Arthas 的 jad 命令 mc 命令 classloader 命令实战

柔光的暖阳◎ 2022-09-10 04:08 334阅读 0赞

# 一 点睛 #

> jad：反编译，将字节码反编译成 java 源码
> 
> mc：内存编译器，编译 java 文件为字节码
> 
> redefine：加载外部的 字节码文件，替换 jvm 已加载的类，推荐使用 retransform 命令替换 redefine
> 
> classloader：将 JVM 中所有的classloader的信息统计出来，并可以展示继承树，urls等。

# 二 代码 #

package chapter03;
    
    import java.util.ArrayList;
    import java.util.concurrent.TimeUnit;
    
    public class JProfilerTest {
        public static void main(String[] args) {
            while (true){
                ArrayList list = new ArrayList();
                for (int i = 0; i < 500; i++) {
                    Data data = new Data();
                    list.add(data);
                }
                try {
                    TimeUnit.MILLISECONDS.sleep(500);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }
    
    class Data{
        private int size = 10;
        private byte[] buffer = new byte[1024*1024]; // 1 mb
        private String info = "hello,China";
    }

# 三 windows下进入命令界面 #

D:\ProgramFiles\arthas-packaging-3.5.4-bin>jps
    10656 Jps
    12736 Launcher
    2864
    10668 JProfilerTest
    
    D:\ProgramFiles\arthas-packaging-3.5.4-bin>as.bat 10668
    环境变量 JAVA_TOOL_OPTIONS 没有定义
    JAVA_HOME: D:\ProgramFiles\Java\jdk1.8.0_251
    telnet port: 3658
    http port: 8563
    信息: 用提供的模式无法找到文件。
    telnet wasn't found, please google how to install telnet under windows.
    Try to visit http://127.0.0.1:8563 to connecto arthas server.

# 四 实战 #

# 反编译已加载的 String 类
    [arthas@13768]$ jad java.lang.String
    
    ClassLoader:
    
    Location:
            /*
             * Decompiled with CFR.
             */
            package java.lang;
    
            import java.io.ObjectStreamField;
            import java.io.Serializable;
            import java.io.UnsupportedEncodingException;
            import java.nio.charset.Charset;
            import java.util.ArrayList;
            import java.util.Arrays;
            import java.util.Comparator;
            import java.util.Formatter;
            import java.util.Locale;
            import java.util.Objects;
            import java.util.StringJoiner;
            import java.util.regex.Matcher;
            import java.util.regex.Pattern;
    
            public final class String
            implements Serializable,
            Comparable<String>,
            CharSequence {
                private final char[] value;
                private int hash;
                private static final long serialVersionUID = -6849794470754667710L;
                private static final ObjectStreamField[] serialPersistentFields = new ObjectStreamField[0];
                public static final Comparator<String> CASE_INSENSITIVE_ORDER = new CaseInsensitiveComparator();
    
                public String(byte[] byArray, int n, int n2) {
    /*545*/         String.checkBounds(byArray, n, n2);
    /*546*/         this.value = StringCoding.decode(byArray, n, n2);
                }
    
                public String(byte[] byArray, Charset charset) {
    /*515*/         this(byArray, 0, byArray.length, charset);
                }
    
                public String(byte[] byArray, String string) throws UnsupportedEncodingException {
    /*491*/         this(byArray, 0, byArray.length, string);
                }
    
                public String(byte[] byArray, int n, int n2, Charset charset) {
    /*460*/         if (charset == null) {
                        throw new NullPointerException("charset");
                    }
    /*462*/         String.checkBounds(byArray, n, n2);
    /*463*/         this.value = StringCoding.decode(charset, byArray, n, n2);
                }
    
                public String(byte[] byArray, int n, int n2, String string) throws UnsupportedEncodingException {
    /*423*/         if (string == null) {
                        throw new NullPointerException("charsetName");
                    }
    /*425*/         String.checkBounds(byArray, n, n2);
    /*426*/         this.value = StringCoding.decode(string, byArray, n, n2);
                }
    
                String(char[] cArray, boolean bl) {
    /*611*/         this.value = cArray;
                }
    
                public String(StringBuilder stringBuilder) {
    /*600*/         this.value = Arrays.copyOf(stringBuilder.getValue(), stringBuilder.length());
                }
    ......
    }
    
    # 反编译某个类中的某个具体方法
    [arthas@13768]$ jad java.lang.String toString
    
    ClassLoader:
    
    Location:
    
            @Override
            public String toString() {
    /*2887*/     return this;
            }
    
    # 反编译已加载的 chapter03.Data 类
    [arthas@13768]$ jad chapter03.Data
    
    ClassLoader:
    +-sun.misc.Launcher$AppClassLoader@18b4aac2
      +-sun.misc.Launcher$ExtClassLoader@17d9dda9
    
    Location:
    /E:/JVMDemo3/out/production/JVMDemo3/
    
    /*
    * Decompiled with CFR.
    */
    package chapter03;
    
    class Data {
        private int size = 10;
        private byte[] buffer = new byte[0x100000];
        private String info = "hello,China";
    
        Data() {
        }
    }
    
    Affect(row-cnt:1) cost in 130 ms.
    
    # 编译 HelloWorld.java 为 HelloWorld.class
    [arthas@13768]$ mc E:/JVMDemo3/src/chapter03/HelloWorld.java
    Memory compiler output:
    E:\JVMDemo3\chapter03\HelloWorld.class
    Affect(row-cnt:1) cost in 580 ms.
    # 替换 JVM 中已加载的 HelloWorld.class
    [arthas@13768]$ redefine E:\JVMDemo3\chapter03\HelloWorld.class
    file does not exist, path:E:JVMDemo3chapter03HelloWorld.class
    
    # JVM 中的类加载器
    [arthas@13768]$ classloader
    name                                       numberOfInstances  loadedCountTotal
    com.taobao.arthas.agent.ArthasClassloader  1                  2983
    BootstrapClassLoader                       1                  2602
    java.net.FactoryURLClassLoader             1                  799
    sun.misc.Launcher$ExtClassLoader           1                  61
    sun.misc.Launcher$AppClassLoader           1                  8
    sun.reflect.DelegatingClassLoader          2                  2
    Affect(row-cnt:6) cost in 6 ms.
    
    # 以继承树的方式展示类加载器
    [arthas@13768]$ classloader -t
    +-BootstrapClassLoader
    +-sun.misc.Launcher$ExtClassLoader@17d9dda9
      +-com.taobao.arthas.agent.ArthasClassloader@449de647
      +-sun.misc.Launcher$AppClassLoader@18b4aac2
        +-java.net.FactoryURLClassLoader@75bcd85d
    Affect(row-cnt:5) cost in 6 ms.
    
    # 以列表的方式展示类加载器
    [arthas@13768]$ classloader -l
    name                                                loadedCount  hash      parent
    BootstrapClassLoader                                2602         null      null
    com.taobao.arthas.agent.ArthasClassloader@449de647  2986         449de647  sun.misc.Launcher$ExtClassLoader@17d9dda9
    java.net.FactoryURLClassLoader@75bcd85d             799          75bcd85d  sun.misc.Launcher$AppClassLoader@18b4aac2
    sun.misc.Launcher$AppClassLoader@18b4aac2           8            18b4aac2  sun.misc.Launcher$ExtClassLoader@17d9dda9
    sun.misc.Launcher$ExtClassLoader@17d9dda9           61           17d9dda9  null
    Affect(row-cnt:5) cost in 4 ms.
    
    # 查看 AppClassLoader 实际的 urls
    [arthas@13768]$ classloader -c 18b4aac2
    file:/D:/ProgramFiles/Java/jdk1.8.0_251/jre/lib/charsets.jar
    file:/D:/ProgramFiles/Java/jdk1.8.0_251/jre/lib/deploy.jar
    file:/D:/ProgramFiles/Java/jdk1.8.0_251/jre/lib/ext/access-bridge-64.jar
    file:/D:/ProgramFiles/Java/jdk1.8.0_251/jre/lib/ext/cldrdata.jar
    file:/D:/ProgramFiles/Java/jdk1.8.0_251/jre/lib/ext/dnsns.jar
    file:/D:/ProgramFiles/Java/jdk1.8.0_251/jre/lib/ext/jaccess.jar
    file:/D:/ProgramFiles/Java/jdk1.8.0_251/jre/lib/ext/jfxrt.jar
    file:/D:/ProgramFiles/Java/jdk1.8.0_251/jre/lib/ext/localedata.jar
    file:/D:/ProgramFiles/Java/jdk1.8.0_251/jre/lib/ext/nashorn.jar
    file:/D:/ProgramFiles/Java/jdk1.8.0_251/jre/lib/ext/sunec.jar
    file:/D:/ProgramFiles/Java/jdk1.8.0_251/jre/lib/ext/sunjce_provider.jar
    file:/D:/ProgramFiles/Java/jdk1.8.0_251/jre/lib/ext/sunmscapi.jar
    file:/D:/ProgramFiles/Java/jdk1.8.0_251/jre/lib/ext/sunpkcs11.jar
    file:/D:/ProgramFiles/Java/jdk1.8.0_251/jre/lib/ext/zipfs.jar
    file:/D:/ProgramFiles/Java/jdk1.8.0_251/jre/lib/javaws.jar
    file:/D:/ProgramFiles/Java/jdk1.8.0_251/jre/lib/jce.jar
    file:/D:/ProgramFiles/Java/jdk1.8.0_251/jre/lib/jfr.jar
    file:/D:/ProgramFiles/Java/jdk1.8.0_251/jre/lib/jfxswt.jar
    file:/D:/ProgramFiles/Java/jdk1.8.0_251/jre/lib/jsse.jar
    file:/D:/ProgramFiles/Java/jdk1.8.0_251/jre/lib/management-agent.jar
    file:/D:/ProgramFiles/Java/jdk1.8.0_251/jre/lib/plugin.jar
    file:/D:/ProgramFiles/Java/jdk1.8.0_251/jre/lib/resources.jar
    file:/D:/ProgramFiles/Java/jdk1.8.0_251/jre/lib/rt.jar
    file:/E:/JVMDemo3/out/production/JVMDemo3/
    file:/D:/ProgramFiles/JetBrains/IDEA/lib/idea_rt.jar
    file:/D:/ProgramFiles/arthas-packaging-3.5.4-bin/arthas-agent.jar
    
    
    Affect(row-cnt:52) cost in 1 ms.