MyBatis开启二级缓存时报错java.io.NotSerializableException

我们在Mapper.xml文件中开启二级缓存时：

    
    
        select * from mybatis.user where id = #{id}
    

    
        update mybatis.user set name = #{name} ,pwd = #{pwd}  where id =#{id} ;
    

在进行测试时：

@Test
    public void test2(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        User user = mapper.queryUser(1);
        System.out.println(user);
        sqlSession.close();
        System.out.println("=========================");
        SqlSession sqlSession2 = MybatisUtils.getSqlSession();
        UserMapper mapper2 = sqlSession2.getMapper(UserMapper.class);
        User user2 = mapper2.queryUser(1);
        System.out.println(user2);
        sqlSession.close();
    }

报以下错误：

org.apache.ibatis.cache.CacheException: Error serializing object.  Cause: java.io.NotSerializableException: com.mam.pojo.User

    at org.apache.ibatis.cache.decorators.SerializedCache.serialize(SerializedCache.java:94)
    at org.apache.ibatis.cache.decorators.SerializedCache.putObject(SerializedCache.java:55)
    at org.apache.ibatis.cache.decorators.LoggingCache.putObject(LoggingCache.java:49)
    at org.apache.ibatis.cache.decorators.SynchronizedCache.putObject(SynchronizedCache.java:43)
    at org.apache.ibatis.cache.decorators.TransactionalCache.flushPendingEntries(TransactionalCache.java:116)
    at org.apache.ibatis.cache.decorators.TransactionalCache.commit(TransactionalCache.java:99)
    at org.apache.ibatis.cache.TransactionalCacheManager.commit(TransactionalCacheManager.java:44)
    at org.apache.ibatis.executor.CachingExecutor.close(CachingExecutor.java:61)
    at org.apache.ibatis.session.defaults.DefaultSqlSession.close(DefaultSqlSession.java:263)
    at com.mam.mapper.MyTest.test2(MyTest.java:33)
    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$2.evaluate(ParentRunner.java:268)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
    at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
    at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
    at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
    at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
    at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)
Caused by: java.io.NotSerializableException: com.mam.pojo.User
    at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1184)
    at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:348)
    at java.util.ArrayList.writeObject(ArrayList.java:762)
    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 java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:1028)
    at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1496)
    at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1432)
    at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178)
    at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:348)
    at org.apache.ibatis.cache.decorators.SerializedCache.serialize(SerializedCache.java:90)
    ... 31 more

解决方案：

将实体类序列化，或者参照官方文档中，对二级缓存进行配置

@Data
@AllArgsConstructor
@NoArgsConstructor
public class User implements Serializable {
    private int id;
    private String name;
    private String pwd;
}

报错原因：

原因就是，cache/中的readOnly默认为false，而可读写的缓存会通过序列化返回缓存对象的拷贝，所以，此时需要实体类（这里是User）实现Serializable接口或者在cache/中配置readonly=true