我正在尝试将一些大型文件从Android设备上传到.Net Web服务。此Web服务已设置为接受这些文件作为POST参数，并且文件必须作为Base64编码的字符串发送。
我已经能够使用Christian d'Heure的this库将文件转换为Base64字符串，以字节为单位计算字符串的大小并将其先前发送，但是我之前使用的方法是将整个文件加载到内存中，这会在处理大文件时导致内存不足错误，这并非意外。
我一直在尝试将文件转换为块中的Base64，并在转换时通过连接（使用数据输出流对象）传输此数据，因此整个文件不需要加载到内存中然而，在转换文件之前，我似乎无法准确计算出请求的Content-Length的大小 - 我通常看起来大概是10个字节 - 令人沮丧的是，它偶尔会起作用！
我还发现，有些时候服务器运行时会返回以下错误消息“Base64 char数组的大小无效”。我认为这是一个填充字符的问题，但我看不出我的代码有问题，这个问题的一些建议将非常感谢！
这是生成请求并流式传输数据的代码：
try
{
HttpURLConnection connection = null;
DataOutputStream outputStream = null;
DataInputStream inputStream = null;
//This is the path to the file
String pathToOurFile = Environment
.getExternalStorageDirectory().getPath()
+ "/path/to/the/file.zip";
String urlServer = "https://www.someserver.com/somewebservice/";
int bytesRead, bytesAvailable, bufferSize;
byte[] buffer;
int maxBufferSize = 456;
//The parameters of the POST request - File Data is the file in question as a Base64 String
String params = "Username=foo&Password=bar&FileData=";
File sizeCheck = new File(pathToOurFile);
Integer zipSize = (int) sizeCheck.length();
Integer paddingRequired = ((zipSize * 8) / 6) % 3;
Integer base64ZipSize = ((zipSize * 8) / 6)
+ ((zipSize * 8) / 6) % 3;
Integer paramLength = params.getBytes().length;
//Code to work out the number of lines required, assuming we create a new
//line every 76 characters - this is used t work out the number of
//extra bytes required for new line characters
Integer numberOfLines = base64ZipSize / 76;
Log.i(TAG, "numberOfLines: " + numberOfLines);
Integer newLineLength = System.getProperty("line.separator")
.getBytes().length;
//This works out the total length of the Content
Integer totalLength = paramLength + base64ZipSize
+ (numberOfLines * newLineLength) + paddingRequired;
Log.i(TAG, "total Length: " + totalLength);
FileInputStream fileInputStream = new FileInputStream(new File(
pathToOurFile));
URL url = new URL(urlServer);
connection = (HttpURLConnection) url.openConnection();
connection.setDoInput(true);
connection.setDoOutput(true);
connection.setUseCaches(false);
connection.setRequestMethod("POST");
connection.setRequestProperty("Connection", "Keep-Alive");
connection.setRequestProperty("Content-Type",
"application/x-www-form-urlencoded;");
connection.setRequestProperty("Content-Length", ""
+ totalLength); // number of bytes
outputStream = new DataOutputStream(
connection.getOutputStream());
//Write out the parameters to the data output stream
outputStream.writeBytes(params);
bytesAvailable = fileInputStream.available();
bufferSize = Math.min(bytesAvailable, maxBufferSize);
buffer = new byte[bufferSize];
bytesRead = fileInputStream.read(buffer, 0, bufferSize);
Integer totalSent = paramLength;
Integer enLen = 0;
//Convert the file to Base64 and Stream the result to the
//Data output stream
while (bytesRead > 0)
{
String convetedBase64 = Base64Coder.encodeLines(buffer);
convetedBase64 = convetedBase64.replace("=", "");
if (totalSent >= (totalLength - 616))
{
Log.i(TAG, "about to send last chunk of data");
convetedBase64 = convetedBase64.substring(0,
convetedBase64.length() - 1);
}
Log.i(TAG,
"next data chunk to send: "
+ convetedBase64.getBytes().length);
Log.i(TAG, "'" + convetedBase64 + "'");
enLen = enLen + convetedBase64.length();
outputStream.writeBytes(convetedBase64);
totalSent = totalSent + convetedBase64.getBytes().length;
Log.i(TAG, "total sent " + totalSent);
Log.i(TAG, "actual size: " + outputStream.size());
bytesAvailable = fileInputStream.available();
bufferSize = Math.min(bytesAvailable, maxBufferSize);
buffer = new byte[bufferSize];
bytesRead = fileInputStream.read(buffer, 0, bufferSize); // read
// into
// the
// buffer
}
Log.i(TAG, "enLen: " + enLen);
Log.i(TAG, "paddingRequired: " + paddingRequired);
for (int x = 0; x < paddingRequired; x++)
{
outputStream.writeBytes("=");
}
InputStream is2 = connection.getInputStream();
String output = IOUtils.toString(is2);
Log.i(TAG, "Got server response: " + output);
fileInputStream.close();
outputStream.flush();
outputStream.close();
}
catch (Exception ex)
{
Log.e(TAG, "caught an exception:" + ex.getMessage());
}
如果有人能指出我的代码中可能导致此错误的任何错误，或者建议更好的转换和上传文件的方式，我将非常感激。
答案 0 :(得分：1)
Soooo ......我确实找到了一些解决这个问题的方法，以防万一有人在这个问题上发现我会把它们留在这里：
第一个是将数据写入一个临时文件，所以我可以在转换后以字节为单位获得大小 - 一开始似乎是一个好主意，但效率低下并且在发现其他方法之后似乎很傻。
另一种方法是不指定内容长度（我不知道你可以这样做！）。不幸的是，Android仍然试图为上传分配足够的内存，这导致了问题。
如果您指定使用ChunkedStreamingMode Android的连接，则播放不错并缓冲上传，保存使用的ram（除了2.2上的奇怪错误）。
这样的代码是这样的：
httppost.setDoInput(true);
httppost.setDoOutput(true);
httppost.setRequestMethod("POST");
httppost.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
httppost.setChunkedStreamingMode(0); //This specifies the size of the chunks - 0 uses the system default
DataOutputStream dos = new DataOutputStream(httppost.getOutputStream());
dos.writeBytes(content); //This code write out the rest of the post body first, for example username or password
try
{
BufferedInputStream dis = new BufferedInputStream(new FileInputStream("path/to/some/file"), 2048);
byte[] in = new byte[512];
while (dis.read(in)) > 0)
{
dos.write(Base64.encode(in, Base64.URL_SAFE)); //This writes out the Base64 data
//I used the web safe base64 to save URL encoding it again
//However your server must support this
dos.write(newLine); //this write out a newline character
}
dos.flush();
dis.close();
dos.close();
我希望这会有所帮助!!!