java Socket无法完全接收返回内容的解决方案

目录

• 错误现象
• 引起错误原因在于
• 可参考以下解决思路

最近在使用Socket通讯时，遇到了接收内容不全（返回内容 = 4字节报文长度 + 内容主体）的问题：客户端发送请求数据，服务器明明返回了73个字节内容，但客户端有时能全部接收，但有时却只能返回4个字节。

一开始是怀疑服务器返回有问题，但使用调试工具连续测试了很多次，结果显示：服务器的确每次都返回了73个字节内容。那很明显了，问题出现在客户端代码上。

错误现象

再来看看调试工具结果：

让我们来看看客户端代码，调用方法如下：（该方法适用于返回报文前两个字节表示长度的情况：2字节报文长度 + 内容主体）

public static void test() {
		SocketClient client = new SocketClient();
		// 建立socket对象
		int iret = client.connect("192.168.1.105", 1234);
		if (iret == 0) {
			// 发送数据
			client.write("helloworld".getBytes());
			// 接收数据
			byte data[] = client.read();
			if ((data != null) && (data.length != 0)) {
				// 处理接收结果
				Utils.print("响应报文字节数组---->" + Arrays.toString(data));
			}
		}
	}

SocketClient.java源码：

public class SocketClient {
	// 存储接收数据
	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;
	}

	/**
	 * 发送请求数据
	 *
	 * @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;
	}

	/**
	 * 读取返回数据
	 *
	 * @return
	 */
	public byte[] read() {
		if (!connected) {
			return null;
		}
		int len = -1;
		try {
			// 长度不正确，有时返回4，有时返回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;
		}
	}
}

通过代码调试，发现问题出现在inputsream.read方法上，java API对其描述如下：

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.

引起错误原因在于

客户端在发送数据后，过快地执行read操作，而这时服务端尚未完全返回全部内容，因此只能读到部分字节。于是换了个思路：

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;
	}

	/**
	 * 发送请求数据
	 *
	 * @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;
	}

	/**
	 * 读取返回数据
	 *
	 * @return
	 */
	public byte[] read() {
		if (!connected) {
			return null;
		}
		try {
			return readStream(m_bufferedinputstream);
		} catch (Exception e) {
			return null;
		}
	}

	/**
	 * @功能 读取流
	 * @param inStream
	 * @return 字节数组
	 * @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对象
		int iret = client.connect("192.168.1.105", 1234);
		if (iret == 0) {
			// 发送数据
			client.write("helloworld".getBytes());
			// 接收数据
			byte data[] = client.read();
			if ((data != null) && (data.length != 0)) {
				// 处理接收结果
				Utils.print("响应报文字节数组---->" + Arrays.toString(data));
			}
		}
	}
}

测试通过.....

可参考以下解决思路

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){
		                //超时错误
		                    throw new RuntimeException(EXCEPTION_TIMEOUT);
		                }
		                continue;
		            }

		            offset += is.read(messageBuffer, offset, is.available());//读出数据
		            TestMessage.showBytes(messageBuffer, 0, offset, "MESSAGE");
		            if(messageStartOffset==-1){ //未找到报文头
		                if(findStartOffset<0)
		                    findStartOffset = 0;
		                messageStartOffset = findStartOffset(messageBuffer, findStartOffset, offset);//查找报文头
		                MyLog.e(TAG, "messageStartOffset="+messageStartOffset);
		                if(messageStartOffset>=0){//找到报文头
		                    if(messageStartOffset<2){
		                        //报文错误
		                        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);

如果想要让程序保证读取到count个字节，最好用以下代码：

int count = 100;
byte[] b = new byte[count];
int readCount = 0; // 已经成功读取的字节的个数
while (readCount < count) {
    readCount += inStream.read(b, readCount, count - readCount);
}  

这样就能保证读取100个字节，除非中途遇到IO异常或者到了数据流的结尾情况！

以上为个人经验，希望能给大家一个参考，也希望大家多多支持我们。