远程通讯——Telnet目标：介绍telnet的相关实现逻辑、介绍dubbo-remoting-api中的telnet包内的源码解析。前言从dubbo 2.0.5开始，dubbo开始支持通过 telnet 命令来进行服务治理。本文就是讲解一些公用的telnet命令的实现。下面来看一下telnet实现的类图：可以看到，实现了TelnetHandler接口的有六个类，除了TelnetHandlerAdapter是以外，其他五个分别对应了clear、exit、help、log、status命令的实现，具体用来干嘛，请看官方文档的介绍。源码分析（一）TelnetHandler@SPIpublic interface TelnetHandler { /** * telnet. * 处理对应的telnet命令 * @param channel * @param message telnet命令 / String telnet(Channel channel, String message) throws RemotingException;}该接口上telnet命令处理器接口，是一个可扩展接口。它定义了一个方法，就是处理相关的telnet命令。（二）TelnetHandlerAdapter该类继承了ChannelHandlerAdapter，实现了TelnetHandler接口，是TelnetHandler的适配器类，负责在接收到HeaderExchangeHandler发来的telnet命令后分发给对应的TelnetHandler实现类去实现，并且返回命令结果。public class TelnetHandlerAdapter extends ChannelHandlerAdapter implements TelnetHandler { /* * 扩展加载器 / private final ExtensionLoader<TelnetHandler> extensionLoader = ExtensionLoader.getExtensionLoader(TelnetHandler.class); @Override public String telnet(Channel channel, String message) throws RemotingException { // 获得提示键配置，用于nc获取信息时不显示提示符 String prompt = channel.getUrl().getParameterAndDecoded(Constants.PROMPT_KEY, Constants.DEFAULT_PROMPT); boolean noprompt = message.contains("–no-prompt"); message = message.replace("–no-prompt", “”); StringBuilder buf = new StringBuilder(); // 删除头尾空白符的字符串 message = message.trim(); String command; // 获得命令 if (message.length() > 0) { int i = message.indexOf(’ ‘); if (i > 0) { // 获得命令 command = message.substring(0, i).trim(); // 获得参数 message = message.substring(i + 1).trim(); } else { command = message; message = “”; } } else { command = “”; } if (command.length() > 0) { // 如果有该命令的扩展实现类 if (extensionLoader.hasExtension(command)) { try { // 执行相应命令的实现类的telnet String result = extensionLoader.getExtension(command).telnet(channel, message); if (result == null) { return null; } // 返回结果 buf.append(result); } catch (Throwable t) { buf.append(t.getMessage()); } } else { buf.append(“Unsupported command: “); buf.append(command); } } if (buf.length() > 0) { buf.append("\r\n”); } // 添加 telnet 提示语 if (prompt != null && prompt.length() > 0 && !noprompt) { buf.append(prompt); } return buf.toString(); }}该类只实现了telnet方法，其中的逻辑还是比较清晰，就是根据对应的命令去让对应的实现类产生命令结果。（三）ClearTelnetHandler该类实现了TelnetHandler接口，封装了clear命令的实现。@Activate@Help(parameter = “[lines]”, summary = “Clear screen.”, detail = “Clear screen.")public class ClearTelnetHandler implements TelnetHandler { @Override public String telnet(Channel channel, String message) { // 清除屏幕上的内容行数 int lines = 100; if (message.length() > 0) { // 如果不是一个数字 if (!StringUtils.isInteger(message)) { return “Illegal lines " + message + “, must be integer.”; } lines = Integer.parseInt(message); } StringBuilder buf = new StringBuilder(); // 一行一行清除 for (int i = 0; i < lines; i++) { buf.append("\r\n”); } return buf.toString(); }}（四）ExitTelnetHandler该类实现了TelnetHandler接口，封装了exit命令的实现。@Activate@Help(parameter = “”, summary = “Exit the telnet.”, detail = “Exit the telnet.")public class ExitTelnetHandler implements TelnetHandler { @Override public String telnet(Channel channel, String message) { // 关闭通道 channel.close(); return null; }}（五）HelpTelnetHandler该类实现了TelnetHandler接口，封装了help命令的实现。@Activate@Help(parameter = “[command]”, summary = “Show help.”, detail = “Show help.")public class HelpTelnetHandler implements TelnetHandler { /* * 扩展加载器 / private final ExtensionLoader<TelnetHandler> extensionLoader = ExtensionLoader.getExtensionLoader(TelnetHandler.class); @Override public String telnet(Channel channel, String message) { // 如果需要查看某一个命令的帮助 if (message.length() > 0) { if (!extensionLoader.hasExtension(message)) { return “No such command " + message; } // 获得对应的扩展实现类 TelnetHandler handler = extensionLoader.getExtension(message); Help help = handler.getClass().getAnnotation(Help.class); StringBuilder buf = new StringBuilder(); // 生成命令和帮助信息 buf.append(“Command:\r\n “); buf.append(message + " " + help.parameter().replace("\r\n”, " “).replace("\n”, " “)); buf.append("\r\nSummary:\r\n “); buf.append(help.summary().replace("\r\n”, " “).replace("\n”, " “)); buf.append("\r\nDetail:\r\n “); buf.append(help.detail().replace("\r\n”, " \r\n”).replace("\n”, " \n”)); return buf.toString(); // 如果查看所有命令的帮助 } else { List<List<String>> table = new ArrayList<List<String>>(); // 获得所有命令的提示信息 List<TelnetHandler> handlers = extensionLoader.getActivateExtension(channel.getUrl(), “telnet”); if (handlers != null && !handlers.isEmpty()) { for (TelnetHandler handler : handlers) { Help help = handler.getClass().getAnnotation(Help.class); List<String> row = new ArrayList<String>(); String parameter = " " + extensionLoader.getExtensionName(handler) + " " + (help != null ? help.parameter().replace("\r\n”, " “).replace("\n”, " “) : “”); row.add(parameter.length() > 50 ? parameter.substring(0, 50) + “…” : parameter); String summary = help != null ? help.summary().replace("\r\n”, " “).replace("\n”, " “) : “”; row.add(summary.length() > 50 ? summary.substring(0, 50) + “…” : summary); table.add(row); } } return “Please input "help [command]" show detail.\r\n” + TelnetUtils.toList(table); } }}help分为了需要查看某一个命令的帮助还是查看全部命令的帮助。（六）LogTelnetHandler该类实现了TelnetHandler接口，封装了log命令的实现。@Activate@Help(parameter = “level”, summary = “Change log level or show log “, detail = “Change log level or show log”)public class LogTelnetHandler implements TelnetHandler { public static final String SERVICE_KEY = “telnet.log”; @Override public String telnet(Channel channel, String message) { long size = 0; File file = LoggerFactory.getFile(); StringBuffer buf = new StringBuffer(); if (message == null || message.trim().length() == 0) { buf.append(“EXAMPLE: log error / log 100”); } else { String str[] = message.split(” “); if (!StringUtils.isInteger(str[0])) { // 设置日志级别 LoggerFactory.setLevel(Level.valueOf(message.toUpperCase())); } else { // 获得日志长度 int SHOW_LOG_LENGTH = Integer.parseInt(str[0]); if (file != null && file.exists()) { try { FileInputStream fis = new FileInputStream(file); try { FileChannel filechannel = fis.getChannel(); try { size = filechannel.size(); ByteBuffer bb; if (size <= SHOW_LOG_LENGTH) { // 分配缓冲区 bb = ByteBuffer.allocate((int) size); // 读日志数据 filechannel.read(bb, 0); } else { int pos = (int) (size - SHOW_LOG_LENGTH); // 分配缓冲区 bb = ByteBuffer.allocate(SHOW_LOG_LENGTH); // 读取日志数据 filechannel.read(bb, pos); } bb.flip(); String content = new String(bb.array()).replace("<”, “<”) .replace(">”, “>”).replace("\n”, “<br/><br/>”); buf.append("\r\ncontent:” + content); buf.append("\r\nmodified:” + (new SimpleDateFormat(“yyyy-MM-dd HH:mm:ss”) .format(new Date(file.lastModified())))); buf.append("\r\nsize:” + size + “\r\n”); } finally { filechannel.close(); } } finally { fis.close(); } } catch (Exception e) { buf.append(e.getMessage()); } } else { size = 0; buf.append("\r\nMESSAGE: log file not exists or log appender is console .”); } } } buf.append("\r\nCURRENT LOG LEVEL:" + LoggerFactory.getLevel()) .append("\r\nCURRENT LOG APPENDER:" + (file == null ? “console” : file.getAbsolutePath())); return buf.toString(); }}log命令实现原理就是从日志文件中把日志信息读取出来。（七）StatusTelnetHandler该类实现了TelnetHandler接口，封装了status命令的实现。@Activate@Help(parameter = “[-l]”, summary = “Show status.”, detail = “Show status.")public class StatusTelnetHandler implements TelnetHandler { private final ExtensionLoader<StatusChecker> extensionLoader = ExtensionLoader.getExtensionLoader(StatusChecker.class); @Override public String telnet(Channel channel, String message) { // 显示状态列表 if (message.equals("-l”)) { List<StatusChecker> checkers = extensionLoader.getActivateExtension(channel.getUrl(), “status”); String[] header = new String[]{“resource”, “status”, “message”}; List<List<String>> table = new ArrayList<List<String>>(); Map<String, Status> statuses = new HashMap<String, Status>(); if (checkers != null && !checkers.isEmpty()) { // 遍历各个资源的状态，如果一个当全部 OK 时则显示 OK，只要有一个 ERROR 则显示 ERROR，只要有一个 WARN 则显示 WARN for (StatusChecker checker : checkers) { String name = extensionLoader.getExtensionName(checker); Status stat; try { stat = checker.check(); } catch (Throwable t) { stat = new Status(Status.Level.ERROR, t.getMessage()); } statuses.put(name, stat); if (stat.getLevel() != null && stat.getLevel() != Status.Level.UNKNOWN) { List<String> row = new ArrayList<String>(); row.add(name); row.add(String.valueOf(stat.getLevel())); row.add(stat.getMessage() == null ? "" : stat.getMessage()); table.add(row); } } } Status stat = StatusUtils.getSummaryStatus(statuses); List<String> row = new ArrayList<String>(); row.add(“summary”); row.add(String.valueOf(stat.getLevel())); row.add(stat.getMessage()); table.add(row); return TelnetUtils.toTable(header, table); } else if (message.length() > 0) { return “Unsupported parameter " + message + " for status.”; } String status = channel.getUrl().getParameter(“status”); Map<String, Status> statuses = new HashMap<String, Status>(); if (status != null && status.length() > 0) { String[] ss = Constants.COMMA_SPLIT_PATTERN.split(status); for (String s : ss) { StatusChecker handler = extensionLoader.getExtension(s); Status stat; try { stat = handler.check(); } catch (Throwable t) { stat = new Status(Status.Level.ERROR, t.getMessage()); } statuses.put(s, stat); } } Status stat = StatusUtils.getSummaryStatus(statuses); return String.valueOf(stat.getLevel()); }}（八）Help该接口是帮助文档接口@Documented@Retention(RetentionPolicy.RUNTIME)@Target({ElementType.TYPE})public @interface Help { String parameter() default “”; String summary(); String detail() default “”;}可以看上在每个命令的实现类上都加上了@Help注解，为了添加一些帮助文案。（九）TelnetUtils该类是Telnet命令的工具类，其中逻辑我就不介绍了。（十）TelnetCodec该类继承了TransportCodec，是telnet的编解码类。1.属性private static final Logger logger = LoggerFactory.getLogger(TelnetCodec.class);/* * 历史命令列表 /private static final String HISTORY_LIST_KEY = “telnet.history.list”;/* * 历史命令位置，就是用上下键来找历史命令 /private static final String HISTORY_INDEX_KEY = “telnet.history.index”;/* * 向上键 /private static final byte[] UP = new byte[]{27, 91, 65};/* * 向下键 /private static final byte[] DOWN = new byte[]{27, 91, 66};/* * 回车 /private static final List<?> ENTER = Arrays.asList(new Object[]{new byte[]{’\r’, ‘\n’} / Windows Enter /, new byte[]{’\n’} / Linux Enter /});/* * 退出 /private static final List<?> EXIT = Arrays.asList(new Object[]{new byte[]{3} / Windows Ctrl+C /, new byte[]{-1, -12, -1, -3, 6} / Linux Ctrl+C /, new byte[]{-1, -19, -1, -3, 6} / Linux Pause */});2.getCharsetprivate static Charset getCharset(Channel channel) { if (channel != null) { // 获得属性设置 Object attribute = channel.getAttribute(Constants.CHARSET_KEY); // 返回指定字符集的charset对象。 if (attribute instanceof String) { try { return Charset.forName((String) attribute); } catch (Throwable t) { logger.warn(t.getMessage(), t); } } else if (attribute instanceof Charset) { return (Charset) attribute; } URL url = channel.getUrl(); if (url != null) { String parameter = url.getParameter(Constants.CHARSET_KEY); if (parameter != null && parameter.length() > 0) { try { return Charset.forName(parameter); } catch (Throwable t) { logger.warn(t.getMessage(), t); } } } } // 默认的编码是utf-8 try { return Charset.forName(Constants.DEFAULT_CHARSET); } catch (Throwable t) { logger.warn(t.getMessage(), t); } return Charset.defaultCharset();}该方法是获得通道的字符集，根据url中编码来获得字符集，默认是utf-8。3.encode@Overridepublic void encode(Channel channel, ChannelBuffer buffer, Object message) throws IOException { // 如果需要编码的是 telnet 命令结果 if (message instanceof String) { //如果为客户端侧的通道message直接返回 if (isClientSide(channel)) { message = message + “\r\n”; } // 获得字节数组 byte[] msgData = ((String) message).getBytes(getCharset(channel).name()); // 写入缓冲区 buffer.writeBytes(msgData); } else { super.encode(channel, buffer, message); }}该方法是编码方法。4.decode@Overridepublic Object decode(Channel channel, ChannelBuffer buffer) throws IOException { // 获得缓冲区可读的字节 int readable = buffer.readableBytes(); byte[] message = new byte[readable]; // 从缓冲区读数据 buffer.readBytes(message); return decode(channel, buffer, readable, message);}@SuppressWarnings(“unchecked”)protected Object decode(Channel channel, ChannelBuffer buffer, int readable, byte[] message) throws IOException { // 如果是客户端侧，直接返回结果 if (isClientSide(channel)) { return toString(message, getCharset(channel)); } // 检验消息长度 checkPayload(channel, readable); if (message == null || message.length == 0) { return DecodeResult.NEED_MORE_INPUT; } // 如果回退 if (message[message.length - 1] == ‘\b’) { // Windows backspace echo try { boolean doublechar = message.length >= 3 && message[message.length - 3] < 0; // double byte char channel.send(new String(doublechar ? new byte[]{32, 32, 8, 8} : new byte[]{32, 8}, getCharset(channel).name())); } catch (RemotingException e) { throw new IOException(StringUtils.toString(e)); } return DecodeResult.NEED_MORE_INPUT; } // 如果命令是退出 for (Object command : EXIT) { if (isEquals(message, (byte[]) command)) { if (logger.isInfoEnabled()) { logger.info(new Exception(“Close channel " + channel + " on exit command: " + Arrays.toString((byte[]) command))); } // 关闭通道 channel.close(); return null; } } boolean up = endsWith(message, UP); boolean down = endsWith(message, DOWN); // 如果用上下键找历史命令 if (up || down) { LinkedList<String> history = (LinkedList<String>) channel.getAttribute(HISTORY_LIST_KEY); if (history == null || history.isEmpty()) { return DecodeResult.NEED_MORE_INPUT; } Integer index = (Integer) channel.getAttribute(HISTORY_INDEX_KEY); Integer old = index; if (index == null) { index = history.size() - 1; } else { // 向上 if (up) { index = index - 1; if (index < 0) { index = history.size() - 1; } } else { // 向下 index = index + 1; if (index > history.size() - 1) { index = 0; } } } // 获得历史命令，并发送给客户端 if (old == null || !old.equals(index)) { // 设置当前命令位置 channel.setAttribute(HISTORY_INDEX_KEY, index); // 获得历史命令 String value = history.get(index); // 清除客户端原有命令，用查到的历史命令替代 if (old != null && old >= 0 && old < history.size()) { String ov = history.get(old); StringBuilder buf = new StringBuilder(); for (int i = 0; i < ov.length(); i++) { buf.append("\b”); } for (int i = 0; i < ov.length(); i++) { buf.append(" “); } for (int i = 0; i < ov.length(); i++) { buf.append("\b”); } value = buf.toString() + value; } try { channel.send(value); } catch (RemotingException e) { throw new IOException(StringUtils.toString(e)); } } // 返回，需要更多指令 return DecodeResult.NEED_MORE_INPUT; } // 关闭命令 for (Object command : EXIT) { if (isEquals(message, (byte[]) command)) { if (logger.isInfoEnabled()) { logger.info(new Exception(“Close channel " + channel + " on exit command " + command)); } channel.close(); return null; } } byte[] enter = null; // 如果命令是回车 for (Object command : ENTER) { if (endsWith(message, (byte[]) command)) { enter = (byte[]) command; break; } } if (enter == null) { return DecodeResult.NEED_MORE_INPUT; } LinkedList<String> history = (LinkedList<String>) channel.getAttribute(HISTORY_LIST_KEY); Integer index = (Integer) channel.getAttribute(HISTORY_INDEX_KEY); // 移除历史命令 channel.removeAttribute(HISTORY_INDEX_KEY); // 将历史命令拼接 if (history != null && !history.isEmpty() && index != null && index >= 0 && index < history.size()) { String value = history.get(index); if (value != null) { byte[] b1 = value.getBytes(); byte[] b2 = new byte[b1.length + message.length]; System.arraycopy(b1, 0, b2, 0, b1.length); System.arraycopy(message, 0, b2, b1.length, message.length); message = b2; } } // 将命令字节数组，转成具体的一条命令 String result = toString(message, getCharset(channel)); if (result.trim().length() > 0) { if (history == null) { history = new LinkedList<String>(); channel.setAttribute(HISTORY_LIST_KEY, history); } if (history.isEmpty()) { history.addLast(result); } else if (!result.equals(history.getLast())) { history.remove(result); // 添加当前命令到历史尾部 history.addLast(result); // 超过上限，移除历史的头部 if (history.size() > 10) { history.removeFirst(); } } } return result;}该方法是编码。后记该部分相关的源码解析地址：https://github.com/CrazyHZM/i…该文章讲解了telnet的相关实现逻辑,本文有兴趣的朋友可以看看。下一篇我会讲解基于grizzly实现远程通信部分。
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