Apache commons NET FTP 读取文件后检索不工作

Question

我正在尝试为我的 Java 桌面应用程序（独立应用程序）制作一个启动器，它必须在服务器上寻找主应用程序的更新版本。我的想法是将应用程序版本存储在每一侧的文本文件中。

我找到了（感谢 Google san）从文本文件中读取版本并下载包含所有内容的 jar 目录的方法（均在服务器端）。我正在使用 Apache Commons Net FTP 库 btw.

当我在读取文本文件后尝试从服务器下载jar 目录时出现问题。我正确获取了文本文件内容，但是文件下载失败。

如果我切换代码行以先下载内容然后读取文本文件，两者都可以正常工作，但我们都知道这不是更新检查的方式。

我一直在寻找，但我不明白我做错了什么。这是我第一次使用这个库。

这是我正在使用的代码：

import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import org.apache.commons.io.IOUtils;
import org.apache.commons.net.ftp.FTP;
import org.apache.commons.net.ftp.FTPClient;
import org.apache.commons.net.ftp.FTPFile;
class FTPUtil{
    private String server = "www.server.host";
    private int port = 21;
    private String user = "user";
    private String pass = "password";
    private FTPClient ftpClient = new FTPClient();
    
    public void Connect() throws IOException{
        ftpClient.connect(server, port);
        ftpClient.login(user, pass);
        ftpClient.enterLocalPassiveMode();
        System.out.println("Connected");
    }
    public void Disconnect() throws IOException{
        ftpClient.logout();
        ftpClient.disconnect();
        System.out.println("Disconnected");
    }
    public double getServerVersion(String remoteDirPath) throws IOException{
        InputStream inputStream = ftpClient.retrieveFileStream(remoteDirPath + "/version.txt");
        return Double.parseDouble(IOUtils.toString(inputStream, "UTF-8"));
    }
    public boolean downloadSingleFile(String remoteFilePath, String savePath) throws IOException{
        File downloadFile = new File(savePath);

        File parentDir = downloadFile.getParentFile();
        if(!parentDir.exists())
            parentDir.mkdir();

        OutputStream outputStream = new BufferedOutputStream(new FileOutputStream(downloadFile));
        try{
            ftpClient.setFileType(FTP.BINARY_FILE_TYPE);
            return ftpClient.retrieveFile(remoteFilePath, outputStream);
        }catch(IOException e){
            throw e;
        }finally{
            if(outputStream != null)
                outputStream.close();
        }
    }
    public void downloadDirectory(String parentDir, String currentDir, String saveDir) throws IOException{
        String dirToList = parentDir;
        if(!currentDir.equals(""))
            dirToList += "/" + currentDir;
        
        FTPFile[] subFiles = ftpClient.listFiles(dirToList);

        if(subFiles != null && subFiles.length > 0){
            for(FTPFile aFile : subFiles){
                String currentFileName = aFile.getName();

                // skip parent directory and the directory itself
                if(currentFileName.equals(".") || currentFileName.equals(".."))
                    continue;

                String filePath = parentDir + "/" + currentDir + "/" + currentFileName;
                if(currentDir.equals(""))
                    filePath = parentDir + "/" + currentFileName;

                String newDirPath = saveDir + parentDir + File.separator + currentDir + File.separator + currentFileName;
                if(currentDir.equals(""))
                    newDirPath = saveDir + parentDir + File.separator + currentFileName;

                if(aFile.isDirectory()){
                    // create the directory in saveDir
                    File newDir = new File(newDirPath);
                    boolean created = newDir.mkdirs();
                    if(created)
                        System.out.println("CREATED the directory: " + newDirPath);
                    else
                        System.out.println("COULD NOT create the directory: " + newDirPath);

                    // download the sub directory
                    downloadDirectory(dirToList, currentFileName, saveDir);
                }else{
                    // download the file
                    boolean success = downloadSingleFile(filePath, newDirPath);
                    if(success)
                        System.out.println("DOWNLOADED the file: " + filePath);
                    else
                        System.out.println("COULD NOT download the file: " + filePath);
                }
            }
        }
    }
}

import java.io.IOException;
public class Main{
    public static void main(String[] args){
        String project = "ServerFolderName";
        String remoteDirPath = "/" + project;
        String saveDirPath = "C:/Users/username/Desktop";
        FTPUtil ob = new FTPUtil();
        try{
            ob.Connect();
            System.out.println(ob.getServerVersion(remoteDirPath));
            ob.downloadDirectory(remoteDirPath, "", saveDirPath);
            ob.Disconnect();
        }catch(IOException e){
            e.printStackTrace();
        }
    }
}

并且控制台输出：

run:
Connected
1.0
Exception in thread "main" org.apache.commons.net.ftp.parser.ParserInitializationException: Unknown parser type: 0.000 seconds (measured here), 37.12 Kbytes per second
    at org.apache.commons.net.ftp.parser.DefaultFTPFileEntryParserFactory.createFileEntryParser(DefaultFTPFileEntryParserFactory.java:170)
    at org.apache.commons.net.ftp.parser.DefaultFTPFileEntryParserFactory.createFileEntryParser(DefaultFTPFileEntryParserFactory.java:94)
    at org.apache.commons.net.ftp.FTPClient.__createParser(FTPClient.java:3381)
    at org.apache.commons.net.ftp.FTPClient.initiateListParsing(FTPClient.java:3338)
    at org.apache.commons.net.ftp.FTPClient.listFiles(FTPClient.java:3016)
    at generateupdateinfo.FTPUtil.downloadDirectory(FTPUtil.java:58)
    at generateupdateinfo.Main.main(Main.java:13)
C:\Users\username\AppData\Local\NetBeans\Cache.2\executor-snippets\run.xml:53: Java returned: 1
BUILD FAILED (total time: 0 seconds)

也许我做错了launcher/updater，我愿意接受建议和新想法来实现它。

编辑： 我注意到如果我在读取文本文件之后和下载文件之前用 Disconnect() 和 Connect() 更新服务器连接，它会起作用。还是觉得应该换个方式，不太好看

ob.Connect();
System.out.println(ob.getServerVersion(remoteDirPath));
ob.Disconnect();
ob.Connect();
ob.downloadDirectory(remoteDirPath, "", saveDirPath);
ob.Disconnect();

Answer 1

我发现了问题。显然我只需要在从文本文件中读取版本后用 ftpClient.completePendingCommand() 刷新服务器回复。我仍然不明白为什么这两个过程之一都会发生，我想了解。

谢谢！:)

Apache commons NET FTP 读取文件后检索不工作

Apache commons NET FTP retrieve not working after file reading

java

apache-commons-net

server