方案都不避免不了專主于業務開發角色的參與。
通過asm動態修改指令，該方案除了能滿足調整日志級別即時生效之外。還可以滿足過濾日志的需求
具體實現如下，在這里就不對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>
<!-- 主程序啟動類 -->
<Agent-Class>
agent.LogbackAgentMain
</Agent-Class>
<!-- 允許重新定義類 -->
<Can-Redefine-Classes>true</Can-Redefine-Classes>
<!-- 允許轉換并重新加載類 -->
<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 />
<!-- 將jdk的依賴jar打入項目中-->
<bootclasspath>${java.home}/lib/rt.jar</bootclasspath>
</compilerArguments>
</configuration>
</plugin>
</plugins>
</build>三、編寫attrach啟動類
package agent;
import java.lang.instrument.Instrumentation;
import java.lang.instrument.UnmodifiableClassException;
/**
* @author dengbp
* @ClassName LogbackAgentMain
* @Description attach 啟動器
* @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("----重新加載Logger開始----");
inst.retransformClasses(classes[i]);
System.out.println("----重新加載Logger完畢----");
break;
}
}
}
}四、實現字節碼轉換處理器
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 字節碼文件轉換器
* @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框架使用到訪問模式和責任鏈模式
// ClassReader 只需要 accept 責任鏈中的頭節點處的 ClassVisitor即可
cr.accept(cv1, ClassReader.SKIP_FRAMES | ClassReader.SKIP_DEBUG);
System.out.println("end...");
return cw.toByteArray();
}
}五、實現Logger元素的訪問者
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類元素訪問者
* @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、最后實現Logger關鍵方法的訪問者
該訪問者(類)，實現日志級別的切換，需要對Logger的三個日志過濾方法進行指令的修改。原理是把命令行入參的日志級別參數值覆蓋其成員變量effectiveLevelInt的值，由于篇幅過大，只貼核心部分代碼，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類日志過濾方法元素訪問者
* @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 在訪問方法的頭部時被訪問
* @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("開始重寫日志級別為："+level);
System.out.println("----準備修改方法----");
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("重寫日志級別成功....");
}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的實現
/**
* Description 修改目標方法：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、最后再編寫加載attach Agent的加載類
import com.sun.tools.attach.VirtualMachine;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
/**
* @author dengbp
* @ClassName MyAttachMain
* @Description jar 執行命令：
* @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("請輸入進程id和日志級別(ALL、TRACE、DEBUG、INFO、WARN、ERROR、OFF),如：31722 info");
return;
}
VirtualMachine vm = null;
try {
System.out.println("修改的進程id:" + args[0]);
vm = VirtualMachine.attach(args[0]);
System.out.println("調整日志級別為：" + 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
感謝各位的閱讀，以上就是“Java ASM使用logback日志級別動態切換的方法”的內容了，經過本文的學習后，相信大家對Java ASM使用logback日志級別動態切換的方法這一問題有了更深刻的體會，具體使用情況還需要大家實踐驗證。這里是億速云，小編將為大家推送更多相關知識點的文章，歡迎關注！
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