用Java实现JVM第三章《解析class文件》-白红宇

用Java实现JVM第三章《解析class文件》

阅读量：618 次

发布时间：2019-03-13

本文共 21690 字，大约阅读时间需要 72 分钟。

案例介绍

本案例主要介绍通过java代码从class文件中解析；class文件、常量池、属性表；

作为类（或者接口）信息的载体，每个class文件都完整地定义了一个类。为了使java程序可以“编写一次，处处运行”，Java虚拟机规范对class文件格式进行了严格的规定。但是另外一方面，对于从哪里加载class文件，给了足够多的自由。Java虚拟机实现可以从文件系统读取和从JAR（或ZIP）压缩包中提取clss文件。除此之外，也可以通过网络下载、从数据库加载，甚至是在运行中直接生成class文件。Java虚拟机规范中所指的class文件，并非特指位于磁盘中的.class文件，而是泛指任何格式符号规范的class数据。

环境准备

jdk 1.8.0

IntelliJ IDEA Community Edition 2018.3.1 x64

配置信息

调试配置

配置位置：Run/Debug Configurations -> program arguments

配置内容：-Xjre “C:\Program Files\Java\jdk1.8.0_161\jre” java.lang.String

代码示例

itstack-demo-jvm-03├── pom.xml└── src    └── main    │    └── java    │        └── org.itstack.demo.jvm	│             ├── classfile    │             │   ├── attributes   {BootstrapMethods/Code/ConstantValue...}    │             │   ├── constantpool {CONSTANT_TAG_CLASS/CONSTANT_TAG_FIELDREF/CONSTANT_TAG_METHODREF...}    │             │   ├── ClassFile.java    │             │   ├── ClassReader.java    │             │   └── MemberInfo.java	    │             ├── classpath    │             │   ├── impl    │             │   │   ├── CompositeEntry.java    │             │   │   ├── DirEntry.java     │             │   │   ├── WildcardEntry.java     │             │   │   └── ZipEntry.java        │             │   ├── Classpath.java    │             │   └── Entry.java        │             ├── Cmd.java    │             └── Main.java    └── test         └── java             └── org.itstack.demo.test                 └── HelloWorld.java

代码篇幅较长，不一一列举。

AttributeInfo.java

package org.itstack.demo.jvm.classfile.attributes;import org.itstack.demo.jvm.classfile.ClassReader;import org.itstack.demo.jvm.classfile.attributes.impl.*;import org.itstack.demo.jvm.classfile.constantpool.ConstantPool;/** * http://www.itstack.org * create by fuzhengwei on 2019/4/26 */public interface AttributeInfo {    void readInfo(ClassReader reader);    static AttributeInfo[] readAttributes(ClassReader reader, ConstantPool constantPool) {        int attributesCount = reader.readU2ToInt();        AttributeInfo[] attributes = new AttributeInfo[attributesCount];        for (int i = 0; i < attributesCount; i++) {            attributes[i] = readAttribute(reader, constantPool);        }        return attributes;    }    static AttributeInfo readAttribute(ClassReader reader, ConstantPool constantPool) {        int attrNameIdx = reader.readU2ToInt();        String attrName = constantPool.getUTF8(attrNameIdx);        int attrLen = reader.readU4ToInt();        AttributeInfo attrInfo = newAttributeInfo(attrName, attrLen, constantPool);        attrInfo.readInfo(reader);        return attrInfo;    }    static AttributeInfo newAttributeInfo(String attrName, int attrLen, ConstantPool constantPool) {        switch (attrName) {            case "BootstrapMethods":                return new BootstrapMethodsAttribute();            case "Code":                return new CodeAttribute(constantPool);            case "ConstantValue":                return new ConstantValueAttribute();            case "Deprecated":                return new DeprecatedAttribute();            case "EnclosingMethod":                return new EnclosingMethodAttribute(constantPool);            case "Exceptions":                return new ExceptionsAttribute();            case "InnerClasses":                return new InnerClassesAttribute();            case "LineNumberTable":                return new LineNumberTableAttribute();            case "LocalVariableTable":                return new LocalVariableTableAttribute();            case "LocalVariableTypeTable":                return new LocalVariableTypeTableAttribute();            // case "MethodParameters":            // case "RuntimeInvisibleAnnotations":            // case "RuntimeInvisibleParameterAnnotations":            // case "RuntimeInvisibleTypeAnnotations":            // case "RuntimeVisibleAnnotations":            // case "RuntimeVisibleParameterAnnotations":            // case "RuntimeVisibleTypeAnnotations":            case "Signature":                return new SignatureAttribute(constantPool);            case "SourceFile":                return new SourceFileAttribute(constantPool);            // case "SourceDebugExtension":            // case "StackMapTable":            case "Synthetic":                return new SyntheticAttribute();            default:                return new UnparsedAttribute(attrName, attrLen);        }    }}

ConstantInfo.java

package org.itstack.demo.jvm.classfile.constantpool;import org.itstack.demo.jvm.classfile.ClassReader;import org.itstack.demo.jvm.classfile.constantpool.impl.*;/** * http://www.itstack.org * create by fuzhengwei on 2019/4/26 */public interface ConstantInfo {    int CONSTANT_TAG_CLASS = 7;    int CONSTANT_TAG_FIELDREF = 9;    int CONSTANT_TAG_METHODREF = 10;    int CONSTANT_TAG_INTERFACEMETHODREF = 11;    int CONSTANT_TAG_STRING = 8;    int CONSTANT_TAG_INTEGER = 3;    int CONSTANT_TAG_FLOAT = 4;    int CONSTANT_TAG_LONG = 5;    int CONSTANT_TAG_DOUBLE = 6;    int CONSTANT_TAG_NAMEANDTYPE = 12;    int CONSTANT_TAG_UTF8 = 1;    int CONSTANT_TAG_METHODHANDLE = 15;    int CONSTANT_TAG_METHODTYPE = 16;    int CONSTANT_TAG_INVOKEDYNAMIC = 18;    void readInfo(ClassReader reader);    int tag();        static ConstantInfo readConstantInfo(ClassReader reader, ConstantPool constantPool) {        int tag = reader.readU1ToInt();        ConstantInfo constantInfo = newConstantInfo(tag, constantPool);        constantInfo.readInfo(reader);        return constantInfo;    }    static ConstantInfo newConstantInfo(int tag, ConstantPool constantPool) {        switch (tag) {            case CONSTANT_TAG_INTEGER:                return new ConstantIntegerInfo();            case CONSTANT_TAG_FLOAT:                return new ConstantFloatInfo();            case CONSTANT_TAG_LONG:                return new ConstantLongInfo();            case CONSTANT_TAG_DOUBLE:                return new ConstantDoubleInfo();            case CONSTANT_TAG_UTF8:                return new ConstantUtf8Info();            case CONSTANT_TAG_STRING:                return new ConstantStringInfo(constantPool);            case CONSTANT_TAG_CLASS:                return new ConstantClassInfo(constantPool);            case CONSTANT_TAG_FIELDREF:                return new ConstantFieldRefInfo(constantPool);            case CONSTANT_TAG_METHODREF:                return new ConstantMethodRefInfo(constantPool);            case CONSTANT_TAG_INTERFACEMETHODREF:                return new ConstantInterfaceMethodRefInfo(constantPool);            case CONSTANT_TAG_NAMEANDTYPE:                return new ConstantNameAndTypeInfo();            case CONSTANT_TAG_METHODTYPE:                return new ConstantMethodTypeInfo();            case CONSTANT_TAG_METHODHANDLE:                return new ConstantMethodHandleInfo();            case CONSTANT_TAG_INVOKEDYNAMIC:                return new ConstantInvokeDynamicInfo();            default:                throw new ClassFormatError("constant pool tag");        }    }}

ClassFile.java

package org.itstack.demo.jvm.classfile;import org.itstack.demo.jvm.classfile.attributes.AttributeInfo;import org.itstack.demo.jvm.classfile.constantpool.ConstantPool;/** * http://www.itstack.org * create by fuzhengwei on 2019/4/26 */public class ClassFile {    private int minorVersion;    private int majorVersion;    private ConstantPool constantPool;    private int accessFlags;    private int thisClassIdx;    private int supperClassIdx;    private int[] interfaces;    private MemberInfo[] fields;    private MemberInfo[] methods;    private AttributeInfo[] attributes;    public ClassFile(byte[] classData) {        ClassReader reader = new ClassReader(classData);        this.readAndCheckMagic(reader);        this.readAndCheckVersion(reader);        this.constantPool = this.readConstantPool(reader);        this.accessFlags = reader.readU2ToInt();        this.thisClassIdx = reader.readU2ToInt();        this.supperClassIdx = reader.readU2ToInt();        this.interfaces = reader.readUInt16s();        this.fields = MemberInfo.readMembers(reader, constantPool);        this.methods = MemberInfo.readMembers(reader, constantPool);        this.attributes = AttributeInfo.readAttributes(reader, constantPool);    }    private void readAndCheckMagic(ClassReader reader) {        String magic = reader.readU4ToHexStr();        if (!"cafebabe".equals(magic)) {            throw new ClassFormatError("magic!");        }    }    private void readAndCheckVersion(ClassReader reader) {        this.minorVersion = reader.readU2ToInt();        this.majorVersion = reader.readU2ToInt();        switch (this.majorVersion) {            case 45:                return;            case 46:            case 47:            case 48:            case 49:            case 50:            case 51:            case 52:                if (this.minorVersion == 0)                    return;        }        throw new UnsupportedClassVersionError();    }    private ConstantPool readConstantPool(ClassReader reader) {        return new ConstantPool(reader);    }    public int minorVersion(){        return this.minorVersion;    }    public int majorVersion(){        return this.majorVersion;    }    public ConstantPool constantPool(){        return this.constantPool;    }    public int accessFlags() {        return this.accessFlags;    }    public MemberInfo[] fields() {        return this.fields;    }    public MemberInfo[] methods() {        return this.methods;    }    public String className() {        return this.constantPool.getClassName(this.thisClassIdx);    }    public String superClassName() {        if (this.supperClassIdx <= 0) return "";        return this.constantPool.getClassName(this.supperClassIdx);    }    public String[] interfaceNames() {        String[] interfaceNames = new String[this.interfaces.length];        for (int i = 0; i < this.interfaces.length; i++) {            interfaceNames[i] = this.constantPool.getClassName(interfaces[i]);        }        return interfaceNames;    }}ClassReader.javapackage org.itstack.demo.jvm.classfile;import java.math.BigInteger;/** * http://www.itstack.org * create by fuzhengwei on 2019/5/13 *  * java虚拟机定义了u1、u2、u4三种数据类型来表示；1字节、2字节、4字节，无符号整数。 * 在如下实现中，用增位方式表示无符号类型： * u1、u2可以用int类型存储，因为int类型是4字节 * u4 需要用long类型存储，因为long类型是8字节 */public class ClassReader {    private byte[] data;    public ClassReader(byte[] data) {        this.data = data;    }    //u1    public int readUint8() {        byte[] val = readByte(1);        return byte2int(val);    }    //u2    public int readUint16() {        byte[] val = readByte(2);        return byte2int(val);    }    //u4    public long readUint32() {        byte[] val = readByte(4);        String str_hex = new BigInteger(1, val).toString(16);        return Long.parseLong(str_hex, 16);    }    public float readUint64TFloat() {        byte[] val = readByte(8);        return new BigInteger(1, val).floatValue();    }    public long readUint64TLong() {        byte[] val = readByte(8);        return new BigInteger(1, val).longValue();    }    public double readUint64TDouble() {        byte[] val = readByte(8);        return new BigInteger(1, val).doubleValue();    }    public int[] readUint16s() {        int n = this.readUint16();        int[] s = new int[n];        for (int i = 0; i < n; i++) {            s[i] = this.readUint16();        }        return s;    }    public byte[] readBytes(int n) {        return readByte(n);    }    private byte[] readByte(int length) {        byte[] copy = new byte[length];        System.arraycopy(data, 0, copy, 0, length);        System.arraycopy(data, length, data, 0, data.length - length);        return copy;    }    private int byte2int(byte[] val) {        String str_hex = new BigInteger(1, val).toString(16);        return Integer.parseInt(str_hex, 16);    }}

MemberInfo.java

package org.itstack.demo.jvm.classfile;import org.itstack.demo.jvm.classfile.attributes.AttributeInfo;import org.itstack.demo.jvm.classfile.attributes.impl.CodeAttribute;import org.itstack.demo.jvm.classfile.attributes.impl.ConstantValueAttribute;import org.itstack.demo.jvm.classfile.constantpool.ConstantPool;/** * http://www.itstack.org * create by fuzhengwei on 2019/4/26 */public class MemberInfo {    private ConstantPool constantPool;    private int accessFlags;    private int nameIdx;    private int descriptorIdx;    private AttributeInfo[] attributes;    public MemberInfo(ClassReader reader, ConstantPool constantPool) {        this.constantPool = constantPool;        this.accessFlags = reader.readU2ToInt();        this.nameIdx = reader.readU2ToInt();        this.descriptorIdx = reader.readU2ToInt();        this.attributes = AttributeInfo.readAttributes(reader, constantPool);    }    public static MemberInfo[] readMembers(ClassReader reader, ConstantPool constantPool) {        int fieldCount = reader.readU2ToInt();        MemberInfo[] fields = new MemberInfo[fieldCount];        for (int i = 0; i < fieldCount; i++) {            fields[i] = new MemberInfo(reader, constantPool);        }        return fields;    }    public int accessFlags() {        return this.accessFlags;    }    public String name() {        return this.constantPool.getUTF8(this.nameIdx);    }    public String descriptor() {        return this.constantPool.getUTF8(this.descriptorIdx);    }    public CodeAttribute codeAttribute() {        for (AttributeInfo attrInfo : attributes) {            if (attrInfo instanceof CodeAttribute) return (CodeAttribute) attrInfo;        }        return null;    }    public ConstantValueAttribute ConstantValueAttribute() {        for (AttributeInfo attrInfo : attributes) {            if (attrInfo instanceof ConstantValueAttribute) return (ConstantValueAttribute) attrInfo;        }        return null;    }}

Main.java

package org.itstack.demo.jvm;import org.itstack.demo.jvm.classfile.ClassFile;import org.itstack.demo.jvm.classfile.MemberInfo;import org.itstack.demo.jvm.classpath.Classpath;import java.util.Arrays;/** * http://www.itstack.org * create by fuzhengwei on 2019/4/24 */public class Main {    public static void main(String[] args) {        Cmd cmd = Cmd.parse(args);        if (!cmd.ok || cmd.helpFlag) {            System.out.println("Usage: 
   
     [-options] class [args...]");            return;        }        if (cmd.versionFlag) {            //注意案例测试都是基于1.8，另外jdk1.9以后使用模块化没有rt.jar            System.out.println("java version \"1.8.0\"");            return;        }        startJVM(cmd);    }    private static void startJVM(Cmd cmd) {        Classpath classpath = new Classpath(cmd.jre, cmd.classpath);        System.out.printf("classpath：%s class：%s args：%s\n",                classpath, cmd.getMainClass(), cmd.getAppArgs());        //获取className        String className = cmd.getMainClass().replace(".", "/");        ClassFile classFile = loadClass(className, classpath);        assert classFile != null;        printClassInfo(classFile);    }    private static ClassFile loadClass(String className, Classpath classpath) {        try {            byte[] classData = classpath.readClass(className);            return new ClassFile(classData);        } catch (Exception e) {            System.out.println("Could not find or load main class " + className);            return null;        }    }    private static void printClassInfo(ClassFile cf) {        System.out.println("version: " + cf.majorVersion() + "." + cf.minorVersion());        System.out.println("constants count：" + cf.constantPool().getSiz());        System.out.format("access flags：0x%x\n", cf.accessFlags());        System.out.println("this class：" + cf.className());        System.out.println("super class：" + cf.superClassName());        System.out.println("interfaces：" + Arrays.toString(cf.interfaceNames()));        System.out.println("fields count：" + cf.fields().length);        for (MemberInfo memberInfo : cf.fields()) {            System.out.format("  %s\n", memberInfo.name());        }        System.out.println("methods count: " + cf.methods().length);        for (MemberInfo memberInfo : cf.methods()) {            System.out.format("  %s\n", memberInfo.name());        }    }}

测试结果

"C:\Program Files\Java\jdk1.8.0_161\bin\java.exe" "-javaagent:D:\Program Files\JetBrains\IntelliJ IDEA Community Edition 2018.3.1\lib\idea_rt.jar=61458:D:\Program Files\JetBrains\IntelliJ IDEA Community Edition 2018.3.1\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_161\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\rt.jar;E:\itstack\git\istack-demo\itstack-demo-jvm\itstack-demo-jvm-03\target\classes;D:\Program Files (x86)\apache-maven-2.2.1\repository\com\beust\jcommander\1.72\jcommander-1.72.jar;D:\Program Files (x86)\apache-maven-2.2.1\repository\org\projectlombok\lombok\1.18.0\lombok-1.18.0.jar;D:\Program Files (x86)\apache-maven-2.2.1\repository\com\alibaba\fastjson\1.2.40\fastjson-1.2.40.jar" org.itstack.demo.jvm.Main -Xjre "C:\Program Files\Java\jdk1.8.0_161\jre" java.lang.Stringclasspath：org.itstack.demo.jvm.classpath.Classpath@4bf558aa class：java.lang.String args：nullversion: 52.0constants count：540access flags：0x31this class：java/lang/Stringsuper class：java/lang/Objectinterfaces：[java/io/Serializable, java/lang/Comparable, java/lang/CharSequence]fields count：5value 		 [Chash 		 IserialVersionUID 		 JserialPersistentFields 		 [Ljava/io/ObjectStreamField;CASE_INSENSITIVE_ORDER 		 Ljava/util/Comparator;methods count: 94
   
     		 ()V
    
      		 (Ljava/lang/String;)V
     
       		 ([C)V
      
        		 ([CII)V
       
         		 ([III)V
        
          ([BIII)V
         
           ([BI)VcheckBounds ([BII)V
          
            ([BIILjava/lang/String;)V
           
             ([BIILjava/nio/charset/Charset;)V
            
              ([BLjava/lang/String;)V
             
               ([BLjava/nio/charset/Charset;)V
              
                ([BII)V
               
                 ([B)V
                
                  (Ljava/lang/StringBuffer;)V
                 
                   (Ljava/lang/StringBuilder;)V
                  
                    ([CZ)Vlength ()IisEmpty ()ZcharAt (I)CcodePointAt (I)IcodePointBefore (I)IcodePointCount (II)IoffsetByCodePoints (II)IgetChars ([CI)VgetChars (II[CI)VgetBytes (II[BI)VgetBytes (Ljava/lang/String;)[BgetBytes (Ljava/nio/charset/Charset;)[BgetBytes ()[Bequals (Ljava/lang/Object;)ZcontentEquals (Ljava/lang/StringBuffer;)ZnonSyncContentEquals (Ljava/lang/AbstractStringBuilder;)ZcontentEquals (Ljava/lang/CharSequence;)ZequalsIgnoreCase (Ljava/lang/String;)ZcompareTo (Ljava/lang/String;)IcompareToIgnoreCase (Ljava/lang/String;)IregionMatches (ILjava/lang/String;II)ZregionMatches (ZILjava/lang/String;II)ZstartsWith (Ljava/lang/String;I)ZstartsWith (Ljava/lang/String;)ZendsWith (Ljava/lang/String;)ZhashCode ()IindexOf (I)IindexOf (II)IindexOfSupplementary (II)IlastIndexOf (I)IlastIndexOf (II)IlastIndexOfSupplementary (II)IindexOf (Ljava/lang/String;)IindexOf (Ljava/lang/String;I)IindexOf ([CIILjava/lang/String;I)IindexOf ([CII[CIII)IlastIndexOf (Ljava/lang/String;)IlastIndexOf (Ljava/lang/String;I)IlastIndexOf ([CIILjava/lang/String;I)IlastIndexOf ([CII[CIII)Isubstring (I)Ljava/lang/String;substring (II)Ljava/lang/String;subSequence (II)Ljava/lang/CharSequence;concat (Ljava/lang/String;)Ljava/lang/String;replace (CC)Ljava/lang/String;matches (Ljava/lang/String;)Zcontains (Ljava/lang/CharSequence;)ZreplaceFirst (Ljava/lang/String;Ljava/lang/String;)Ljava/lang/String;replaceAll (Ljava/lang/String;Ljava/lang/String;)Ljava/lang/String;replace (Ljava/lang/CharSequence;Ljava/lang/CharSequence;)Ljava/lang/String;split (Ljava/lang/String;I)[Ljava/lang/String;split (Ljava/lang/String;)[Ljava/lang/String;join (Ljava/lang/CharSequence;[Ljava/lang/CharSequence;)Ljava/lang/String;join (Ljava/lang/CharSequence;Ljava/lang/Iterable;)Ljava/lang/String;toLowerCase (Ljava/util/Locale;)Ljava/lang/String;toLowerCase ()Ljava/lang/String;toUpperCase (Ljava/util/Locale;)Ljava/lang/String;toUpperCase ()Ljava/lang/String;trim ()Ljava/lang/String;toString ()Ljava/lang/String;toCharArray ()[Cformat (Ljava/lang/String;[Ljava/lang/Object;)Ljava/lang/String;format (Ljava/util/Locale;Ljava/lang/String;[Ljava/lang/Object;)Ljava/lang/String;valueOf (Ljava/lang/Object;)Ljava/lang/String;valueOf ([C)Ljava/lang/String;valueOf ([CII)Ljava/lang/String;copyValueOf ([CII)Ljava/lang/String;copyValueOf ([C)Ljava/lang/String;valueOf (Z)Ljava/lang/String;valueOf (C)Ljava/lang/String;valueOf (I)Ljava/lang/String;valueOf (J)Ljava/lang/String;valueOf (F)Ljava/lang/String;valueOf (D)Ljava/lang/String;intern ()Ljava/lang/String;compareTo (Ljava/lang/Object;)I
                   
                     ()VProcess finished with exit code 0