问题已得到解决，还是参考之前的文章：
1、加密后的字符未进行字符转换，所以无法进行解密，缺少一个步骤。
2、参考我发的文章链接，PHP类完全通用。可忽略我之前发布的代码，我会再整理一份对的。

java

import java.security.Security;
import javax.crypto.Cipher;
import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;

public class ThreeDES {

private static final String Algorithm = "DESede"; //定义 加密算法,可用 DES,DESede,Blowfish

//keybyte为加密密钥，长度为24字节
//src为被加密的数据缓冲区（源）
public static byte[] encryptMode(byte[] keybyte, byte[] src) {
   try {
        //生成密钥
        SecretKey deskey = new SecretKeySpec(keybyte, Algorithm);

        //加密
        Cipher c1 = Cipher.getInstance(Algorithm);
        c1.init(Cipher.ENCRYPT_MODE, deskey);
        return c1.doFinal(src);
    } catch (java.security.NoSuchAlgorithmException e1) {
        e1.printStackTrace();
    } catch (javax.crypto.NoSuchPaddingException e2) {
        e2.printStackTrace();
    } catch (java.lang.Exception e3) {
        e3.printStackTrace();
    }
    return null;
}

//keybyte为加密密钥，长度为24字节
//src为加密后的缓冲区
public static byte[] decryptMode(byte[] keybyte, byte[] src) {      
try {
        //生成密钥
        SecretKey deskey = new SecretKeySpec(keybyte, Algorithm);

        //解密
        Cipher c1 = Cipher.getInstance(Algorithm);
        c1.init(Cipher.DECRYPT_MODE, deskey);
        return c1.doFinal(src);
    } catch (java.security.NoSuchAlgorithmException e1) {
        e1.printStackTrace();
    } catch (javax.crypto.NoSuchPaddingException e2) {
        e2.printStackTrace();
    } catch (java.lang.Exception e3) {
        e3.printStackTrace();
    }
    return null;
}

//转换成十六进制字符串
public static String byte2hex(byte[] b) {
    String hs="";
    String stmp="";

    for (int n=0;n<b.length;n++) {
        stmp=(java.lang.Integer.toHexString(b[n] & 0XFF));
        if (stmp.length()==1) hs=hs+"0"+stmp;
        else hs=hs+stmp;
        if (n<b.length-1)  hs=hs+":";
    }
    return hs.toUpperCase();
}

public static void main(String[] args)
{
    //添加新安全算法,如果用JCE就要把它添加进去
    Security.addProvider(new com.sun.crypto.provider.SunJCE());

    final byte[] keyBytes = {0x11, 0x28, 0x4F, 0x58, (byte)0x88, 0x10, 0x40, 0x38
                           , 0x28, 0x25, 0x79, 0x51, (byte)0xCB, (byte)0xDD, 0x55, 0x66
                           , 0x77, 0x29, 0x74, (byte)0x98, 0x30, 0x40, 0x36, (byte)0xE2};    //24字节的密钥
    String szSrc = "12345678";
    
    System.out.println("加密前的字符串:" + szSrc);
    
    byte[] encoded = encryptMode(keyBytes, szSrc.getBytes());        
    System.out.println("加密后的字符串:" + new String(encoded));
    
    byte[] srcBytes = decryptMode(keyBytes, encoded);
    System.out.println("解密后的字符串:" + (new String(srcBytes)));
}

}

以上代码完全取至 /q/10... 中

以下是PHP代码。

<?php

class EasyCrypt3Des {

private $_key = "";

public function __construct() {
    $keyItem = array(
        '0x11','0x28','0x4F','0x58','0x88','0x10','0x40','0x38','0x28','0x25','0x79','0x51',
        '0xCB','0xDD','0x55','0x66','0x77','0x29','0x74','0x98','0x30','0x40','0x36','0xE2'
    );
    foreach($keyItem as $kitem) {
        //转换成字符
        $this->_key .= chr($kitem);
    }
}

public function encrypt($str) {
    $td = $this->gettd();
    $ret = mcrypt_generic($td, $this->pkcs5_pad($str, 8));
    mcrypt_generic_deinit($td);
    mcrypt_module_close($td);
    return $this->strToHex($ret);
}

public function decrypt($str) {
    $td = $this->gettd();
    $ret = $this->pkcs5_unpad(mdecrypt_generic($td, $this->hexToStr($str)));
    mcrypt_generic_deinit($td);
    mcrypt_module_close($td);
    return $ret;
}

private function pkcs5_pad($text, $blocksize) {
    $pad = $blocksize - (strlen($text) % $blocksize);
    return $text . str_repeat(chr($pad), $pad);
}

private function pkcs5_unpad($text) {
    $pad = ord($text{strlen($text) - 1});
    if ($pad > strlen($text)) {
        return false;
    }
    if (strspn($text, chr($pad), strlen($text) - $pad) != $pad) {
        return false;
    }
    return substr($text, 0, -1 * $pad);
}

private function getiv() {
    return pack('H16', '0000000000000000');
}

private function gettd() {
    $iv = $this->getiv();
    $td = mcrypt_module_open(MCRYPT_3DES, '', MCRYPT_MODE_ECB, '');
    mcrypt_generic_init($td, $this->_key, $iv);
    return $td;
}

private function strToHex($string){
    $hex = '';
    for ($i=0; $i<strlen($string); $i++){
        $ord = ord($string[$i]);
        $hexCode = dechex($ord);
        $hex .= substr('0'.$hexCode, -2);
    }
    return strToUpper($hex);
}

private function hexToStr($hex){
    $string='';
    for ($i=0; $i < strlen($hex)-1; $i+=2){
        $string .= chr(hexdec($hex[$i].$hex[$i+1]));
    }
    return $string;
}

}
$EasyCrypt3Des = new EasyCrypt3Des();
$code = $EasyCrypt3Des->encrypt('12345678');
echo $code .'<br/>';
echo $EasyCrypt3Des->decrypt($code);
exit;

主要在于字符转换这块。