/**
 * 从 buf 中查找 "\r\n"，并返回这段（包括 \r\n）空间的长度。
 * 如果 buf 中没有，则返回 0 。
 */
private static int findLineEnd(final byte[] buf, int rlen) {
    int splitbyte = 0;
    while (splitbyte + 1 < rlen) {
        if (buf[splitbyte] == '\r' && buf[splitbyte + 1] == '\n' && splitbyte + 1 < rlen) {
            return splitbyte + 2;
        }
        splitbyte++;
    }
    return 0;
}

/**
 * 半包、粘包问题解决：
 *      从 InputStream 中找一行数据并返回。「一行」的标志是截止到 \r\n，不包括 \r\n 。
 */
private static String readLine(InputStream inputStream) throws IOException, RuntimeException {
    int splitbyte = 0;
    int rlen = 0;
    byte[] buf = new byte[BUFSIZE];
    int read = -1;
    inputStream.mark(BUFSIZE);
    try {
        read = inputStream.read(buf, 0, BUFSIZE);
    } catch (Exception e) {
        throw new SocketException("Could not Read");
    }

    if (read == -1) {
        throw new SocketException("Could not Read");
    }

    /* buf 中存储的数据区间为： buf[0] ... buf[read-1]，共 read 个字节。 */

    while (read > 0) {
        rlen += read;
        splitbyte = findLineEnd(buf, rlen);
        if (splitbyte > 0) {
            break;
        }

        read = inputStream.read(buf, rlen, BUFSIZE - rlen);
    }

    /* buf 中存储的数据区间为： buf[0] ... buf[splitbyte-1]，共 splitbyte 个字节。其中包含 \r\n 在内。*/

    // -2 的目的是返回的结果内容中不包含 \r\n 。
    return new String(buf, 0, splitbyte - 2);
}

private static void safeClose(Closeable closeable) {
    try {
        if (closeable != null) {
            closeable.close();
        }
    } catch (IOException e) {
        System.out.println("Could not close: " + e.getMessage());
    }
}

private static void safeClose(Socket socket) {
    try {
        if (socket != null && !socket.isClosed()) {
            socket.close();
        }
    } catch (IOException e) {
        throw new IllegalArgumentException("Cloud not close socket: " + e.getMessage());
    }
}

private static void safeClose(ServerSocket serverSocket) {
    try {
        if (serverSocket != null && !serverSocket.isClosed()) {
            serverSocket.close();
        }
    } catch (IOException e) {
        throw new IllegalArgumentException("Cloud not close socket: " + e.getMessage());
    }
}

测试：

 String message = "hello world\r\ngoodbye";
 byte[] bytes = message.getBytes(StandardCharsets.UTF_8);
 //System.out.println(findLineEnd(bytes, bytes.length));

InputStream stream = new ByteArrayInputStream(bytes);

String line = readLine(stream);

System.out.println(line);