解决了困扰几天的问题---java.sql.SQLException: Cannot set uid: incompatible types. Query: select * from orders

      最近在学着做一个jsp+servlet的商城项目，在做的过程中使用到了一个Order实体类用于对应我数据库中的orders表，可是在查询正确的情况下报了这个错误 java.sql.SQLException: Cannot set uid: incompatible types. Query: select * from orders where uid = ? Parameters: [f164918b-ffda-4baf-809a-158203477228]，思考了很久一直无法解决，Order实体类如下：

 

public class Order {
	private String oid;
	private String ordertime;
	private double total;
	private int state;
	private String address;
	
	private String name;
	private String telephone;
	private User uid;
	
	List orderItems = new ArrayList();
        ---get、set方法-----

以下是我的orders表

以下是我的dao查询语句

public List findAllOrders(String uid)  {
		// 订单查询
		 QueryRunner runner = new QueryRunner(JDBCUtils_V3.getDataSource());
		String sql = "select * from orders where uid = ?";
		List query = null;
		try {
			query = runner.query(sql, new BeanListHandler(Order.class),uid);
		} catch (SQLException e) {
			e.printStackTrace();
		}
		return query;
	}

写完之后，我尝试着跑了起来，出现以下错误

java.sql.SQLException: Cannot set uid: incompatible types. Query: select * from orders where uid = ? Parameters: [f164918b-ffda-4baf-809a-158203477228]
	at org.apache.commons.dbutils.AbstractQueryRunner.rethrow(AbstractQueryRunner.java:320)
	at org.apache.commons.dbutils.QueryRunner.query(QueryRunner.java:349)
	at org.apache.commons.dbutils.QueryRunner.query(QueryRunner.java:287)
	at com.iteason.dao.ProductDao.findAllOrders(ProductDao.java:108)
	at com.iteason.service.ProductService.findAllOrders(ProductService.java:107)
	at com.iteason.web.servlet.MyOrdersServlet.doGet(MyOrdersServlet.java:39)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:620)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:501)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)
	at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
	at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1040)
	at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:607)
	at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:315)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
	at java.lang.Thread.run(Thread.java:745)

很明显的错误，我把它给圈红了，提示的是uid这个类型出错，无法把查询的结果存储在BeanListHandler结果集里，接下来我又进行了调试，一开始我以为我的uid是无效的，orders表里找不到数据，所以我在orders表里c了一个uid去作为参数，还是一样的结果，那么说明我的查询是有结果的，是封不进结果集的原因，封装类型出错。

我回忆起前几天写过的Product实体类，里面也有封装着一个Category实体类，如图

public class Product {
	private String pid;
	private String pname;
	private double market_price;
	private double shop_price;
	private String pimage;
	private String pdate;
	private int is_hot;
	private String pdesc;
	private int pflag;
	private Category category;
        --------get、set方法-----

我将dao层用于查询List的字段进行打印

                                                                                       

public List getProductByCategory(String cid, int index, int currentCount) throws SQLException {
		// 获得分页的数据
		QueryRunner runner = new QueryRunner(JDBCUtils_V3.getDataSource());
		String sql = "select * from product where cid = ? limit ?,?";
		List list = runner.query(sql, new BeanListHandler(Product.class),cid,index,currentCount);
		for(Product product:list){
			System.out.println(product.getCategory());
		}
		return list;
	}

运行结果如图所示

这说明我从数据库查询到的数据也并没有完全封装到Product实体类中，因为数据库中查出来的category字段是varchar类型的，而Product实体类中的private Category category类型的，所以打印这个Product类中的category，结果都是null，无法封装，但是在正常情况下不会报错，而是不封装这个部分。

所以接下来我的解决方法是，在Order实体类中将private User uid改成private User user，多添加一行private String uid（对应名称封装的原则），顺利完成了封装查询，不报错！

问题虽然解决了，可是我还是不知道为什么在查询List时会报类型错误，而查询List时不报错误，希望知道其中缘由的大佬告诉我一声啊！ 第一次写博客，写得不好，大家海涵（有人看的话！）