我正在使用apache的FTPClient从FTP服务器下载文件。我的方案是 - FTP服务器可能会丢失网络连接，并可能最多保持断开连接1天。当它连接回来时，文件的下载应该从它离开的地方开始。我使用以下代码连接到服务器，然后从服务器下载文件
public void retrieve(String server, int port, String username,
String password, String remote, String local, int fileType,
ProgressHandler progressHandler) throws Exception {
final FTPClient ftp = new FTPClient();
Date date = new Date();
long startTime_ms = date.getTime();
if (progressHandler != null) {
ftp.setCopyStreamListener(new FtpCopyStreamListener(progressHandler));
}
ftpConnect(server,ftp, port,startTime_ms);
if(ftp.getReplyCode()==0 || !String.valueOf(ftp.getReplyCode()).startsWith("2")){
cleanup(ftp, "Could not log into server: " + server, null);
return;
}
boolean loggedIn = false;
try {
if (username == null || username.isEmpty()) {
username = "anonymous";
password = System.getProperty("user.name") + "@"
+ InetAddress.getLocalHost().getHostName();
}
if (!ftp.login(username, password)) {
ftp.logout();
cleanup(ftp, "Could not log into server: " + server, null);
}
loggedIn = true;
ftp.setFileType(fileType);
ftp.enterLocalPassiveMode();
OutputStream output = null;
try {
output = new FileOutputStream(local);
LOGGER.info("About to download " + remote + " from " + server
+ " on " + (port > 0 ? port : ftp.getDefaultPort())
+ " to " + local);
ftp.setControlKeepAliveTimeout(300);
boolean isFileDownloaded = false;
try{
isFileDownloaded = ftp.retrieveFile(remote, output);
}
catch(IOException ex){
if(ftp.isConnected()){
try{
int retryCode = 0;
while (!String.valueOf(retryCode).startsWith("2") && (new Date().getTime() < (startTime_ms + TOTAL_DURATION_MSECS))){
try{
retryCode = ftp.retr(local);
}catch(Exception e1){
Thread.sleep(1000);
System.out.println("File not downloaded !! " + e1.toString());
ftpConnect(server, ftp, port, startTime_ms);
}
}
}catch(Exception e){
//ftp.getReplyCode()
//throw e;
//disconnect(ftp);
//ftpConnect(server, ftp, port, startTime_ms);
System.out.println("File not downloaded !! " + e.toString());
}
}
}
if(isFileDownloaded){
LOGGER.info("Finished downloading " + remote + " from "
+ server + " on "
+ (port > 0 ? port : ftp.getDefaultPort()) + " to "
+ local);
}
else{
System.out.println("File not downloaded !! ");
}
}catch(IOException io){
io.printStackTrace();
throw io;
}
finally {
if (output != null) {
try {
output.close();
} catch (IOException f) {
LOGGER.severe("output.close() error: "
+ ServiceUtils.stackToString(f));
}
}
}
}
catch (FTPConnectionClosedException e) {
LOGGER.severe("Server closed connection: " + server + " "
+ ServiceUtils.stackToString(e));
throw e;
} catch (IOException e) {
LOGGER.severe("IOException, server: " + server + " "
+ ServiceUtils.stackToString(e));
throw e;
} finally {
if (loggedIn) {
try {
ftp.logout();
} catch (IOException f) {
LOGGER.severe("ftp.logout() error: "
+ ServiceUtils.stackToString(f));
}
}
disconnect(ftp);
}
}
我的问题基本上是如果retrieveFile（）方法失败，无论如何我可以重新连接并从断开连接点开始下载。
现在我使用的是Microsoft IIS服务器作为我的FTP服务器，但在生产环境中，它将是一个FileZilla FTP服务器。
感谢任何帮助。 感谢
答案 0 :(得分：1)
很抱歉很晚才回复。这就是我为解决问题所做的工作：
保持写入的字节数并使用相同的输出流进行写入。
BufferedInputStream inputStream = null;
BufferedOutputStream outputStream = null;
InputStream in = null;
int osCount = 0;
in = ftp.retrieveFileStream(remote);
inputStream = new BufferedInputStream(in);
File localFile = new File(local, fileName);
outputStream = new BufferedOutputStream(new FileOutputStream(localFile));
for (int read = inputStream.read(); read != -1; read = inputStream.read()) {
outputStream.write(read);
osCount++;
}
outputStream.flush();
if (osCount < fileSize) {
System.out.println(fileName + ": Errored out !!!");
BufferedInputStream inputStream1 = null;
InputStream in1 = null;
if (ftp.isConnected()) {
try {
while (osCount < fileSize && new Date().getTime() < (startTime_ms + TOTAL_DURATION_MSECS)) {
try {
disconnect(ftp);
ftpConnect(server, ftp, port, startTime_ms);
ftp.login(username, password);
ftp.setRestartOffset(osCount);
System.out.println(fileName + ": Re reading from position " + osCount);
in1 = ftp.retrieveFileStream(remote);
inputStream1 = new BufferedInputStream(in1);
for (int read = inputStream1.read(); read != -1; read = inputStream1.read()) {
outputStream.write(read);
osCount++;
}
outputStream.flush();
if(FTPReply.isPositiveCompletion(ftp.getReplyCode())){
isErrored = true;
break;
}
} catch (Exception e1) {
Thread.sleep(1000);
LOGGER.severe(fileName + ": File not downloaded " + server + " " + ServiceUtils.stackToString(e1));
}
}
} catch (Exception e) {
LOGGER.severe(fileName + ": File not downloaded " + server + " " + ServiceUtils.stackToString(e));
}
}
}
答案 1 :(得分：0)
FTPCLient.restart(...)是protected。我认为setRestartOffset(...)和retrieveFile(...)是可行的方法：“注意：如果您使用了setRestartOffset（long），则文件数据将从选定的偏移量开始。”。
我还会捕获CopyStreamException而不只是IOException：“CopyStreamException允许您确定传输的字节数”'。
在进入重试块之前检查ftp.isConnected()但是您编写“FTP服务器松散的网络连接并且可能保持断开连接”。我想如果你输入这个catch块连接已经丢失了，这就是进入这个块的原因之一。
ftp.retr(...)在做什么？重试，是的，但它是否按预期工作？
如果您通过以下方式调试代码，您会得到什么：
ftp.isConnected() ftp.isConnected() true（不太可能，但谁知道）ftp.retr(...)会返回什么？