147 lines
4.2 KiB
Java
147 lines
4.2 KiB
Java
package com.njzscloud.jt808.protocol;
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import io.netty.buffer.ByteBuf;
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import io.netty.channel.ChannelHandlerContext;
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import io.netty.handler.codec.MessageToByteEncoder;
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/**
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* JT808协议编码器
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* 将JT808Message对象编码为符合协议规范的字节流
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*/
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public class JT808Encoder extends MessageToByteEncoder<JT808Message> {
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// 消息起始符和结束符
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private static final byte MSG_DELIMITER = 0x7e;
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@Override
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protected void encode(ChannelHandlerContext ctx, JT808Message msg, ByteBuf out) throws Exception {
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// 1. 创建缓冲区存储消息内容（不含起始符和结束符）
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ByteBuf contentBuf = ctx.alloc().buffer();
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try {
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// 2. 写入消息ID
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contentBuf.writeShort(msg.getMessageId());
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// 3. 写入消息体属性
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contentBuf.writeShort(msg.getMessageBodyProps());
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// 4. 写入终端手机号（BCD编码）
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byte[] phoneBytes = stringToBcd(msg.getTerminalPhone(), 6);
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contentBuf.writeBytes(phoneBytes);
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// 5. 写入消息流水号
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contentBuf.writeShort(msg.getFlowId());
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// 6. 写入消息包封装项（如果需要）
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if (msg.isPackaged() && msg.getPackageInfo() != null) {
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contentBuf.writeShort(msg.getPackageInfo().getTotalPackages());
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contentBuf.writeShort(msg.getPackageInfo().getCurrentPackageNo());
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}
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// 7. 写入消息体
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byte[] messageBody = msg.getMessageBody();
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if (messageBody != null && messageBody.length > 0) {
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contentBuf.writeBytes(messageBody);
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}
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// 8. 计算并写入校验码
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byte checkCode = calculateCheckCode(contentBuf);
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contentBuf.writeByte(checkCode);
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msg.setCheckCode(checkCode);
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// 9. 处理转义
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ByteBuf escapedBuf = handleEscape(contentBuf);
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// 10. 写入起始符
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out.writeByte(MSG_DELIMITER);
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// 11. 写入转义后的内容
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out.writeBytes(escapedBuf);
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// 12. 写入结束符
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out.writeByte(MSG_DELIMITER);
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} finally {
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// 释放缓冲区
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if (contentBuf.refCnt() > 0) {
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contentBuf.release();
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}
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}
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}
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/**
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* 处理转义字符
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*/
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private ByteBuf handleEscape(ByteBuf buf) {
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ByteBuf out = buf.alloc().buffer(buf.readableBytes() * 2); // 预留足够空间
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buf.resetReaderIndex();
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while (buf.readableBytes() > 0) {
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byte b = buf.readByte();
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if (b == MSG_DELIMITER) {
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out.writeByte(0x7d);
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out.writeByte(0x01);
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} else if (b == 0x7d) {
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out.writeByte(0x7d);
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out.writeByte(0x02);
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} else {
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out.writeByte(b);
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}
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}
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return out;
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}
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/**
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* 计算校验码
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* 校验码 = 消息头 + 消息体 中所有字节的异或
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*/
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private byte calculateCheckCode(ByteBuf buf) {
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byte checkCode = 0;
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int readerIndex = buf.readerIndex();
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while (buf.readableBytes() > 0) {
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checkCode ^= buf.readByte();
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}
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buf.readerIndex(readerIndex);
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return checkCode;
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}
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/**
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* 字符串转BCD码
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*/
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private byte[] stringToBcd(String str, int length) {
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if (str == null || str.length() == 0) {
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return new byte[length];
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}
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// 补0至偶数长度
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int strLen = str.length();
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if (strLen % 2 != 0) {
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str = "0" + str;
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}
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// 确保不超过指定长度
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if (str.length() > length * 2) {
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str = str.substring(0, length * 2);
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}
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byte[] bcd = new byte[length];
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int index = 0;
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for (int i = 0; i < str.length(); i += 2) {
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if (index >= length) {
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break;
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}
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// 高4位
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byte high = (byte) (Character.digit(str.charAt(i), 16) << 4);
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// 低4位
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byte low = (byte) Character.digit(str.charAt(i + 1), 16);
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bcd[index++] = (byte) (high | low);
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}
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return bcd;
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}
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}
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