fix: 打印任务不显示的问题

src/main/java/com/goeing/printserver/main/PrintController.java

@@ -107,6 +107,22 @@ public class PrintController implements PrintService {
         return result;
     }
     
+    /**
+     * 清空打印队列
+     * 
+     * @return 清空结果
+     */
+    @DeleteMapping("queue/clear")
+    public Map<String, Object> clearQueue() {
+        int clearedCount = printQueueService.clearQueue();
+        Map<String, Object> result = new HashMap<>();
+        result.put("success", true);
+        result.put("clearedCount", clearedCount);
+        result.put("message", "队列已清空，共清空 " + clearedCount + " 个任务");
+        result.put("timestamp", System.currentTimeMillis());
+        return result;
+    }
+    
     /**
      * 搜索打印任务
      * 

src/main/java/com/goeing/printserver/main/service/PrintQueueService.java

@@ -64,6 +64,7 @@ public class PrintQueueService {
      * 打印任务内部类，封装打印请求和WebSocket会话
      */
     private static class PrintTask {
+        private final String id;
         private final PrintRequest printRequest;
         private final WebSocketMessageDTO messageDTO;
         private final Session session;
@@ -73,6 +74,7 @@ public class PrintQueueService {
         private String status; // queued, processing, completed, failed
 
         public PrintTask(PrintRequest printRequest, WebSocketMessageDTO messageDTO, Session session) {
+            this.id = "TASK_" + System.currentTimeMillis() + "_" + (int)(Math.random() * 1000);
             this.printRequest = printRequest;
             this.messageDTO = messageDTO;
             this.session = session;
@@ -80,6 +82,10 @@ public class PrintQueueService {
             this.status = "queued";
         }
         
+        public String getId() {
+            return id;
+        }
+
         public PrintRequest getPrintRequest() {
             return printRequest;
         }
@@ -124,6 +130,7 @@ public class PrintQueueService {
             Map<String, Object> map = new HashMap<>();
             DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
             
+            map.put("id", id);
             map.put("fileUrl", printRequest.getFileUrl());
             map.put("printerName", printRequest.getPrinterName());
             map.put("status", status);
@@ -224,6 +231,7 @@ public class PrintQueueService {
 
         try {
             // 执行打印
+            Thread.sleep(20000L);
             printService.print(printRequest);
             log.info("打印任务完成: {}", printRequest.getFileUrl());
 
@@ -362,6 +370,19 @@ public class PrintQueueService {
         return maxQueueSize;
     }
     
+    /**
+     * 清空打印队列
+     * 注意：此操作不会影响当前正在处理的任务
+     *
+     * @return 清空的任务数量
+     */
+    public int clearQueue() {
+        int clearedCount = printQueue.size();
+        printQueue.clear();
+        log.info("打印队列已清空，共清空 {} 个任务", clearedCount);
+        return clearedCount;
+    }
+    
     /**
      * 获取历史服务实例
      *