我们都知道,Java编译器负责将.java文件编译成.class文件,class文件存储的是java字节码,与.java文件无关(只要你愿意写一个编译器,也可以将别的语言写的源代码编译成.class文件),本文准备详细解剖class文件的内部结构,并且把class文件结构读取并显示出来。
Class文件的格式由JVM规范规定,一共有以下部分:
1. magic number,必须是0xCAFEBABE,用于快速识别是否是一个class文件。 2. version,包括major和minor,如果版本号超过了JVM的识别范围,JVM将拒绝执行。 3. constant pool,常量池,存放所有用到的常量。 4. access flag,定义类的访问权限。 5. this class和super class,指示如何找到this class和super class。 6. interfaces,存放所有interfaces。 7. fields,存放所有fields。 8. methods,存放所有methods。 9. attributes,存放所有attributes。 先写一个Test.java:
package example.test; 然后编译,放在C:\Documents and Settings\Administrator\桌面\解析class文件\TestClass.java。
我们用Java来读取和分析class,ClassAnalyzer的功能便是读取Test.class,分析结构,然后显示出来,DOS下显示的内容比较少,我们通过StringBuffer最后输出到txt文件,实现由文件到文件的转变:
import java.io.*; public class ClassAnalyzer
{ public static StringBuffer sb = new StringBuffer(); public static byte[] analyzeConstant_tag; public static String[] analyzeConstant_utf8; public static DataOutputStream dataout; public static void main(String[] args)
{ DataInputStream input = null; try { FileOutputStream out = new FileOutputStream("C:\\Documents and Settings\\Administrator\\桌面\\解析class文件\\ReadClass.tmp"); BufferedOutputStream buffout = new BufferedOutputStream(out); dataout = new DataOutputStream(buffout); input = new DataInputStream(new BufferedInputStream(new FileInputStream( "C:\\Documents and Settings\\Administrator\\桌面\\解析class文件\\TestClass.class" ))); //获取文件大小
FileSize(new DataInputStream(new BufferedInputStream(new FileInputStream( "C:\\Documents and Settings\\Administrator\\桌面\\解析class文件\\TestClass.class" )))); //解析数据 analyze(input); } catch (Exception e) { System.out.println("解析失败!"); } finally { try { input.close(); dataout.close();} catch (Exception e) {} } } public static void FileSize(DataInputStream input) throws IOException {
int length = 0; //长度,字节,B double kblength = 0.0D; //长度,千字节,KB while (input.read() != -1) ++length; kblength = length / 1024.0D; System.out.println("文件大小(字节):" + length + "\n文件大小(KB):" + kblength); input.close(); } public static void analyze(DataInputStream input) throws IOException
{ // 读取幻数 int magic = u4(input); if (magic == 0xCAFEBABE) //-889275714 System.out.println("magic number = 0xCAFEBABE -----标准class文件"); else { throw new RuntimeException("无效的幻数!"); } // 读取副、主版本号
int minor_ver = u2(input); int major_ver = u2(input); System.out.println("Version = " + major_ver + "." + minor_ver); add(" 常规信息 "); add("Minor version: " + minor_ver); add("Major version: " + major_ver); // 读取常量池表中表项的个数
short const_pool_count = u2(input); System.out.println("constant pool size = " + const_pool_count); add("Constant pool count: " + const_pool_count); // 读取每个常量
analyzeConstant_tag = new byte[const_pool_count]; //存储常量数据类型 analyzeConstant_tag[0] = 0; //系统保留,class中不存在 for (int i = 1; i < const_pool_count; ++i) analyzeConstant(input, i); //分析常数 jiexitmp(); //解析tmp文件
// 读取Class的声明中使用的修饰符掩码并解析
short access_flags = u2(input); System.out.print("access_flags = " + access_flags); String access_flags_16= "0x"+Integer.toHexString(access_flags); int[] access = {0x0001,0x0010, 0x0020,0x0200,0x0400}; String[] access_str = {"public","final","","interface","abstract"}; //NO.2--super String access_tmp = ""; for(int i=0;i<access.length;i++) { if((access_flags & access[i]) == access[i]) { if(i == 0)access_tmp += access_str[i]; else if(i != 2)access_tmp += " " + access_str[i]; } } System.out.println(" [" + access_tmp + " ]"); add("Access flags: " + access_flags_16 + " [" + access_tmp + " ]"); //读取类或者接口的全限定名称
short this_class_index = u2(input); short super_class_index = u2(input); System.out.println("This class = " + this_class_index); System.out.println("Super class = " + super_class_index); add("This class: " + this_class_index); add("Super class: " + super_class_index); // read interfaces count: short interfaces_count = u2(input); System.out.println("超接口个数 = " + interfaces_count); add("Interfaces count: " + interfaces_count); // read each interface: for(int i=1; i<=interfaces_count; i++) { short interface_index = u2(input); System.out.println("No. " + i + " interface index = " + interface_index); } } public static byte u1(DataInputStream input) throws IOException
{ return input.readByte(); } public static Short u2(DataInputStream input) throws IOException
{ return input.readShort(); } public static int u4(DataInputStream input) throws IOException
{ return input.readInt(); } public static long u8(DataInputStream input) throws IOException
{ return input.readLong(); } public static void add(String str) throws IOException
{ sb.append(str+"\n"); } public static void analyzeConstant(DataInputStream input, int index) throws IOException {
// 用于读: byte n8; short n16; int n32; long n64; float f; double d; byte[] buffer; byte tag = input.readByte(); //读取数据类型标签 analyzeConstant_tag[index] = tag; //存储常量数据类型 System.out.println("\n常量索引 = " + index + ", 数据类型标签 = " + (int)tag); switch(tag) { case 1: // utf-8 string System.out.println(" 常量类型 = Utf8 //Utf8存储格式"); //Utf8存储格式 n16 = u2(input); System.out.println(" length = " + n16); dataout.writeShort(n16); buffer = new byte[n16]; input.readFully(buffer); //数组读满才返回 System.out.println(" value = " + new String(buffer)); dataout.writeUTF(new String(buffer)); break; case 3: // integer System.out.println(" 常量类型 = Integer //Integer存储格式"); //Integer存储格式 n32 = u4(input); System.out.println(" value = " + n32); dataout.writeInt(n32); break; case 4: // float System.out.println(" 常量类型 = Float //Float存储格式"); //Float存储格式 f = u4(input);//input.readFloat(); System.out.println(" value = " + f); dataout.writeFloat(f); break; case 5: // long System.out.println(" 常量类型 = Long //Long存储格式"); //Long存储格式 n64 = u8(input); System.out.println(" value = " + n64); dataout.writeLong(n64); break; case 6: // double System.out.println(" 常量类型 = Double //Double存储格式"); //Double存储格式 d = u8(input); System.out.println(" value = " + d); dataout.writeDouble(d); break; case 7: // class or interface reference System.out.println(" 常量类型 = Class //类索引"); //类索引 n16 = u2(input); System.out.println(" index = " + n16 + " (在哪里可以找到类名)"); dataout.writeShort(n16); break; case 8: // string System.out.println(" 常量类型 = String //字符串索引"); //字符串索引 n16 = u2(input); System.out.println(" index = " + n16); dataout.writeShort(n16); break; case 9: // field reference System.out.println(" 常量类型 = Fieldref //领域参数"); //领域参数 n16 = u2(input); System.out.println("class index = " + n16 + " (在哪里可以找到类名)"); dataout.writeShort(n16); n16 = u2(input); System.out.println("nameAndType = " + n16 + " (在哪里可以找到的名称和类型)"); dataout.writeShort(n16); break; case 10: // method reference System.out.println(" 常量类型 = Methodref //方法参考"); //方法参考 n16 = u2(input); System.out.println("class index = " + n16 + " (在哪里可以找到类)"); dataout.writeShort(n16); n16 = u2(input); System.out.println("nameAndType = " + n16 + " (在哪里可以找到名称和类型)"); dataout.writeShort(n16); break; case 11: // interface method reference System.out.println(" 常量类型 = InterfaceMethodref //接口方法参考值"); //接口方法参考值 n16 = u2(input); System.out.println("class index = " + n16 + " (在哪里可以找到接口)"); dataout.writeShort(n16); n16 = u2(input); System.out.println("nameAndType = " + n16 + " (在哪里可以找到名称和类型)"); dataout.writeShort(n16); break; case 12: // name and type reference System.out.println(" 常量类型 = NameAndType //名称和类型"); //名称和类型 n16 = u2(input); System.out.println(" name index = " + n16 + " (在哪里可以找到这个名字)"); dataout.writeShort(n16); n16 = u2(input); System.out.println(" descripter = " + n16 + " (在哪里可以找到描述符)"); dataout.writeShort(n16); break; default: throw new RuntimeException("Invalid constant pool flag: " + tag); } //end switch } public static void jiexitmp()
{ DataInputStream input = null; try { input = new DataInputStream(new BufferedInputStream(new FileInputStream( "C:\\Documents and Settings\\Administrator\\桌面\\解析class文件\\ReadClass.tmp" ))); /**********analyzeConstant_tag[]存储常量池表中常量数据类型(共11种)**********/
int[] tagSpecies = new int[11]; //存储常量池表中常量各种数据类型的计数 int const_pool_count = analyzeConstant_tag.length; // 读取常量池表中表项的个数 for(int i=0;i<const_pool_count;i++) //对数据类型的计数数组进行赋值
{ System.out.println(analyzeConstant_tag[i]); //按顺序输出各种数据的类型 switch (analyzeConstant_tag[i]) { case 1: ++tagSpecies[0]; break; case 3: ++tagSpecies[1]; break; case 4: ++tagSpecies[2]; break; case 5: ++tagSpecies[3]; break; case 6: ++tagSpecies[4]; break; case 7: ++tagSpecies[5]; break; case 8: ++tagSpecies[6]; break; case 9: ++tagSpecies[7]; break; case 10: ++tagSpecies[8]; break; case 11: ++tagSpecies[9]; break; case 12: ++tagSpecies[10]; break; } } for(int i=0;i<tagSpecies.length;i++) System.out.println("数量"+tagSpecies[i]);/* analyzeConstant_utf8 = new String[analyzeConstant_utf8_num]; int j = 0; for(int i=0;i<const_pool_count;i++) if(analyzeConstant_tag[i]==1)analyzeConstant_utf8[j++] = "r"; for(int i=0;i<analyzeConstant_utf8.length;i++) System.out.println("NO."+i+" "+analyzeConstant_utf8[i]); */ } catch (Exception e) { System.out.println("解析失败!"); } finally { try { input.close(); } catch (Exception e) {} } }
} //End /***** byte u1 Short u2 int u4 ClassFile表结构
ClassFile { u4 magic; //幻数 u2 minor_version; //副版本号
u2 major_version; //主版本号
u2 constant_pool_count; //常量池表中表项的个数
cp_info constant_pool[constant_pool_count-1]; //每个常量的信息
u2 access_flags; //类修饰符掩码
u2 this_Class; //类或者接口的全限定名称
u2 super_Class; //父类全限定名称
u2 interfaces_count;
u2 interfaces[interfaces_count];
u2 fields_count;
field_info fields[fields_count];
u2 methods_count;
method_info methods[methods_count];
u2 attributes_count;
attribute_info attributes[attributes_count];
}
1//Utf8存储格式
dataout.writeShort(n16); //length dataout.writeUTF(new String(buffer)); //字符串 3//Integer存储格式
dataout.writeInt(n32); 4//Float存储格式
dataout.writeFloat(f); 5//Long存储格式
dataout.writeLong(n64); 6//Double存储格式
dataout.writeDouble(d); 7//类索引
dataout.writeShort(n16); 8//字符串索引
dataout.writeShort(n16); 9//领域参数
dataout.writeShort(n16); //类名 dataout.writeShort(n16); //名称和类型 10//方法参考
dataout.writeShort(n16); //类名 dataout.writeShort(n16); //名称和类型 11//接口方法参考值
dataout.writeShort(n16); //接口 dataout.writeShort(n16); //名称和类型 12//名称和类型
dataout.writeShort(n16); //名字索引 dataout.writeShort(n16); //描述符索引 *****/ 代码还有很多不足,还有很多没有解析,下次继续吧!
作者:qq379264347
论坛:http://zcb.
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