今日在写OrderDaoImpl类，进行测试一直报错，起初以为是Order类的名字与数据库不同引起，在查询函数中起了别名来解决，但一直报Cannot set createTime错误，上网找了说法，都说是名字要对上，偶然间看到一篇sql错误记录中有一样的错误，照着改可以运行出结果。
sql错误记录错误链接
未改变之前的Order类
public class Order {
private String orderId;
private Date createTime;
private BigDecimal totalMoney;
// 0 未发货，1 已发货，2 表示已签收
private Integer status;
private Integer userId;
public Order() {
}
t_order数据库：
OrderDaoImpl类
public ListqueryOrders() { String sql = "select `order_id` orderId,`create_time` createTime,`total_money` totalMoney,`status`,`user_id` userId from t_order"; return queryForList(Order.class,sql); }
八月 08, 2022 10:16:33 下午 com.alibaba.druid.support.logging.JakartaCommonsLoggingImpl info
信息: {dataSource-1} inited
java.sql.SQLException: Cannot set createTime: incompatible types. Query: select `order_id` orderId,`create_time` createTime,`total_money` totalMoney,`status`,`user_id` userId from t_order Parameters: []
at org.apache.commons.dbutils.QueryRunner.rethrow(QueryRunner.java:542)
at org.apache.commons.dbutils.QueryRunner.query(QueryRunner.java:399)
at com.study.dao.Impl.BaseDao.queryForList(BaseDao.java:71)
at com.study.dao.Impl.OrderDaoImpl.queryOrders(OrderDaoImpl.java:24)
at com.study.test.OrderDaoImplTest.queryOrders(OrderDaoImplTest.java:26)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:69)
at com.intellij.rt.junit.IdeaTestRunner$Repeater$1.execute(IdeaTestRunner.java:38)
at com.intellij.rt.execution.junit.TestsRepeater.repeat(TestsRepeater.java:11)
at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:35)
at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:235)
at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:54)
java.lang.NullPointerException
at com.study.test.OrderDaoImplTest.queryOrders(OrderDaoImplTest.java:27)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:69)
at com.intellij.rt.junit.IdeaTestRunner$Repeater$1.execute(IdeaTestRunner.java:38)
at com.intellij.rt.execution.junit.TestsRepeater.repeat(TestsRepeater.java:11)
at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:35)
at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:235)
at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:54)
修改后的Order类，其中导入包为import java.sql.Timestamp;
public class Order {
private String orderId;
private Timestamp createTime;
private BigDecimal totalMoney;
// 0 未发货，1 已发货，2 表示已签收
private Integer status;
private Integer userId;
public Order() {
}
解决方法：可以看到create_time在数据库中是datetime类型，在Order类中是Date()类型，结果报错，将Order类中createTime类型由Data改为Timestamp就可以了。
小结：
- 查询中表中字段名要与bean类中的对应字段命名相同，不然就需要在查询语句中用别名。
- 查询中表中字段类型要与bean类中的对应字段命名类型相对应
- 在bean类中要创建一个无参构造器
1对应Cannot set createTime: incompatible types
2和3 对应该错误：java.sql.SQLException:Cannot create
> 数据库字段类型 bean字段类型 > int int > varchar String > datetime timestamp >
