feat: 添加打印机管理模块，支持局域网打印

src/main/java/com/example/building/service/PrinterService.java

@@ -0,0 +1,20 @@
+package com.example.building.service;
+
+import com.baomidou.mybatisplus.extension.service.IService;
+import com.example.building.entity.Printer;
+
+/**
+ * 打印机服务接口
+ */
+public interface PrinterService extends IService<Printer> {
+
+    /**
+     * 获取默认打印机
+     */
+    Printer getDefaultPrinter();
+
+    /**
+     * 打印订单小票
+     */
+    void printOrder(String orderId);
+}

src/main/java/com/example/building/service/impl/PrinterServiceImpl.java

@@ -0,0 +1,151 @@
+package com.example.building.service.impl;
+
+import com.baomidou.mybatisplus.core.conditions.query.LambdaQueryWrapper;
+import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
+import com.example.building.entity.Order;
+import com.example.building.entity.Printer;
+import com.example.building.mapper.OrderMapper;
+import com.example.building.mapper.PrinterMapper;
+import com.example.building.service.PrinterService;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.stereotype.Service;
+
+import java.io.OutputStream;
+import java.net.Socket;
+import java.nio.charset.StandardCharsets;
+import java.time.LocalDateTime;
+import java.time.format.DateTimeFormatter;
+
+/**
+ * 打印机服务实现
+ */
+@Service
+public class PrinterServiceImpl extends ServiceImpl<PrinterMapper, Printer> implements PrinterService {
+
+    @Autowired
+    private OrderMapper orderMapper;
+
+    @Override
+    public Printer getDefaultPrinter() {
+        return this.getOne(new LambdaQueryWrapper<Printer>()
+                .eq(Printer::getIsDefault, 1)
+                .eq(Printer::getStatus, 1)
+                .last("LIMIT 1"));
+    }
+
+    @Override
+    public void printOrder(String orderId) {
+        Printer printer = getDefaultPrinter();
+        if (printer == null) {
+            throw new RuntimeException("未找到默认打印机，请先配置打印机");
+        }
+
+        // 获取订单信息
+        Order order = orderMapper.selectById(orderId);
+        if (order == null) {
+            throw new RuntimeException("订单不存在");
+        }
+
+        // 生成ESC/POS指令
+        byte[] data = buildReceipt(order);
+
+        // 发送到打印机
+        sendToPrinter(printer.getIp(), printer.getPort(), data);
+    }
+
+    /**
+     * 生成小票ESC/POS指令
+     */
+    private byte[] buildReceipt(Order order) {
+        StringBuilder sb = new StringBuilder();
+        
+        // 初始化打印机
+        sb.append("\u001B@"); // ESC @
+        
+        // 居中对齐
+        sb.append("\u001Ba\u0001"); // ESC a 1
+        
+        // 打印标题
+        sb.append("\u001B!\u0038"); // ESC ! 56 大字+居中
+        sb.append("【订单小票】\n");
+        sb.append("\u001B!\u0000"); // ESC ! 0 恢复正常
+        
+        // 分隔线
+        sb.append("--------------------------------\n");
+        
+        // 左对齐
+        sb.append("\u001Ba\u0000"); // ESC a 0
+        
+        // 订单信息
+        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm");
+        sb.append("订单号: ").append(order.getOrderNo()).append("\n");
+        sb.append("时间: ").append(order.getCreatedAt().format(formatter)).append("\n");
+        sb.append("客户: ").append(order.getCustomerName() != null ? order.getCustomerName() : "散客").append("\n");
+        sb.append("电话: ").append(order.getCustomerPhone() != null ? order.getCustomerPhone() : "-").append("\n");
+        
+        // 分隔线
+        sb.append("--------------------------------\n");
+        
+        // 商品表头
+        sb.append(String.format("%-10s %4s %8s %8s\n", "商品", "数量", "单价", "小计"));
+        sb.append("--------------------------------\n");
+        
+        // TODO: 获取订单明细，这里暂时用固定内容演示
+        sb.append(String.format("%-10s %4d %8.2f %8.2f\n", 
+                "商品示例", 1, order.getTotalAmount().doubleValue(), order.getActualAmount().doubleValue()));
+        
+        // 分隔线
+        sb.append("--------------------------------\n");
+        
+        // 金额信息
+        sb.append(String.format("%-16s %10s\n", "原价合计:", "¥" + order.getTotalAmount()));
+        sb.append(String.format("%-16s %10s\n", "优惠金额:", "-¥" + order.getDiscountAmount()));
+        sb.append("\u001B!\u0008"); // ESC ! 8 放大
+        sb.append(String.format("%-16s %10s\n", "实付金额:", "¥" + order.getActualAmount()));
+        sb.append("\u001B!\u0000"); // ESC ! 0 恢复正常
+        
+        // 支付方式
+        String paymentMethod = getPaymentText(order.getPaymentMethod());
+        sb.append("支付方式: ").append(paymentMethod).append("\n");
+        
+        // 备注
+        if (order.getRemark() != null && !order.getRemark().isEmpty()) {
+            sb.append("备注: ").append(order.getRemark()).append("\n");
+        }
+        
+        // 尾部
+        sb.append("--------------------------------\n");
+        sb.append("\u001Ba\u0001"); // 居中
+        sb.append("谢谢惠顾，欢迎下次光临！\n");
+        sb.append("\n\n\n");
+        
+        // 切纸指令
+        sb.append("\u001Bd\u0003"); // ESC d 3 走纸3行
+        sb.append("\u001Bv\u0000"); // GS v 0 切纸
+        
+        return sb.toString().getBytes(StandardCharsets.UTF_8);
+    }
+
+    private String getPaymentText(String method) {
+        if (method == null) return "-";
+        switch (method) {
+            case "cash": return "现金";
+            case "wechat": return "微信";
+            case "alipay": return "支付宝";
+            default: return method;
+        }
+    }
+
+    /**
+     * 发送数据到打印机
+     */
+    private void sendToPrinter(String ip, int port, byte[] data) {
+        try (Socket socket = new Socket(ip, port);
+             OutputStream out = socket.getOutputStream()) {
+            out.write(data);
+            out.flush();
+        } catch (Exception e) {
+            throw new RuntimeException("打印失败: " + e.getMessage());
+        }
+    }
+}