网上书城网站开发意义,网站和搜索引擎,想做运营怎么入手,如何才能看到国外的设计网站解析class文件案例介绍本案例主要介绍通过java代码从class文件中解析#xff1b;class文件、常量池、属性表#xff1b;作为类(或者接口)信息的载体#xff0c;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#xff0c;处处运行”#xff0c;Java虚拟…解析class文件案例介绍 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 配置位置Run/Debug Configurations - program arguments 配置内容-Xjre C:Program FilesJavajdk1.8.0_161jre java.lang.String代码示例https://github.com/fuzhengwei/itstack-demo-jvm/tree/master/itstack-demo-jvm-03itstack-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.javapackage 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.javapackage 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.javapackage 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.javapackage 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.javapackage 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