JVM class逆コンパイル

Nix.long 2017-10-20
文書ディレクトリ

1. Code Demo

2.javac

3.javap

4.Batスクリプト

1. Code Demo
[java]サンプルdemo、Main.javaとして保存

package com.test.Main;
public class Main{
    void main(String args[]){
        int i = 0;
        i = 5;
        return;
    }
}

2.javac
JAvac Main.java生成Main.class
javac Main.java
3.javap
Javapコマンドを使用してclassファイルを逆コンパイルし、アシストコマンドを表示
javap -c -v Main.class

Classfile /G:/Mess/test/Main.class
  Last modified 2017-10-16; size 279 bytes
  MD5 checksum a8b7efbdef220ee87f1d79cd549cf26c
  Compiled from "Main.java"
public class com.test.Main.Main
  minor version: 0
  major version: 52
  flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
   #1 = Methodref          #3.#12         // java/lang/Object."":()V
   #2 = Class              #13            // com/test/Main/Main
   #3 = Class              #14            // java/lang/Object
   #4 = Utf8               <init>
   #5 = Utf8               ()V
   #6 = Utf8               Code
   #7 = Utf8               LineNumberTable
   #8 = Utf8               main
   #9 = Utf8               ([Ljava/lang/String;)V
  #10 = Utf8               SourceFile
  #11 = Utf8               Main.java
  #12 = NameAndType        #4:#5          // "":()V
  #13 = Utf8               com/test/Main/Main
  #14 = Utf8               java/lang/Object
{
  public com.test.Main.Main();
    descriptor: ()V
    flags: ACC_PUBLIC
    Code:
      stack=1, locals=1, args_size=1
         0: aload_0
         1: invokespecial #1                  // Method java/lang/Object."":()V
         4: return
      LineNumberTable:
        line 3: 0
  void main(java.lang.String[]);
    descriptor: ([Ljava/lang/String;)V
    flags:
    Code:
      stack=1, locals=3, args_size=2
         0: iconst_0
         1: istore_2
         2: iconst_5
         3: istore_2
         4: return
      LineNumberTable:
        line 6: 0
        line 7: 2
        line 8: 4
}
SourceFile: "Main.java"

ここでjavapの使い方:
javap

  : javap  
  ,        :
  -help  --help  -?               
  -version                     
  -v  -verbose                   
  -l                                 
  -public                           
  -protected                     /      
  -package                      /    /   
                               (  )
  -p  -private                     
  -c                               
  -s                               
  -sysinfo                          
                                (  ,   ,   , MD5   )
  -constants                     
  -classpath                     
  -cp                            
  -bootclasspath               

4.Batスクリプト
java2opcode.bat

REM =====================================================================
REM Author:     nix.long
REM Date:        2017.10.17
REM Function:     compile x.java to jvm byte-code    
REM =====================================================================

@echo off
if "%1"=="" (
    goto help
)
set input=%1%
IF %input% == help (
    goto help
) ELSE IF %input% == clean (
    IF EXIST *.class (
        del /f /s /q *.class
    )
    
    IF EXIST *.dex (
        del /f /s /q *.dex
    )
) ELSE (
    IF EXIST %input%.class (
        del /f /s /q %input%.class
    )
    
    IF EXIST %input%.dex (
        del /f /s /q %input%.dex
    )
    echo 'to make:'  %input%.java
    echo 'to gen class:'  %input%.class
    javac %input%.java
    echo 'to show opcode:'
    echo -----------------------------------------------------------------
    echo=
    echo=
    echo=
    
    javap -v -p -s %input%.class
    
    echo=
    echo=
    echo=
    echo -----------------------------------------------------------------
)
goto end
:help
    echo -----------------------------------------------------------------
    echo     help [JVM Bytecode]:
    echo        java2opcode.bat help     - show help
    echo        java2opcode.bat clean    - clean mid-files
    echo        java2opcode.bat X        - gen bytecode for X.java
    echo -----------------------------------------------------------------
:end