最近在使用Socket通訊時，遇到了接收內容不全（返回內容 = 4字節報文長度 + 內容主體）的問題：客戶端發送請求數據，服務器明明返回了73個字節內容，但客戶端有時能全部接收，但有時卻只能返回4個字節。
一開始是懷疑服務器返回有問題，但使用調試工具連續測試了很多次，結果顯示：服務器的確每次都返回了73個字節內容。那很明顯了，問題出現在客戶端代碼上。
錯誤現象
再來看看調試工具結果：
讓我們來看看客戶端代碼，調用方法如下：（該方法適用于返回報文前兩個字節表示長度的情況：2字節報文長度 + 內容主體）
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public static void test() { SocketClient client = new SocketClient(); // 建立socket對象 int iret = client.connect("192.168.1.105", 1234); if (iret == 0) { // 發送數據 client.write("helloworld".getBytes()); // 接收數據 byte data[] = client.read(); if ((data != null) && (data.length != 0)) { // 處理接收結果 Utils.print("響應報文字節數組---->" + Arrays.toString(data)); } } } |
SocketClient.java源碼：
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public class SocketClient { // 存儲接收數據 private byte m_buffer[] = new byte[0x10000]; private Socket m_socket; private InputStream m_inputstream; private OutputStream m_outputstream; private BufferedInputStream m_bufferedinputstream; private BufferedOutputStream m_bufferedoutputstream; private boolean connected; public int connect(String host, int port) { try { SocketAddress socketAddress = new InetSocketAddress(host, port); m_socket = new Socket(); m_socket.connect(socketAddress, 5000); m_socket.setSoTimeout(60000); m_inputstream = m_socket.getInputStream(); m_bufferedinputstream = new BufferedInputStream(m_inputstream); m_outputstream = m_socket.getOutputStream(); m_bufferedoutputstream = new BufferedOutputStream(m_outputstream); } catch (Exception e) { return -1; } connected = true; return 0; } /** * 發送請求數據 * * @param data * @param start * @param end * @return */ public int write(byte data[]) { if (data == null || data.length == 0 || !connected) { return 0; } try { m_bufferedoutputstream.write(data, 0, data.length); m_bufferedoutputstream.flush(); } catch (Exception e) { return -1; } return 0; } /** * 讀取返回數據 * * @return */ public byte[] read() { if (!connected) { return null; } int len = -1; try { // 長度不正確，有時返回4，有時返回73 len = m_bufferedinputstream.read(m_buffer, 0, 0x10000); } catch (Exception e) { len = 0; } if (len != -1) { return null; } else { byte ret[] = new byte[len]; for (int i = 0; i < len; i++) { ret[i] = m_buffer[i]; } return ret; } }} |
通過代碼調試，發現問題出現在inputsream.read方法上，java API對其描述如下：
int java. io. BufferedInputStream.read( byte[] buffer, int offset, int byteCount) throws IOException
Reads at most byteCount bytes from this stream and stores them in byte array buffer starting at offset offset. Returns the number of bytes actually read or -1 if no bytes were read and the end of the stream was encountered. If all the buffered bytes have been used, a mark has not been set and the requested number of bytes is larger than the receiver's buffer size, this implementation bypasses the buffer and simply places the results directly into buffer.
Overrides: read(...) in FilterInputStream
Parameters:
buffer the byte array in which to store the bytes read.
offset the initial position in buffer to store the bytes read from this stream.
byteCount the maximum number of bytes to store in buffer.
Returns:
the number of bytes actually read or -1 if end of stream.
Throws:
IndexOutOfBoundsException - if offset < 0 or byteCount < 0, or if offset + byteCount is greater than the size of buffer.
IOException - if the stream is already closed or another IOException occurs.
引起錯誤原因在于
客戶端在發送數據后，過快地執行read操作，而這時服務端尚未完全返回全部內容，因此只能讀到部分字節。于是換了個思路：
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public class SocketClient { private Socket m_socket; private InputStream m_inputstream; private OutputStream m_outputstream; private BufferedInputStream m_bufferedinputstream; private BufferedOutputStream m_bufferedoutputstream; private boolean connected; public int connect(String host, int port) { try { SocketAddress socketAddress = new InetSocketAddress(host, port); m_socket = new Socket(); m_socket.connect(socketAddress, 5000); m_socket.setSoTimeout(60000); m_inputstream = m_socket.getInputStream(); m_bufferedinputstream = new BufferedInputStream(m_inputstream); m_outputstream = m_socket.getOutputStream(); m_bufferedoutputstream = new BufferedOutputStream(m_outputstream); } catch (Exception e) { return -1; } connected = true; return 0; } /** * 發送請求數據 * * @param data * @param start * @param end * @return */ public int write(byte data[]) { if (data == null || data.length == 0 || !connected) { return 0; } try { m_bufferedoutputstream.write(data, 0, data.length); m_bufferedoutputstream.flush(); } catch (Exception e) { return -1; } return 0; } /** * 讀取返回數據 * * @return */ public byte[] read() { if (!connected) { return null; } try { return readStream(m_bufferedinputstream); } catch (Exception e) { return null; } } /** * @功能 讀取流 * @param inStream * @return 字節數組 * @throws Exception */ public static byte[] readStream(InputStream inStream) throws Exception { ByteArrayOutputStream outSteam = new ByteArrayOutputStream(); byte[] buffer = new byte[1024]; int len = -1; while ((len = inStream.read(buffer)) != -1) { outSteam.write(buffer, 0, len); } outSteam.close(); inStream.close(); return outSteam.toByteArray(); } public static void test() { SocketClient client = new SocketClient(); // 建立socket對象 int iret = client.connect("192.168.1.105", 1234); if (iret == 0) { // 發送數據 client.write("helloworld".getBytes()); // 接收數據 byte data[] = client.read(); if ((data != null) && (data.length != 0)) { // 處理接收結果 Utils.print("響應報文字節數組---->" + Arrays.toString(data)); } } }} |
測試通過.....
可參考以下解決思路
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protected byte[] readMessage(BufferedInputStream is) throws IOException { // MyLog.d(TAG,"=======>readMessage--inputStream=" ); int offset = 0; int messageStartOffset = -1; int wait = 0; int messageEndOffset = -1; int findStartOffset = -1; while(messageEndOffset==-1||(messageEndOffset+2)>offset){ if(is.available()==0){ try { Thread.sleep(MESSAGE_WAIT_INTERVAL); wait += MESSAGE_WAIT_INTERVAL; } catch (InterruptedException ex) { } if(wait>=MESSAGE_OVERTIME){ //超時錯誤 throw new RuntimeException(EXCEPTION_TIMEOUT); } continue; } offset += is.read(messageBuffer, offset, is.available());//讀出數據 TestMessage.showBytes(messageBuffer, 0, offset, "MESSAGE"); if(messageStartOffset==-1){ //未找到報文頭 if(findStartOffset<0) findStartOffset = 0; messageStartOffset = findStartOffset(messageBuffer, findStartOffset, offset);//查找報文頭 MyLog.e(TAG, "messageStartOffset="+messageStartOffset); if(messageStartOffset>=0){//找到報文頭 if(messageStartOffset<2){ //報文錯誤 throw new RuntimeException(EXCEPTION_MSG_PARSE_ERROR); }else{ int iMessageLength = ((messageBuffer[messageStartOffset-2]&0xff)<<8)+ (messageBuffer[messageStartOffset-1]&0xff); // MyLog.e(TAG, "iMessageLength="+iMessageLength); int ignoreInvalidLength = messageStartOffset-4; messageEndOffset = iMessageLength + ignoreInvalidLength; // MyLog.e(TAG, "messageStartOffset="+messageStartOffset); MyLog.e(TAG, "messageEndOffset="+messageEndOffset); |
如果想要讓程序保證讀取到count個字節，最好用以下代碼：
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int count = 100; byte[] b = new byte[count]; int readCount = 0; // 已經成功讀取的字節的個數 while (readCount < count) { readCount += inStream.read(b, readCount, count - readCount); } |
這樣就能保證讀取100個字節，除非中途遇到IO異常或者到了數據流的結尾情況！
以上為個人經驗，希望能給大家一個參考，也希望大家多多支持服務器之家。
原文鏈接：https://blog.csdn.net/LVXIANGAN/article/details/72817478
