HTTP POST输出流与内存优化

来源：互联网发布：求圆面积的编程编辑：程序博客网时间：2024/05/04 22:32

起因

有个功能，比如上传文件，想在HTTPPOST时候想打开一个OutputStream，然后将File Content通过FileInputStream边读边上传。以节省内存。

之前一直理解不到位，以前是这样实现的：

URL url = new URL("http://ddaitp.sinaapp.com/test.php");       HttpURLConnection conn =(HttpURLConnection) url.openConnection();       conn.setRequestMethod("POST");       conn.setDoOutput(true);       conn.setDoInput(true);       conn.connect();    OutputStreamos = conn.getOutputStream();

后来发现这样没有解决问题，当文件比较大的时候依然会OutOfMemory。

原因

但是仔细读代码发现这样不能解决问题，还是将要上传的内容都读到内存，然后在flush() 时上传。

因为打印conn发现实际为libcore.net.http.ChunkedOutputStream。conn.getOutputStream()得到的OutputStream为RetryableOutputStream。

如果要实现目的，需要setFixedLengthStreamingMode()或者setChunkedStreamingMode(int)。

RetryableOutputStream中关键实现如下：

private final ByteArrayOutputStream content;public RetryableOutputStream() {        this.limit = -1;        this.content = new ByteArrayOutputStream();    }public synchronized void write(byte[] buffer, int offset, int count)            throws IOException {        checkNotClosed();        Arrays.checkOffsetAndCount(buffer.length, offset, count);        if (limit != -1 && content.size() > limit - count) {            throw new IOException("exceeded content-length limit of " + limit + " bytes");        }        content.write(buffer, offset, count);    }

所有的内容都写到了ByteArrayOutputStream中，存在于在内存。

关键代码如下：

libcore.net.http.HttpURLConnectionImpl

https://android.googlesource.com/platform/libcore/+/4f81a06/luni/src/main/java/libcore/net/http/HttpURLConnectionImpl.java

public final OutputStream getOutputStream() throws IOException {        connect();         OutputStreamresult = httpEngine.getRequestBody();        if (result == null) {            throw new ProtocolException("method does not support a request body:" + method);        } else if (httpEngine.hasResponse()) {            throw new ProtocolException("cannot write request body afterresponse has been read");        }         return result;     }

libcore.net.http.HttpEngine

https://android.googlesource.com/platform/libcore/+/4f81a06/luni/src/main/java/libcore/net/http/HttpEngine.java

protected void initRequestBodyOut() throws IOException {        int chunkLength = policy.getChunkLength();        if (chunkLength > 0 || requestHeaders.isChunked()) {            sendChunked = true;            if (chunkLength == -1) {                chunkLength = DEFAULT_CHUNK_LENGTH;            }        }         if (socketOut == null) {            throw new IllegalStateException("No socket to write to; was a POSTcached?");        }         if (httpMinorVersion == 0) {            sendChunked = false;        }         intfixedContentLength = policy.getFixedContentLength();        if (requestBodyOut != null) {            // request body was already initialized bythe predecessor HTTP engine        } else if (fixedContentLength != -1) {            writeRequestHeaders(fixedContentLength);            requestBodyOut = new FixedLengthOutputStream(requestOut, fixedContentLength);        } else if (sendChunked) {            writeRequestHeaders(-1);            requestBodyOut = new ChunkedOutputStream(requestOut, chunkLength);        } else if (requestHeaders.getContentLength() != -1) {            writeRequestHeaders(requestHeaders.getContentLength());            requestBodyOut = new RetryableOutputStream(requestHeaders.getContentLength());        } else {            requestBodyOut = new RetryableOutputStream();        }    }}

修改

结论，修改办法也简单。有两种办法

Chunked Streaming
添加conn.setChunkedStreamingMode(0);

修改后如下：

     HttpURLConnection conn;           try {              conn = (HttpURLConnection) new URL(                     "http://10.2.167.14/").openConnection();              conn.setRequestMethod("POST");              conn.setRequestProperty("User-Agent", "ddai-agent");              conn.setChunkedStreamingMode(0);              conn.setConnectTimeout(0);              conn.setReadTimeout(0);              conn.setDoOutput(true);              conn.setDoInput(true);              conn.connect();              BufferedOutputStream os = new BufferedOutputStream(                     conn.getOutputStream());              upload(os, conn);              os.flush();              os.close();              conn.disconnect();           } catch (MalformedURLException e) {              e.printStackTrace();           } catch (IOException e) {              e.printStackTrace();           }

Fixed Length

设置POST内容的总长度：

conn.setFixedLengthStreamingMode();

由于我写出只是一个File，所以长度不包括HTTP标准的其他内容。

HttpURLConnection conn;           try {              conn = (HttpURLConnection) new URL(                     "http://ddaitp.sinaapp.com/test.php").openConnection();              conn.setRequestMethod("POST");              conn.setDoOutput(true);              conn.setDoInput(true);              conn.setFixedLengthStreamingMode((int) uploadFile.length());              conn.connect();              OutputStream os =conn.getOutputStream();              upload(os, conn);              conn.disconnect();           } catch (MalformedURLException e) {              e.printStackTrace();           } catch (IOException e) {              e.printStackTrace();           }