请问如何将此段PHP代码转换成Java代码

Question

<?php


function res2json($sql_str)
{
  $rcnt=0;

  
  $jsstr="\"items\":[\n";
  try
  {
    $cnn=new PDO("mysql:host=127.0.0.1;port=3306;dbname=dbexam;","db2user","dirabc");
    $sql="SET names utf8";
    $cnn->exec($sql);
  }catch (Exception $e)
  {
    echo("db connect error.\n");
    $cnn=null;
    return null;
  } 

  $res=$cnn->query($sql_str);
  if($res!=null)
  {
    $res->setFetchMode(PDO::FETCH_NUM);
    while($cols=$res->fetch())
    {
        if($rcnt>0){$jsstr.=",\n";}
        $jsstr.="{\n";
        //���������
        $jsstr.="\"department_id\":".$cols[0].",\n";
        $jsstr.="\"department_name\":\"".$cols[1]."\",\n";
        $jsstr.="\"department_type\":".$cols[2]."\n";
        
        //��������������
        $sql2="select department_id,department_name,department_type from department where parent_id=$cols[0] ";
        $subjs=res2json($sql2);//�ݹ����
        if($subjs!=null)
        {
           $jsstr.=",";
           $jsstr.=$subjs;//���¼�
        }
        
        $jsstr.="\n}\n";
        $rcnt++;
    }//while
  }//res!=null
  $res=null;
  $cnn=null;
  $jsstr.="]";
  
  if($rcnt<1)
  {
    return null;
  }
  return $jsstr;
}

$sql="select department_id,department_name,department_type from department where parent_id is null";
$json="{\n".res2json($sql)."}\n";

//д���ļ�
$fp=fopen("outjson.txt","wt+");
if($fp)
{
  fwrite($fp,$json);
  fclose($fp);
}

?>