java ftp上传时断网，文件损坏

以二进制流上传，然后实现断点续传。

/**

* 上传文件到FTP服务器，支持断点续传

* @param local 本地文件名称，绝对路径

* @param remote 远程文件路径，使用/home/directory1/subdirectory/file.ext 按照Linux上的路径指定方式，支持多级目录嵌套，支持递归创建不存在的目录结构

* @return 上传结果

* @throws IOException

*/

public UploadStatus upload(String local,String remote) throws IOException{

FTPClient ftpClient = new FTPClient()

//设置PassiveMode传输

ftpClient.enterLocalPassiveMode()

//设置以二进制流的方式传输

ftpClient.setFileType(FTP.BINARY_FILE_TYPE)

UploadStatus result

//对远程目录的处理

String remoteFileName = remote

if(remote.contains("/")){

remoteFileName = remote.substring(remote.lastIndexOf("/")+1)

String directory = remote.substring(0,remote.lastIndexOf("/")+1)

if(!directory.equalsIgnoreCase("/")&&!ftpClient.changeWorkingDirectory(directory)){

//如果远程目录不存在，则递归创建远程服务器目录

int start=0

int end = 0

if(directory.startsWith("/")){

start = 1

}else{

start = 0

}

end = directory.indexOf("/",start)

while(true){

String subDirectory = remote.substring(start,end)

if(!ftpClient.changeWorkingDirectory(subDirectory)){

if(ftpClient.makeDirectory(subDirectory)){

ftpClient.changeWorkingDirectory(subDirectory)

}else {

System.out.println("创建目录失败")

return UploadStatus.Create_Directory_Fail

}

}

start = end + 1

end = directory.indexOf("/",start)

//检查所有目录是否创建完毕

if(end <= start){

break

}

}

}

}

//检查远程是否存在文件

FTPFile[] files = ftpClient.listFiles(remoteFileName)

if(files.length == 1){

long remoteSize = files[0].getSize()

File f = new File(local)

long localSize = f.length()

if(remoteSize==localSize){

return UploadStatus.File_Exits

}else if(remoteSize >localSize){

return UploadStatus.Remote_Bigger_Local

}

//尝试移动文件内读取指针,实现断点续传

InputStream is = new FileInputStream(f)

if(is.skip(remoteSize)==remoteSize){

ftpClient.setRestartOffset(remoteSize)

if(ftpClient.storeFile(remote, is)){

return UploadStatus.Upload_From_Break_Success

}

}

//如果断点续传没有成功，则删除服务器上文件，重新上传

if(!ftpClient.deleteFile(remoteFileName)){

return UploadStatus.Delete_Remote_Faild

}

is = new FileInputStream(f)

if(ftpClient.storeFile(remote, is)){

result = UploadStatus.Upload_New_File_Success

}else{

result = UploadStatus.Upload_New_File_Failed

}

is.close()

}else {

InputStream is = new FileInputStream(local)

if(ftpClient.storeFile(remoteFileName, is)){

result = UploadStatus.Upload_New_File_Success

}else{

result = UploadStatus.Upload_New_File_Failed

}

is.close()

}

return result

}

UDP是并不是可靠的传输方式,字节序列并没有得到校验,所以传输文件时出现错误也是难免的.因为,txt,doc和jpg本身即使出错也不会影响打开,顶多出现个别字符或是个别像素错误不会影响整体,而exe则是cpu的指令执行序列你错一个就将会导致程序无法执行,如果你懂hash的话可以将文件hash一下看看传输前后的hash码是否相同若不相同说明了传输过程出现了错误需要重传.

UDP一般应用在海量的并对准确性要求不高的传输上,并一般伴随有重传机制

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