Java - รบกวนช่วยอธิบายโค้ด Java หน่อยคะ และตีความให้เป็น Flowchart

package th.co.vlink.tg.csv;

import java.io.IOException;
import java.io.InputStreamReader;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.HashMap;
import java.util.Locale;
import java.util.Map;

import org.apache.commons.net.ftp.FTP;
import org.apache.commons.net.ftp.FTPClient;
import org.apache.commons.net.ftp.FTPFile;

import au.com.bytecode.opencsv.CSVReader;

public class CrewCSVManager {
	private static SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd-hh-mm-ss", Locale.US);
	public Map getCrewMap(String server,String username,String password,String filePath){
		Map users= new HashMap<String, String>();		
		 FTPClient ftp = new FTPClient();
	        try {
	        	//ftp.connect("57.59.2.187");
	        	ftp.connect(server); 
				//if (!ftp.login("patcels", "P@tcEl$5"))
	        	if (!ftp.login(username,password))
				{
				    ftp.logout(); 
				}
				ftp.setFileType(FTP.BINARY_FILE_TYPE); 
				FTPFile[] files = ftp.listFiles(filePath);
	             String filenameMax="";
	        	 Date timesMax=null;
	        	 boolean haveFiles=false;
	        	 boolean firstTime=false;
	             if(files!=null && files.length>0){
	            	 int size=files.length;
	            	 Date[] times=new Date[size];
	            	 String[] name=new String[size];            	
	            	 for (int i = 0; i < size; i++) {
	            		 FTPFile file =files[i];
	            		 times[i]=file.getTimestamp().getTime();
	            		 name[i]=file.getName();
	            		 if(name[i].indexOf(".csv")!=-1){
	            			 String[] filename=name[i].split(".csv");
	            			 Date d=null;
	            			 try {
								d=dateFormat.parse(filename[0]);
							} catch (ParseException e) {
								// TODO Auto-generated catch block
								e.printStackTrace();
							}
	            			 if(!firstTime){
	            				 timesMax=d;// times[i];
	                			 filenameMax=name[i];
	                			 firstTime=true;
	            			 }else{
	            				 if(d.after(timesMax)){
	                				 timesMax=d;
	                				 filenameMax=name[i];
	                			 }
	            			 }
	            				 
	            		 } 
	            		 
					}
	            	 haveFiles=true;
	             }
	             if(haveFiles && filenameMax!=null && filenameMax.length()>0){
	            	 CSVReader reader=null;
	            	 InputStreamReader inReader=new  InputStreamReader(ftp.retrieveFileStream(filePath+filenameMax));
	         		try {
	         			//reader= new CSVReader(new FileReader(filePath), '|');
	         			reader= new CSVReader(inReader, ',');
	         			String [] nextLine;
	         			try {
	         				while ((nextLine = reader.readNext()) != null) {
	                     		String staffNum=nextLine[0];;//STAFF_NUM
	                     		if(staffNum!=null && staffNum.length()<7){
	                     			int offset=5-staffNum.length();
	                     			String offset0="";
	                     			for (int i = 0; i < offset; i++) {
	                     				offset0=offset0+"0";
									}
	                     			staffNum="TG"+offset0+staffNum; // uid
	                     		}
	                         	String crewPosFly=nextLine[4];;//CREW_POS_FLY //job_type
	         					users.put(staffNum, crewPosFly);
	         					 	
	         				}
	         			} catch (IOException e) {
	         				// TODO Auto-generated catch block
	         				e.printStackTrace();
	         			} 
	         		}finally{
	         			if(inReader!=null){
	         				inReader.close();
	         			}
	         			if(reader!=null){
	         				try {
	         					reader.close();
	         				} catch (IOException e) {
	         					// TODO Auto-generated catch block
	         					e.printStackTrace();
	         				}
	         			}
	         		}
	             }
	             ftp.noop(); // check that control connection is working OK

	             ftp.logout();
			} catch (IOException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			} finally
	        {
	            if (ftp.isConnected())
	            {
	                try
	                {
	                    ftp.disconnect();
	                }
	                catch (IOException f)
	                {
	                    // do nothing
	                }
	            }
	        }		
		return users;
	}
	public static void main(String[] args) throws IOException {
		long start = System.currentTimeMillis();
	/*	PaeManager a = new  PaeManager();
		a.getPaeMap("/tmp/test.csv");
 */
		long end = System.currentTimeMillis();
		System.out.println("uses time="+((end-start)/1000d));
	
	}
 
}