【java】Mybatis返回int类型为空时报错 attempted to return null from a method with a primitive return type (int)

喜欢ヅ旅行 2022-05-14 16:10 210阅读 0赞

**一、前言**  
在往常敲代码的时候没有留意过int和Integer的区别，今天在敲代码的时候，ORM框架使用的是Mybatis，一个简单的查询，返回查询的条数。当查询为null的时候，就报错了。

**二、报的错误**  
试图从具有原始返回类型（int）的方法返回null

org.apache.ibatis.binding.BindingException: Mapper method 'com.dmsdbj.itoo.basicInfo.dao.RoomDao.selectSumCountCapacity attempted to return null from a method with a primitive return type (int).
    
        at org.apache.ibatis.binding.MapperMethod.execute(MapperMethod.java:93)
        at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:59)
        at com.sun.proxy.$Proxy35.selectSumCountCapacity(Unknown Source)
        at com.dmsdbj.itoo.basicInfo.service.impl.PlaceManageServiceImpl.selectSumCountCapacity(PlaceManageServiceImpl.java:858)
        at com.dmsdbj.itoo.basicInfo.service.impl.PlaceManageServiceImpl$$FastClassBySpringCGLIB$$c31f6b08.invoke(<generated>)
        at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204)
        at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:669)
        at com.dmsdbj.itoo.basicInfo.service.impl.PlaceManageServiceImpl$$EnhancerBySpringCGLIB$$49d6b6e3.selectSumCountCapacity(<generated>)
        at com.dmsdbj.itoo.basicInfo.facade.impl.PlaceManageFacadeImpl.selectSumCountCapacity(PlaceManageFacadeImpl.java:439)
        at com.dmsdbj.itoo.basicInfo.facade.test.PlaceManageFacadeTest.testselectSumCountCapacity_false(PlaceManageFacadeTest.java:342)
        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:497)
        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.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
        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$2.evaluate(ParentRunner.java:268)
        at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
        at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
        at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
        at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:51)
        at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:237)

**三、解决方案**  
Mybatis的mapper文件的返回类型resultType为Integer：  
返回类型设置为封装类型Integer而不是基本类型int。

<select id="selectSumCountCapacity"  resultType="Integer">
            SELECT
            IFNULL( SUM(room_capacity),0)
            FROM
            t_room
            <if test="roomTypeId !=null">
            WHERE
            roomType_id = #{roomTypeId}
            </if>
            <if test="roomIds !=null and roomIds.size()>0">
            AND id NOT IN (
    
                <foreach collection="roomIds" item="item" separator=",">
                    #{item}
                </foreach>
    
            )
            </if>
        </select>

Service之间的返回值也是Ingeger：

/**
         * 查询未安排考场的教室总容量-王雷-2017年9月1日15:09:25
         * @param roomIds
         * @param roomTypeId
         * @return
         */
        public Integer selectSumCountCapacity(List<String> roomIds ,String roomTypeId){
            if (roomIds==null||roomTypeId==""){
                logger.debug("查询未安排考场的教室总容量,已使用的房间id为空，将查询所有的房间容量");
            }
    
            return roomDao.selectSumCountCapacity(roomIds, roomTypeId);
        }

另外：若遇到该问题，可使用MySQL的IFNULL函数和MAX函数，将返回的NULL值转换为0。例如，可将上述SQL语句改为：

SELECT IFFULL(MAX(name),0) AS name FROM user WHERE id = #{id}

**四、int和integer的区别**  
以前一直没有思考，为啥要有一个int还要有一个integer。实际上：

*  1.Ingeter是int的包装类，int的初值为0，Ingeter的初值为null；
 *  2.初始化的时候，int i =1；Integer i= new Integer(1);(要把integer 当做一个类看)；但由于有了自动装箱和拆箱使得对Integer类也可使用：Integer i= 1；
 *  3.int 是基本数据类型（面向过程留下的痕迹，不过是对java的有益补充），Integer 是一个类，是int的扩展，定义了很多的转换方法
 *  4.Integer是对象，用一个引用指向这个对象，而int是基本类型，直接存储数值。

**五、小结**  
java中的数据类型分为基本数据类型和复杂数据类型，int是基本数据类型，integer是复杂数据类型，复杂基本类型也就是一个类，所以初始化为null。

从基本知识出发，能更加夯实自己的基础。

【java】Mybatis返回int类型为空时报错 attempted to return null from a method with a primitive return type (int)

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