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[j2me]跟我学制作pak文件

[j2me]跟我学制作pak文件
作者：cleverpig

版权声明：本文可以自由转载，转载时请务必以超链接形式标明文章原始出处和作者信息及本声明
作者:cleverpig(http://blog.matrix.org.cn/page/cleverpig)
原文:http://www.matrix.org.cn/resource/article/43/43966_j2me_pak.html
关键字:pak,j2me,减肥


序言：

    由于前些时间，一些matrixer常问关于j2me中使用pak文件的问题。本人虽学艺不深，但满怀热心的做了一番探索，现将制作pak文件的看法和方法公布出来，大家多多提意见。

一、什么是pak文件：

    pak文件就是将多个文件打包为一个单独文件，在这个文件中保存着多个文件的数据，当然还有一些描述文件结构的数据。所以将“pak”作为文件的后缀是一种常规的用法，大家可以自定义其它的文件后缀。

二、为什么使用pak文件：

    由于midp对发布安装的j2me程序大小进行了限制，所以缩小发布程序就意味着能够提供更多的程序或者内容（如图片、音乐）给用户。而通过研究发现zip/jar算法对大文件的压缩率高于对等量的多个小文件的压缩率。

    当然还有其它方法，这里简单做一下讨论比如使用混淆器proguard的“-overloadaggressively”选项使jar文件缩小，但也会导致一些错误，因为这种方法生成jar中的class符合java byte code标准，但是与java语法相悖，严重的可能造成一些jre对object的序列化错误。

    所以使用pak方法将程序中要用到的资源（图片、音乐、文本）组合为单一文件是一个安全有效的方法。而且对于一些商用程序，完全可以在pak文件中对文件数据进行加密，很好的保护了作者和公司的权益。本人的sample中使用了简单的“加减法”加密，对于手机这类设备来讲是一个效率较高的选择。

三、pak文件的结构：

    大家可以自己设计pak文件结构，本人这里只是抛砖引玉的作个sample。下面就是本人设计的pak文件结构：

pak file header：pak文件的头部

  * 签名：6字节char数组
 * 版本号：32位float
 * 文件table数量：32位整数
 * 密码行为：8位字节
 * 密码：8位字节
 * 文件唯一id：10字节char数组
 * 保留位：32位整数(4字节)

file table：pak文件中包含文件的列表，在一个pak文件中一个被包含的文件对应一个file table。

 * 文件名：30字节char数组
 * 文件大小：32位整型
 * 文件在pak文件中的位移：32位整数

concatenated file data：按file table的顺序连接在一起的文件数据。

 * 文件数据

四、程序框架：
    
    说明：由于pak文件的制作和使用分别要使用两个java应用领域：j2se和j2me，所以本人将pakutil类制作了2个版本（j2se和j2me）。

    程序框架如下：
    1。pakheader类，定义了pak文件头。
    2。pakfiletable类，定义pak文件table。
    3。pakutil类（j2se版），具备两个功能：将多个png图片合成一个pak文件，并使用简单的加减加密法对其进行加密；从pak文件中取出png图片，构造byte数组（可以用来构造image对象）或者写为文件。
       pakutil类（j2me版），具备的功能：从pak文件中取出png图片，构造byte数组（可以用来构造image对象）。

五、pakheader和pakfiletable类：
    
pakheader.java：

package cn.org.matrix.gmatrix.gamelab.util.pak;

/**
 * pak文件头：
 * 结构：
 *   签名：6字节char数组
 *   版本号：32位float
 *   文件table数量：32位整数
 *   密码行为：8位字节
 *   密码：8位字节
 *   文件唯一id：10字节char数组
 *   保留位：32位整数(4字节)
 * @author cleverpig
 *
 */
class pakheader {
        //定义文件唯一id长度
        public static final int uniqueid_length=10;
        //定义文件签名长度
        public static final int signature_length=6;
        //定义加法运算
        public static final int addition_cipheraction=0;
        //定义减法运算
        public static final int subtract_cihoeraction=1;
        //文件签名
        private char[] signature=new char[signature_length];
        //版本号
        private float version=0f;
        //文件table数量
        private long numfiletableentries=0;
        //密码使用方法：在原数据上进行加法还是减法
        private byte cipheraction=addition_cipheraction;
        //密码值
        private byte ciphervalue=0x00;
        //唯一id
        private char[] uniqueid=new char[uniqueid_length];
        //保留的4字节
        private long reserved=0;
        
        public pakheader(){        
        }
        
        /**
         * 构造方法
         * @param signature 签名
         * @param version 版本
         * @param numfiletableentries 文件table数量
         * @param cipheraction 密码使用方法
         * @param ciphervalue 密码值
         * @param uniqueid 唯一id
         * @param reserved 保留的2字节
         */
        public pakheader(char[] signature,float version,
                        long numfiletableentries,byte cipheraction,
                        byte ciphervalue,char[] uniqueid,long reserved){
                for(int i=0;i<signature_length;this.signature&#91;i&#93;=signature&#91;i&#93;,i++)
                        ;
                this.version=version;
                this.cipheraction=cipheraction;
                this.numfiletableentries=numfiletableentries;
                this.ciphervalue=ciphervalue;
                for(int i=0;i<uniqueid_length;this.uniqueid&#91;i&#93;=uniqueid&#91;i&#93;,i++)
                        ;
                
                this.reserved=reserved;
        }
        
        public byte getciphervalue() {
                return ciphervalue;
        }
        public void setciphervalue(byte ciphervalue) {
                this.ciphervalue = ciphervalue;
        }
        public long getnumfiletableentries() {
                return numfiletableentries;
        }
        public void setnumfiletableentries(long numfiletableentries) {
                this.numfiletableentries = numfiletableentries;
        }
        public long getreserved() {
                return reserved;
        }
        public void setreserved(long reserved) {
                this.reserved = reserved;
        }
        public char&#91;&#93; getuniqueid() {
                return uniqueid;
        }
        public void setuniqueid(char&#91;&#93; uniqueid) {
                for(int i=0;i<uniqueid_length;this.uniqueid&#91;i&#93;=uniqueid&#91;i&#93;,i++)
                        ;
        }
        public float getversion() {
                return version;
        }
        public void setversion(float version) {
                this.version = version;
        }
        public byte getcipheraction() {
                return cipheraction;
        }

        public void setcipheraction(byte cipheraction) {
                this.cipheraction = cipheraction;
        }

        public char&#91;&#93; getsignature() {
                return signature;
        }

        public void setsignature(char&#91;&#93; signature) {
                for(int i=0;i<signature_length;this.signature&#91;i&#93; = signature&#91;i&#93;,i++)
                        ;
        }
        
        /**
         * 返回pakheader的大小
         * @return 返回pakheader的大小
         */
        public static int size(){
                return signature_length+4+4+1+1+uniqueid_length+4;
        }
        
        public string tostring(){
                string result=&quot;&quot;;
                result+=&quot;\t签名:&quot;+new string(this.signature).trim()
                        +&quot;\t版本号:&quot;+this.version
                        +&quot;\t文件table数量:&quot;+this.numfiletableentries
                        +&quot;\t密码行为:&quot; +this.cipheraction
                        +&quot;\t密码:&quot;+this.ciphervalue
                        +&quot;\t文件唯一id:&quot;+new string(this.uniqueid).trim()
                        +&quot;\t保留位:&quot;+this.reserved;
                return result;
        }

}

pakfiletable.java

package cn.org.matrix.gmatrix.gamelab.util.pak;

/**
 * pak文件table类
 * 文件table结构：
 *         文件名：30字节char数组
 *         文件大小：32位整型
 *         文件在pak文件中的位移：32位整数
 * @author cleverpig
 *
 */
class pakfiletable {
        public static final int filename_length=30;
        //文件名
        private char[] filename=new char[filename_length];
        //文件大小
        private long filesize=0l;
        //文件在pak文件中的位移
        private long offset=0l;
        
        public pakfiletable(){
        }
        
        /**
         * 构造方法
         * @param filename 文件名
         * @param filesize 文件大小
         * @param offset 文件在pak文件中的位移
         */
        public pakfiletable(char[] filename,
                        long filesize,long offset){
                for(int i=0;i<filename_length;this.filename&#91;i&#93;=filename&#91;i&#93;,i++)
                        ;
                this.filesize=filesize;
                this.offset=offset;
        }
        
        public char&#91;&#93; getfilename() {
                return filename;
        }
        public void setfilename(char&#91;&#93; filename) {
                for(int i=0;i<filename.length;this.filename&#91;i&#93;=filename&#91;i&#93;,i++)
                        ;
        }
        public long getfilesize() {
                return filesize;
        }
        public void setfilesize(long filesize) {
                this.filesize = filesize;
        }
        public long getoffset() {
                return offset;
        }
        public void setoffset(long offset) {
                this.offset = offset;
        }
        /**
         * 返回文件table的大小
         * @return 返回文件table的大小
         */
        public static int size(){
                return filename_length+4+4;
        }
        
        public string tostring(){
                return &quot;\t文件名:&quot;+new string(this.filename).trim()
                        +&quot;\t文件大小:&quot;+this.filesize
                        +&quot;\t文件位移:&quot;+this.offset;
        }
}

六、pakutil类（j2se版）：

pakutil.java

package cn.org.matrix.gmatrix.gamelab.util.pak;

import java.io.*;
import java.util.vector;
/**
 * pak工具类
 * 功能：
 * 1.将多个png图片合成一个pak文件，并使用简单的加减加密法对其进行加密；
 * 2.从pak文件中取出png图片，构造byte数组（可以用来构造image对象）或者写为文件
 * @author cleverpig
 *
 */
public class pakutil {

        public pakutil(){
        }
        
        /**
         * 返回文件长度
         * @param filepath 文件路径
         * @return 文件长度
         */
        private long getfilesize(string filepath){
                file file=new file(filepath);
                return file.length();
        }
        
        /**
         * 返回文件名
         * @param filepath 文件路径
         * @return 文件名
         */
        private string getfilename(string filepath){
                file file=new file(filepath);
                return file.getname();
        }
        
        /**
         * 计算文件位移的起始点
         * @return 文件位移的起始点
         */
        private long workoutoffsetstart(pakheader header){
                //计算出文件头+文件table的长度
                return pakheader.size()+header.getnumfiletableentries()*pakfiletable.size();
        }
        
        /**
         * 计算文件位移
         * @param fileindex 文件序号
         * @param lastfileoffset 上一个文件位移
         * @return  文件在pak文件中的位移
         */
        private long workoutnextoffset(long sourcefilesize,long lastfileoffset){
                return lastfileoffset+sourcefilesize;
        }
        
        /**
         * 生成文件table
         * @param sourcefilename 源文件名
         * @param sourcefilesize 源文件长度
         * @param currentfileoffset 当前文件位移
         * @return 生成的pakfiletable对象
         */
        private pakfiletable generatefiletable(string sourcefilename,
                        long sourcefilesize,long currentfileoffset){
                pakfiletable ft=new pakfiletable();
                ft.setfilename(sourcefilename.tochararray());
                ft.setfilesize(sourcefilesize);
                ft.setoffset(currentfileoffset);
                return ft;
        }
        
        /**
         * 将char字符数组写入到dataoutputstream中
         * @param towritechararray 被写入的char数组
         * @param dos dataoutputstream
         * @throws exception
         */
        private void writechararray(char[] towritechararray,dataoutputstream dos) throws exception{
                for(int i=0;i<towritechararray.length;dos.writechar(towritechararray&#91;i&#93;),i++);
        }
        
        /**
         * 使用文件头中的密码对数据进行加密
         * @param buff 被加密的数据
         * @param bufflength 数据的长度
         * @param header 文件头
         */
        private void encryptbuff(byte&#91;&#93; buff,int bufflength,pakheader header){
                for(int i=0;i<bufflength;i++){
                        switch(header.getcipheraction()){
                        case pakheader.addition_cipheraction:
                                buff&#91;i&#93;+=header.getciphervalue();
                                break;
                        case pakheader.subtract_cihoeraction:
                                buff&#91;i&#93;-=header.getciphervalue();
                                break;
                        }
                }
        }
        
        /**
         * 使用文件头中的密码对数据进行解密
         * @param buff 被解密的数据
         * @param bufflength 数据的长度
         * @param header 文件头
         */
        private void decryptbuff(byte&#91;&#93; buff,int bufflength,pakheader header){
                for(int i=0;i<bufflength;i++){
                        switch(header.getcipheraction()){
                        case pakheader.addition_cipheraction:
                                buff&#91;i&#93;-=header.getciphervalue();
                                break;
                        case pakheader.subtract_cihoeraction:
                                buff&#91;i&#93;+=header.getciphervalue();
                                break;
                        }
                }
        }
        
        /**
         * 制作pak文件
         * @param sourcefilepath 源文件路径数组
         * @param destinatefilepath 目的文件路径（pak文件）
         * @param cipheraction 密码行为
         * @param ciphervalue 密码
         * @throws exception
         */
        public void makepakfile(string&#91;&#93; sourcefilepath,
                        string destinatefilepath,pakheader header) throws exception{
                
                pakfiletable&#91;&#93; filetable=new pakfiletable&#91;sourcefilepath.length&#93;;
                //计算文件位移起始点
                long fileoffset=workoutoffsetstart(header);
                //逐个建立文件table
                for(int i=0;i<sourcefilepath.length;i++){
                        string sourcefilename=getfilename(sourcefilepath&#91;i&#93;);
                        long sourcefilesize=getfilesize(sourcefilepath&#91;i&#93;);
                        pakfiletable ft=generatefiletable(sourcefilename,sourcefilesize,fileoffset);
                        //计算下一个文件位移
                        fileoffset=workoutnextoffset(sourcefilesize,fileoffset);
                        filetable&#91;i&#93;=ft;
                }
                //写入文件头
                file wfile=new file(destinatefilepath);
                fileoutputstream fos=new fileoutputstream(wfile);
                dataoutputstream dos=new dataoutputstream(fos);
                writechararray(header.getsignature(),dos);
                dos.writefloat(header.getversion());
                dos.writelong(header.getnumfiletableentries());
                dos.writebyte(header.getcipheraction());
                dos.writebyte(header.getciphervalue());
                writechararray(header.getuniqueid(),dos);
                dos.writelong(header.getreserved());
                //写入文件table
                for(int i=0;i<filetable.length;i++){
                        writechararray(filetable&#91;i&#93;.getfilename(),dos);
                        dos.writelong(filetable&#91;i&#93;.getfilesize());

                        dos.writelong(filetable&#91;i&#93;.getoffset());
                }
                //写入文件数据
                for(int i=0;i<filetable.length;i++){
                        file ftfile=new file(sourcefilepath&#91;i&#93;);
                        fileinputstream ftfis=new fileinputstream(ftfile);
                        datainputstream ftdis=new datainputstream(ftfis);
                        byte&#91;&#93; buff=new byte&#91;256&#93;;
                        int readlength=0;
                        while((readlength=ftdis.read(buff))!=-1){
                                encryptbuff(buff,readlength,header);
                                dos.write(buff,0,readlength);
                        }
                        ftdis.close();
                        ftfis.close();
                }
                dos.close();        
        }
        
        /**
         * 从datainputstream读取char数组
         * @param dis datainputstream
         * @param readlength 读取长度
         * @return char数组
         * @throws exception
         */
        private char&#91;&#93; readchararray(datainputstream dis,int readlength) throws exception{
                char&#91;&#93; readchararray=new char&#91;readlength&#93;;
                
                for(int i=0;i<readlength;i++){
                        readchararray&#91;i&#93;=dis.readchar();
                }
                return readchararray;
        }
        
        /**
         * 从pak文件中读取文件头
         * @param dis datainputstream
         * @return pakheader
         * @throws exception
         */
        private pakheader readheader(datainputstream dis) throws exception{
                pakheader header=new pakheader();
                char&#91;&#93; signature=readchararray(dis,pakheader.signature_length);
                header.setsignature(signature);
                header.setversion(dis.readfloat());
                header.setnumfiletableentries(dis.readlong());
                header.setcipheraction(dis.readbyte());
                header.setciphervalue(dis.readbyte());
                char&#91;&#93; uniqueid=readchararray(dis,pakheader.uniqueid_length);
                header.setuniqueid(uniqueid);
                header.setreserved(dis.readlong());
                return header;
        }
        
        /**
         * 读取所有的文件table
         * @param dis datainputstream
         * @param filetablenumber 文件表总数
         * @return 文件table数组
         * @throws exception
         */
        private pakfiletable&#91;&#93; readfiletable(datainputstream dis,int filetablenumber) throws exception{
                pakfiletable&#91;&#93; filetable=new pakfiletable&#91;filetablenumber&#93;;
                for(int i=0;i<filetablenumber;i++){
                        pakfiletable ft=new pakfiletable();
                        ft.setfilename(readchararray(dis,pakfiletable.filename_length));
                        ft.setfilesize(dis.readlong());
                        ft.setoffset(dis.readlong());
                        filetable&#91;i&#93;=ft;
                }
                return filetable;
        }
        
        /**
         * 从pak文件读取文件到byte数组
         * @param dis datainputstream
         * @param filetable pakfiletable
         * @return byte数组
         * @throws exception
         */
        private byte&#91;&#93; readfilefrompak(datainputstream dis,pakheader header,pakfiletable filetable) throws exception{
                dis.skip(filetable.getoffset()-workoutoffsetstart(header));
                //
                int filelength=(int)filetable.getfilesize();
                byte&#91;&#93; filebuff=new byte&#91;filelength&#93;;
                int readlength=dis.read(filebuff,0,filelength);
                if (readlength<filelength){
                        system.out.println(&quot;读取数据长度不正确&quot;);
                        return null;
                }
                else{
                        decryptbuff(filebuff,readlength,header);
                        return filebuff;
                }
        }
        
        /**
         * 将buffer中的内容写入到文件
         * @param filebuff 保存文件内容的buffer
         * @param filename 文件名
         * @param extractdir 文件导出目录
         * @throws exception
         */
        private void writefilefrombytebuffer(byte&#91;&#93; filebuff,string filename,string extractdir) throws exception{
                string extractfilepath=extractdir+filename;
                file wfile=new file(extractfilepath);
                fileoutputstream fos=new fileoutputstream(wfile);
                dataoutputstream dos=new dataoutputstream(fos);
                dos.write(filebuff);
                dos.close();
                fos.close();
        }
        
        /**
         * 从pak文件中取出指定的文件到byte数组，如果需要的话可以将byte数组写为文件
         * @param pakfilepath  pak文件路径
         * @param extractfilename pak文件中将要被取出的文件名
         * @param writefile 是否需要将byte数组写为文件
         * @param extractdir 如果需要的话可以将byte数组写为文件，extractdir为取出数据被写的目录文件
         * @return byte数组
         * @throws exception
         */
        public byte&#91;&#93; extractfilefrompak(string pakfilepath,
                        string extractfilename,boolean writefile,string extractdir) throws exception{
                file rfile=new file(pakfilepath);
                fileinputstream fis=new fileinputstream(rfile);
                datainputstream dis=new datainputstream(fis);
                pakheader header=readheader(dis);
                pakfiletable&#91;&#93; filetable=readfiletable(dis,(int)header.getnumfiletableentries());

                boolean find=false;
                int fileindex=0;
                for(int i=0;i<filetable.length;i++){
                        string filename=new string(filetable&#91;i&#93;.getfilename()).trim();
                        if (filename.equals(extractfilename)){
                                find=true;
                                fileindex=i;
                                break;
                        }
                }
                if (find==false){
                        system.out.println(&quot;没有找到指定的文件&quot;);
                        return null;
                }
                else{
                        byte&#91;&#93; buff=readfilefrompak(dis,header,filetable&#91;fileindex&#93;);
                        if (writefile){
                                writefilefrombytebuffer(buff,extractfilename,extractdir);
                        }
                        else{
                                dis.close();
                                fis.close();
                        }
                        return buff;
                }
        }
        
        
        /**
         * 从pak文件中取出指定的pak文件的信息
         * @param pakfilepath  pak文件路径
         * @return 装载文件头和文件table数组的vector
         * @throws exception
         */
        public vector showpakfileinfo(string pakfilepath) throws exception{
                file rfile=new file(pakfilepath);
                
                fileinputstream fis=new fileinputstream(rfile);
                datainputstream dis=new datainputstream(fis);
                
                pakheader header=readheader(dis);
                pakfiletable&#91;&#93; filetable=readfiletable(dis,(int)header.getnumfiletableentries());

                vector result=new vector();
                result.add(header);
                result.add(filetable);
                return result;
        }
        
        public static void main(string&#91;&#93; argv) throws exception{
                pakutil pu=new pakutil();
                
                //构造文件头
                char&#91;&#93; signature=new char&#91;pakheader.signature_length&#93;;
                signature=new string(&quot;012345&quot;).tochararray();
                char&#91;&#93; uniqueid=new char&#91;pakheader.uniqueid_length&#93;;
                uniqueid=new string(&quot;0123456789&quot;).tochararray();
                pakheader header=new pakheader();
                header.setsignature(signature);
                header.setnumfiletableentries(3);
                header.setcipheraction((byte)pakheader.addition_cipheraction);
                header.setciphervalue((byte)0x0f);
                header.setuniqueid(uniqueid);
                header.setversion(1.0f);
                header.setreserved(0l);
                
                string&#91;&#93; filepatharray={&quot;f:\\eclipse3.1rc3\\workspace\\gmatrixproject_j2se\\testfiles\\apple.png&quot;,
                                &quot;f:\\eclipse3.1rc3\\workspace\\gmatrixproject_j2se\\testfiles\\cushaw.png&quot;,
                                &quot;f:\\eclipse3.1rc3\\workspace\\gmatrixproject_j2se\\testfiles\\flash.png&quot;};
                string extractfilepath=&quot;f:\\eclipse3.1rc3\\workspace\\gmatrixproject_j2se\\testfiles\\test.pak&quot;;
                //制作pak文件
                system.out.println(&quot;制作pak文件...&quot;);
                pu.makepakfile(filepatharray,extractfilepath,header);
                system.out.println(&quot;制作pak文件完成&quot;);
                
                //从pak文件中取出所有的图片文件
                vector pakinfo=pu.showpakfileinfo(extractfilepath);
                header=(pakheader)pakinfo.elementat(0);
                system.out.println(&quot;pak文件信息:&quot;);
                system.out.println(&quot;文件头:&quot;);
                system.out.println(header);
                
                pakfiletable&#91;&#93; filetable=(pakfiletable&#91;&#93;)pakinfo.elementat(1);
                for(int i=0;i<filetable.length;i++){
                        system.out.println(&quot;文件table&#91;&quot;+i+&quot;&#93;:&quot;);
                        system.out.println(filetable&#91;i&#93;);
                }
                
                string restoredir=&quot;f:\\eclipse3.1rc3\\workspace\\gmatrixproject_j2se\\testfiles\\extract\\&quot;;
                string restorefilename=null;
                byte&#91;&#93; filebuff=null;
                for(int i=0;i<filetable.length;i++){
                        restorefilename=new string(filetable&#91;i&#93;.getfilename()).trim();
                        system.out.println(&quot;从pak文件中取出&quot;+restorefilename+&quot;文件...&quot;);
                        filebuff=pu.extractfilefrompak(extractfilepath,restorefilename,true,restoredir);
                        system.out.println(&quot;从pak文件中取出&quot;+restorefilename+&quot;文件保存在&quot;+restoredir+&quot;目录&quot;);
                }
        }
}

七、pakutil类（j2me版）：

pakutil.java

package cn.org.matrix.gmatrix.gamelab.util.pak;

import java.io.*;
import java.util.vector;
/**
 * pak工具类
 * 功能：
 * 从pak文件中取出png图片，构造byte数组（可以用来构造image对象）
 * @author cleverpig
 *
 */
public class pakutil {
        
        public pakutil(){
        }
        
        /**
         * 计算文件位移的起始点
         * @return 文件位移的起始点
         */
        private long workoutoffsetstart(pakheader header){
                //计算出文件头+文件table的长度
                return pakheader.size()+header.getnumfiletableentries()*pakfiletable.size();
        }
        
        /**
         * 从datainputstream读取char数组
         * @param dis datainputstream
         * @param readlength 读取长度
         * @return char数组
         * @throws exception
         */
        private char[] readchararray(datainputstream dis,int readlength) throws exception{
                char[] readchararray=new char[readlength];
                
                for(int i=0;i<readlength;i++){
                        readchararray&#91;i&#93;=dis.readchar();
                }
                return readchararray;
        }
        
        /**
         * 从pak文件中读取文件头
         * @param dis datainputstream
         * @return pakheader
         * @throws exception
         */
        private pakheader readheader(datainputstream dis) throws exception{
                pakheader header=new pakheader();
                char&#91;&#93; signature=readchararray(dis,pakheader.signature_length);
                header.setsignature(signature);
                header.setversion(dis.readfloat());
                header.setnumfiletableentries(dis.readlong());
                header.setcipheraction(dis.readbyte());
                header.setciphervalue(dis.readbyte());
                char&#91;&#93; uniqueid=readchararray(dis,pakheader.uniqueid_length);
                header.setuniqueid(uniqueid);
                header.setreserved(dis.readlong());
                return header;
        }
        
        /**
         * 读取所有的文件table
         * @param dis datainputstream
         * @param filetablenumber 文件表总数
         * @return 文件table数组
         * @throws exception
         */
        private pakfiletable&#91;&#93; readfiletable(datainputstream dis,int filetablenumber) throws exception{
                pakfiletable&#91;&#93; filetable=new pakfiletable&#91;filetablenumber&#93;;
                for(int i=0;i<filetablenumber;i++){
                        pakfiletable ft=new pakfiletable();
                        ft.setfilename(readchararray(dis,pakfiletable.filename_length));
                        ft.setfilesize(dis.readlong());
                        ft.setoffset(dis.readlong());
                        filetable&#91;i&#93;=ft;
                }
                return filetable;
        }
        
        /**
         * 从pak文件读取文件到byte数组
         * @param dis datainputstream
         * @param filetable pakfiletable
         * @return byte数组
         * @throws exception
         */
        private byte&#91;&#93; readfilefrompak(datainputstream dis,pakheader header,pakfiletable filetable) throws exception{
                dis.skip(filetable.getoffset()-workoutoffsetstart(header));
                //
                int filelength=(int)filetable.getfilesize();
                byte&#91;&#93; filebuff=new byte&#91;filelength&#93;;
                int readlength=dis.read(filebuff,0,filelength);
                if (readlength<filelength){
                        system.out.println(&quot;读取数据长度不正确&quot;);
                        return null;
                }
                else{
                        decryptbuff(filebuff,readlength,header);
                }
                return filebuff;
        }
        
        /**
         * 使用文件头中的密码对数据进行解密
         * @param buff 被解密的数据
         * @param bufflength 数据的长度
         * @param header 文件头
         */
        private void decryptbuff(byte&#91;&#93; buff,int bufflength,pakheader header){
                for(int i=0;i<bufflength;i++){
                        switch(header.getcipheraction()){
                        case pakheader.addition_cipheraction:
                                buff&#91;i&#93;-=header.getciphervalue();
                                break;
                        case pakheader.subtract_cihoeraction:
                                buff&#91;i&#93;+=header.getciphervalue();
                                break;
                        }
                }
        }
        
        /**
         * 从pak文件中取出指定的文件到byte数组
         * @param pakresourceurl  pak文件的资源路径
         * @param extractresourcename pak文件中将要被取出的文件名
         * @return byte数组
         * @throws exception
         */
        public byte&#91;&#93; extractresourcefrompak(string pakresourceurl
                        ,string extractresourcename) throws exception{
                inputstream is=this.getclass().getresourceasstream(pakresourceurl);
                datainputstream dis=new datainputstream(is);
                pakheader header=readheader(dis);
//                system.out.println(&quot;文件头:&quot;);
//                system.out.println(header);
                pakfiletable&#91;&#93; filetable=readfiletable(dis,(int)header.getnumfiletableentries());
//                for(int i=0;i<filetable.length;i++){
//                        system.out.println(&quot;文件table&#91;&quot;+i+&quot;&#93;:&quot;);
//                        system.out.println(filetable&#91;i&#93;);
//                }
                boolean find=false;
                int fileindex=0;
                for(int i=0;i<filetable.length;i++){
                        string filename=new string(filetable&#91;i&#93;.getfilename()).trim();
                        if (filename.equals(extractresourcename)){
                                find=true;
                                fileindex=i;
                                break;
                        }
                }
                if (find==false){
                        system.out.println(&quot;没有找到指定的文件&quot;);
                        return null;
                }
                else{
                        byte&#91;&#93; buff=readfilefrompak(dis,header,filetable&#91;fileindex&#93;);
                        return buff;
                }
        }
        
        
        /**
         * 从pak文件中取出指定的pak文件的信息
         * @param pakresourcepath  pak文件资源路径
         * @return 装载文件头和文件table数组的vector
         * @throws exception
         */
        public vector showpakfileinfo(string pakresourcepath) throws exception{
                inputstream is=this.getclass().getresourceasstream(pakresourcepath);
                datainputstream dis=new datainputstream(is);
                
                pakheader header=readheader(dis);
                pakfiletable&#91;&#93; filetable=readfiletable(dis,(int)header.getnumfiletableentries());

                vector result=new vector();
                result.addelement(header);
                result.addelement(filetable);
                return result;
        }
        
        public static void main(string&#91;&#93; argv) throws exception{
                pakutil pu=new pakutil();
                string extractresourcepath=&quot;/test.pak&quot;;
                //从pak文件中取出所有的图片文件
                vector pakinfo=pu.showpakfileinfo(extractresourcepath);
                pakheader header=(pakheader)pakinfo.elementat(0);
                system.out.println(&quot;pak文件信息:&quot;);
                system.out.println(&quot;文件头:&quot;);
                system.out.println(header);
                
                pakfiletable&#91;&#93; filetable=(pakfiletable&#91;&#93;)pakinfo.elementat(1);
                for(int i=0;i<filetable.length;i++){
                        system.out.println(&quot;文件table&#91;&quot;+i+&quot;&#93;:&quot;);
                        system.out.println(filetable&#91;i&#93;);
                }
                
                string restorefilename=null;
                byte&#91;&#93; filebuff=null;
                for(int i=0;i<filetable.length;i++){
                        restorefilename=new string(filetable&#91;i&#93;.getfilename()).trim();
                        system.out.println(&quot;从pak文件中取出&quot;+restorefilename+&quot;文件数据...&quot;);
                        filebuff=pu.extractresourcefrompak(extractresourcepath,restorefilename);
                        system.out.println(&quot;从pak文件中取出&quot;+restorefilename+&quot;文件数据完成&quot;);
                }
        }
}

八、源代码使用简介：

    pak过程：j2se版的pakutil将testfiles目录中的三个png文件pak成为test.pak文件。
    unpak过程：j2se版的pakutil将testfiles目录中test.pak文件释放到testfiles\extract目录下；j2me版的pakutil从res目录中的test.pak文件读取出其中所包含的3个png文件数据并装入到byte数据，用来构造image对象，大家请运行pakutiltestmidlet.java便可看到输出的信息。

九、源代码下载：

j2se版源代码[下载文件]
j2sme版源代码[下载文件]

资源
·cleverpig的blog:http://blog.matrix.org.cn/page/cleverpig
·matrix-java开发者社区:http://www.matrix.org.cn/
·proguard
·j2me.org上的topic: give me all your tricks for minimizing jar file size

 

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