讀書筆記之java反編譯(2)

 有了筆記(1)的閱讀經驗，來看看下面一點點代碼。先從讀取class的版本信息開始，應用面向對象的思想

 爲什麼從版本開始呢因爲他位於class二進制文件的頂部

1.定義版本Version類

package readnote; import java.io.DataInputStream; import java.io.IOException; public final class Version { int iMagicNumber; int iMinorVersion; int iMajorVersion; void read(DataInputStream dis) throws IOException { //注意每讀取一次，指針自動下移 //每個Class文件的前4個字節被稱爲它的魔數（magic number） iMagicNumber = dis.readInt(); //Class文件的下面4個字節包含了次、主版本號 iMinorVersion = dis.readUnsignedShort(); iMajorVersion = dis.readUnsignedShort(); } //給出詳細的版本信息 public String toString() { String sRetStr; sRetStr = ("Magic number: " + getMagicNumberString() + ", "); sRetStr += ("Minor version: " + iMinorVersion + ", "); sRetStr += ("Major version: " + iMajorVersion + ", "); return sRetStr; } public int getMagicNumberInteger() { return iMagicNumber; } public String getMagicNumberString() { return (Integer.toHexString(iMagicNumber)); } public void setMagicNumberString(String sMagicNumber) { iMagicNumber = Long.valueOf(sMagicNumber, 16).intValue(); } public String getMajorVersionString() { return Integer.toString(iMajorVersion); } public String getMinorVersionString() { return Integer.toString(iMinorVersion); } public void setMajorVersionString(String sVer) { iMajorVersion = Integer.parseInt(sVer); } public void setMinorVersionString(String sVer) { iMinorVersion = Integer.parseInt(sVer); } }

2.定義CalssFile類

package readnote; import java.io.BufferedInputStream; import java.io.DataInputStream; import java.io.File; import java.io.FileInputStream; import java.io.IOException; public class ClassFile { public Version version = new Version();//版本信息放到Version 類中 public void read(DataInputStream dis) throws IOException { //第一步讀取版本信息 version.read(dis); dis.close(); } public static void main(String[] args) throws IOException { ClassFile classFile = new ClassFile(); DataInputStream dis; dis = new DataInputStream(new BufferedInputStream(new FileInputStream(new File("D:/test/a.class"))));//爲什麼要用DataInputStream？那就看看java的api吧 classFile.read(dis); System.out.println("版本信息："+classFile.version.toString()); } }  

版本信息：Magic number: cafebabe, Minor version: 3, Major version: 45,

搞定了，有時間再貼其他的